Chapter3 Diesel

Nguyen Van Sn 57 Biosys.com.vn

3. COMBUSTION AND FUEL INJECTION SYSTEM

3.1 Briefly describe the principle of the fuel injection pump and give reasons for the important points of design.

There is one pump for each cylinder. Fuel is pumped by a ram working in a sleeve, the ram being operated in the pumping stroke by cam, and on the return stroke by a spring. It works at constant stroke, and the amount of fuel delivered is varied by varying the point in the stroke at which the pressure side of the ram is put into communication with the suction side. When this point is reached the pressure drops suddenly, fuel ceases to be delivered to the engine cylinder, and for the remainder of the stroke of the ram oil is merely pumped back to the suction side of the pump. In the Bosh pumps, the means of putting the pressure side of the ram into communication with the suction side is a helix-shaped groove on the side of the ram, registering with a hole in the sleeve; according to the rotational position of the ram the helix-shaped groove will register with the hole early or late in the stroke of the ram. The requirements that lead to fuel injection pumps being of this design are:

1) The need to build up to full pressure very rapidly at the beginning of injection so as to ensure full atomization immediately. Cams lend themselves to design for very rapid initial movement of the ram.

3. S CHAY VA HE THONG PHUN NHIEN LIEU

3.1 Mo ta tom tat nguyen ly cua he thong bm cao ap nhien lieu va ly giai cac ac iem thiet ke quan trong.

Moi xilanh co mot bm. Nhien lieu c bm bi mot piston lam viec trong nong smi xilanh bm, piston thc hien hanh trnh bm nh cam quay va hanh trnh ngc lai la do lo xo tac ong. Piston lam viec hanh trnh khong oi, va lng nhien lieu cung cap c thay oi bang cach thay oi iem tren hanh trnh cua piston longgi co ap suat pha tren piston thong vi vi pha nap. Khi ti iem nay ap suat sut ot ngot, nhien lieu ngng cap vao xilanh ong c, va phan hanh trnh con lai, dau c bm ch thut ngc ve pha nap cua bm. bm Bo-s, chi tiet lam pha ap suat cua bm thong vi pha nap la ranh xeo canh cua piston phoi hp vi cac lo smi xilanh vo bm; tuy theo v tr quay c cua piston ranh xeo se m lo o sm hay muon tren hanh trnh cua piston.

Cac yeu cau co tnh nh hng cua bm cao ap thiet ke theo kieu nay la:

1) Yeu cau tao ap suat cao rat nhanh luc bat au phun e bao am tao sng hoan toan ngay lap tc. Chnh cac cam giup cho muc ch tao chuyen ong ban au rat nhanh nay cua piston


2) The need to cut off ram pressure as suddenly as possible to prevent dribble. The opening of a port does this more effectively than the ending of a (variable) stroke.

3) The need to deliver extremely small quantities of fuel when engine is running light, with the same requirements of rapid build-up, rapid cut-off, and full atomization. Cam drive and port cut-off is the most effective way of achieving this.

When the cut-off point occurs and fuel discharge stops, the rapid drop of pressure causes a shock on the inlet line to the pump. This may be damped out by a shock absorber fitted on the side of the fuel pump and connected with the oil supply line to the pump. Guard plates are fitted round the bottom of the ram to prevent fuel oil leakages going into the engine lubrication system.

Some fuel pumps are fitted with delivery valves. Where delivery valves are fitted the wings on the valve are not cut through to the valve miter; this part of the valve acts as a piston. When the delivery valve opens, a large lift is required to give it opening area; when delivery stops, the volume of the space between the pump and the injection valve is increased rapidly as the pump delivery valve closes. This sharp increase in volume allows the injection valve to seat quickly and prevent dribble.

The parts of fuel pump are very robust to withstand the discharge pressure in the fuel system. These pressures may be up to 1000 bar (approx 1000 kg/cm2)

2) Yeu cau ngat ap suat nen ot ngot ti mc co the e tranh nho giot. S m thong ca lam ieu nay at hieu qua hn cach ket thuc hanh trnh (loai hanh trnh thay oi c).

3) Yeu cau cung cap lng cc nho nhien lieu khi ong c chay nhe tai thoa man cac yeu cau tng t cua viec tao nhanh, ngat nhanh, va phun sng hoan toan. Truyen ong cam va ngat bang ca so la cach hieu qua nhat e at ieu nay.

Khi s ngat xay ra va nhien lieu ngng cap, o sut ap nhanh gay mot xung ong ng dan ti bm. ieu nay co the triet tieu bi bo giam chan lap pha bm cao ap va c noi vi ng cap ti bm. Mot tam chan c lap quanh ay cua piston e tranh nhien lieu lot vao he thong dau nhn cua ong c.

Mot so bm c lap van cap dau. Tai ni van cap dau c lap, cac canh dan hng tren van khong cat xuyen qua vanh giam tai; phan vanh giam tai tac ong nh la mot piston. Khi van cap dau m, yeu cau mot o nang ln e tao tiet dien m cho van; khi ngng phun, the tch cua khong gian gia bm va voi phun c tang nhanh khi van cap dau cua bm ong. ieu nay lam tang ve the tch cho phep kim phun ong xuong nhanh va tranh nho giot.

Cac phan cua bm cao ap rat chac chan e chu ng ap suat ay he thong nhien lieu. Ap suat nay co the tang ti 1000 bar ( xap x 1000 kg/cm2).


The rotation of the fuel ram to meter the volume of fuel delivered by the fuel may be controlled by a governor, in generators and alternation, or the fuel lever , in propulsion engines.

3.2 Describe how the fuel quantity

delivered by a fuel injection pump may be controlled through the pump suction valve.

The amount of fuel delivered is controlled by the clearance or lost motion of a tappet positioned under the fuel pump suction valve. The tappet lever is connected into a collar or slot on the fuel pump ram. The lever fulcrum is a section of a small shaft which is made eccentric to the shaft bearings; rotation of the shaft alter the eccentric position and in turn varies the tappet clearance. The shaft may be connected to a governor or to the engine fuel lever.

When the fuel pump ram is in the bottom position, the suction valve is held open by the tappet. Upward movement of the ram moves one end of the lever ( connected to the ram) upwards and the other end ( connected to the tappet ) downwards, and the suction valve comes on its seat. Further upward movement of the ram builds up pressure in the fuel line; the fuel delivery valve opens and fuel is injected into the cylinder until the pump comes to the end of its stroke. This type of fuel pump is fitted with a delivery valve on the top of the pump chamber. Downward movement of the pump ram allows fuel to flow into the pump through the suction valve as in a normal pump.

S quay cua piston nham nh lng the tch cua nhien lieu cung cap bi bm co the c ieu khien bi bo ieu toc nh ong c may phat va may dao ien, hoac tay ga nhien lieu nh ong c lai chan vt.

3.2 Mo ta lam the nao lng nhien

lieu cung cap bi bm cao ap co the c ieu chnh qua van nap bm?

Lng nhien lieu cung cap c ieu chnh bi khe h hoac s chuyen dnh khong tac ong cua can van at di van nap cua bm cao ap. on bay ti van c noi vao mot co hoac mot ranh soi piston bm cao ap. Goi ty cua on la phan truc nho c lam lech tam so vi o ; viec quay truc lam thay oi v tr lech tam va theo o lam thay oi khe h ti van. Truc co the c noi ti bo ieu toc hoac ti can nhien lieu ong c.

Khi piston bm cao ap v tr di cung, van nap c gi m bi ti van. Chuyen ong len cua piston lam au on bay ( c noi ti piston ) chuyen dch len va au kia (c noi ti ti ay ) chuyen dch xuong, va van nap ha xuong e cua no. Chuyen ong len tiep theo cua piston lam tang ap suat tren ng nhien lieu; van cap nhien lieu m va nhien lieu phun vao xilanh cho ti khi bm ket thuc hanh trnh cua no. Loai nay cua bm cao ap co van cap nhien lieu at nh buong bm. Chuyen dch xuong cua piston bm cho phep nap nhien lieu vao bm qua van nap nh bm thong thng.


3.3 How may fuel be taken off a cylinder without stopping the engine?

If it becomes necessary to take fuel off a cylinder without stopping the engine, the fuel pump crosshead is lifted until the roller is clear of the cam peak. The by-pass on the fuel valve must be opened before lifting the crosshead.

A lever is supplied by the engine builder which connects to the pump crosshead through a bolt and finger-plate. Lifting the bolt with the lever connects the finger-plate to the underside of the pump crosshead, and lifts it as the lever is pushed downwards or upwards depending on the linkage arrangement. After lifting, the crosshead may be fastened in the lifted position.

In some cases the pump crosshead is lifted by a small pin on an axle. The pin is eccentric to the axle axis, and movement of the axle connects the pin with the crosshead, lifting the roller clear of the cam

3.4 What do you understand by the terms atomization, penetration and turbulence?

Atomization is the break-up of the fuel charge into very small particles when it is injected into the cylinder.

Penetration refers to the distance that the fuel particles travel or penetrate into the combustion chamber.

Turbulence or swirl refers to the air movement pattern within the combustion chamber at the end of compression.

3.3 Lam the nao co the dng viec cap nhien lieu vao xilanh ma khong dng ong c?

Neu can ngat nhien lieu mot xilanh ma khong ngng ong c, au ch thap bm nhien lieu c nang len cho ti khi con oi ri khoi vau cam. ng noi tat van nhien lieu phai m thong trc khi nang au ch thap.

Mot thanh on do nha che tao cung cap noi ti au ch thap thong qua bulong va tam chan. Khi nang bulong bang thanh on noi tam chan vao pha di cua au ch thap bm, va no nang len khi thanh on c ay xuong hoac len tuy theo bo tr moi lien ket. Sau khi nang len, au ch thap co the c co nh tai v tr c nang o.

Trong mot so trng hp au ch thap bm c nang bi chot nho tren mot truc. Chot la loai lech tam so vi tam truc, va chuyen dch cua truc noi chot vi au ch thap nhac con oi ri khoi cam.

3.4 Anh hieu cac thuat ng tao sng, o phun xa va xoay cuon la g?

Tao sng la phan ra nho nhien lieu cap thanh cac hat vo cung nho khi no c phun vao xilanh.

Phun xa am ch khoang cach cac hat nhien lieu dch chuyen hoac xam nhap vao trong buong ot.

