1
Q
What do you need to run compression ignition?
A
- air
- compression
- fuel- adequately atomised
2
Q
What do you need to run spark ignition engine?
A
- air
- fuel -
- compression
- spark
3
Q
What is spark ignition?
A
- 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
4
Q
Components of spark ignition?
A
- spark plugs
- HT leads - high tension
- distribution- an older engines
- coil/coil pack
5
Q
What is compression ignition ?
A
- 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
6
Q
Why diesel engine need high pressure atomised injection?
A
- lower flash point
- more of a surface area
7
Q
What are 2 types of injection?
A
- direct and indirect injection
8
Q
What does direct injection mean?
A
Fuel is injected directly into the combustion chamber
9
Q
What does indirect injection mean?
A
Fuel is injected into a pre combustion chamber above the cylinder
10
Q
What are the main fuel systems in diesel?
A
- common rail
- pump-line-nozzle
- unit injection
11
Q
What is common rail?
A
- 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
12
Q
What is pump-line-nozzle system?
A
- 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
13
Q
What is the unit injection
A
- 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
14
Q
When does ignition occur and why?
A
- 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
15
Q
What happens if timing it too advanced?
A
- risks causes knocking or ‘pinging’
- which is when peak combustion pressures occurs before the piston reaches TDC
16
Q
What’s happen if timing is too retarded?
A
- causes power loss due to lower peak combustion
- this happens because the piston has already started heading down the bore, increasing cylinder volume
17
Q
What does the spray pattern on top of the piston mean?
A
- how many holes the injectors has
- same pattern also means injectors are working correctly
- solid colour could be a fault
