Fuel system basic

8/7/2019 Fuel system basic

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First year- First semester

Prepared ByKT Ariyawansha

Department of Agric Engineering,Faculty of Agriculture,

University of RuhunaSri Lanka


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To gain basic knowledge aboutFuel

Combustion of fuelFuel Property

Petrol fuel system

Ignition systemDiesel fuel system

Prepared by KT Ariyawansha - Department of Agric Engineering, University of Ruhuna


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Materials burn as a source of

energy.(Oxford dictionary)

Fuel

Solid

Liquid

Gases

Prepared by KT Ariyawansha - Department ofAgric Engineering, University of Ruhuna


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For Tractors

Liquid fuels(diesel) are populer

Liquid fuels are made form crude

petrolium refining

Crude Petrolium is combination of

the C & H ( ~C-86% & H-14%)

Most of refined fuels combinationof following

Parafine( CnH2n+2)

Olifine (CnH2n)

Diolefin (CnH2n-2)

Naphthene (CnH2n)

Aromatics (CnH2n-6)

If N= 1-4 Gas (@ Normal T0 & P)Prepared by KT Ariyawansha - Department of Agric Engineering

, University of Ruhuna


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Paraffin( CnH2n+2) Olefin (CnH2n) Diolefin (CnH2n-2)

Naphthalene (CnH2n) Aromatics (CnH2n-6)

Prepared by KT Ariyawansha - Department of AgricEngineering, University of Ruhuna


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Chemically combining of OXYGEN with

CARBON andHYDROGEN in the fuel -resulting this HEAT is liberated and

PRESSURE is Increased



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Representative molecules for combustion calculations.

Fuel Molecule Formula Molecular Weight

Natural gas Methane CH4

16

LPG Propane C3H8 44

Gasoline Octane C8H18 114

Kerosene Dodecane C12H26 170

Diesel fuel Cetane C16H34 226

Methanol Methyl alcohol CH4O 32Ethanol Ethyl alcohol C2H6O 46

Butanol Butyl alcohol C4H10O 74

Methyl soyate C19H36O2 296



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C8H18 + 12.5O2 + 47N2 47N2 + 8CO2 + 9H2O1(114) 12.5(32) 47(28) 47(28) 8(44) 9(18)

1 3.51 11.54 11.54 3.05 1.42

a. Calculate the stoichiometric air-to-fuel ratio and the exhaust products when Ethyl

Alcohol(C2H6O) is used as an engine fuel. Show the balanced combustion equation.b. State whether C2H6O can be use to existing gasoline engine. (Yes /No)c. If No what is the reason.



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1. Antiknock quality- Ability to resist knockKnockEngine produce audible "ping" knock due to

spontaneously detonation of fuel in localized area of the

combustion chamber.Tendancy to resist detonation is measures of,

Octain number(Gasoline)

Cittain bumber(Diesel)



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iso-octane(C8H18) - anti-knocking rate -100

heptane (C7H16) - anti-knocking rate- 0

Adjust compression

ration up to engineproduce knock

Adjust iso-octaneand heptane %



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n-Cetane(C16H34) cetane number-100

Heptamethylnonane - cetane number-15

Adjust compression

ration up to engineproduce knock

Adjust cetane andHeptamethylnonane

%



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2. Volatility of the fuel- releases vapour,particularly at ambient temperatures

Affects the performance through following Ease of starting the engine

Degree of crankcase oil dilution

Formation of vapor locks in the fuel system

Accelerating characteristics of the engine Distribution of fuel in multi cylinder engine

Quicker vaporizing the fuel helps inproducing more power swiftly which

accelerates the engine.Prepared by KT Ariyawansha - Department of

Agric Engineering, University of Ruhuna


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3. Calorific/Heating value of the fuel

Higher Calorific Value- HCV- (or Gross Calorific Value - GCV) supposethat the water of combustion is entirely condensed and that theheat contained in the water vapor is recovered.

Lower Calorific Value- LCV-(or Net Calorific Value - NCV) supposethat the products of combustion contains the water vapor and thatthe heat in the water vapor is not recovered.Eg- HCV of some fuels

~Gasoline 47300 kJ/kg

~ Diesel - 44,800kJ/kg

~ Coal - 15,000 - 27,000 kJ/kg~ Ethanol - 29,700 kJ/kg

~Methane - 55,530 kJ/kg

~Hydrogen - 141,790 kJ/kg

~Biodiesel - 36,000 - 48,000 kJ/kg

~Wood (dry) - 14,400 - 17,400 kJ/kg

The heat liberated by combustion of a fuel is known as calorific value

or heat value of the fuel, KJ/kg(kcal/kg) of fuel .(4.19J = 1 cal)



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4. Specufic gravity

Ratio of the density of the substance, but usually expressed inAPI(American Petroleum Institute) degrees.

