What controls detonation? There is no knock sensor, so is there something else in place to control heat on the heads?

The fundamental difference between diesels and spark ignition engines is that the diesel relies on compression heat to ignite the fuel. This fuel is injected near TDC and burns as soon (while) it is being injected. The spark ignition engine has the fuel in the air already, so hopefully it won't ignite until the spark plug fires it. If it does ignite prematurely, this is a detonation. It can be caused by hot spots in the combustion chamber, too high of compression ratio for the octane rating of the fuel, etc. The diesel cannot ignite prematurely, because there is no fuel there until it is injected.

Thanks for your help. I can assume if the air that makes up the ignition charge is 200 degrees hotter, it WILL ignite sooner than cooler charge. Is fuel timing changed to compensate for this, via the ECM?

I don't think that higher air temp would change anything. The fuel begins burning as it leaves the injector, as long as the air temp is as high or higher than the flash point, which it is very soon after the engine starts. So, once the air is above flash point, further increases in temp wouldn't matter with regard to when the fuel starts to burn.

I don't think that higher air temp would change anything. The fuel begins burning as it leaves the injector, as long as the air temp is as high or higher than the flash point, which it is very soon after the engine starts. So, once the air is above flash point, further increases in temp wouldn't matter with regard to when the fuel starts to burn.


Each time a cylinder bangs, it is an event that depends on enough pressure to attain the needed temp for detonation. Fuel begins burning as it leaves the injector? I'm not a diesel mechanic, but the internal combustion engine still works the same , doesn't it? Fuel is sprayed, then the mixture compressed to detonation. Hotter charge temps make for detonation sooner in the compression cycle, am I wrong?


I just want to know if EGT or head temps or intake temps are monitored to change injector timing.

OK, got a little educated with my favorite site


http://auto.howstuffworks.com/diesel1.htm


Sorryhttp://www.dieselplace.com/forum/smileys/smiley9.gif I know a little better now. Thanks for putting up with a hack.

I was looking on howstuffworks.com to find something that backed me up when my email popped up showing your last post. Must be a pretty popular info site. Anyway, everything is a learning experience. If you really want to get confused, do a search on gasoline direct injection. Mitsubishi claims that it gets as good of mileage as a diesel. Edited by: marcdeluca