Engine operating parameter

Question 1

What is the use of engine operating parameters? State six examples.

Answer 1

• new engine design
• comparison of engines
• estimating power output
• estimating fuel consumption
• estimating mech. stress
• estimating thermodynamic stress

Question 2

How can engine parameters be classified? Name four examples for each category.

Answer 2

Engine parameters: 
- stroke
- bore
- cylinder capacity
- compression ratio
- mean piston speed
Operating parameters
- power output
- torque
- revolution speed (RPM)
- mean efficiency
- Fuel consumption

Question 3

Define the engines’ displacement.

Answer 3

Vd=B²pis*i/4

Question 4

How does the cylinder capacity affect the engines’ height, width and length?

Answer 4

B² (bore)->squared influence on engines length, width
s (stroke)-> linear influence on height, mean piston speed
Vd=B²pis/4

Question 5

State the formula for the compression ratio and briefly explain the terms.

Answer 5

epsilon=Vc+Vd/Vc
Vc=clearence volumen
Vd=swept volumen=Ap*s

Question 6

State a common compression ratio for Otto PFI, Otto DI and Diesel engines. Briefly explain your answer

Answer 6

Otto PFI 8-12 (evaporating causes heat lossen-> lower pressure)
Otto DI 11-14
Diesel 17-21 -> self-ignition, higher compression ratio

Question 7

Draw a sketch of the piston speed and the mean piston speed. Label the axes!

Answer 7

Mean piston speed Sp=2sn
n=revolution speed
F14

Question 8

Draw a sketch of a typical brake torque and brake power diagram. Label the axes!

Answer 8

F21

Question 9

Briefly explain the terms brake, indicated and frictional regarding the power output of an internal combustion engine.

Answer 9

Brake power:
maximum amount of mech. engine power output at the flange/clutch, including all friction losses of an engine (oil pump etc.)
indicated Power:
theoretical power of an engine without friction losses, pure work done on the pistons by combustion
Friction power:
Indication power - brake power, power lost through friction

Question 10

What is meant by the term mean effective pressure? State its SI-unit!

Answer 10

mean effective pressure: ratio of work output and swept volume F24

Question 11

Explain what is meant by the term efficiency and show how different efficiencies transfer fuel power to brake power

Answer 11

Efficiency in general is the ratio of work output to work input
- Fuel power
- Converted fuel power
- Theoretical power
- Indicated power
- Brake power
F29

Question 12

Briefly explain the term volumetric efficiency.

Answer 12

volumetric efficiency:
ratio of the actual captured mass air over the max. theoretical mass of air (swept air)
𝜂𝑣=𝑚𝑎/𝜌𝑎𝑖𝑟⋅𝑉𝑑⋅𝑐=actual captured airmass/max.theoretical airmass

Question 13

What does the term air-fuel-ratio mean?

Answer 13

AFR=mair/mf
mixture less than 14,7:1 -> rich
mixture more than 14,7:1 -> lean
lambda=AFR/AFRstoich 
lambda>1 lean
lambda<1 rich
AFRstoich: air mass to combust all the injected fuel

Question 14

Give examples of mechanical and thermal stress parameters of ICEs.

Answer 14

mechanical stress: run rate , stroke to bore ratio
thermal stress: brake specific power, piston surface power
F50