SG = /refAPI degrees = (141.5/Specific Gravity at 15.6 0C)-131.5

5. Kinematics Viscosity

viscosity is the fluid resistance to shear or flow

6. Flash PointThe flash point is the lowest temperature at which an appliedignition source will cause the vapors of a sample to ignite.

7. Distillation Temperature

8. Sulfated ash content

9. Sulfur Content10. Water and sediment content

11. Copper Strip Corrosion

The corrosiveness of a fuel is measured using the copper stripcorrosion

12. Gum content- due to unsaturated HCPrepared by KT Ariyawansha - Department of Agric Engineering, University of Ruhuna


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http://www.ceypetco.gov.lk/Products_and_Servi

ces.htm#11

For the fuel stranded in Sri Lanka



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Petrol / Gasoline fuel system

Carburetor systems

Petrol injector systems

Ignition systemDiesel fuel system



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Fuel tank Fuel line Fuel filter

Lift pump Carburetor Air cleaner

Carburetor

Fuel tankFuel line

Fuel filterLift pumpPrepared by KT Ariyawansha - Department of Agric Engineering, University of Ruhuna


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Device that blends air and fuel

Carburetors - up until the mid 1980s,

Some engines use multiplecarburetors.

Older engines used updraftcarburetors, where the air entersfrom below the carburetor and exitsthrough the top.

Beginning in the late 1930s,downdraft carburetors were themost popular type for automotiveuse.



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The carburetor works on Bernoulli'sprinciple:

The throttle (accelerator) linkage does notdirectly control the flow of liquid fuel.

Instead, it actuates carburetor mechanismswhich meter the flow of air being sucked intothe engine.

The speed of this flow, and therefore its

pressure, determines the amount of fueldrawn into the air stream.



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Air Cleaner

Choke valve

Fuel

VenturiFloat valve

Float Arm

FloatFloat Chamber

Jet

Throttle valvePrepared by KT Ariyawansha - Department of Agric Engineering, University of Ruhuna


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http://1.mpg/


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The carburetor must:

Measure the airflow of the engine

Deliver the correct amount of fuel tokeep the fuel/air mixture in the proper

range (1 part of fuel to 15 parts of air byweight )

Mix the two finely and evenly

A carburetor must provide the proper fuel/air

mixture across a wide range of ambienttemperatures, atmospheric pressures, enginespeeds and loads, and centrifugal forces

Prepared by KT Ariyawansha - Department of AgricEn ineerin Universit of Ruhuna


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Under different operation conditions demand of airfuel mixture is greatly varying.

Therefore modern carburetor provide different

circuits

Ideal and low speed circuit Low speed circuit

High speed part load circuit

High speed full powered circuit

Accelerator pump circuit



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Prevents dirt or dust. Essential ne in muddy or dusty environment .

Dust or dirt or grit enter the cylinder cause veryrapid wear of valves, pistons, cylinders or allbearings.

There could be rapid build up of carbon in thecombustion and on the valves.

Air cleaners can remove up to 95% of harmfulparticles from the air that enters the engine



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1. The Oil-bath Type, Three-stage Air Cleaner

2. Dry Element-type Air Filters



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Popular as can be fullycleaned, serviced and cheap

Following figure shows a

sectional view of the oil-bath-type cleaner

3 stage cleaning in the

dome, oil and oil-damp wiregauze



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Prepared by KT Ariyawansha - Department of Agric Engineering, University

Dome

Oil

Oil-

damp

wire

gauze


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Purpose - to create a sparkthat will ignite the fuel-airmixture in the cylinder of

an engine.Job - to produce that highvoltage(20000V 50000V)from a 12 volt source and

get it to each cylinder in aspecific order, at exactlythe right time.

http://en.wikipedia.org/wiki/Bowden_cablehttp://en.wikipedia.org/wiki/Bowden_cablehttp://en.wikipedia.org/wiki/Bowden_cable


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compression ratio efficiency

Compression ratio has to be limited to avoid pre-

ignition of the fuel-air mixture which would causeengine knocking and damage to the engine.

