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16 views26 pagesUnit Test
Jb
Uploaded by
91karanbadakCopyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
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/ 26
oes Enginwarng an Mamigoration a Internat Commntion trig
Clearance volume (V.) : Clearance volume the nominal volume ofthe spac on the combustion side of
plinder volume (V) : Cylinder vohime is the sum of piston swept volume and the numerical value oft
om eit 10 fs the ratio of the numerical value of the cylinder volume and
Compression ratio () = Ciearance vokime
8. Piston speed EEEER : the average distance travelled by the piston per minute in an engine is known as
+ Itis linear speed of piston.
easved in m/min.
Piston speed = 2 LN m/min
L_= Length of stroke
in fur sre exe engine, cee completed nto rvokons of ara or four sro operations of
oh stroke consists of 180° of crankshaft rotation. Therefore, the cycle consists of 720° of crankshaft rotation.
ey. SP. ty. EV.fopen) tv
a-|
rank shaft
‘ eZ
n stroke" (b) Compression stroke (c) Expansion stroke (4) Exhaust stroke
pam teeting of foor stroke petrol engine
wing four strokes
2. Compression stroke.
wer stroke, 4, Exhaust stroke.
- (a) Suctio
1s bottom dead centre, the charge consisting of
created by the motion of the piston towards
ion stroke the inlet valve closes.
ue to low pressure c
air mixed with the fuel is drawn into eylinder. At the end of sucti
he suction stroke is as shown in Fig. 1.3 (2).
2. Compression stroke :
ring compression stroke, the compression of charge takes place by return stroke of piston, le. ‘when piston
moves from bottom dead centre to top dead centre. 1 is called as ‘spark i
I combustion of fuel takes place due to production of spark, therefore engin
engine.
The compression stroke is as shown in Fig. 13 ()
3. Expansion or power stroke: burnt gases, piston
Piston gets downward thrust by explosion of charge. Oue to high pressure of
‘downwards to the bottom dead centre, Fig. 13 (0
During expansion stroke, both inlet and exhaust valves remain closed as shown in F
so called as ‘power stroke
snus Power is obtained by expansion of products of combustion. Therefore i a
Both pressure as well as temperature decreases during expansion stroke.
4. Exhaust stroke :
At the end of ex
trom bo
wed and the piston
;Pansion stroke, the exhaust valve opens, the inet valve remains clo
ttom dead centre to top dead centre as shown in Fig. 1.3 (6)
ve closes at the’
[During exhaust stroke the burnt gases inside the cylinder are expelled out. The exhaust va
the exhaust stroke but stil some residual gases remain in cyinder 2 cpekicll
Each cycle of four stroke engine completes the above four strokes or operations in two crank re
es and the second revolutio
(One revolution of crank shaft occurs during the suction and compression strokes and
during the power and exhaust stroke.
oft
Thus, for one complete cycle ie. for two revolutions of crankshaft, there is only one power stroke.
Example of four-stroke engine is passenger car.
1.5.1 Actual and Theoretic:
Valve Timing Diagram of 4-Stroke Petrol Engine
£ yl
f ; 5
tev
soc
(@) Theoretical (b) Actual
Fig. 14: Valve timing diagram of 4-stroke petrol engine
Fig. 14 (a) and (b) shows the theoretical and actual valve timing diagram of 4
In theoretical valve timing diagram, valves are opened and close
exactly at TDC and ap actual prac
tis difficult to open or close the valve instantaneously; so as to get better petformance bive titinall
re modified,
ral practice, inlet v: pened upto 1 of TOC, wh eo,
er the cylinder and helps the pr ic
pel out of cylind In actual P-V diagram, comers are rounded off because, ia
suddenly but takes some time to do $0. mee =.
