3. INTRODUCTION
• The power out put of an engine
depends upon the amount of air
inducted per unit time and the
degree of utilization of this air , and
the thermal efficiency of the engine.
Indicated engine Power
IP=P*L*A*n*K/60000 ……………..(1)
Where, IP= indicated power (kW)
P=indicated mean effective pressure(N/m2
)
L=length of stroke
A= area of piston
n= no of power stroke, for 2-s engine-N and for 4-s engine N/2, N= rpm
K= No of cylinders
4. Three possible methods utilized to increase the air
consumption of an engine are as follows:
Increasing the piston displacement: This increases the size and
weight of the engine, and introduces additional cooling
problems.
Running the engine at higher speeds: This results in increased
mechanical friction losses and imposes greater inertia stresses
on engine parts.
Increasing the density of the charge: This allows a greater
mass of the charge to be inducted into the same volume.
5. Definition
The most efficient method of increasing the power
of an engine is by supercharging, i.e. increasing
the flow of air into the engine to enable more
fuel to be burnt.
• A Supercharger is run by the mechanical drive,
powered by engine power .
• A turbocharger uses the otherwise unused
energy in the exhaust gases to drive a turbine
directly connected by a co-axial shaft to a rotary
compressor in the air intake system.
8. Need of turbocharger and super charger
• For ground installations, it is used to produce
a gain in the power out put of the engine.
• For aircraft installations, in addition to
produce a gain in the power out put at sea-
level, it also enables the engine to maintain a
higher power out put as altitude is increased.
9. Working principle of a
turbocharger:
• A turbocharger is a small radial fan pump driven by the
energy of the exhaust gases of an engine.
• A turbocharger consists of a turbine and a compressor on
a shared shaft.
• The turbine converts exhaust to rotational force, which is in
turn used to drive the compressor.
• The compressor draws in ambient air and pumps it in to
the intake manifold at increased pressure, resulting in a
greater mass of air entering the cylinders on each intake
stroke.
10. Based on the use of compressor
• Centrifugal type
• Roots type
• Vane type
Types of super charger:
Components of turbocharger
•Air compressor
•Turbine
•Intercooler
12. 0
2
3
4
1
FIG. 6 Four-stroke cycle of an SI engine equipped with a supercharger
turbocharger, plotted on p-v coordinates.
Thermodynamic analysis of turbocharged engine cycle
13. Net work output Wnet
= work done by piston + Gas exchange work
= area A + area
Area A= .......................(2)
Area B= work done by turbocharger= ..............
(3)
Wnet = Work done per unit of air mass.
Where, p0 = atmospheric pressure,
p1= pressure after compression,
T0= atmospheric air temperature,
V1= volume of boosted air,
rp =pressure ratio,
r = compression ratio, cp=Specific heat of air
and η = turbocharger efficiency,
14. Selection process of turbocharger
• The concept of turbocharger is illustrated in Figure 7.
Figure7. Illustration of the concept of a turbocharger.
•Compressor air inlet,Point1- p1,
T1
•Compressor air out let, point2-
p2, T2
•Turbine exhaust gas inlet, point
3-p3,T3
•Turbine exhaust gas outlet-
P4, T4
15. Air Consumption and Air-Delivery Ratio:
Where
mat
= theoretical air consumption rate, kg/h atm &
De
= engine displacement, L
Ne
= engine speed, rpm
ρa
= density of air entering compressor, kg/m3
The air-delivery ratio is the ratio of the measured over the theoretical air
consumption of an engine:
where
ev
= air-delivery ratio
mat= theoretical air consumption of the engine, kg/h
ma= actual air consumption of the engine, kg/h
Terms essential for turbocharger selection
…………………….(4)
…………………..(5)
16. • A turbocharger air delivery ratio.
•The turbine pressure ratio is defined as , κpt = p3 / p4
• Pressure ratio across the compressor, κpc, as
•The temperature ratio across the compressor
Where ec
= compressor efficiency, decimal.
……………………(5)
……………….(6)
………………….(7)
……………………..(8)
17. • The compressor efficiency = ( theoretical temperature rise across the
compressor)/(the actual temperature rise). ec is always less than 1.0.
• The turbine efficiency = ( the actual temperature drop across the
turbine )/(the theoretical temperature drop). The turbine efficiency is
also always less than 1.0.
18. • The following procedure may be used in selecting a turbocharger for an
engine.