Xoay cuon hoac xoay loc am ch ti hng chuyen ong cua khong kh trong buong chay cuoi thi ky nen.


3.5 Describe a fuel injection valve. What size are the holes in the sprayer tip?

The body of a fuel injection valve is normally flanged at its upper end. The lower end is threaded to accommodate the sprayer nozzle and nozzle capnut.

The body of the valve contains four holes. One is for the fuel inlet and another for the fuel priming valve; these two holes are connected through a common space within the fuel nozzle or by an annular space. The remaining pair of holes accommodate the fuel valve cooling service inlet and outlet connections.

The center part of the body is drilled through and along its axis. This hole is tapped at the end for the spring adjusting screw and may also house an adjustment screw to control the fuel valve needle lift. The lower end of the center hole is counterbored to house the spring which holds the needle valve on its seat.

The end of the fuel valve or nozzle may be made in one, two, or three pieces depending on the design.

The valve needle and spindle are in one piece, and are lapped into a very accurately machined guide. Valves produced for operation on diesel fuel or gas oil have a very small clearance while valve made for operation on high-viscosity have slightly larger clearance to allow for temperature changes when working with heated fuel. The lower end of the valve spindle is of smaller diameter and has a conical end which forms the valve. The conical end comes onto the valve seat, below which is an open space.

3.5 Mo ta voi phun nhien lieu. Cac lo trong au bep phun co kch thc bao nhieu ?

Than voi phun thng c lam dang mat bch tai au pha tren cua no. au pha di c lam ren e noi au bep va ai mu chup au bep.

Than voi phun co bon lo. Mot cho nhien lieu vao va cai kia cho van xa e nhien lieu; hai lo nay c noi thong qua khong gian trong au bep hoac bi khong gian hnh xuyen. Cap lo con lai tao ieu kien cho cac moi noi vao ra lam mat voi phun.

Phan gia cua than c khoan suot va doc tam cua no. Lo nay c lam ren au cho van vt ieu chnh sc cang lo xo va co the cha ca vt ieu chnh e ieu khien o nang kim phun. au di cua lo doc tam c khoan rong e cha lo xo gi kim phun tai e cua no.

au voi phun hoac bep co the c che tao thanh mot, hai hoac ba phan tuy theo thiet ke.

Kim phun va ti ay c noi lai vi nhau va c ra kht vao phan dan hng c che tao rat chnh xac. Cac voi phun c che tao hoat ong dau diesel hoac gazoan co khe h rat nho trong khi voi phun c lam danh cho lam viec dau o nht cao co khe h hi ln hn cho phep thay oi nhiet o khi lam viec vi dau nang. au di cua kim phun co ng knh nho hn va co mot au con tao nen c cau van. au con ty vao e kim phun, pha di no la mot khong gian m.


The sprayer holes are drilled through the tip and connect into the space below the needle.

The end of the valve spindle is of

reduced diameter and forms an annulus within the guide end, into which both fuel inlet drilling and priming valve drilling lead.

On the upper end of the valve spindle is a disc on which the valve spring bears. A similar disc on the top of the spring bears on the spring adjustment screw.

The nozzle end is fastened to the body by capnut. The faces between the parts carrying high-pressure fuel are lapped together to make them oil-tight.

The valve is held in the cylinder cover by studs passing through the flanged end of the valve body. O rubber ring may be fitted around the top of the valve to prevent fluids and dirt entering the valve pocket. Gas-tightness is made by a lapped joint between the end of the valve and the cylinder cover.

The valve is opened by a shock wave and by oil pressure within the annular formed at the end of the valve spindle where it is machined to a smaller diameter. Once the needle valve lifts off its seat the effective area subject to oil pressure increases from the annular area to the full cross-section area of the spindle. This gives the valve a good effective lift and prevent any bleeding action occurring across the valve seat.

Cac lo phun c khoan qua au bep va noi vi khong gian di kim phun.

au cua cac kim phun co ng

knh nho bac va tao mot vanh trong au dan hng ma ca ng khoan nhien lieu vao va ng xa e eu hng vao o.

au tren cua kim phun la mot a

co lo xo ty tren o. Mot a tng t nh cua lo xo vt ieu chnh lo xo.

au bep c gan chat vao than bi

mu chup bep. Be mat gia cac phan dan nhien lieu ap suat cao c ra kht vi nhau e kn dau.

Voi phun c gan vao nap xilanh

nh gujong xo qua mat bch cua than voi phun. Vong O ring cao su co the c lap quanh nh cua voi phun e tranh chat long hoac chat ban chui vao khoang voi phun. Su kn kh c thc hien bi joang kht gia au voi phun va nap xilanh.

Voi phun c m do song xung

ong va bi ap suat dau trong vanh khan c tao nen au kim phun la ni c che tao e co ng knh nho hn. Mot khi van kim phun c nang len khoi e cua no, tiet dien hieu dung chu ap lc tang t dien tch vanh khan ti tiet dien ngang toan bo cua kim phun. ieu nay cho voi phun co hieu qua nang tot va tranh dien ra ro r xay ra ngang e kim phun.


The number of sprayer holes in a fuel injection valve tip varies between three and eight, and they may have a diameter of 0.075 mm to 0.5 mm. They will be located to give the most effective spray pattern. Some valve atomizer tips have holes of two different sizes.

Small high-speed engines with pre-combustion chambers may have only one centrally located hole in the tip. The fuel valves of small engines do not have cooled atomizer tips.

3.6 When a fuel valve is being tested the spray coverage is much greater than the cylinder diameter. If the injection test pressure and valve lift are correct, what occurs in the cylinder to prevent the fuel particles coming into contact with the piston or cylinder?

When a fuel valve is tested the spray emerges into air at normal temperature and pressure, which is less dense than the air in a cylinder at the end of compression. Resistance to movement of the fuel particles in dense air is much greater than in air at atmospheric pressure; hence the spray coverage will be much less when it emerges into air at high pressure and temperature, as in the combustion chamber.

3.7 What is the shape of the spray extending from a hole in a fuel atomizer during injection of fuel?

The spray pattern of the fuel is cone shaped. The density of the fuel particles is greater towards the center or core of the cone.

So lo phun trong au bep phun thay oi gia ba va tam lo, va chung co the co ng knh 0.075 mm ti 0,5 mm. Chung se c khoan tai ni tao hng phan bo chum tia hieu qua nhat. mot so au bep cac lo co hai kch thc khac nhau.

ong c cao toc nho co buong d

chay co the ch co mot lo phun au bep. Voi phun ong c nho khong lam mat au bep.

3.6 Khi voi phun c th th mc

o bao phu chum tia ln hn nhieu ng knh xilanh. Neu ap suat th va o nang ung, cai g xay ra trong xilanh e tranh hat nhien lieu tiep xuc vi piston hoac xilanh?

Khi voi phun c th chum tia xuat hien trong khong kh ap suat va nhiet o bnh thng co ty trong nho hn kh trong xilanh cuoi ky nen. S can tr chuyen ong cac hat nhien lieu trong kh am ac nhieu hn khong kh trong ieu kien ap suat kh quyen; do vay o bao phu chum tia nhien lieu se nho hn nhieu khi no the hien trong moi trng kh ap suat va nhiet o cao, nh la trong buong chay.

3.7 Dang cua chum tia phat trien t

lo phun au phun trong khi phun nhien lieu co hnh dang g?

Dang cua chum tia nhien lieu co dang hnh chop, mat o cua cac hat nhien lieu ln hn loi hoac tam cua chum tia dang hnh chop.


3.8 Describe the action that takes place in the fuel pump, piping and injection valves just prior to and during injection of fuel.

Before fuel can be injected into a cylinder the pressure must rise to the point at which the fuel valve lifts. The pressure required will depend on various factors, but will be between 245 and 445 bars. Whilst the pressure is rising the parts of the system including the fuel pump, piping and valve will be subjected to an increasing total strain. The increase in strain causes an increase in the volume of the space containing the fuel and requires some time period for the effect to take place; the time period is very small.

The cam and fuel pump design is such that the initial upward movement of the fuel ram continues with increasing acceleration. During this initial acceleration fuel is discharged back into the suction side of the fuel pump, and by the time the inlet port or suction valve is closed the fuel-pump ram is moving at high velocity.

The rate of pressure rise is very high and transmits a shock wave through the oil contained in the fuel-pressure piping: this shock wave causes the injection valve to lift, and injection commences. The fuel pressure continues to rise after injection commences at a rate dependent on the rate of fuel injection. The time taken for valve opening during the rising pressure period is referred to as injection lag. It may be given as a measurement of time or as a crank displacement angle.

3.8 Mo ta hoat ong dien ra bm nhien lieu, ng ong va voi phun trc va trong khi phun nhien lieu.

Trc khi nhien lieu c phun vao xilanh, ap suat phai tang ti mc tai o kim phun nhac len. Ap suat yeu cau se phu thuoc vao cac yeu to khac nhau, nhng se nam trong khoang 245 ti 445 bars. Trong khi ap suat tang cao cac phan cua he thong ke ca bm cao ap, ng ong va van se chu s gia tang do keo dan tong cong. Viec tang s gian n gay tang mot the tch trong khong gian cha nhien lieu va yeu cau mot khoang thi gian danh cho hieu ng nay; giai oan nay rat nho.

Thiet ke cam va thiet ke bm cao ap theo cai cach chuyen dch len khi au cua piston bm cao ap se tiep tuc vi s tang gia toc. Trong luc gia toc khi au nay, nhien lieu c ay ngc ve pha nap cua bm cao ap, va vao luc ca nap hoac hut c ong, piston bm ang chuyen ong vi toc o cao. Mc tang ap se rat cao va truyen mot song ap lc qua nhien lieu cha trong ong co ap; song xung ong nay lam kim phun nang len, va s phun bat au. Ap suat nhien lieu tang tiep sau khi bat au phun toc o tuy thuoc toc o phun nhien lieu. Thi gian danh cho giai oan tang ap ti khi voi phun m ra c goi la thi gian tre. No co the c nhan gia tr nh thi gian o c hoac goc quay cua truc khuyu


When the fuel pressure falls at the end of injection the material of the parts of the fuel system reverts to its normal size.

3.9 Fuel may be metered by controlling the fuel pump suction valve or by helix and port control. What important difference in effect does each system have on injection timing with change of load.