Because of resistance of the inlet valve of the enter
ee Bere less than the atmospheric pressure.
similarly, because of resistance of the exhaust valve to the ce ci cao
f st ¥ exhaust gases leaving
ne Oflinder during exraust stroke is sightly higher than the atmosphere precomne oe the
shaded is shaded area is known as ‘Pumping loss’. This area is f
from the area of larger loop to get net work output. ——
Pet
ing charge, the actual pressure inside the oytinder during
5__ Exhaust <—
—* Suction
v
(a) Theoretical indicator diagram -—_(b) Actual indicator diagram
Fig. 1.5 : Indicator diagram for 4-stroke petrol engine
1.5.3 Various Efficiencies of 4-Stroke Pe' Engine
‘Mechanical efficiency (nq)
Efficiency% —=
k 5000
1000 200000 i
‘Speed (rpm) —»
6 : Efficiency of 4-stroke petrol engine
petrol engine run at full throttle over its speed range.
. 2022.10.17 12:42 In compresion stroke the piston moves up tom
During compression stroke, bot ‘and ext
The compression ratio of d
Few degrees before the mpression stroke
air which is at high temperature. Th nites sp ously. The injection of fuel into combustion channel
assumed to occur at constant pressut
3. Expansion stroke :
During expansion stroke both the inlet and exhaust valve remain closed and piston is forced to move to BDC
due to thrust of explosion.
The heat energy released by the combustion fuel, results in the rise in pressure of the gases. This high pressure
Product of combustion gives downward thrust to piston producing some useful work. This is the only stroke during
which power is produced, r 7
4. Exhaust stroke :
During exhaust stroke, piston moves from BDC to TDC,
The inlet valve remains closed whereas the exhaust valve is opened,
The upward movement of the piston expels the burnt gases out of
1.6.4 Actual and Theoretical Valve Timing Diagram
timing diagram, inlet valve opens 10° to 25° in advant
1 and closes 10° to 15° after the TDC position. The
15° past TDC. ( soc
ts (6) Actual
/alve timing diagram of 4-stroke diesel
1.6.2 ion
Actual and Theoretical Indicator Diagram of 4-Stroke Diesel Engine
Exnaust
OOS ee
Ww,
+ Exhaust —
(2) Theoretical indicator diagram (©) Actual indicator diagram
Fig. 1.8 : Indicator diagram for 4-stroke diesel engi
Fig, 18 shows the theoretical and actual P-V diagram.
‘Actual P-V diagram deviates from theoretical P-V diagram
diagram the comers are rounded off because inlet and exhaust valves do not open and close
ut they take some time to do so.
In a
instantane
During suction stroke, pressure inside cylinder is slightly less than the atmospheric pressure and during exhaust
stroke, the pressure inside the eylinder ishigher than atmosphere.
Thus, the shaded loop is considered as negative loop known as pumping loss. This shaded area is subtracted
from the area of larger loop to get net work.
[1.7 GARNOT CYcLI
Carnot cycle is an deal eycl
tant temperature is a quasi-statie process (very slow process) and t
e, whieh is not possible in actual practice because heat addition and rejection at
his process cannot be achieved in actual
processes in ths cyeleare reversible. The efficiency of Carnot cycle is maximum.
sther cycle will have efficientey more than efficiency of Carnot cycle
i TT 2022.10.17 12:43 ¥-@"
ce
wen"
* T= Ter
Substitute the value of fy and T; in equation (14)
Conclusion
2+ Air standard efficiency of Otto cycle depends on com ratio (9.
‘on compression
2__As the value of compression ratio increases, air standard efficie
v
Fig. 1.11 : Diesel cycle
Diesel cycle is a cycle on which diesel engine i. compression ignition engine works. It is an idealized cycle. In
diasel cycle, addition of heat takes place at constant pressure and rejection of heat takes place at constant volume.
Diesel cycle consists of four processes
Process 1-2: Isentropic compression raising pressure and temperature,
Process 2-3 : Addition of heat at constant pressure.
Process 3-4 : Isentropic expansion from high pressure and temperature to low pressure and temperature.
Process 4-1 : Rejection of heat at constant volume.
