Why are our injection pumps retarded?

[tradergem]

I used my new to me injection timing tool to set my injection pump to 8.5 degrees BTDC @ 2000 rpm. In the process of doing this I noticed that the injection pump retarded the timing as the the rpms were increased. I am new to diesels and this runs counter to what I am used to in gas motors where the timing is advanced as the rpms are increased. Just would like to know the engineering behind this thats all? By the way my truck really rattles when it is first started cold untill it warms up and the cold advance and the fast idle kicks off. Thanks. Jim

 

[Diesel JD]

Well I think that's the case to help keep EGTs under control and so you don't crack a piston when you're under heavy throttle. Really as bad as it sounds at idle that advanced timing shouldn't be too ******* the engine its when you're working it that it could break something. I could be wrong and will be corrected if that's the case I'm sure. By the way if you get it to 8.5*BTDC at 2000RPM with the pulse method, that is spot on and will give you the best compromise between power, durability, economy, and emissions.

 

[tradergem]

Thanks JD, just looking for more education that I can't seem to find in the mauals I have. Jim

 

[Agnem]

Cylinder temperatures increase at higher RPM's, so the fuel ignites faster.

IP injection cycle completes faster (I.E. line presure is generated faster, and time from injection to pintle release is faster).

Pick a theory. Any theory. And get me a theory while I'm waiting.

 

[tradergem]

More Info

After Googleing diesel timing I found the following website that has some good info on Stanadyne DB2 pumps and timing.

http://www.oliverdiesel.com/tech.htm

Thanks, Jim

 

[GTFD]

Tradergem, Nice link, thank you.

 

[tradergem]

Your welcome