Fuel pumps using the suction valve to control fuel quantity complete injection at the same crank position, irrespective of load. As the load increases the suction valve must close earlier and injection commence earlier.

Fuel pumps metering fuel quantity by lower helix and port control commence injection at the same crank position, irrespective of load. As the load increases completion of injection must occur later.

3.10 Why is it necessary to atomize the fuel charge when it is injected into the cylinder?

The time available for combustion of fuel is very small and by atomizing the fuel it is possible to complete combustion within this time.

The time required to complete combustion will be related to the time required for a fuel particle to burn, which is in turn dependent on its size, and to the length of the injection period.

Combustion also depends on an adequate supply of air, and as the particles are reduced in size the total surface of all the particles is increased, allowing air to be more easily available to the particles.

Khi ap suat sut xuong luc ket thuc phun, vat lieu cac chi tiet cua he thong phun phuc hoi lai kch thc bnh thng cua no.

3.9 Nhien lieu co the c nh lng bang cach ieu khien van nap bm hoac bi ieu khien ranh xeo va ca nap. S khac nhau quan trong nao ve hieu qua moi he thong co thi iem phun vi s thay oi tai ?

Bm cao ap s dung van nap ieu khien ket thuc phun lng nhien lieu cung v tr khuyu, bat luan tai nao. Khi tai tang van nap phai ong sm hn va nhien lieu bat au phun sm hn.

Bm cao ap nh lng nhien lieu bi ieu khien ranh xeo di va ca nap bat au phun cung v tr khuyu, khong ke g ti tai. Khi tai tang viec ket thuc phun nhat nh xay ra tre hn.

3.10 Tai sao can phun sng nhien lieu khi no c phun vao xilanh?

Thi gian danh cho s chay nhien lieu rat nho va nh s hoa sng cua nhien lieu ma cho kha nang ket thuc chay trong thi gian nay.

Thi gian yeu cau ket thuc chay lien quan ti thi gian can cho cac hat nhien lieu chay, no phu thuoc lan lt vao kch thc cua no, va o lau dai cua giai oan phun.

S chay cung phu thuoc vao viec cung cap u khong kh va khi cac hat nhien lieu giam kch thc xuong th be mat tong cong cua tat ca cac hat nhien lieu c tang len, cho phep khong kh de tiep can hn vi hat nhien lieu.


3.11 Describe how the combustion of fuel commences and proceeds in a diesel engine cylinder.

Combustion of the fuel charge takes place in three distinct phases, which are shown on a pressure-crank displacement diagram or an out-of-phase indicator card.

The fuel emerges into the cylinder as small liquid particles which are surrounded by hot compressed air. They receive heat from the air, and the more volatile constituents of the fuel vaporize. The vapor formed surrounds each particle and leaves a trail as the particle moves into the combustion chamber.

The shape of the spray from each nozzle hole is conical and the particles are at a greater density at the central core of the cone; the fuel particles on the outside of the cone therefore receive heat faster than those towards the core. After the start of injection, self-ignition of the vapor occurs and combustion commences. The time span between commencement of injection and the start of ignition is referred to as the ignition delay period. During the ignition delay period a large part of the fuel charge is prepared for combustion. After ignition commences flame propagation proceeds very quickly in the fuel particles/fuel vapor/air mixture, accompanied by rapid temperature and pressure increase. The pressure increase is accentuated by upward movement of the piston.

4.11 Mo ta nhien lieu bat au chay va dien tien trong xilanh ong c diesel nh the nao?

S chay cua nhien lieu dien ra theo ba pha ro ret thay c o thc ap suat-dch chuyen cua khuyu hoac la gian o khai trien may o o thc.

Nhien lieu xam nhap vao xilanh nh cac hat chat long nho nhanh chong c bao quanh bi kh nong. Chung nhan nhiet t khong kh nong, va cac hp chat de hoa hi cua nhien lieu se bay hi. Hi c tao bao quanh tng hat mot va e lai mot vet khi hat chuyen ong vao trong buong chay.

Dang cua chum tia t tng lo phun co dang chop non va cac hat co t trong ln hn tap trung loi gia cua chop; cac hat nhien lieu pha ngoai cua chop do vay nhan nhiet nhanh hn cac hat pha loi. Sau khi bat au phun, s t chay cua hi xay ra va s chay bat au. Khoang thi gian gia luc bat au phun va bat au chay uc goi la giai oan cham chay. Trong giai oan cham chay mot phan ln nhien lieu phun c chuan b cho s chay. Sau khi s chay bat au ngon la lan toa rat nhanh trong hon hp hat / hi nhien lieu / khong kh, cung vi tang nhiet o va ap suat nhanh. Ap suat tang c nhan manh them bi s i len cua piston.


This second phase of combustion is shown on the pressure-crank displacement diagram as a turning point in the compression curve, after which the pressure rise is very rapid; this point marks the commencement of the second phase of combustion.

Towards the end of the rapid pressure rise a point will be reached where the rate of pressure rise falls away quickly, and the curve flattens out towards the maximum-pressure point. The point where the rate of pressure rise changes, near and approaching the maximum-pressure point, marks the end of the second phase of combustion. This point usually occurs just prior to the end of injection.

The third phase of combustion shows only a small pressure rise, as the rate is decreased due to downward movement of the piston. The end of combustion occurs approximately at or slightly beyond the maximum-pressure point.

3.12 What is afterburning and how

is it caused? Afterburning is said to occur when

the third phase of combustion extends over a long period. It may be caused by incorrect fuel grade, bad atomization, poor or excess penetration, incorrect fuel temperature, incorrect timing, insufficient air supply, or any combination of these.

3.13 What effects does afterburning

have on an engine?

Pha th hai cua s chay nay c thay tren o thc ap suat goc quay truc khuyu nh iem oi hng ng cong nen, ma sau iem o ap suat tang rat nhanh; iem nay anh dau s bat au cua pha chay th hai.

Ve pha cuoi cua giai oan tang nhanh ap suat co mot iem tai o o tang ap suat giam xuong nhanh chong, ng cong hi be ra ve pha iem ap suat cc ai. iem tai o mc tang ap suat thay oi, gan va tiep can vi iem ap suat cc ai se anh dau s ket thuc cua pha th hai cua s chay. ieu nay thng xay ra ngay trc thi iem ket thuc phun.

Giai oan th ba cua s chay ch cho thay mot s tang ap suat nho, v toc o b giam do chuyen dch xuong cua piston. Ket thuc cua s chay xay ra xap x tai hoac vt qua mot chut iem ap suat cc ai.

3.12 S chay rt la g va no co nguyen nhan nh the nao?

Chay rt c noi ti xay ra khi pha th ba cua chay keo dai tren mot giai oan dai. No co the co nguyen nhan t loai nhien lieu khong ung, phun sng kem, o phun xa kem hoac qua mc, nhiet o nhien lieu khong ung, nh thi sai, kh cap khong u, hoac bat ky s ket hp nao cua nhng cai o.

3.13 Chay rt gay anh hng g ong c?


Afterburning creates high exhaust temperatures and may cause overheating of the engine in severe cases. It is usually accompanied by some drop in the maximum firing pressure. There is a loss of thermal efficiency when afterburning occurs, due to a greater loss of heat to exhaust gases and the transfer of larger amounts of heat to the cooling water. There is a risk of damage to exhaust valves and of scavenge fires.

3.14 how does the viscosity of a fuel change with increase of pressure?

As the pressure rises in the fuel system during injection there is a considerable rise in the viscosity of the oil under pressure.

The following table shows the approximate viscosity increase for an oil under pressure at constant temperature. Pressure - bar Appro. Increasing of

positive viscosity 0

100 200 300 400 500

0 1.26 1.63 2.09 2.68 3.44

If fuel injection pressure is 400 bars it can be seen that the increase in absolute viscosity is 2.68 times the absolute viscosity at zero gauge pressure.

3.15 What is the fuel viscosity range

within which fuel injector valves are designed to work.

Chay rt lam nhiet o kh xa cao va co the lam qua nhiet ong c trong cac trng hp nghiem trong. No thng ong hanh vi sut chut t ap suat cc ai. Ton that nhiet khi chay rt xay ra do ton that nhiet kh xa ln hn va truyen mot lng ln hn nhiet cho nc lam mat. Co nguy c h hong suppap xa va chay khoang quet.

3.14 o nht cua dau thay oi nh

the nao vi viec tang ap suat? Khi tang ap suat trong he thong

nhien lieu trong khi phun co mot s tang ang ke o nht cua dau di tnh trang ap suat.

Bang sau ay cho thay s tang o nht xap x oi dau co ap nhiet o khong oi

Ap suat - bar o tang gan ung cua

o nht tng oi 0

100 200 300 400 500

0 1.26 1.63 2.09 2.68 3.44

Neu ap suat phun la 400 bar co the thay o nht tuyet oi bang 2.68 lan o nht tuyet oi khi ap suat ong ho bang zero

3.15 Voi phun c thiet ke lam viec vi khoang o nht nao cua nhien lieu ?


The size of the hole in the sprayer nozzle is designed for fuels within a viscosity range 40 to 90 second Redwood N0 1. at 38 0 C and at atmospheric pressure. In engines using high-viscosity fuel blends the temperature of the fuel is raised until a suitable viscosity is obtained.

3.16 What is the consequence of operating an engine on high-viscosity fuel at too low a temperature?

If an engine is operated with a fuel of the high-viscosity type at too low a temperature the injection viscosity will be too high. This will affect the degree of atomization and penetration.

With a small decrease below the correct fuel temperature poor atomization and penetration will cause afterburning to occur. Further decrease of the fuel temperature increases the amount of afterburning. Eventually the point will be reached when fuel will come into contact with the piston crown, the sides of the piston, and the cylinder walls and will burn on the surfaces of these parts. The fuel coming into contact with the cylinder walls destroys the lubricant and causes increases wear. Fuel on the piston sides enters the ring grooves, forms carbon, and eventually seizes the rings in the grooves so that blow-past occurs; finally the sides of the piston burn away in localized areas.

Whilst an engine will continue to operate with fuel at quite low temperatures, the consequences are disastrous and result in very costly repair

Kch thc lo phun au phun c thiet ke cho nhien lieu trong khoang o nht 40 ti 90 Second Redwood N0 1 tai 38 0 C va tai ap suat kh quyen. ong c s dung nhien lieu nang pha tron, nhiet o cua nhien lieu can c tang len ti khi at o nht phu hp.