\
In case of diesel engine, compression ratio (0) = y+ and cut-off ratio (ay) =
Consider for 1 kg of air
Heat supplied, qa = Cp (Ts ~T2)
Heat rejected, ga = Cy(Ta~T;
Work done = qa~qa = Cp (Tg=T)-C (Tasty) ‘Pome Engineering and Retigeration an
‘Alc standard efficiency of diese cycle
< der process 2-3: p onstar ‘ : =
wey os a9
a
Wave vd
act (0 (8) ag 110
Conclusion : :
440 puaLcycie
™ | et y
MS
fl
is
9
it
fu
i
cy eceue of 19h weight ond aplly Gy
ence of vie ts alee
a
The cow of piston f provided wh dee
Meereovors,
Used where Hight and compact engine requ
[/eg. scooters. awn movers |
but intwo stroke engi as ach SO takes place separate therfore beter cemon aks play
2 AS independent at OMe rte ached rene ee
{We stroke engine pi SES provided four se ene tere avenging takes pce. case of
having combustion wich ee Pt Temin open simultaneous eh che aot coer aa
AS speed of ee cl RSE Righ Ancona em Tete
ces thermal git eng Incenes, lca ee seacee ea efclnay. scavenging, which mechanisms betes
reduces thermal eff ; _ adjstmens isthe
Greater we power stroke in each revolution, bt)» AGRStMENs made
ation arrangement is not provided in tw fsB0nsble orth
o (PETROL) AND C.l, (DIESEL) a
‘Spark Ignition Engine (Petrol) Com
Petrol engine works on Otto cycle im
air is] 2. | Diese!
In petro!
to the cylinder during suction stroke
The pone out,
Compression Ignition Engine (Diese) £ ens
ted direct
engine, a mixture of petrol and Toincrease
ombustion
chamber at pressure at the end of ‘The sacond af
th the help of carburetor, ‘compression stroke, Carburet liminated but ‘Thus, increasi
high pressure uel pump andinector rege one by spa
hrottle valve in carburetor controls the | 3. ‘Quantity of fuels regulated by fuel pump. a pressure-boost
of mixture introduced in combustion Objects of Supe
i ak The objets
4. ‘trol engine requires an ignition system with | 4. No spark plug is required as combustion of fuel is | 1. To incre
k plug in combustion chamber. spontaneous due to very high pressure and and ma
temperature in combustion chore | 2 Ate!
% > 1 gives te
empress bout 6 son | oe
her pum. due to lighter weight Maximum Epi. lower | che
eficency slower (about 30%) ue | 7. | Higher eldeney about 40 R) due Yo Vhs lion
Z ti | compression ati a
= behead) GMs Gg jie caMnot be started easily due toh He |
= | reson ati wal
“ d ght} 40. ngines ar enerally emp both:
Bs. coc vehicles ke Bos, tuck ete 3 Tet
~ it bette
ie to low prea eval Heavy in weight h pressure developed oa Fm normal non-WT o non-WT Pr
: mn of non-T engines the vahe tings are conta
non engines the a ote by a set of cam
SMD Tere loon aa se teaver ats ar sng oes pom
The disadvantage of this ack offen
‘optimum valve timings vary with engine
heeees
Scns
Prd sll elites
tl re, engine efficiency and engine power. In short, we can sz Fotthe Wrieguae CE
'e technology is respor Lae
Adjustments made in the over
inte oeroy rey bore ceed
Tesponsible for higher efficiency of the engine. SS
SUPERCHARGING . a Senn
The power output of an engine depends upon the amount of air inducted per unit time.
The amount of air inducted per unit time can be increased by increasin
| gf 8 by ing the engine speed or by increasing the
To increase the engine speed, the engine construction is required to be robust. Therefore it has a limit.
The second alternative is to increase the density of intake air, which is used to increase the power output
‘Thus, increasing the engine power by increasing the density of intake air is called as ‘supercharging’. This can be
done by supplying the air at a higher pressure at which the engine naturally aspirates air from atmosphere by using
a pressure-boosting device called as ‘supercharger
Objects of Supercharging :
The objects of supercharging are as follows
|. To increase the power output for a given weight and bulk of the engine, which i important forthe aircraft
and marine engines where weight and space is of importance.
