Tuesday, April 12, 2011

Engines week 2

1.What is the firing order of a four stroke engine?

The firing order is the sequence in which the cylinders ignite the air/fuel mixture and use the resulting energy to turn the crank. In a four stroke engine the crankshaft is shared by the pistons and each piston will need two revolutions of the crank shaft to complete its cycle and the firing order will need to be in sequence that will put even load on the crank.

2.What is the difference between a S.I and C.I engine?


Compression Ignition engine 4 stroke cycle
A spark ignition engine uses a spark from a spark plug to ignite the air/fuel mixture when the cylinder is top dead center on the compression stroke.

Compression ignition engine uses compression it ignite the air/fuel mixture. on the intake stroke air is introduced into the cylinder then at the top of the compression stroke fuel is introduced into the hot compressed air which evaporates and expands and then ignites. Compression ignition engines use a less volatile fuel and have more compression than SI engines







3.Is there any difference between a S.I and C.I piston if so what?



Diesel piston
A compression ignition engine piston have a deep groove in the top so that when the air is compressed the fuel has somewhere to be injected to. The pistons are usually larger and stronger to be able to handle more pressure

4.What year was the diesel engine invented and by whom?

 Rudolf Diesel. The first successful compression ignition engine was in the year1897

5.What is the purpose of the oil jet on the connectng rod, and where does it spray?

The oil jet sprays oil onto the cylinder wall to provide lubrication between the piston and the bore. Without this the piston could seize or damage the bore. Also provides cooling to the engine.

6.On the connecting rod where is the big end and little end?

The big end is connected to the crankshaft and the little end is connected to the piston


7.What is the purpose of the thrush washers on the crankshaft?

Thrust washers are in between the connecting rod big end and the crankshaft with a film of oil it helps stop the unwanted movement. When the hole in the thrust washers lines up with the hole in the connecting rod oil travels through and sprays the bore and piston

8.On a diesel engine whats the difference between direct injection and a indirect injection type?

 In a direct injection the fuel is injected directly into the combustion chamber. An indirect injection the fuel is injected into a prechamber which is off the combustion chamber. The combustion starts in the prechamber and then spreads into the combustion chamber

9.Explain the term valve timing?

 Valve timing is the precise timing of  the opening and closing of the valves controlled by the camshaft. The valves need to be able to open and close at the right time for the fuel/air mixture to enter the combustion chamber and for the exhaust to exit

10.Why do we have valve clearance?

 Correct valve clearance ensures that the valves open and close properly. if the clearance was too much then the valves wouldnt open to their full capacity. If the gap was too small then the valve wouldnt fully close

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