3.16 Hau qua cua s khai thac ong c nhien lieu co o nht cao tai nhiet o qua thap la g?

Neu ong c hoat ong vi nhien lieu loai o nht cao tai nhiet o qua thap th o nht cua nhien lieu phun se qua cao. ieu nay se anh hng ti o phun sng va phun xa.

Vi s giam nho di nhiet o chnh xac cua nhien lieu, s phun sng va o phun xa kem se lam chay rt xay ra. S giam hn na cua nhiet o nhien lieu tang qua trnh chay rt. Cuoi cung, s gii han xay en la khi nhien lieu phun se tiep xuc vi nh piston, mat canh piston va thanh xilanh va se chay tren be mat cac phan o.

Nhien lieu phun tiep xuc vi vach xilanh se pha huy dau nhn va lam tang mai mon. Nhien lieu tren be mat canh piston se vao ranh vong xecmang, tao carbon va cuoi cung la lam ket vong xec mang trong ranh va e xay ra lot kh. Cuoi cung mat canh cua piston chay xem cuc bo.

Khi nhien lieu lien tuc hoat ong vi nhien lieu tai nhiet o thap hoan toan, hau qua se la tham hoa va oi hoi gia chi ph rat cao cho sa cha e khac phuc h hong.


3.17 Brief describe the various causes of dard-coloured smoke in the exhaust gas of a diesel engine.

Dark-coloured smoke is caused by fine unburn carbon particles being present in the exhaust gases owing to poor or incomplete combustion of the fuel. The shade darkens as the amount of carbon particles in the gas increases. Poor combustion is usually due to faults in the fuel injection equipments or to insufficient air supply.

Possible faults in injection equipment are dirty injector tips, incorrect spring setting pressure, incorrect valve lift, or incorrect timing of fuel-injection pumps, leakage of fuel from individual fuel pumps, pipes and valves can cause imbalance of power and overloading of the other cylinders.

Air supply may be insufficient because of dirty air filters, faults in turboblows, worn-out inlet valve cams, or dirty scavenge ports.

3.18 How would you investigate and

find the causes of an engine smoking? When starting to investigate the

cause of smoke there may be some difficulty in locating which engine is smoking, since wind may drift the smoke from one exhaust pipe over another. When the offending engine has been identified it must be investigated to find if one cylinder is causing the trouble or whether the fault is in all cylinders.

3.17 Mo ta ngan gon cac nguyen nhan khac nhau cua khoi en tao ra kh xa cua ong c diesel.

Khoi en c tao t cac hat muoi than khong chay rat mn ton tai kh xa do s chay khong hoan toan cua nhien lieu. Mau en kt do lng hat cac bon trong kh xa tang. S chay kem thng do h hong thiet b nhien lieu hoac do khong kh khong ay u.

H hong co the he thong nhien

lieu la au bep phun ban, ap suat at lo so sai, o nang kim phun khong ung, hoac nh thi khong ung bm cao ap, ro r nhien lieu t cac bm cao ap at rieng, ong va van co the lam lech cong suat va qua tai cac xilanh khac.

Cung cap khong kh co the khong

am bao do phin loc kh b ban, h turbine tang ap, cam nap kh b mon, hoac ca quet b ban.

3.18 Anh se nghien cu va tm

nguyen nhan mot ong c co khoi nh the nao?

Khi bat au kiem tra nguyen nhan khoi co mot so kho khan trong viec xac nh ong c b khoi, v gio se lam dat khoi t ng kh xa nay len ng kia. Khi phat hien ong c co van e nhat nh phai nghien cu e tm mot xilanh tao ra s co hoac xem lieu co phai la tat ca cac xilanh khong gay ra truc trac ky thuat hay khong.


The plugs or cocks that are usually found on each exhaust elbow or branch leading into the manifold should be removed one at a time, and the exhaust gases examined for smoke as they blow out. It is sometimes helpful to use a white surface with good light-reflecting qualities and extra lighting to assist in the observations. If all the cylinders are found to be smoking, then the following points should be checked.

Engines operating on heavy fuel should have the fuel temperatures checked and corrections made if necessary

If the fuel temperature is correct and the engine is pressure charged, the air-inlet filters and downstream air pressure should be checked and related to engine load and turbo-blower revolutions. A common cause of trouble is dirty air filters, particularly if the atmosphere is dusty as can occur in certain parts of the world or when handling dusty cargoes in port. Dirty air filters usually increase the exhaust temperature on all cylinders, but the rise may not be the same on each. Most naturally aspirated engines are fitted an air-intake filter to the inlet manifold, but it is not usual to find instrumentation on the manifold. Dirty air filters on these engines will show up on the induction pressure line on a light-spring indicator card. If an indicator and spring suitable for the engine speed are available a light spring card should be taken. If no indicator is available then the air filter should be temporarily removed and a check made to

Cac nut bt hoac van van thng thay tng cho khuyu vong hoac nhanh xa dan ti ong gop kh se phai c thao rieng tng cai ra, va kh xa phai c kiem tra xem chung co khoi muoi khi chung thoi ra khong. Thnh thoang nen dung dung be mat trang co o phan anh tot va nguon sang phu e ho tr quan sat v chung se rat hu ch. Neu moi xilanh c phat hien co khoi, th cac iem sau ay se c kiem tra ke o:

ong c hoat ong dau nang se phai kiem tra nhiet o nhien lieu va tien hanh sa lai cho ung neu can.

Neu nhiet o nhien lieu ung va ong c c tang ap, phin loc kh va ap suat ay se phai c kiem tra va phai lien he ti tai va vong quay may nen. Nguyen nhan thong thng cua s co la ban phin loc, ac biet neu moi trng bui ban la ieu co the xay ra mot so ni tren the gii hoac khi lam hang co bui ban cang. Phin loc kh ban thng lam tang nhiet o kh xa moi xilanh, nhng s tang khong giong nhau moi cai.

Hau het cac ong c nap kh t nhien co at mot phin loc kh nap ong gop nap, nhng khong thng thay dung cu o khoang gop kh. Phin loc kh ban cac ong c nay se the hien ro ng ap suat nap tren o thc o indicator dung lo xo yeu. Neu co san mot indicator va lo xo phu hp cho toc o ong c th co the lay o thc dung lo xo yeu c. Neu khong co indicator th phin loc se c thao tam thi va kiem tra xem lieu ong c co khoi khong.


In some cases the air filter can be removed without stopping the engine, but if there is any danger, the engine should be shut down to remove the filter and then re-started the check to make the check, which must be made with the engine on the same load as before.

Two-stroke port-scavenged engines may smoke when the scavenge ports become fouled, but this fault will be indicated by a rise in scavenge pressure or turbo-blower discharge pressure.

Smoke from an individual cylinder is usually found to be due to a dirty fuel valve or valves. If, after the fuel valve has been changed, the cylinder unit is still found to smoke, then checks will have to be made on the fuel-pump delivery pressure, fuel-pump delivery valves (if fitted), maximum firing pressure, and exhaust temperatures. If the engine speed is such that an out-of-phase indicator card can be taken, the combustion pressure rise and compression pressure should be checked-with the indicator by taking an out-of phase card and a compression card, which should be checked for abnormalities.

When a fuel valve is changed the old valve should be checked for leakage, setting pressure, and lift. The condition of the sprayer holes, hole edges and diameter of the hole should also be carefully checked. If any condition is found that might cause smoke it can be corrected when the valve is overhauled.

Trong mot so trng hp phin loc kh co the c thao ra khong can dng ong c, nhng neu co bat ky mot nguy c nao, ong c nen c ngng e thao phin loc roi khi ong lai e kiem tra vi tai tng t nh luc trc.

Cac ong c hai ky, quet vong co the b khoi khi ca quet ban nhng sai lech nay se c ch th bi s tang cao ap suat quet hoac ap suat ay cua turbine tang ap.

Khoi t nhng xilanh rieng biet thng c thay do voi phun hoac suppap ban. Neu, sau khi voi phun a c thay, xilanh van thay co khoi, th tiep o se phai kiem tra ap suat bm cao ap, van cap dau ( neu lap), ap suat chay max, va nhiet o kh xa. Neu toc o ong c gia tr cho phep lay o thc bang indicator, s tang ap suat chay va ap suat nen se c kiem tra bang o thc lay kieu khong phan chia pha va o thc qua trnh nen la th dung e kiem tra cac s bat thng.

Khi voi phun c thay th voi phun cu se c kiem tra mc ro r, ap suat at, va o nang. Tnh trang cua cac lo phun, ra lo phun va ng knh cua lo phun se c kiem tra can than. Neu bat ke tnh trang nao thay co the tao khoi, no co the c hieu chnh lai khi voi phun c thao kiem tra toan bo.


3.19 What is the cause of patterned carbon formations building up on fuel-valve nozzle?

This phenomenon may be found on any fuel-valve nozzle but is usually seen on fuel valves using high-viscosity fuel. The carbon builds up into petal or trumpet formations that interfere with the spray pattern and cause poor combustion resulting in smoke, high exhaust temperatures, and increased fuel consumption.

Between the fuel-valve seat and the spray holes is a small space, sometimes called the sac. After fuel injection the sac contains fuel which can become overheated.

This, in mild cases, causes some fuel to issue from the spray holes, which burns or cokes and forms carbon around the edge of the holes. The carbon formation gradually builds up and interfere with the spray pattern, affecting atomization and penetration and consequently causing afterburning. In severe cases the lighter constituents of the fuel may boil and burn within the sac. The trouble is usually caused by operating the fuel-valve cooling service at too high a temperature, in which case lowering the temperature of the coolant discharge, will solve the problem.

A secondary cause is poor closing of the fuel valve e.g. sluggish shut-off, which allows oil to bleed slowly at and towards the end of injection. If this secondary cause is present with the first then serious combustion problems may arise.

3.19 Nguyen nhan cua tao muoi than ac trng bam au bep phun la g?

Hien tng nay co the thay c bat ky au bep phun nhng no thng c thay voi phun s dung nhien lieu o nht cao. Muoi than ong thanh dang canh hoa hoac loa ken lam anh hng ti dang chum tia va lam chay xau gay khoi, nhiet o kh xa cao va suat tieu hao nhien lieu tang.

