Fuel System

Question 1

What do you need to run compression ignition?

Answer 1

• air
• compression
• fuel- adequately atomised

Question 2

What do you need to run spark ignition engine?

Answer 2

• air
• fuel -
• compression
• spark

Question 3

What is spark ignition?

Answer 3

• low pressure fuel pump to feed either a car by (older engines) or an injector fuel rail
• send to the injectors usually located in the intake manifold p
• petrol atomisation happens at low pressures
• injectors are electronically actuated

Question 4

Components of spark ignition?

Answer 4

• spark plugs
• HT leads - high tension
• distribution- an older engines
• coil/coil pack

Question 5

What is compression ignition ?

Answer 5

• low pressure lift pump
• which supplies either a high pressure injection pump or unit injectors
• which raise the fuel pressure to achieve atomisation
• 20-30000 psi

Question 6

Why diesel engine need high pressure atomised injection?

Answer 6

• lower flash point
• more of a surface area

Question 7

What are 2 types of injection?

Answer 7

• direct and indirect injection

Question 8

What does direct injection mean?

Answer 8

Fuel is injected directly into the combustion chamber

Question 9

What does indirect injection mean?

Answer 9

Fuel is injected into a pre combustion chamber above the cylinder

Question 10

What are the main fuel systems in diesel?

Answer 10

• common rail
• pump-line-nozzle
• unit injection

Question 11

What is common rail?

Answer 11

• modern technology that uses a high pressure fuel pump to supple a high pressure “common” fuel rail from which injector is fed.
• timing is controlled electronically at the injector

Question 12

What is pump-line-nozzle system?

Answer 12

• an older technology
• it has an injection pump with individual lines to each injector
• injection timing is controlled by the pump
• there are multiple different pump types

Question 13

What is the unit injection

Answer 13

• uses a low pressure pump
• to supply the injectors
• the injectors create the pressure needed for atomisation
• timing is electronically controlled at the injector solenoid determines timing and metering

Question 14

When does ignition occur and why?

Answer 14

• ignitions happen BTDC on compression
• so reach peak combustion pressure
• ignition starts at the point of injection or at the spark plug
• takes time to to reach the piston
• this is times so that combustion pressure occurs just at the piston starts to move back down the cylinder (about 2 degrees ATDC)
• this provides a more smoother and more efficient power delivery
• at idle between 10-15 degrees BTDC:
• advanced- increase degrees BTDC
• retard - decrease degreee BTDC

Question 15

What happens if timing it too advanced?

Answer 15

• risks causes knocking or ‘pinging’
• which is when peak combustion pressures occurs before the piston reaches TDC

Question 16

What’s happen if timing is too retarded?

Answer 16

• causes power loss due to lower peak combustion
• this happens because the piston has already started heading down the bore, increasing cylinder volume

Question 17

What does the spray pattern on top of the piston mean?

Answer 17

• how many holes the injectors has
• same pattern also means injectors are working correctly
• solid colour could be a fault