BACHELOR OF TECHNOLOGY IN MECHANICAL ENGINEERING
EMMI 3244: AUTOMOTIVE TECHNOLOGY PRACTICE
TUTORIAL QUESTIONS
1. Explain why air-standard cycles are used to represent the performance of real internal
combustion engines.
2. Outline the short-comings of simple ideal cycles and explain how the fuel-air cycle and
computer models can overcome these problems.
3. A six-cylinder two-stroke engine with a compression ratio 𝑟 = 9 produces a torque of 1100
Nm at a speed of 2100 rpm. It has a bore 𝑏 of 123 mm and a stroke 𝑠 of 127 mm. Determine;
(i) The displacement volume and the clearance volume of a cylinder
(ii) The engine bmep, brake power, and mean piston speed
4. A four-cylinder 2.5 L spark-ignited engine is mounted on a dyno and operated at a speed
of 𝑁 = 3000 rpm. The engine has a compression ratio of 10:1 and mass air--fuel ratio of
15:1. The inlet air manifold conditions are 80 kPa and 313 K. The engine produces a torque
of 160 Nm and has a volumetric efficiency of 0.82. Determine:
(i) The engine brake power
(ii) The brake specific fuel consumption bsfc (g/kWh)
5. A 3.8 L four-stroke four-cylinder fuel-injected automobile engine has a power output of 88
kW at 4000 rpm and volumetric efficiency of 0.85. The bsfc is 0.35 kg/kW h. If the fuel
has a calorific value of 42 MJ/kg, calculate:
(i) The engine bmep
(ii) Brake thermal efficiency
(iii) Air to fuel ratio
Assume atmospheric conditions of 298 K and 1 bar.
6. A four-stroke 2.6 L direct injection automobile engine is tested on a dynamometer at a
speed of 2400 rpm. It produces a torque of 150 N, and its volumetric efficiency is measured
to be 0.85. Given that the inlet air pressure and temperature are 80 kPa and 45℃, determine;
(i) The brake power of the engine
(ii) The mass airflow rate through the engine
Take the specific gas constant of dry air, 𝑅 = 287 𝐽/𝑘𝑔. 𝐾)
7. A six-cylinder four-stroke engine is designed to produce 70 kW at 2200 rpm with a bsfc of
310 g/kWh and a bmep of 12 bar. If the engine is to have equal bore and stroke, and is
fuelled with gasoline with a heat of combustion of 43900 kJ/kg, calculate;
(i) The mean piston speed at the design point
(ii) The fuel consumption per cycle per cylinder
(iii) The brake thermal efficiency
8. A 4.0 L six-cylinder engine is operating at 3000 rpm. The engine has a compression ratio
of 10:1, and volumetric efficiency of 0.85. If the bore and stroke are equal, what is the
stroke, the mean piston speed, cylinder clearance volume, and air mass flow rate into the
engine? Assume standard inlet conditions.
9. A 2L four-stroke indirect injection diesel engine is designed to run at 4500 rpm with a
power output of 45 kW. At test conditions of 1 bar and 20℃, the engine has a volumetric
efficiency of 80%, sfc of 0.071 kg/MJ, and uses a fuel with a calorific value of 42 MJ/kg.
Calculate:
(i) bmep
(ii) Arbitrary overall efficiency
(iii) Air-fuel ratio
10. A twin-cylinder two-stroke engine has a swept volume of 150 cm3. The maximum power
output is 19 kW at 11000 rpm. At this condition, the sfc is 0.11 kg/MJ and the gravimetric
air/fuel ratio is 12:1. If the ambient test conditions were 10℃ and 1.03 bar, and the fuel has
a calorific value of 44 MJ/kg, calculate;
(i) bmep
(ii) Arbitrary overall efficiency
(iii) Volumetric efficiency
11. A four-stroke 3L V6 SI engine has a maximum power output of 100 kW at 5500 rpm, and
a maximum torque of 236 Nm at 3000 rpm. The minimum sfc is 0.090 kg/MJ at 3000 rpm,
and the air flow rate is 0.068 m3/s. The engine compression ratio is 8.9:1, and the
mechanical efficiency can be assumed to be 90%. The engine was tested under ambient
conditions of 20℃ and 1 bar. Taking the calorific value of the fuel to be 44 MJ/kg,
determine:
(i) The power output at 3000 rpm and the torque output at 5500 rpm
(ii) The bmep and imep at both speeds
(iii) The arbitrary overall efficiency at 3000 rpm. How does the value of the arbitrary
overall efficiency at this speed compare with the corresponding air standard Otto
cycle efficiency?
(iv) The volumetric efficiency and air-fuel ratio at 3000 rpm