Gia e kim phun va cac lo phun co mot khong gian nho, thnh thoang c goi la tui dau. Sau khi phun nhien lieu tui dau van cha nhien lieu, nhien lieu nay co the tr thanh qua nhiet.

ieu nay, trong trng hp nhe, lam mot so nhien lieu r t cac lo phun chay hoac ong ket va tao muoi than bao quanh ra cua lo phun. Hnh dang muoi than t t nh hnh va gay tr ngai dang phun, anh hng ti phun sng va o phun xa va ket qua la gay chay rt. Trong trng hp nghiem trong cac hp phan nhe cua nhien lieu co the soi va chay trong tui dau. Van e thng c gay bi hoat ong lam mat voi phun nhiet o qua cao, trng hp o ha thap nhiet o lam mat se giai quyet c van e.

Nguyen nhan th hai la s ong kn voi phun kem, ngha la ong khong dt khoat, cho phep dau r cham tai va gan luc ket thuc phun. Neu nguyen nhan th hai nay ton tai cung vi nguyen nhan au th van e chay kem nghiem trong co the nay sinh.


3.20 What is the shape and angle for fuel valves and fuel-valve seats?

Fuel valves and seats are usually conical, but some valves are flat on the end and land on to a flat seat.

There is no set angle for the needle end of the valve, as manufacturers decide on the angle which they feel gives the best service. Generally the included angle of the needle used by the various markers is between 400 to 700 .

When conical ends are used the outer end of the cone is ground to a slightly larger angle than the angle between the contact surface of the valve and seat. This difference in angle then provide an increasing linear clearance from the outer contact line of the valve and seat to the end of the needle seat. In practice it is found that this clearance gives sharper closing of the valve and reduces any tendency to dribble during the cut-off period. The clearance also allows for longer periods between fuel valve changes or overhauls.

3.21 How does atomization and penetration occur during injection?

When the fuel passes from the valve to the combustion space it is at high pressure. As it passes between the valve and its seat, the small clearance ( when the valve is open ) causes eddies to occur as the fuel passes into the sac. From the sac the fuel passes through the sprayer holes. As the fuel is moving through the sprayer the friction between the hole and the fuel causes further eddies to be set up in the layers of fuel adjacent to the sides of the sprayer hole. The fuel in the center of the hole has less disturbance.

3.20 Hnh dang va goc oi vi kim phun va e kim phun la g?

Kim phun va e thng la hnh con, nhng mot so kim phun la phang au va nam tren e phang.

Khong co gia tr goc quy c trc cho au kim phun v nha may che tao se quyet nh goc o ma ho thay hoat ong tot nhat. Thng goc c biet en cua kim phun s dung bi cac nha che tao khac nhau nam trong khoang 400 700.

Khi au hnh con c s dung, au ngoai cua con c mai ra co goc ln hn chut t goc gia phan be mat tiep xuc cua kim phun va e. S khac nhau nay goc cho tiep kha nang tang khoang thang t ng tiep xuc pha ngoai cua kim phun va e ti iem ket thuc cua e kim phun. Thc te thay rang khoang nay lam cho viec ong kn hn cua kim phun va giam moi khuynh hng nho giot trong giai oan ngat phun. Khoang nay cung cho phep thi gian gia cac lan thay the hoac thao bao dng voi phun dai hn.

3.21 S phun sng va phun xa xay ra trong khi phun nh the nao?

Khi nhien lieu qua au phun vao khong gian buong chay, nhien lieu co ap suat cao. Khi no qua vung gia au kim phun va e cua no, khe h nho ( khi voi phun m ) lam xay ra xoay loc khi nhien lieu chay vao tui dau. T tui dau nhien lieu chay qua lo phun. Khi nhien lieu chuyen ong qua au phun, ma sat gia nhien lieu va thanh lo gay xuat hien s xoay cuon manh hn na cac lp cua nhien lieu ke can vi cac canh cua lo phun. Nhien lieu trung tam lo co t van ong roi hn.


As the fuel issues from the sprayer hole it meets the dense air in the combustion chamber. The fuel at the outer surface of the jet emerging from the hole is in a turbulent state from the eddies created within the sprayer hole. The friction from the dense air causes these fuel particles to separate from the outer layers of the jet. The fuel from the center of the hole has much less turbulence and penetrates further into the combustion chamber. As the outer layers of fuel break off into separate particles the inner parts of the jet become subject to air friction.

By the time this happened the pressure within the cylinder has risen owing to the heat and pressure rise from combustion of the outer layers, and the friction effects increase as the gas pressure in the cylinder rises.

Since the fuel in the center of the jet has less turbulence, the density of the particles in the central core is greater than that of the particles at the outer layers of the spray pattern.

The degree of atomization and penetration is dependent on the viscosity of the fuel. If the viscosity is too high atomization is reduced and penetration is increased; if the viscosity is too low atomization increases and penetration decreases.

3.22 What is the direction of fuel spray relative to air movement or turbulence within an engine with an open combustion chamber?

Khi nhien lieu phun t cac lo phun, no gap kh am ac trong buong chay. Nhien lieu be mat ngoai cua dong phun tnh t lo phun se tnh trang chay roi do xoay cuon tao trong lo phun. Ma sat t kh am ac lam cac hat nhien lieu nay tach khoi cac lp ngoai cua chum tia. Nhien lieu t trung tam cua lo co t van ong roi hn va phun xa hn vao buong chay. Khi cac lp ngoai vi cua nhien lieu v thanh cac hat sng th cac phan ben trong cua chum tia tr thanh oi tng cua ma sat khong kh.

Vao luc ieu nay xay ra ap suat trong xilanh tang len do tang nhiet o va ap suat t phan ng chay cua cac lp ngoai chum tia nhien lieu, va anh hng ma sat se tang khi ap suat kh trong xilanh tang.

V nhien lieu tam cua chum tia nhien lieu t van ong roi hn, mat o cua cac hat loi trung tam ln hn mat o cac hat tai cac lp ben ngoai cua chum tia.

Mc o sng va phun xa phu thuoc vao o nht cua nhien lieu. Neu o nht qua cao o phun sng giam xuong va o phun xa c tang len; neu o nht qua thap o phun sng tang va o phun xa giam.

3.22 Hng cua chum tia nhien lieu quan he vi chuyen ong kh hoac van ong roi trong ong c co mot buong chay thong nhat nh the nao?


Usually the spray direction is approximately 900 to the direction of air motion. Some engines with two or more fuel valves inject it is tangential to the cylinder bore and in the same direction as the rotation of the air. There is no clear formula or rules on fuel spay direction relative to direction of air movement. Generally a small amount of turbulence is preferred to large amounts. Perfecting of combustion is conducted on the test bed during development of new engines, and sometimes very small changes have large overall effect on combustion and fuel consumption.

3.23 What is the shape of the hole and the material section surrounding a fuel valve sprayer?

The spray holes are drilled with small-diameter drills from the outer part of the tip into the sac space. The transverse section of the hole is circular.

The thickness of the metal of the tip is arranged to give a certain ratio of length of hole to hole diameter, which is often of the order of 3 to 1, although wider variations may however be found. And increased length of hole in relative to hole diameter increases the amount of fuel penetration. There is also a relationship between cylinder diameter and hole diameter.

The ends of the hole are usually left clean and square as any further work on them greatly increases production costs.

Thng hng phun la xap x 900 oi vi hng chuyen ong cua khong kh. Mot so ong c co hai voi phun hoac nhieu hn hng se tiep tuyen vi smi xilanh va cung hng vi chieu quay vong cua khong kh. Khong co cong thc cu the hoac nh luat ro rang ve quan he hng phun vi hng chuyen ong cua khong kh. Thng mot lng nho chuyen ong roi lai tot hn s chuyen ong roi ln. S hoan thien chay c thc hien gia th trong khi nghien cu phat trien ong c, va thnh thoang co cac thay oi rat nho se gay anh hng toan bo ti s chay va tieu thu nhien lieu.

3.23 Hnh dang cua lo phun va mat cat ngang bao quanh mot au phun nhien lieu la g?

Cac lo phun c khoan bang mui khoan rat nho t phan ben ngoai cua bep vao khong gian tui dau. Mat cat ngang cua lo la hnh tron.

o day cua kim loai au bep c bo tr cho ty so gia o dai lo vi ng knh lo gia tr nao o, thng la 3 tren 1, mac dau cung co the gap cac gia tr khac ln hn. Mot chieu dai lo tang tng oi so vi ng knh cua lo se lam tang o phun xa. ng knh lo phun cung co quan he vi ng knh xilanh.

Cac au cua lo thng e trn va ngay ngan v bat ky cong oan tiep theo nao tren o cung se lam tang chi ph che tao len nhieu.


3.24 How would you decide whether a fuel-valve nozzle end was fit for further service?

The decision whether to scrap a fuel-valve nozzle or use it is sometimes difficult to make. Engine instruction books should be consulted for information applicable to the engine concerned.

The diameter of the hole should be checked to see that it is not over-size to the engine builders limits. This check must be made carefully. First, the hole must be cleaned, either by soaking in solvent or by using the cleaning drills and hand chuck provided by the engine builder.

After cleaning with solvent the hole diameter should be checked with go/no-go wire gauges or if the valves are large, with the largest cleaning drill supplied in the cleaning kit. In checking hole sizes care must be taken not to damage the holes, or to break the gauge or drill in the hole. If the hole is oversize to the makers recommendation the nozzle should be scrapped. The condition of the outer surface of the hole is also an indication of fitness or otherwise. If it rounded-off and has lost its square edges it should be scrapped. Comparison of the old nozzle end with a new unused nozzle gives a good indication of whether it is fit for further use, especially if that particular valve has been changed previously because of a tendency to cause smoking when the engine was on load.

3.24 Anh se quyet nh the nao e xem lieu mot au bep phun nhien lieu co con phu hp cac hoat ong ke tiep ?

Thnh thoang kho ma quyet nh lieu nen thai bo mot bep phun nhien lieu hay la dung no. Cac sach ch dan ong c se c dung e tham khao cho cac thong tin ng dung danh cho ong c lien quan.

ng knh cua lo phun se c kiem tra e xem no co vt qua gii han cua nha che tao ong c khong. Kiem tra nay nhat nh phai tien hanh can than. Trc het, lo phun nhat nh phai c lam sach hoac bang cach xuc trong dung dch tay hoac dung au mui khoan sach va au kep s dung bang tay c cung cap bi nha che tao ong c.

