Thread: c.h.i.e.f 's 110 Isuzu county

Originally Posted by Bush65

Likewise I have not measured the volumes to know what the variations are like.

Rick was making a good point, but in a direct injection diesel, once ignition starts the combustion pressure rise is extremely rapid - this is what causes the noise and also results in high torque. Combustion is over in a very short time and the pressure drops as the piston descends.

Pressure rise in petrol engines starts low and reaches a maximum toward the end of combustion (opposite to diesel).

For higher torque the diesel has to burn more fuel at around TDC. The difficulty here (neglecting production of NOx and noise for this thread) is to get enough oxygen to where the fuel droplets are. This mixing is why the shape of the bowls and inlet ports is so important. Change the combustion between one cylinder and the other by upsetting the critical shape of the bowls could result in far worse vibrations than small variations in volumes.

If you could see the shape of the piston bowl and the spray from the nozzle holes in the injector, you can see how the bowl is shaped so the spay doesn't impinge on the walls of the combustion chamber. However this doesn't show what is done to promote mixing and the importance of the lip shape.

In reality the bottom line is to leave well enough alone unless you really know what you are doing.
I forget I've been lucky enough to have been taught and to have hung around some very, very switched on people in the past.

Originally Posted by rick130

In reality the bottom line is to leave well enough alone unless you really know what you are doing.
I forget I've been lucky enough to have been taught and to have hung around some very, very switched on people in the past.

That is what I was driving at. You stated it more elegantly than I.

For anyone interested, Volumes 1 and 2 of The Internal Combustion Engine in Theory and Practice by Taylor is a good starting point.