diesel timing questions

[SBSP]

I am trying to find information on timing of the mechanical injector pump on a 6.2L GM diesel. I can find no information on the correct dynamic timing of this engine. I have read conflicting settings on a few forums, one site said ~3 deg BTDC and another stated that ~6 deg ATDC is the correct way to go. I need to educate myself on the functions of these type of pump arraignment.

Thanks for any help.

John

 

[MikeHalloran]

Did the two sites give an RPM to go with the timing? I think these beasts have a 'spark advance', so dynamic timing will vary with speed and be different from static timing.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[icrman]

Don't have the book handy, but I think it is set by alining marks, or pinning it.
Most non advancing pumps are set anywhere from 5 to 15 btc. depending on crank chain geometery.

 

[SBSP]

Mike,

The RPMs stated for the advanced settings are around 1300 RPM. I am under the impression that the pump actually redards as the engine RPMs increase.

icrman,

There are static timing marks on this engine and the manual shows how to reset them if need be. My engine has had the timing chain replaced with a set of timing gears for more precise pump timing. The problem with the static timing marks is you can vary the pump timing several degrees +/- without changing the marks just by wiggling it.

Thanks for the input. I am looking for indepth knowage on the results of timing settings on engine performance and efficiency.

Along with the cam gear drive, I have turbo charged the engine and reduced the compression from ~22:1 to ~19:1. This last step may not have been a good idea as it has lead to cold start problems. I'd like to figure out how the Cummings guys solved that problem...

Thanks again,

John

 

[icrman]

It has been a while since working on a 6.2, or checking out the book. As far as retard as speed increases. For that engine I'm not sure. But logic says it should be advanced, that is if you care to extract some power from the higher speed. The speed at which the fuel charge burns, does not increase with speed. That is why you advance the ignition point in a spark ignition engine.
You want combustion going as the piston arrives at TDC, it does no good to have it just starting to burn as the piston is already desending. So why then would you want it to retard?

 

[TexasDieselGuy]

Hey, if you guys are looking for some real answers on 6.2, or any other diesel engine, try

http://www.dieselplace.com.

The knowledge pool we have there is fantastic. Open a thread in the 6.2 forum and we'll get you figured out.

 

[dgallup]

In general, advancing timing will decrease (improve) BSFC, increase power, increase NOx emmissions & significantly increase peak cylinder pressure. The increased cylinder pressure can destroy your engine so be careful. Did you add an intercooler with your turbo? If not, it is the best thing you can do now. Reducing the charge air temp is all good: reduced BSFC, increased power, reduced NOx and reduced peak cylinder pressure.

 

[SBSP]

icrman,

Being a spark ignition guy, I follow your logic about advance. I am unsure about the mechanics of the combustion dynamics of a diesel engine so I am questioning the function of the injector pump. Am I correct to assume that the conditions in the cylinder are above the flash point of the fuel when it is injected? If so then I could see the logic of slight advancement with RPM.

TexasDieselGuy,

Good site, thanks for the link and the suggestion.

dgallup,

I have found a graph covering what you have just stated over at

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

where he took a page from the diesel emissions handbook (I need to find this book). A intercooler is in the works for this year as well as bringing the compression back up to near stock (23:1) as I don’t think the 18:1 setup I currently will provide any real gain in performance to offset the starting problems.

Thank you all for your help in my education on this.

John

 

[Artsi]

Here's some about 25 year old research data on 4-cylinder Volkswagen 1.6 liter TurboDiesel engine data:

http://www.4crawler.com/Diesel/SAE/vwtdsae.shtml

injection timing:

http://www.4crawler.com/Diesel/SAE/figure_43.jpg

injection pump advance (pls multiply pump speed by two to get engine rpm)

http://www.4crawler.com/Diesel/SAE/figure_41.jpg

 

[SBSP]

Artsi,

Thanks for the links. That SAE paper is great, lots of information. I am also plowing thru Internal Combustion Engines and Air Polution by Edward Obert. Chapter 15 covers Compression-Ignition Engines with lots of experimental data.

Who know learning new stuff could be so much fun!

Thanks for you help.

John

 

[Artsi]

Thank's for the feedback.

BTW, if you happen to play with 'P2P' type of file exhange programs, please do run a search by a filenime of "Diesel Engine Reference Book". You'll be pleasantly surprised. It'll result in 61megs of pure pdf compressed joy! (Out of dozens of P2P programs do try out 'Shareaza'. That'll do the job for you.)