Sau khi lam sach bang dung dch tay ra, ng knh lo nhat nh phai c kiem tra bi dung cu calip hoac vi voi phun kch thc ln, bang mui khoan lam sach to nhat c cung cap trong hop dung cu lam sach. Phai can than tranh lam h hong lo hoac gay dung cu hoac mui khoan trong lo khi kiem tra kch thc lo. Neu lo vt qua gia tr khuyen cao cua ngi che tao th au bep phun se phai loai bo.

Tnh trang be mat ben ngoai cua lo cung la dau hieu cho s phu hp hay khong. Neu no b mai tron hoac ra canh khong ngay ngan no se phai b loai bo. So sanh mot au bep cu voi au bep mi cha dung cho gi y tot ve viec lieu no co con phu hp cho hoat ong tiep tuc, ac biet neu voi phun ca biet nao o a c thay the trc o do khuynh hng tao khoi en khi ong c hoat ong co tai.


Fuel leakage across the seat is not usual a cause for scrapping a nozzle end , as leakage can nearly always be rectified.

Sometimes fuel valves are returned to the makers for overhaul, and when this is the case, any valve giving doubts as to condition should be suitably tagged and the facts reported to the superintendent.

3.25 What is the difference between a fuel priming pump and a fuel surcharge pump? How long and when should each be used?

A fuel priming pump is used to prime the fuel pressure pumps, pipe lines and fuel valves on engines fitted with a common-rail fuel system as found on some opposed piston engines. The priming pump should only be used for a few seconds, and if no response is seen on the fuel pressure gauge the cause should be investigated and found before the priming pump is used again.

The common-rail system should be checked for open drains and open bypass valves. The fuel injector valves should also be checked with the hand fork lever to see that they are properly closed. If any are found open, or some doubt exists as to their being properly closed, the scavenge trunk doors should be opened for the presence of fuel oil. If any is present it should be cleaned out.

When the scavenge doors are off, the priming pump may be used again to check the fuel valves for leakage, since any leakage can be seen through the scavenge doors and ports, as the leaking fuel usually runs down the cylinder liner.

Ro r nhien lieu qua e bep phun thng khong la nguyen nhan e loai bo au bep phun v ro r gan nh luon co the khac phuc c.

Mot so voi phun c tra ve cho ngi che tao e kiem tra toan dien va khi thc hien ieu nay, moi voi phun nghi ng nh can lam lai se c gan nhan phu hp va cac s kien c thong bao cho ngi quan ly biet.

3.25 S khac nhau gia bm s cap va bm cap nhien lieu la g? Moi cai can c s dung bao lau va khi nao?

Mot bm s cap c dung e moi cac bm cao ap, ng ong va voi phun ong c co he thong nhien lieu chung nh thay mot so ong c piston oi nh. Bm moi ch c phep chay th vai giay ong ho, va neu khong co bieu hien thay c ong ho ap suat nhien lieu th nguyen nhan can phai c tm hieu va xac nh trc khi bm moi c s dung tr lai.

He thong nhien lieu chung se c kiem tra xem co m xa can va m van tat khong. Voi phun nhien lieu cung phai c kiem tra bang thanh cha lac bang tay e xem rang chung a hoan toan ong cha. Neu bat ky cai g thay la ang m, hoac mot so nghi ng tnh trang ong khong ung, cac ca khoang quet kh phai c m e xem co xuat hien dau. Neu co no phai c lam sach het ngay. Khi cac ca quet kh ang m, bm moi co the c chay lai e kiem tra s ro r voi phun nhien lieu, v moi ro r co the thay c qua cac ca quet cac ca so, do nhien lieu ro r thng chay xuong smi xilanh


The cause of any lack of pressure response on the fuel-pressure gauges, when using the priming pump, must be found before any attempt is made to turn the engine on starting air. Before the engine is put on starting air it must be turned a complete revolution with the turning gear, with the indicator cocks open for observation and the scavenge drains being watched for the presence of fuel oil.

Fuel surcharge pumps are used with high-viscosity fuel to keep the suction side of fuel injection pumps under pressure, thus preventing the hot oil from gassing and forming vapor lock s within the fuel pump.

In most installations the surcharge pump is kept in service from preparing the engine for standby, during maneuvering and passage, and until after the finished with engines order is received.

The fuel surcharge pump is sometimes used only during standby and maneuvering periods if the head from the daily service tank is sufficient to prevent gassing of the fuel in the suction lines and fuel pumps.

Use of the fuel surcharge pump will be different if the engine is maneuvered on diesel fuel. After full away the surcharge pump will be brought into use for the change over to high-viscosity fuel and then kept in use or closed own depending on the head of the daily service tank above the main engine fuel-injection pumps.

Phai c tm ra trc khi co gang lam ong c khi ong bang khong kh nen nhng nguyen nhan cua moi s thieu ap lc the hien ong ho ap suat nhien lieu khi s dung bm moi. Trc khi ong c khi ong bang khong kh nen nhat nh phai quay no mot vong hoan chnh bang may via cung vi van biet xa m e quan sat va can phai quan sat cac ng xa kh quet xem co s hien dien cua nhien lieu khong.

Cac bm cap c dung vi nhien lieu o nht cao e luon duy tr ap suat cao pha nap cua bm cao ap, tranh hien tng dau nong bay hi va tao cac khoa hi trong bm cao ap.

Trong hau het cac bo tr lap at, bm cap c duy tr hoat ong t khi chuan b may e ch lenh, trong khi man va hanh trnh, va cho ti ca luc sau nhan c lenh dng may .

Bm cap ch thnh thoang mi dung khi chuan b va giai oan man neu cot ap cua ket trc nhat u e tranh tao kh cua dau tren ng hut va bm cao ap.

Viec s dung bm cap se khac nhau

neu ong c man bang dau DO. Sau khi hanh trnh bm cap se c a sang chuyen oi dau o nht cao va t o c duy tr hoat ong hoac ngat tuy thuoc vao cot ap cua ket trc nhat pha tren tren bm cao ap ong c chnh.


If no surcharge pump is used during full away operation then temperature of the fuel in the daily service tank must be kept sufficiently high to prevent pipeline friction becoming too much for the head available. If the temperature of the fuel in the tank drops, the fuel viscosity increases and causes line drag. Gassing may then occur on the downstream side of the fuel heater and allow a vapor lock to form in the fuel pumps.

3.26 Describe the removal overhauling procedures and requirement and replacement of large fuel-injection valves.

Removal of fuel-injection valves. The local area around the fuel valve should first be cleaned to prevent an dirt or other material entering or draining into the cylinder. The cooling services must be shut off. After all connections have been removed the valve should be lifted out from the cylinder cover with a direct lead so that the pull is in line with the axis of the valve.

When the valve is removed from the cylinder the nozzle end must be capped off to protect it during transport into racks or stores area. The opening into the cylinder should also be protected with plug or blank to prevent ingress of liquids, dirt and solid objects.

Overhaul of fuel valves. The external parts of the fuel valve must be cleaned, and the fuel valve tested first for lift and injection pressure, and then for leakage or bleed at a pressure just below the lifting pressure. If the valve is found to be fuel-tight it will be a guide to the amount of work required on the valve.

Neu bm tang ap khong c s dung trong hanh trnh th nhiet o ket nhien lieu trc nhat nhat nh phai c gi u cao e tranh ma sat ng ong qua cao oi vi cot ap hien co. Neu nhiet o cua nhien lieu ket giam, o nht nhien lieu tang lam cho ong b can tr. S sinh kh co the xay ra pha ap thap cua phan ham say nhien lieu va cho phep tao cac khoa hi bm cao ap.

3.26 Mo ta trnh t thao kiem toan

bo va yeu cau va thay the cac voi phun nhien leu ln.

Thao voi phun nhien lieu. Khu vc lan can voi phun can phai lam sach trc tien e tranh chat ban hoac vat khac lot hoac chay vao xilanh. Cac hoat ong cua nc lam mat nhat nh phai c ngat. Sau khi moi ng noi c thao voi phun se c nhac khoi nap xilanh vi hng thang e viec keo ra trung tam vi tam truc cua voi phun.

Khi voi phun c thao khoi xilanh au phun nhat nh phai c che chup lai e bao ve no khi van chuyen vao ngan hoac khu vc bao quan. Lo h thong vao xilanh cung se c bao ve bang nut hoac tam chan e tranh cac chat ran, long hoac at ri vao. Thao kiem tra toan bo voi phun. Cac phan ben ngoai cua voi phun nhat nh phai c lam sach, va voi phun c th trc tien xem o nang va ap suat phun, ke o la mc ro lot hoac ro r ap suat di ngay ap suat nang kim phun. Neu voi phun c cho thay la kn nhien lieu th o se la cai c dung e quyet nh quy mo cong viec yeu cau voi phun.


After testing, the valve must be stripped down, the internal parts cleaned with paraffin or solvent and a lint-free rag, and then carefully examined. Any edge-type filters on the valve should also be carefully cleaned. The spray holes and sac should be cleaned either by soaking in solvent or cleaning with the kit supplied by the engine builder. After cleaning, the sac and holes should be washed out with clean paraffin or solvent using a syringe.

The valve seating surface requires very careful examination. If the valve has a conical end, it should be given the lightest smear of blue marking and then put into the cleaned guide and seat and carefully rotated. After removal the conical end should be checked for indication of seating width. If the seating width is narrow and the valve was found to be leaking , it may be lapped with any one of the variety of special lapping compounds available or with jeweler rouge. After lapping , a check should again be made for seat width and if in order then the valve may be reassembled and tested. The condition of the seat should also be checked.

Flat-seated valves should be treated in a similar manner, with the exception of the blue marking check for seat width. The construction of a flat-seated valve is such that width remains very nearly constant. If the end of the flat-seated valve is not counterbored it may be lightly lapped to prevent any small ridges forming, but lapping should be kept to a minimum.

Sau khi th, voi phun nhat nh phai c thao ra, cac chi tiet ben trong c lam sach bang paraphin hoac dung dch tay ra va re lau khong si, va tiep o kiem tra that can than. Moi phin loc kieu ranh kha noi voi phun cung phai c lam sach can than. Cac lo phun va tui dau se phai lam sach hoac bang cach xuc trong dung dch tay ra hoac lam sach bang cac dung cu cung cap bi nha che tao ong c. Sau khi lam sach, tui dau va lo phun phai c ra bang paraphin hoac dung dch sach s dung mot xyranh phun.

