ICE Revision

8/19/2019 ICE Revision

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Problems for Homework

n S.I. Engine has a fuel-air ratio of 0.07:1.

How

many kilograms of air per hour are

for an output of 75 kW at an overall efficiency

of 20%? How many m3of air are

per hour if the density of air is 1.2 ~ g / m ~ ?f the fuel vapor has density four

that of the air, how many m3 per hour of the mixture is required. The calorific

of the fuel is 43700 kJ/Kg.

n

engine develops 50 kW at

full

load.

If

its mechanical efficiency is 80%, what is the

power? What will be the mechanical efficiency if the load is halved, if the

efficiency and friction power remainsconstant?

two-stroke C.I. engine delivers 5000 kW while using 1000 kW to overcome frictional

It consumes 2300 Kg of

fuel

per hour at an air-fuel ratio of 20:l. The heating

of the fuel is 42000 kJIKg. Find the following: indicated power, mechanical

air consumption per hour, indicated thermal efficiency, and, brake thermal

haster

,----

---

---

@ :

-.----.-.------.---ir Standard ~ycledj

..

an ideal Otto cycle the compression ratio is 8. The initial pressureand temperature of

air are 1 bar and 100 oC. The maximum pressure in the cycle is 50 bar. For 1 kg of

calculate the values of the pressure, volume, and temperature at the all pointsof

cycle. What is the ratio of heat supplied to the heat rejected, mep, work done, and

of

compressionto expansionwork?

diesel engine has a cylinder of 25 cm diameter and 40 cm stroke. Cut-off takes place

5% of the stroke. Estimate the air standard efficiency & mep. Assume clearance

and pressureat the end of suction stroke are 1.2 litersand 1 bar respectively.

compression-ignitionengine working on diesel cycle operates at a compression ratio

15 using diesel fuel of calorific value 42000 kJ1kg. The inlet air pressure and

are 1 bar and 300 K. The air-fuel ratio is 21. Calculate the temperatureand

at salient points, air standard efficiency, and mep.

engine of compression ratio 6 uses fuel with calorific value 44000 kJ1kg. The air-

ratio is 15:1. The temperature and pressure of the charge at the end of the suction

are 60 C and 100 kPa respectively. Determine the maximum pressure in the

if the index of compression is 1.32 and the specific heat at constant volume is

as Cv = 0.71 + 20*10-~ kJ/kg.K, where T is in K.

R

= 0.287 kJ1kg.K.

this value with that for Cv = 0.71

8

kJ1kg.K.

an oil (Diesel) engine working on dual combustion cycle. The temperature and

at the beginning of compression are 90 C and 1 bar respectively. The

ratio is 13:

1.

The heat supplied per kg of air is 1675 kJ, half of which is

at constant volume and half is supplied at constant pressure. Calculate the

pressure of the cycle and the percentage of the stroke at which cut-off takes

Take Cv

=

0.71 + 20'10 T kJ/kg.K, where T is in K. Compare your results with



The heat added is 1400 kJIkg. Using the air tables, determine the maximum cycle

temperature and pressure, thermal efficiency, power and the available portion of heat

rejected. The inlet conditions are 100 kPa and 300 K. Compare your results with those

at ideal conditions.

. A test was carried out on single cylinder, two-cylinder diesel engine, gave the following

data: cylinder diameter = 200mm, stroke

=

250mm, engine speed

=

300rpm, net brake

N-m, indicated mean effective pressure 4.9*105 ~ / m fuel consumption

=

rise of cooling water = 55K specific heat capacity of water =

mechanical efficiency, specific fuel consumption and draw up

an energy balance.

During the trial on a four-cylinder petrol engine running at 3000 rpm, the brake loadwas

267 N when all cylinders were working. When each cylinder was cut off in turn and the

speed returned to 3000 rpm the break readings were 178 N, 187 N, 182 N, and 182 N.

The engine brake power follows the following law :

BP

=

(W

RPM) 27300 kW, where W is the brake load in Newton. Determine the

brake power of the engine and estimate the indicatedpowerand mechanical efficiency.

The following readingswere obtained from a test on a single cylinder oil engine working

on the four stroke cycle: Area of the indicator diagram = 4.1 cm2, length of the indicator

diagram

=

6.25

crn

indicator spring rating

=

0.9mm, cylinder bore = 105mm, engine

stroke length

=

150mm, mean diameter of brakewhee

) =

0.6m, brake load

=

18kg, spring balance reading

=

3kg, engine speed

=

culate: brake power,

indicated power and mechanicalefficiency.

The air flow to a four-cylnder four-stroke il eryine is measured by means o f 5cm

diameter orifice having coefficient o f discharye of 0.6. During the

test

on this

engine the following data were recorded: 0ore = 1@5cmsfroke = 1Z5cm engine

speed

=

1200rpm brake torque

=

147N-m fuel consumption

=

55kg/hr calorific

value = 431m k m g head across orifice = 57cm o f water ambient conditionsare

1.013 bar and

20 L:

Calculate: brake thermal efficiency BMEP and volumetric

efficiency.

. A four stroke cycle petrol engine has six single-acting cylinders of

Z

cm bore

and 9 cm stroke. 73eeqine is coupled to a brake having a torque arm radius of 38

cm. At 3300 rev/min with all cylinders operating the net brake load is 324

N

When each cylinder in turn is rendered inoperative the average net brake load

produced at the same speed by the remainiry five cylinders is 245 N Estimate the

indicatedmean effective pressure of engine. With all cylinders operatiry the fuel

consumption is 0.3 @/mini fuel calorific value 42000 kJ/kg; the acket water flow

rate and temperature rise are 65 kg/min and 12

L:

On test the eryine is enclosed

in a thermally and acoustically insulated box throqh which the output drive

water fue[ air and exhaust connectionspass. Ventilatiry air blown up throwh fhe

box at the rate of

14

kg/min enters at

10

C and leaves at

OL

Draw up a heat

balance of the egine stating the items aspercentage o f total eneryy in.



