Powerplant Diesel

Question 1

Diesel vs. Petrol compression ratio

Answer 1

Diesel: 14:1 - 28:1
AVGAS: 9:1

Question 2

Are there spark plugs in a Diesel engine?

Answer 2

No

Question 3

When is the diesel injected into the cylinder (what part of the cycle)?
When does it combust?

Answer 3

Just before TDC, a precisely metered quantity of fuel is injected into the cylinder:
It immediately ignites due to cylinder temperature (compression Ignition).

Question 4

Is there risk of detonation?
Is there a mixture control?
How is power output controlled?

Answer 4

No risk of detonation so diesels operate much leaner
No mixture control lever required:
Power output is controlled by the amount of fuel injected into the cylinder

Question 5

What pressure would the engine reach?

Answer 5

Must cope with the very high pressures experienced in the cylinder:
Injectors must operate at anything up to 1600 bar (24 000psi).

Question 6

There are two types of injection system. What are they?

Answer 6

Two types of injection system:
Mechanical Injection - High pressure fuel is fed to each injector from a dedicated fuel pump (crankshaft driven)
Common Rail - A high pressure pump supplies fuel to a common rail from where fuel is distributed to each electronic injector
Most modern diesel designs use the common rail system because it gives more efficient combustion, cleaner emissions and quieter operation.

Question 7

Two pumps: what drives them, why are there two?

Answer 7

Engine, Electric.
Redundancy, priming

Question 8

The common rail system has:

Answer 8

A high pressure pump with a pressure regulator and metering valve
A common rail acting as an accumulator for high pressure fuel.
Electromagnetically operated injectors.
An engine control unit (ECU) control fuel pressure and the injectors.