Be mat e kim phun yeu cau kiem tra rat can than. Neu kim co dang au con, no se c xoa bot sn loai mn nhat co mac xanh va at vao phan dan hng va e kim phun a c lam sach va quay can than. Sau khi thao ra au kim hnh con phai c kiem tra xem dau hieu cua be rong e kim. Neu be rong e kim hep va thay van ro r, no co the phai ra vi mot trong cac loai bot ra ac biet hoac vi bot anh bong o trang sc. Sau khi ra, viec kiem tra phai tien hanh lai e xem o rong cua e va neu tot roi th voi phun co the c lap lai va th. Tnh trang cua e cung phai c kiem tra.

Voi phun loai e bang se c x ly theo cach tng t tr viec dung bot mau lam dau mau xanh e kiem tra o rong cua e. Cau truc cua voi phun e bang lam be rong e van duy tr gan nh la khong oi. Neu au cua voi phun e bang khong tot no co the c ra nhe e tranh bat ky mot gn nao tao thanh, nhng viec ra phai duy tr mc toi thieu.


If the valve was fuel-tight under pressure it should not be lapped but must be retested for fuel tightness after assembly.

When reassembling fuel valves the threads of the cap nut should be lubricated with the lubricant recommended by the engine builder. In the absence of any instructions molybdenum disulfide grease is often used, but with this grease care must be taken to avoid overtightening parts. If the parts are assembled and tightened to rated torque figures the correct lubricant must be used; if the correct lubricant is replaced by another giving a much lower coefficient of friction the parts will be overstrained during assembly and tightening.

Some fuel valves are constructed in such a manner that the spray comes from one side of the valves or must point in some special direction. These fuel injection valve have locating pins within the various parts to ensure that the spray direction is maintained correctly. Care must be taken during assembly to see that the locating pins are fitted and that they are not damaged or bent.

Testing of fuel valves requires that the valve be set to the correct injection pressure and tested for tightness at a pressure just below the injection pressure.

The lift of the fuel valve should also be correctly set. Some fuel valves have internal spacer ring which are used to limit lift; if the valve is so fitted the lift need usually only be checked and regulated when fitting new parts to the valve.

Neu voi phun kn nhien lieu trong ieu kien ap suat, no khong can phai ra nhng phai th lai xem mc kn nhien lieu the nao sau khi lap rap.

Khi voi phun c lap rap cac ren cua mu chup phai c boi dau nhn bang loai dau nha che tao ong c khuyen cao. Khi khong co mot ch dan nao th m disunfua molipden thng c dung, nhng vi m nay can can than tranh lam cac phan b xiet chat qua. Neu cac phan c lap lai va xiet ti mc mo men quy nh th dau ung quy nh phai c s dung; neu loai dau nay c thay bang dau khac cho he so ma sat thap hn nhieu th cac chi tiet se b qua cang khi lap va xiet oc.

Mot so voi phun co cau truc theo

kieu chum tia phun t mot pha cua au phun hoac iem can thiet mot so hng ac biet. Voi phun nhien lieu nay co chot nh v trong cac phan khac nhau e bao am hng chum tia c duy tr chnh xac. Phai can than khi lap rap e xem xem cac chot c lap va chung khong b h hoac cong.

Th cac voi phun yeu cau voi phun

c at ap suat chnh xac va th kn tai ap suat thap hn ap suat phun mot chut.

o nang cua voi phun se phai c

at ung. Mot so voi phun co vanh nh khoang ben trong s dung e gii han o nang. Neu voi phun c lap nh vay o nang thng ch can kiem tra va ieu chnh khi lap mi cac phan vao voi phun.


The angle of the spray must also be checked. Some engine builders supply a gauge or shroud to carry out this test. This fitted over the nozzle end of the valve and the jets from nozzle must pass through the holes or slots without wetting the surfaces around the hole or slots.

The cooling space or the tip is sealed from the pressure space by lapped surfaces or composition O rings, if the valves are fitted with O-rings they should be renewed at each valve overhaul.

When the seat between the pressure space and the cooling space is made by lapped surfaces, difficulties sometimes arise through leakage of fuel into the cooling space, thus contaminating the coolant. Testing for leakage into the cooling space may be carried out by filling the cooling space with coolant and plugging one of the coolant connections. The other side is connected to a pressure gauge which will register low pressures. Air must be removed from the cooling space before fitting the pressure gauge. The pressure side of the fuel valve is then put under pressure with the test pump and the pressure held at a value approaching the injection pressure. Leakage will show by lowering of pressure on the fuel side and a rise in pressure on the coolant side. Testing for fuel leakage into the cooling spaces requires the test pump to be in first-class condition, and the fuel bypass valve on the fuel valve must be absolutely tight.

Goc cua chum tia nhat nh cung phai c kiem tra. Mot so nha che tao ong c cung cap cong cu hoac vanh bao e thc hien viec th nay. Cai nay gan len tren au bep cua voi phun va chum tia t voi phun nhat nh phai qua cac lo hoac cac khoang ranh khong lam t be mat bao quanh lo hoac ranh trong.

Khong gian lam mat hoac au bep c lam kn t khong gian ap suat bi cac be mat ra kht hoac vong O ring, neu voi phun c lap O ring chung phai c thay mi moi khi thao kiem tra.

Khi e kim phun gia khong gian ap suat va khong gian lam mat c hnh thanh bi be mat ra kht, thnh thoang s kho khan nay sinh do viec ro lot nhien lieu vao khong gian lam mat, v the ma lam nhiem ban nc mat. Co the tien hanh th kiem tra ro lot cua nhien lieu vao khoang nc mat bang cach nap nuc lam mat vao khong gian lam mat va nut bt mot au noi dan lam mat lai. au kia noi ti ong ho ap suat ch ap suat thap. Khong kh nhat nh phai c xa khoi khong gian lam mat trc khi lap ong ho ap suat. Pha ap suat cua voi phun nhien lieu khi o c cap ap suat bi bm th va ap suat c gi gia tr at ti ap suat phun. S ro lot se thay c bi s ha ap suat pha nhien lieu va tang ap pha nc lam mat.

Th ro lot nhien lieu vao khong gian lam mat yeu cau bm th tnh trang hoan hao va van noi tat van voi phun phai c ong chat tuyet oi.


The working space where fuel valves are overhauled and tested must be kept perfectly clean because of the precision required during fitting and assembly: spanners and wrenches used to dismantle and assemble valves must be good fit on the part to be loosened or tightened, as any slackness causes damage and raises burrs. This creates difficulties when subsequently working on the valves. Fuel valves held in a vice should be protected with copper vice clamps.

Fuel test pumps should only be filled with clean filtered oil from clean vessels.

Tins of lapping compound should have the lids replaced so that the compound does not become contaminated with any coarse material which might damage the valve.

When fuel valves are stored in racks after testing , the nozzle protecting caps should be fitted in place and the fuel and cooling connections must be off to prevent entry of dirt or foreign matter. Replacement of fuel valves. After removal of a fuel valve the pocket should be carefully cleaned out and the landing seat in the pocket lapped with the lapping jig. Afterwards the seat must be cleaned and the pocket examined for condition. Prior to the fitting of a fuel valve the landing seat on the fuel valve must be cleaned, and lapped if necessary. The seal ring used to prevent ingress of dirt into the pocket must be fitted on the valve.

Khong gian lam viec ni voi phun c thao kiem tra va th phai gi sach hoan hao do s chnh xac yeu cau trong khi lap rap; cac dung cu mo let, cha khoa s dung e thao lap voi phun phai va kht vi phan can ni long hay xiet chat, v bat ky s d lech nao eu gay h hong hoac tang cac vet xc. ieu nay tao ra s kho khan khi lam viec lan sau vi voi phun. Voi phun nhien lieu gi trong mo cap nen c bao ve bang kep ong.

Cac bm th nhien lieu ch c nap

dau c loc sach t ket sach. Cac hop ng chat bot ra phai co

nap ay e cac bot ra khong b nhiem ban vi bat ky nguon chat tho nao lam hong voi phun.

Khi voi phun c bao quan trong

cac gia sau khi th, cac nap chup bao ve au bep phai at ung v tr va cac ng noi cua nhien lieu va lam mat phai che lai tranh chat ban hoac vat la chui vao.

Thay the voi phun nhien lieu. Sau khi thao voi phun lo lap voi phun phai c lam sach can than va ra bang ban ra cho at voi phun trong lo lap voi phun. Sau o e phai c lam sach va lo lap c kiem tra tnh trang ky thuat. Trc khi lap voi phun phan e t voi phun phai c lam sach, va ra no neu can thiet. Vong kn dung e tranh ro lot chat ban vao lo lap voi phun phai c lap vao voi phun.


Examination of the cylinder space prior to fitting a valve must be done with the piston on bottom center as this obviates blind spots and prevents any object being hidden. After making certain nothing has fallen into the cylinder the fuel valve should be immediately placed in the cylinder cover. The tightening and hardening up of the fuel valve securing studs must be done carefully to ensure that each stud is taking the same load. This prevents distortion of the valve, which may cause difficulties in operation, and it also reduces the chances of gas leakage across the landing face of the valve and cover.

After the engine is under way and at working temperature it is usually necessary to further tighten the fuel-valve securing studs.

In unmanned engine rooms, when the high-pressure fuel pipe connections have been checked following engine operation, the screens and high-pressure pipe covering must be replaced before the engine room is left unmanned. In some cases the coverings must be fitted at the time the fuel pipes are connected; in this case the drain connections from the covering must be broken and the drain checked for oil outflow from any high- pressure connection.

3.27 Describe the methods of checking maximum cylinder pressures. What effects are likely to be experience following operation with too high and too low maximum cylinder pressures? How may the maximum cylinder pressure be

Kiem tra khong gian xilanh trc khi lap voi phun nhat nh phai thc hien vi viec e piston t iem di v ieu nay phong tranh cac lo kho nhn va tranh moi vat b che i. Sau khi khang nh khong co vat g lot vao xilanh, voi phun se c at ngay vao nap xilanh. Viec xiet oc va gi cng cac gujong gi voi phun phai c tien hanh can than e am bao tng gujong chu cung tai nh nhau. ieu nay tranh lam h hong voi phun, ma viec h hong nay gay kho khan trong hoat ong va cung lam giam thieu kha nang ro r kh ngang qua mat ty cua voi phun va nap xilanh.