1 )

An S.I. Engine has a fuel-air ratio of 0.07: Mow many kilograms of alr per

hour are required for an output

o f 75

kW

a t an

overall efficiency of 20':'0' How

many m3 of air are required per hour if the density of air is 1.2 ~ g / n 1 ~ ?f the fuel

vapor has density four times that of the air, how many

m3 per hour of the mixture

is required? The calorific value of the fuel is 43700 kJ/Kg.

(2)

A diesel engine develops 5 kW. Its indicated thermal efficiency is 30% and

mechanical efficiency is 57%. Estimate the fuel consumption of engine in (a)

K g h ,

b)

litershr,

C)

indicated specific fuel consumption, and (d)

BSFC

Take

the density of diesel oil as 0.87 kg/m3. Take fuel calorific value = 42000 kJ/kg,

fuel SG

=

0.87.

(3)

An engine develops 50 kW at full load. If its mechanical efficiency is 80%,

what is the friction power? What will be the mechanical efficiency of the engine at

half load, if the mechanical losses (friction power) remains constant.

4)

A

two-stroke C.I. engine delivers 5000 kW while using 1000 kW to overcome

frictional losses. It consumes 2300 Kg of fuel per hour at an air-&el ratio of

20:

1

The heating value of the fuel is 42000 kJIKg. Find the following

(a) The Indicated power

(b) The mechanical efficiency

(6)

The air consumption per hour

( 4

The Indicated thermal efficiency, and,

(el The Brake thermal efficiency

(5)

A single cylinder, C I engine has thermal efficiency of 25% using fuel of

calorific value 39000 Wlkg. If the mechanical efficiency is 74%, calculate

ISFC,

BSFC, and, Indicated Thermal Efficiency.



PROBLEMSFOR

PRACTICE

o

Basic Intend

Combustion Engines.

1 A

fwrr cylidx

engine

ojxxates on four stroke

cycle

ha stroke 7cm

and

bore 5cm.

The

p d m bas

a cavity

top of

it@aEasphere)of-e lcm3. 'Ihevokrme above the pistan

l d ~ i t i s a t ~ ~ ~ i s 8 c m ~ .

i b c d ~ p f c s s i o n d , e n g i n e ~ ~ a n d e a l g 2 n e ~

2. ~~

with ne t sketch

the

difikmce

between

the

ctu l and

theoretical

valve timing

6 r

4-

Stroke

S.L

engine.

3.

A

diesel

engine develops 5 kW. ts indicated thermal dc iency is

30

and mechanical

efficiency is 5 . Calculate:ISFC, IP,BSFC, BP,mfand thermal efficiency.

Air-Standard

Cydes

4. An engine working an the

tto

cycle has a compression r tio 8, total

cylinder

volume of 3.8

Liters,

The

i i

cmdtbm

are

P

14.95

ar

and

TI=

17

OC

at

the

begbmg

of

cmqms n

stroke. The amouut of heat added during the canstant

volume

combustion is 7.5.

Calculate

pressure and

kmpemtm

at all

pints,

MEP and Thermal Hliciency.

Take Cv

0.718W/Kg-K,y=

1.4fbr

air.

Z

5 The initial u m d i h fbr an air standard

d i d

cycle peding with

campression ratio

of 1 5 1

are 0.95 bar and 17 C. The heat added is 1800 M/kg.

Calculate

the pressure lnnd temperature at

the

end of

ewh process of

the cycIe

and

determine the engine's

e n d Bciency and

MEP.

TakeCp 1.005kJ/Kg-K,

y

1.4fbr air.

6 . Pnrvsthal k

ideal

air standarddiesel cyclef l l F 2 L

~ 4 m )

EngineTestingTechnque.

A

Stroke, QCyliodns petrol engine having

bore 86-

and

stroke

lOOnrm

wit compression

ratio

=

6. A test

was carried

out an

this

ngin

and

the

foblaving dab

was collected

engine

speed

2400

RPM,

Brake

Load

20

Kg,

Effective Brake

Arm

0.5

m,

IMEP

bar, Fuel

ammnption =10 Kg/hr. Fwl

Calorific Value =

44 kJ .

Caiculate: BP,

IP

FP BMEP,

FMEP

Brake Indicated ' I h e d EBciency, Brake

ndicated

SFC,

Mecholnical

and

Redative l icie.ucy. Takey 1.4fix air.

~ m d r e ~ o l ~ h ~ b c r e 5 7 n n n a d s b o k e = 9 0 m m ~

is 28

RPM and it is

tested

at

this

speed

@t a

brake which

has a torque arm of 0.356 m.

'ihe t et brake load is

155

N

and

the find amsumption is

6.74

Whr. The specific gravity

of

th

petrol used is 0.735 and

has a

lower calorific v lue of 44200 kJ/Kg. A

Marse

test

is carried

out

he

cylinders

ate

cut

out

in

th

order

1,2,3,4,

with

correqmdmg

brake

loads

of

111, 106.5,

104.2

and

111 N reqxxtively. Calculate

for this

speed,

the

engine Torque, BMEP BBSFC

IMH,,

Brake'llmml

andMechmical

mciency

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ICE Revision