Generic Diesel Injection Fundamentals

Honest John Back Room » Technical matters
View Threaded
Mon 19 Feb 2007 20:21
Generic Diesel Injection Fundamentals - sine
Hi

I was wondering if anyone could describe the injection timing variations of a diesel engine, or post a good link (i've looked but not found much)

I'm interested in roughly what angle BTDC the average engine /(injection pump) will inject the bulk of fuel and how this will change with speed and load. Also is the injection advanced or retarded when the engine is cold?

I assume injection will advance with increasing speed but I can't find how much by. And I have no idea about load changes (although I recall petrol ignition gets retarded with increased load)

Any info would be very useful for some lab prep work:)
Thanks
Reply | Report as offensive | Link
Tue 20 Feb 2007 08:20
Generic Diesel Injection Fundamentals - Ross_D
Well after playing about with some of the ECU maps on my HDi, I have sussed that injection timing occurs at around 12 degress BTDC, rising towards peak power and then falls back off again. Obviously on a more modern diesel the ECU is able to change this as other factors come into the equation. (Such as pre-injection, load calculations etc)

I have a manual at home for the XUD/XUDT engine as fitted to Peugeots/Citroens, the non-turbo has more injection advance on it than the turbo model (Static) but I can't remember off the top of my head what it was. The purely mechanical VE pump had a cold start device that would increase the engine speed when cold by slightly advancing the timing. It also had a pretty linear 'ramp' which advanced the injection timing as revs rose.

I'll see if I can dig out the documents.
Reply | Report as offensive | Link
Tue 20 Feb 2007 21:00
Generic Diesel Injection Fundamentals - sine
Thanks Ross thats most useful.
So is the 12 degrees BTDC at idle speed and that would increase to say 22 degress BTDC at 4000 odd rpm?

Also if the car did have a modern ECU, how would the timing change with load, e.g. if the engine is doing 3000rpm on a flat road, what happens to the timing when you start climbing a hill at 3000rpm flat out?
Reply | Report as offensive | Link
Wed 21 Feb 2007 08:23
Generic Diesel Injection Fundamentals - mrmender
As i've mentioned previously i work with large diesel plant engines (marine and the like) the usual was 25 to 15 BTDC, i work with a large modern engine with all mechanical injection, (very high pressure) where it's down to 8 BTDC
Reply | Report as offensive | Link