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Question 1

SI engine have what flammability limits? And what does this mean

Answer 1

narrow flammability limits, meaning the fuel and
air mixture must be carefully controlled to a perfect amount of air to fuel
(“stoichiometric”)

Question 2

How should be intake air in SI

Answer 2

throttle the intake air art lower engine loads
(i.e. reduce the air flow in proportion to the fuel flow)

Question 3

Draw out the PV diagram

Answer 3

Compression, Expansion, Exhaust, Intake, and Ignition.

Expansion Ratio, Compression Ratio

Question 4

What mix do current SI engines require

Answer 4

A stoichiometric mix of air and fuel.

Question 5

As engine load (torque) reduces, what must also reduce. SI

Answer 5

The Air

Question 6

How is the air reduced. SI

Answer 6

By the throttle valve

Question 7

What pressure condition is created under part load. SI

Answer 7

A vacuum under part load, as low as 0.5 bar below atmosphere.

Question 8

What extra work must the engine do. SI

Answer 8

Extra “p.dV” work to expel burned gases back against higher atmospheric pressure (negative work region).

Question 9

What does the slide say about HCCI engines and throttling? SI

Answer 9

HCCI engines run stoichiometric but do not have an intake throttle.

Question 10

How do HCCI engines avoid throttling (per slide)? SI

Answer 10

Use a variable valvetrain to trap previously burned gases from the last cycle.

Question 11

What does trapping burned gases eliminate (per slide)? SI

Answer 11

The negative work region, as pressure stays at atmospheric in the intake.

Question 12

Under lower loads, what changes (per slide)? SI

Answer 12

More burned gases are trapped by changing timing of the exhaust and intake valves.