1. Select the desired, achievable power output, Pb; verify that the
chosen power level does not require an excessive pbme. Realistically,
pbme ≤ 1250 kPa is achievable.
2. Calculate mf = Pb× BSFC, using an achievable value for BSFC.
Typically, for a well-designed engine, it is possible to achieve , 0.2 <
BSFC < 0.25 kg/kW h.
3. Calculate ma = mf× (A/F), using the desired A/F ratio of the
turbocharged engine. For a CI engine running on diesel fuel,
typically 25 < (A/F) < 32.
4. Select the compressor and the point on the compressor map (see
Figure 8 for an example map) at which the compressor will operate
at rated load and speed of the engine. Equations 3 through 4 can be
reworked into
20. 5. Select the turbine and the operating point on the turbine map. The turbine and
compressor must rotate at the same speed, the turbine flow must equal the compressor
flow times (1 + FA), and the turbine must supply enough power to drive the compressor
while overcoming bearing friction.
The mechanical efficiency of the turbocharger
…………………..(9)
21. Equation 10 can be reworked into characteristic-value equations that incorporate the
speed, flow and power constraints:
where
τ avaiablel
= characteristic value available
τ required
= characteristic value required
u = − (k′ − 1)/k′
et
= turbine efficiency, decimal
em
= turbocharger mechanical efficiency, decimal
Cpc
= constant-pressure specific heat of ambient air, kJ/kg·K
Cpt
= constant-pressure specific heat of heated air, kJ/kg·K
The available characteristic value depends upon the FA ratio, the
turbocharger efficiencies, and the temperature ratio across the engine.
…………….(10)
……………….(11)
22.
23. Advantages of supercharger and
turbocharger
• The more increase the pressure of the intake air above the local atmospheric
pressure (boost), the more power the engine produces. Automotive superchargers
for street use typically produce a maximum boost pressure between 0.33 to 1.0 bar
, providing a proportionate increase in power.
• Engines burn air and fuel at an ideal (stoichiometric) ratio of about 14.7:1, which
means that if you burn more air, you must also burn more fuel.
• This is particularly useful at high altitudes: thinner air has less oxygen, reducing
power by around 3% per 1,000 feet above sea level, but a supercharger can
compensate for that loss, pressurizing the intake charge to something close to sea
level pressure.
25. Performance evaluation of the Turbo charged
Agricultural Tractor Engine
Place: Agricultural
Machinery Research
Centre, Massey University,
Palmerston North, New
Zealand in 1990.
Tractor- John Deere 3140
No of cylinder-6
Compression ratio- 16.8: 1
Fuel – 10% tallow ester +
90% diesel
26. Experimental Setup
• Monitor exhaust temperature with (Fe/ Cn thermocouple and
oil sump temperature with (Cu/Cn thermocouple).
• Before each run the engine was worked under load for 10-15
min to achieve normal operating conditions.
• Using a calibrated A W Nebraska 200 p.t.o. dynamometer, a
series of steady state measurements of p.t.o. speed, torque
and hence power was taken
• Settings an injection pressure of 210 bar and fuel pump
calibration to provide 51 mm3 of fuel at rated speed and full
load.
• A Campbell 21X data logger
27. Experimental Conditions
1. Naturally aspirated engine
2. Naturally aspirated + servicing and
3. Turbocharged engine.
In the experiment the following parameters were
measured.
1. Torque
2. Power
3. Exhaust gas temperature
4. Turbocharger Oil Temperature.
35. Results and discussion:
• Torque: Torque-rise percentage (from torque at maximum power at
approximately 570 rev/min at the p.t.o. to maximum torque, which
represents the torque back-up, or “lugging ability” of the tractor), was
18.9% for the original naturally aspirated mode, rose to 21.6% after
servicing, and reached 33% after turbocharging.
• Power:Due to the increased torque after servicing, maximum power
increased from 63.1 kW to 65.9 kW at 570 rev/min and remained higher
throughout the working speed range. The turbocharged version produced
a maximum power of 77.1 kW
• Exhaust gas temperature:
• Oil temperatures
36. Conclusions:
• Due to low speed of operation and less power in
agricultural tractor, turbocharger is used not
supercharger for more power generation and to
operate it higher altitude.
• Turbo-charging a tractor engine is an acceptable
method of increasing its performance if carried out
within manufacturers’ specifications.
• Lower engine operating temperatures result which
can be beneficial.
• Since the engine lubricating oil is subjected to high
temperatures as it passes through the turbocharger
the correct oil must be used as specified for
turbocharged engines.
