Question

Increase of pressure increases the self ignition temperature and the induction period.

(a) True

(b) False

I got this question in an interview for internship.

Question is taken from Knocking in S.I. Engine in portion Combustion and Combustion Chambers of IC Engine

Answer 1

The correct answer is:

(b) False

Explanation: In general, increase in pressure decreases the self-ignition temperature and reduces the induction period.

Here’s why:

• Self-ignition temperature: As pressure increases, the temperature required for auto-ignition of the fuel decreases. This is because at higher pressures, the molecules of the fuel-air mixture are compressed closer together, making ignition easier.

• Induction period: The induction (or delay) period is the time between fuel injection and the actual ignition. With higher pressures, the induction period tends to be shorter because the increased pressure accelerates the chemical reactions leading to ignition.

Thus, increasing the pressure in an engine generally makes it easier for combustion to occur, reducing both the self-ignition temperature and induction period, contrary to what the statement suggests.