Modern engine - between 9:1 and 10:1,

In high-performance engines 11 or 12:1



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Battery

Ignition switch

Ignition Coil

Distributor

Distributor base

Rotor arm

Contact breaker

Condenser

Distributor cap

Spark plugPrepared by KT Ariyawansha - Department of Agric

Engineering, University of Ruhuna


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Prepared by KT Ariyawansha - Department of Agric



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Source of electrical energy needed to operate

the ignition system

Two heavy lead terminals- Positive & Negative

Negative terminal - grounded



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Connect or disconnect theflow of electricity



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Act as pulse typetransformer

Step up the battery

voltage to, andexceeding, 20000

volts



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Prepared by KT Ariyawansha - Department of Agric Engineering,Universit of Ruhuna


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Primary current flow can be interrupted in oneof three basic ways,

1. By using a set of breaker points to break

current flow2. By using a set of breaker points in

conjunction with a transistor switch

3. By using a fully electronic switching unit inwhich the mechanical breaker points arecompletely eliminated



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1 2 3 4



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High voltage from the coil iscarried by an insulated wire

to the center terminal of the

distributor cap

Additional terminals, one percylinder, will be arranged in a

circle around the center

terminal

Each one of these will have a

heavily insulated wire

connecting it with a spark

plug. Prepared by KT Ariyawansha - Department of Agric Engineering, University of Ruhuna


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Carry the secondary voltage from center

terminal to anyone side terminal by rotor



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A distributor capfor the six

cylinder engine



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It is essential that the plug wire be arranged in

the proper sequence

Firing order in a typical six cylinder engine is

1,5,3,6,2,4

Order - in which piston reach TDC on the

compression stroke (few degrees before TDC)



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Electrode of a spark plug must be constructedof material that will be resistant to heat,oxidization and burning

Typical material is nickel alloyTwo electrodes-

Center electrode

Side electrode

The space between the two- the plug GAP

Gap varies- 0.762-1.524 mm (.030-060 in.)



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Made up of three major

parts,

1. The electrode

2. Insulator

3. Shell

Prepared by KT Ariyawansha - Department of Agric



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With diesel engines ,

Only air is taken into the cylinder andcompressed at high pressure (3450 4140kN/m2)

It becomes hot enough (3500 4000c) to ignitefuel when it is sprayed in to the cylinder. (dropletsize 0.001- 0.025 mm)

Resulting explosion pushes the piston.

As a result Diesel engines require a fuel injectionsystem to provide the proper amount of fuel atthe proper times and intervals.



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Fuel tank

Fuel filter Lift Pump

Fuel Injection pump

Injector



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Direct-The fuel spray directly into the cylinder

Indirect-

The fuel spray into the intake manifold justahead of the intake valve

delivers fuel into a chamber, off the combustionchamber, called a pre chamber or sub-chamber,

combustion begins in sub-chamber and thenspreads into the main combustion chamber

allows for a smoother, quieter running engine



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Direct injection system Sub chamber system



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Less fuel consumption

The injection pressure required is low, therefore

making the injector cheaper to produce.

The injection direction is of less importance Indirect injection is much simpler to design and

manufacture

The lower stresses that indirect injection imposes oninternal components

Higher engine speeds can be reached



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High Specific fuel consumption due to heat loss due

to large exposed areas and pressure loss due to air

motion through the throats.

Glowplugs are needed for a cold engine start.


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Mechanical injection

Used an engine driven

injector pump that

distributed fuel, under

pressure, to fuel injection

nozzle

Electronic injection

No injector pump

distributor setup

Employs an electric fuelpump to provide sufficient

pressure to produce a

proper injection



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Distributer type Inline Type



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Have one pump element for each engine cylinder wich arranged in

a row.

The injection pump is driven by the gear wheels or chains of thecombustion engine.

The fuel reaches the nozzle-holder

assemblies with the injection nozzles

via high-pressure lines.

The in-line fuel-injection pump is the

classic among injection systems.

Nowadays it is only to be found in

commercial vehicles, buses, building-site

and agricultural machines or in stationary

diesel engines.

injection pressures of up to 1,300 bar.Prepared by KT Ariyawansha - Department of Agric Engineering, University of Ruhuna


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Has comparatively few moving parts, but so ina complex way


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Advantages of Diesel engines


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Advantages of Diesel engines

Lower fuel consumption because of

higher heat efficiency Diesel 170 to 220g/PS-hr

Gasoline 220 to 300g/PS-hr

Lower operating cost

Negligible torque variation over a

wide Speed range



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Higher flash point of fuel decreases fire

hazards. Smoother operation because of Misfires

are virtually nil.

Super charging easily improvesperformance.

The exhaust gas is not as toxic or pollutingas that of gasoline engines.


Drawbacks


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Drawbacks

The higher explosion pressure requires

stronger engine parts.

The compression ignition system limits themaximum injection amount of fuel so operating

speed is limited. A precision fuel injection system is required.

The high compression ratio requires higher

capacity starter and battery.

These factors increase the construction cost.



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Fuel system basic