Diesel Fuel Injection System

Question 1

List Six significant differences between a Diesel Fuel Injection System and a typical Multiport Gasoline Injection System.

Answer 1

1. Diesel Fuel Injection Systems use a mechanical fuel pump, while Gasoline Fuel Injection Systems use an Electric fuel pump.
2. Diesel engines’ compression ratios range from 17:1 - 25:1. Gasoline engines’ compression ratios range from 8:1 - 9:1.
3. Diesel engines operate on compression ignition, while Gasoline engines operate on spark ignition.
4. Diesel engines have no throttle valve, while Gasoline engines do in the throttle body.
5. Diesel engines use Direct Injection, while Gasoline engines use Indirect Injection.
6. Diesel engines only compress air, while gasoline engines compress both air and fuel.

Question 2

List Four major Components of the Diesel Injection System.

Answer 2

1. Injection Pump.
2. Injection Lines
3. Injector Nozzles
4. Glow Plugs

Question 3

How does the Diesel Injection Pump work? Four steps.

Answer 3

1. The fuel supply pump fills the barrel with fuel.
2. The Camshaft lobes then force the roller tappet and plunger upward in the barrel.
3. Fuel is then forced through the delivery valve, to the injection line and nozzle.
4. The Delivery Valve closes when the plunger reaches the end of its stroke.

Question 4

What is the purpose of the Diesel Lift Pump?

Answer 4

The Diesel Lift pump feeds the injection pump low pressure fuel from the fuel tank.

Question 5

What is the purpose of the Governor?

Answer 5

The Governor controls the engine’s idle speed and limits the maximum engine speed.

Question 6

What is the purpose of the Glow Plug?

Answer 6

Glow plugs warm air in the cylinder pre-combustion chambers and aids the starting of a cold engine.

Question 7

How is Injector Timing Controlled?

Answer 7

The Injector Timing is controlled by spring - loaded weights. As the engine speed increases, the weights fly outward to advance injection timing, providing more time to ignite and burn fuel.

Question 8

How does the Diesel Injector Work?

Answer 8

1. High pressure fuel flows into the injector nozzle.
2. Fuel flows down the fuel passage in the body of the injector into the pressure chamber.
3. The needle is forced upward, compressing the spring.
4. Fuel sprays out in a conical pattern.
5. Fuel that leaks past the needle returns to the fuel tank through the return lines.