Diesel Engine Compressions

[Joe T]

What sort of Compression readings would you expect to see on a Modern Turbo Diesel engine, common rail or normal, 20 Bar? 30 Bar?
Do Turbo diesels run a lower compression ratio than the normally aspirated version of the same engine. Hence lower Compression readings? Like in petrol engines?
I am interested in actual readings people have taken, not necessarily what the manual states.

Thanks

[GavinPearson]

Common rail injection systems run at around 25,000 psi, and the cylinder CR is around 18.5:1.

[knightly]

as for compression readings - typically around 150 Bar peak cylinder pressure.....but these figures are now creeping towards 200Bar for the latest Turbo-diesels......aluminium pistons cannot handle the loads so they are now using steel pistons.

As for compression ratio - yes I would agree with the 18.5:1 figure.....but anywhere between 15 to 20:1 .....the compression ratio is a function of the speed the engine is revving to, and the required cylinder pressure.......the general trend is that the higher the engine revs, and the more cylinder pressure - the lower the compression ratio is........so as a guide......high power diesels have a lower compression ratio......low power diesels have a high compression ratio.

as for the normally aspirated/turbo question.....I honestly cant remember......but its not just about compression - its more about in-cylinder swirl in order to mix the fuel and air - otherwise the fuel will not burn and it will just create black smoke.......a normally aspirated diesel engine will typically have a high amount of swirl designed into the intake port, otherwise known as a helical/snail port, typically 3 to 4 DCS.....a turbo engine will be slightly less.....and a high power turbo diesel will be quite low swirl, about 0.7-1.3 DCS

let me know if you want to know more - hope that all helps!

Edited by knightly on Tuesday 12th December 11:50

[Joe T]

Thanks for this what I am actually interested in is real readings from cranking an engine with a compression gauge attached to individual cylinders.
I appreciate theoretical pressures have changed but interested to see if this is replicated in mechanical terms to tradtional testing methods.