Sau khi ong c ang hoat ong va tai nhiet o lam viec thng thng can xiet them cac gujong gi voi phun.

cac buong may khong ngi ieu khien, khi au noi ong voi phun ap suat cao c kiem tra sau khi ong c hoat ong, cac man chan va ong che cac ong ap suat cao phai c at lai cho cu trc khi buong may che o khong ngi ieu khien. Trong mot so trng hp cac ong bao che phu nhat nh phai at vao luc ong dau c noi lai; trong trng hp nay viec noi cac ng xa t cac bao che phu nhat nh phai c m va viec xa c kiem xem dau co chay ra t bat ky ng noi ap suat cao nao.

3.27 Mo ta cac phng phap kiem tra ap suat cc ai trong xilanh. Cac tac ong nao co the dien ra sau khi hoat ong vi ap suat xilanh qua cao hoac qua thap? Lam the nao e ap suat cc ai xilanh c tang len hoac giam i


Maximum cylinder pressures may be checked with a normal indicator on slow speed engine; on medium-speed engines they may also be checked with special indicators which have low inertia.

On high-speed engines the maximum cylinder pressure may be checked with a maximum pressure indicator which gives a reading of the cylinder pressure.

When an indicator is used to check maximum pressures, a paper should be fitted on the drum, the atmospheric line should be marked and the cord slowly pulled when making the pressure recording. This will give a wave formed line, the height of the wave peaks giving the maximum pressures when related to the spring number. If there are variations in maximum pressures a mean value must be taken. When taking maximum cylinder pressures the compression pressures should also be recorded. The difference between the maximum pressure and the compression pressure gives the pressure rise from combustion of fuel in the cylinder. If an engine is operated with maximum combustion pressures in excess of the designed maximum combustion, the crankshaft will be subjected to greater stresses than the designed allows for. This may initiate fatigue crack in the crankshaft or engine structure. With modern two-stroke engines, trouble may be experienced with the crosshead bearings or gudgeon pin bearings owing to the excess load. Normally cylinder relief valves should lift and give warning of excess pressure, but if there is any malfunction of the valve then serious damage may occur.

Ap suat cc ai trong xilanh co the c kiem tra bang indicator ong c thap toc; ong c trung toc chung cung co the c kiem tra bang ong ho indicators co quan tnh thap.

ong c cao toc ap suat cc ai co the c kiem tra bang ong ho o ap suat cc ai the hien ap suat xilanh.

Khi mot indicator c s dung e

kiem tra ap suat cc ai, dung mot giay gan vao trong, ng ap suat kh quyen se c anh dau va loi trong c keo nhe tao s ghi ap suat. Lam ieu nay se cho mot ng ve dang song, chieu cao cua nh cac song cho gia tr ap suat cc ai khi lien he vi so cua lo xo. Neu co cac s khac nhau gia tr ap suat cc ai phai lay gia tr trung bnh.

Khi lay ap suat cc ai trong xilanh,

ap suat nen cung se c ghi lai. S chenh lech gia ap suat cc ai va ap suat nen cho mc thay oi ap suat do chay nhien lieu xilanh.

Neu ong c b lam viec vi ap suat

chay cua xilanh qua gia tr chay cc ai thiet ke, truc khuyu se chu ng suat ln hn gia tr cho phep thiet ke. ieu nay co the khi au nt do moi truc hoac cau truc ong c. Vi cac ong c hai ky hien ai, cac s co co the xuat hien cac o cua au ch thap hoac cac o co khuyu do qua tai. Thng van an toan xilanh se no va canh bao ap suat vt qua, nhng neu co s sai lech g o van an toan th cac h hong nghiem trong co the se xay ra.


Operating an engine at low maximum combustion pressure increases fuel consumption progressively as the maximum combustion pressure falls.

The maximum combustion pressure may be increased or decreased by advancing or retarding the fuel-pump cam relative to the crank position. Helix and port control type fuel pumps may also be lowered or raised on their foundation to increase or decrease the maximum cylinder pressure.

In fuel pumps controlled by suction or spill valves, the cam can be advance or retarded by means of a radial spline with very fine teeth cut on the side of a collar and the side of the cam, which is bolted to the collar. The bolts must be released and the cam eased away from the spline in order to advance or retard the cam as required; after adjustment the bolts must be tightened and locked.

Alteration of the cam position by advancing or retarding does not alter the amount of fuel injected.

With helix and port-control fuel pumps one method of advancing or retarding commencement of fuel injection is to raise or lower the fuel pump. Pumps designed for adjustment in this way have a machined plate fitted between the fuel-pump base and the fuel pump foundation or bracket. As wear takes place on cams, bearings, and shafting, it is sometimes necessary to lift off the fuel pump, remove the plate and reduce its thickness by accurate machining. This compensates for the wear which has taken place and restores the maximum pressure to its original value.

Hoat ong ong c ap suat chay cc ai cua xilanh thap lam tang mc tieu thu nhien lieu mot cach t t v ap suat chay cc ai giam. Ap suat chay cc ai co the c tang hoac giam bi ieu chnh tang sm hoac lam muon cam nhien lieu tng oi so vi v tr khuyu. Cac bm cao ap loai ieu khien ranh xeo va ca so cung co the c ha thap hoac nang phan ay cua chung e tang hoac giam ap suat cc ai xilanh. bm cao ap c ieu chnh bi van nap hoac van ngat, cam co the c chnh tang sm hoac chnh muon bi ong long hng knh vi cac rang c cat rat mn tren canh cua vong ai va phan canh cua cam, la cai c gan bang bu long vi vong ai. Cac bulong nhat nh phai c ni long va cam c xe dch khoi ong long e chnh tang hoac chnh muon cam nh yeu cau; sau khi ieu chnh cac bulong nhat nh phai c xiet chat va khoa lai.

S thay oi cua v tr cam bang cac chnh tang sm hoac chnh muon khong lam thay oi lng phun nhien lieu. Vi cac bm cao ap ieu khien bi ranh xeo va ca so, mot phng phap lam chnh tang sm hoac chnh muon thi iem bat au phun la nang bm cao ap len hoac ha thap xuong hn. Cac bm c thiet ke e ieu chnh theo cach nay co cac tam la c che tao chuan at gia e bm cao ap va be bm hoac gia bm. Khi s mon xay ra cac cam, be va truc, can nhac bm cao ap ra, thao tam la em va giam o day cua no bang may cong cu chnh xac. ieu nay bu ap cho s mon a dien ra va s phuc hoi ap suat cc ai tr ve gia tr ban au cua no.


This method of adjustment is only used for making small pressure increases.

Lowering the fuel pump body causes injection to commence earlier and also to finish earlier. The actual stroke of the fuel pump ram remains the same. The effective stroke of the fuel pump ram also remains unchanged.

One type of engine using a helix and port-control type fuel pump has an arrangement consisting of a thread on a circular projection of the fuel-pump cover which fits into the pump casing. A cage is screwed on to the threaded projection. The outer portion of the cage has a gear cut on it which is matched to a pinion on a spindle passing through the cover. Turning the spindle causes the cage to turn and move up or down on the thread. The cage is cut in the outer edge of the barrel and this engages with a dowel screw. By slacking off the pump cover nut it is possible to turn the sleeve of cage and move it up or down. Up-and down movement of the sleeve forces the pump barrel up or down and the dowel screw prevents rotation of the pump barrel. A true axial movement of the pump barrel is consequently obtained without altering the circumferential relationship of the helix and port. Easy control of the maximum pressure is obtained as movement downwards causes injection to take place earlier without altering the period of injection, since the effective stroke and the actual stroke of the fuel pump have not been altered.

Phng phap ieu chnh nay ch c dung cho s tang ap suat nho.

S ha thap hn than bm cao ap lam phun bat au sm hn va cung ket thuc sm hn. Hanh trnh thc te cua piston bm cao ap c duy tr tng t. Hanh trnh co ch cua piston bm cao ap cung duy tr khong oi.

Mot loai ong c s dung bm cao ap loai ieu khien cap nhien lieu dung ranh xeo va ca so co mot cach bo tr mot ben phan nho vong quanh cua nap bm cao ap lap trong vo bm. Mot ong long van vao phan nho co ren. Phan ngoai cua ong long co cat ren khp vao mot rang mot truc chui qua nap. Quay truc lam cho ong long quay va lam chay len hoac xuong tren ren. Ong long c gan vao ra ngoai cua smi xilanh bm cao ap ( barrel) va cai nay gan vi mot vt kieu chot.

Bang cach ni long ai oc nap bm cho kha nang quay ong long cua long va chuyen dch no len hoac xuong. Chuyen dch len va xuong cua ong long ay s mi xilanh (barrel) chuyen dch len hoac xuong va vt kieu chot bao am khong cho smi xilanh nay quay. Mot chuyen dch chnh tam cua smi xilanh ( barrel) bm cao ap cuoi cung cung at c khong lam thay oi moi lien he theo ng tron cua ranh xeo va ca so. Ta co c s ieu khien de dang ap suat cc ai khi dch chuyen i xuong e thc hien phun sm hn ma khong lam thay oi giai oan phun, v hanh trnh co ch va hanh trnh toan bo cua bm cao ap khong b thay oi.


3.28 Describe how you would determine whether the maximum firing or combustion pressure was correct for propulsion engines and auxiliary engines? Modern turbo-charged engines show a considerable rise in compression pressure and firing pressure as the load on the engine is increased, in order to check that the firing pressure is correct, it is desirable to put the engine on to full load conditions; this is easy to arrange with diesel auxiliary engines used for electrical generating purposes. When the engine is on full load the maximum pressure and the compression pressure should be checked out for each cylinder, and the figures tabulated.

The maximum firing pressure obtain during the test should be compared with the test-bed data for engine in question. If they are low then compression pressure may be checked to ascertain whether the low maximum firing pressure is caused by low compression pressure.

With high-powered slow-speed direct coupled engines and multi-engined geared installations it is not always possible to operate the main engines at full power (excep

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Chapter3 Diesel