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Vehicle dynamics and powertrain > Powertrain > Flashcards

Powertrain Flashcards

1
Q

What is the approximate thermal efficiency of IC engines?

A

The worst 30%. The best 50% In the real world, around 40%

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2
Q

What is the air fuel mixture in diesel engines like?

A

Very lean. 30:1 is common

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3
Q

How does power, torque and fuel consumption vary with RPM with petrol and diesel engines?

A
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4
Q

Why is engine efficiency lower at lower speeds?

A

1) poorer mixing 2) poorer combustion; 3) relatively higher losses

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5
Q

What are the relative ignition tempertatures of petrol and diesel?

A

450 for petrol

350 for diesel.

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6
Q

What is IMEP?

A

Indicated mean effective pressure

Fictional consant pressure that would provide the same power if it acted on the pisston all the way down. It is independent of engine speed and volume

A good measure of effectiveness of the design of the engine.

Also known as net mean effective pressure

Roughly between 0.9 and 1.3 MPa

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7
Q

How is conrod length defined?

A

λ=r/I

Ratio of crank and control length

Normally around 1/3

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8
Q

How do you find BMEP?

A

BMEP=IMEP-FMEP

BMEP=2πTn / Vd

T=torque

n=number of revs per power stroke(normally 2)

Vd=engine displacement

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9
Q

Which pressures corespond to the different areas?

A

A=gross mean effective pressure

B=pumping mean effective pressure

IMEP=A-B

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10
Q

What bore/stroke ratios are used for which applications?

A
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11
Q

What are the relative merrits of two-stoke and four stroke engines?

A
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12
Q

What is volatility?

A

How readily a fluid becomes vapour

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13
Q

What is the relative volatility, flash point and ignition temperature of petrol and diesel?

A

Petrol is more volatile and has the lower flash point. Diesel has the lower autoignition temperature.

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14
Q

What is the equation for the distance between shafts of a gearbox?

A
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15
Q

What is Rg?

A

Ratio of the top gear ratio to the bottom gear ratio

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16
Q

What are the typical largest smallest gear ratios in different types of vehicles?

A

Top gear ratio= 0.7-1

Bottom gear ratio= 3-4.5 for passenger vehicles

5-8 for commercial vehicles

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17
Q

What is the equation relating the distance between gear shafts and the number of teeth on engaging gears?

A

Z1+Z2=2A*cos(β)*(1/M)

M is the module

Z is the number of teeth

A is the distance between the shafts

β is the helix angle of the gears.

18
Q

What equation gives the ratio of first gear from the number of gear teeth?

A

ratio=(driven/drive)*(driven/driver)

19
Q

What equation gives the power of an engine from the torque?

A

2πTn/Vd

T is the torque

n is the number of revolutions per power stroke (2 for 4 stroke engine)

Vd is the total volume of the engine

20
Q

What is the mean piston speed?

A

stroke of engine*RPM / 30

21
Q

What is the effect of increasing the number of cyclinders and the bore of the engine?

A

When n increases for given other design conditions total engine mass and size decrease but length increases

Increasing D is commonly used to upgrade an engine design for higher power

22
Q

What are the typical engine compresstion ratios?

A

10 to 12 for gasoline

14 to 18 for diesel

23
Q

Draw the diagram that explains how the force acting on the piston becomes torque

A
24
Q

What is the valve timing clock for the best engine performance?

A
25
Q

What is the valve timing clock diagram like for a more efficient engine?

A
26
Q

What does a theoretical valve clock diagram for a petrol engine look like?

A
27
Q

What is the definition of a gear ratio ?

A

Driven gear teeth no. / driver gear teeth no.

28
Q

What is GMEP?

A

the work delivered to the piston from the compression and expansion strokes of the four stroke engine cycle. GMEP is the positive work extracted by the piston.

29
Q

What is PMEP?

A

Pumping Mean Effective Pressure, or PMEP is the work required by the piston during the intake and exhaust strokes of the four stroke engine cycle. PMEP is the negative work required by the piston to draw the fresh charge into the cylinder and to push the exhaust from the cylinder.

30
Q

What is FMEP?

A

Friction Mean Effective Pressure, or FMEP is work which is lost due to mechanical friction and parasitic losses. Mechanical friction is for example, the friction between the piston rings and the cylinder walls whilst parasitic losses are for example, the driving of the oil pump, water pump and alternator. Engine friction is largely a function of engine speed and you feel the friction of the engine as engine braking.

31
Q

How do you find mechanical efficiency?

A

BMEP/ IMEP

32
Q

What are first order reciprocating inertial forces?

A

Forces produced from reciprocating components that happen every 360 degrees of rotation

33
Q

How are crankshafts made?

A

Highly stressed crankshafts are usually drop-forged. In smaller and less highly stressed engines, casting is used (lower weight and lower cost)

34
Q

What are the different in cylinder pressures?

A

4-6Mpa for gasoline engine

6-20Mpa for diesel engines

35
Q

What is the typical gas temperature in engines?

A

>2300k

36
Q

What is the local maximum temperature of a piston head?

A

Up to 600k

37
Q

What does an engine fuel map look like?

A
38
Q

What is the Taylor aproximation used in the derivation of normalised displacement?

A
39
Q

What is the human perception of noise with respect to frequency curve?

A
40
Q

How is a single cylinder engine balanced?

A

Vehicle dynamics and powertrain (2 decks)

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