Thread: Timing and EGT's

I'm not sure about diesels, especially modern direction injection ones with multiple injections per power stroke, though when I was racing 2-strokes advancing the ignition made the engine crisper but increased the EGT's. Retarding it did the opposite.

Originally Posted by Slunnie

I'm not sure about diesels, especially modern direction injection ones with multiple injections per power stroke, though when I was racing 2-strokes advancing the ignition made the engine crisper but increased the EGT's. Retarding it did the opposite.

yeah same with chainsaws, when you start porting them, adding more fuel etc, there comes a point where you need to adv. the timing....2 strokes are pretty simple more power=more heat...

but i have no idea whats going on in the diesel and if the turbo etc is changing this, is it more fuel with retarding that increases egts?

Serg

Definate correlation between retarded timing and EGT. Basically, the fuel is injected LATER in the compression stroke and therefore is still burning and realeasing heat etc in the exhaust manifold/ turbocharger= higher gas temps.

Whenn advancing a diesel engines timing(increasing Plunger lift is how it's done ) you are pushing in earlier fuel, therefore the gasses have ignited and have supplied there heat energy for longer INSIDE the cylinder, where it is supposed to be. Late injection = high heat(energy) losses= less efficiency=less power.
Earlier injection = less heat(energy) lost = more efficiency= more power.
BUT, The degree of advancement of injection timing is totally individual for every engine designer/manufacturer. Some respond well and others don't due to cylinder head/ combustion chamber design, (Indirect or direct injection) comp ratio, turbocharger/ manifolding, etc etc. The Tdi responds very well to a plunger lift increase from factory 1.54mm to 1.6mm.


JC

We only discussed this in another thread last week.

There is a direct correlation between EGT's, and injection timing.

As JC said, in a nutshell,
advance injection, derive more work out of charge = lower EGT's
retard injection, less time for work to be done so fuel is still burning as exhaust valve opens = higher EGT's (relatively speaking)
BUT you will derive much higher piston temps when you advance injection timing, and conversely you lower them when you slightly retard them. As with everything, it's a tradeoff.

There's some good stuff in this thread very high egt

The reason Nissan started to retard injection timing on the old TD42T was in concert with the installation of the intercooler and it was purely to reduce NOx to meet the increasingly stringent emissions for diesels.
Lower combustion temps = lower NOx.
You are reducing efficiency, but meeting the emissions obligations.