Combustion Chamber Design

Question 1

What are the two types of CI engine combustion chambers?

Answer 1

Direct Injection (DI) – Fuel injected directly into the piston cavity.(Open/Swirl Combustion chamber)

2. Indirect Injection (IDI) – Fuel injected into a pre-chamber for better mixing.

Question 2

how does direct injection work?

Answer 2

Fuel is injected into a piston crown cavity, using air swirl for mixing. It improves thermal efficiency and cold starts.

Question 3

How does indirect injection work?

Answer 3

Fuel is injected into a separate pre-chamber where air swirl enhances mixing, leading to smoother operation but lower efficiency.

Question 4

What are the typical compression ratios for CI engines?

Answer 4

Indirect injection: 22:1 to 24:1

Direct injection: 12:1 to 17:1

Question 5

What are the pros & cons of direct injection?

Answer 5

✔️ Lower compression, good efficiency, no cold-start aids (large engines)
❌ High injection pressure, poor turbulence, noisy operation

Question 6

What are the pros & cons of indirect injection?

Answer 6

✔️ Good swirl, smooth running, allows higher rpm
❌ Higher compression, more heat loss, requires cold-start aids