2. As the altitude increases, the density of air decreases. So normal LC. engine when operated at high altude
Gives less power output due to decrease in density of intake at. Therefore to compensate the loss of power
sete high altitudes of aircraft supercharging is done. There is 1% loss of power per 100 m of attude:
3. To generate the more power from existing engine,
Effects of Supercharging :
The effects of supercharging are as follows ;
‘A supercharged engine has ainjsupplied to it at a pressure and density hhigher than atmosphere. This
increases the volumetric efficieney.
The mechanical efficiency of supercharged engine is more than that of naturally aspirate
th are running at same speed
The specific fuel consumption of a supercharged e!
better turbulence.
harged engine, chances of detonation increases due to higher pressure
1d engine when
gine is less due to proper combustion achieved! by
TT 3. To run compressor it uses the
itself,
1.16 VARIABLE
Variable Geometry turbocharger is tu ger to control exhaust flow against
turbine blades. This is done to allow effective aspect ¢ running conditions. If the aspect
is too large, the turbo will fail to create boost at low: p ''s too small, the turbo will choke th
engine at high speeds. By altering the geometry of the gine accelerates, the turbo's asp:
ratio can be maintained at its optimum. This is done b
Advantages of Variable Geometry Turbochargers:
‘As compared to fixed geometry turbocharger, variable geometry ti
1. Higher low-end maximum torque : ;
Variable geometry turbocharger improves the maxi
the ability of the turbocharger to provide a higher
mean effective pressure and torque. : ____Fig. 113 ea
6 air enters into intake m
jnifold the manifold | As arenes into the intake manifold the aw |
ne eso", detects the intake manifold | sensor measures the amount of at and sends
vacuum and sends the ink
nto the ECU | information to ECU. |
1-18 TYPES OF SENSORS
In an automotive engine ¢ hater ition to a Rovere pu
n 2 Keyboard bee gndine control computer known as a Powertrain Control Module (PCM), the input data is not
inputs i veeag tiving conditions. Consequently, the Powertrain Control Module (PCM) cannot do thief the
receives are faulty or missing. Many Powertrain Control Modules
‘Switching fo
'5 running. 1
misture that
combustion
feedback ca
systems and
CMs) today have 16-bit or 32-bit
M H the
cciloscone
interacts wath rhe ices: the PCM also regulates charging system voltage, operates the cooling fan ON and fll beets!
interacts with the antilock brake system (ABS) module to reduce power ifthe vehicle has traction control and:
*y even interact with the Automatic Temperature Control (ATC) module to operate the cycling of the aie
'ctioning compressor clutch. The PCM may also be assigned vehicle security tasks: For example. the engine Onsen
trol system will not go into “closed loop’, if the PCM does not receive a good signal from the coolant sensor or 3: Mani
xyger nor can it balance the fuel mixture correctly if it does not receive good inputs from the throttle The §
ensor, MAP sensor or airflow sensor. The engine may not even stat ifthe PCM does not get a signal from Ml volage q
ankshaft position sensor JF ignitons
monitor all the key functions necessary to manage ignition timing mission control mae
n shifting, cruise control, engine torque reduction (if the vehicle ha: brakes with traction M4. Thre
2rging output of the alternator. On many vehicles of Toyota, Nissan etc, the PCM even controls the Mol
ere sno direct cable linkage connection tothe trate Reliable sensor inputs are an absohite Mak
em is to operate smooth accelere
ed in automobile are PcM to
Coolant Sensor a
he cylinder head oF intake manifold, the coolant sens > monitor the temperatur@l fal
j an. Is resistance changes in proportion to coolant temperature, Input from the coolant sensor om,
hen the engine is warm so the PCM can go into closed loop feedba ontrol and handieliiganaa
ons (EGR etc) that may be temperature dependent. om
pre ine control system from going T a
ive fuel cons and elevated carbon monoxide (CO) emissi nay cause the lm TT
