Page 747 - Automotive Engineering Powertrain Chassis System and Vehicle Body

CHAP TER 2 2. 1 Exterior noise: Assessment and control

1.018
1400 rev/min, full load
1.016

1.014

1.012
Pressure (bar) 1.01

1.008

1.006

1.004

1.002
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Number of four-stroke cycles

Fig. 22.1-14 Intake pressure trace for a four-cylinder engine.
cylinders. Fig. 22.1-14 shows such a trace for a four Q hv ¼ heating value of fuel, typically 42–44 MJ kg 1
6
cylinder engine. (M ¼ 1 10 )
Ohata and Ishida (1982) measured the intake pres- h V ¼ volumetric efficiency
sure trace in PORT # 2 of a four-cylinder engine with h f ¼ fuel conversion efficiency
3
only one cylinder operating at any given time. When they V d ¼ swept volume (m )
summed the four pressure traces they found that the Assuming those variables connected with fuelling and
sum matched the pressure trace recorded in PORT # 2 combustion (h f, Q HV , F/A) are to be kept constant, in-
when all four-cylinders were activated. spection of the torque equation reveals the following
The Ohata and Ishida experiment supports the notion mechanisms for increasing torque:
that the wave action in the intake system is linear as the
additivity part of the theory of superposition seems to increase h v ;
hold (see Chapter 21.1, Appendix 21.1A). increase V d ;
increase r a,i .
22.1.3.10.7 On turbo and supercharging
the engine to improve performance Increasing engine capacity has always been an option
for increasing torque (witness the massive aero en-
Torque is a useful description of engine performance (see gines fitted to early twentieth-century racing cars).
Section 22.1.3.10). Low-speed torque strongly affects More recently, design skills have been applied with
driveability. High-speed power affects maximum speed modern multi-point fuel injection technologies to raise
and high-speed torque affects elasticity in the gear h V by careful tuning of the intake and exhaust mani-
selection. folds and appropriate valve lift timing (and multi-valve
Torque and power are simply related by engine speed engines).
N (rev/s) Raising torque by increasing the intake air density is
P the subject here. It requires additional work on the
T ¼
2pN intake gas beyond the pumping work found in the NA
engine. This work may be supplied by either:
The governing torque equation is:
Supercharging where a mechanical drive from the
h h V Q r ðF=AÞ
f v d
hv a;i
T ¼ engine powers a positive displacement device (a
l
4p sweep or a pump basically) or
where
Turbocharging where a turbine runs off the engine’s
T I ¼ indicated engine torque (Nm) exhaust gas and is used to power a compressor (a
F/A ¼ fuel air ratio _ m = _ m a high-speed impeller).
f
758