inject
" move
2. Oxygen (0,) Sensor ;
1 injected engine 7
1ust manifold, the O2 sensor monitors the amount of unburned oxyc xhaust 1
; gnal that is proportional to the amount off unburned oxyge iheid Wiivred ioe aie are mene about 0.9 volts when the fuel mixture is rich and ‘there is little or
in exhaust When the mintr s lan the sensor cupatvetege ‘or
Bom Ween siivlis Balanced (A/F ratio 145 1) tho sare wil rad aromas en oe
Sensor output s monitored
F the computer and i
Used 1 rebalance the hel mature forme coisnee,
When the sensor reads “lean” the PCM increases the on
time of the injectors to make the fuel mitre go eh
Conversely, when the sensor teads “Teh” the PCM
Shortens the on-time of the injectors to make the fue
Misture go lean. This causes a rapid back-and forth
Switching from rich to lean and back again asthe engine
is running. These even waves results in an average”
Mixture that is almost perfecty balanced for clean
combustion. The switching rate is slowest in elder
feedback carburetors, faster in throttle body injection
systems and fastest in multiport sequential fuel injection,
If the ©; sensor's output is monitored on an
oscilloscope, it will produce a zig-zag line that dances
bback and forth from rich to lean.
vat << M81 TT
tt rao
Fig. 1.15 : 0; sensor voltage
2 sensor should be replaced every 50,000 to 75,000 km to assure reliable performance.
Manifold Absolute Pressure (MAP) Sensor :
The MAP sensor is mounted on or connected to the intake manifold to monitor intake vacuum. It changes
voltage or frequency as manifold pressure changes. The computer uses this information to measure engine load so
ignition timing can be advanced and retarded as needed.
MAP sensor also help the PCM to estimate airflow.
4. Throttle Position Sensor :
Mounted on the throttle shaft of the carburettor or throttle body, the throttle position sensor (TPS) changes
resistances as the throttle opens and closes. The computer uses this information to monitor engine load,
‘acceleration, deceleration and when the engine is at idle or wide open throttle. The sensor's signal is used by the
PCM to enrich the fuel mixture during acceleration and to retard and advance ignition timing
5. Mass Airflow Sensor (MAF) :
Mounted ahead of the throttle body on multiport fuel injected engines, the MAF sensor monitors the volume of
air entering the engine. The sensor uses either a hot wire or heated filament to measure both airflow and air
density
6. Vane Airflow Sensor (VAF) :
The VAF sensor has a mechanical flap-style sensor that is used on Bosch and other import multiport bee
Injected engines. The function is the same as a mass airflow sensor, but air pushing against a spring-loaded flap
Moves a rhegstat to generate an electronic signal
7. Manifold Air Temperature (MAT) Sensor :
Mounted on the intake manifold, this sensor changes resistance to monitor incoming air temperatu
Sensor's input is used to adjust the fuel mixture for changes in air density. re and |
* Ganka Postion semor:
same pursea”9® with dtr gntin stems the crankshaft postion (CK) sensor seve estrtay
Pen pubot® asthe igntion pckup and tigger wheel in an electronic dstibutr generates 2 Signal tha
to-contrel gra stermine the position ofthe crankshaft and the number one cinder, This information is mec,
Fw fa ont" ning and the operation ofthe fel ijctrs. Te signal rm the crank sensor so tls the
engines engine is running (engine rpm) so ignition timing can be advanced or retarded as needed. On sony
engine wat abate camshatt positon sensor is ako used 1 hep the PCM to determine the core fing Ode. Thy
nel no rat whet thes esos pet
ere ae two basc types of cranshlt potion sensors
@ topes shat pos
(©) Hallefect.
Fie TEE PRO ee poner ve cent or rari bac
rmeth causes a change nthe magnet ld tat produces an aterating curent sgn
The requeny ofthe signal gives the PCM the normaton nee 0 con ing
cian il lect ye ocak sensor uses notches or ute los on the crank cam ge blanc
stupt a magnetic fed inthe Hal ete sensor window. This causes te sensor to atch ON and OF, producing