Engine/Transmission (1998.5 - 2002) EGT/Fuel Question

[Bobalos]

Im fairly new to this Diesel thing so be gentile. LOL.



Is it correct to say, if I keep everything else constant, & add more fuel, that I will make more HP than I was a second ago & get higher EGT's?



Is it correct to say, if I keep everything else constant, & add more boost, that I will not make any more HP than I was a second ago, but get lower EGT's?



Is it correct to say, if I have cooler air temps going into the turbo that I will get lower EGT's. for example, will my EGT's be lower early in the morning when the air it cold than in the afternoon when its 30* hotter out?



I realize that there are exceptions to every rule, but Im talking about general terms with a relatively stock truck.



thanks guys I appreciate it.

Bob

 

[GCULP]

Is it correct to say, if I keep everything else constant, & add more fuel, that I will make more HP than I was a second ago & get higher EGT's?

your logic sounds correct here.

Is it correct to say, if I keep everything else constant, & add more boost, that I will not make any more HP than I was a second ago, but get lower EGT's?

from what I've read on here, more boost isn't always a good thing, and I don't know how you would create more boost without more heat since it is an indirect result of burning more fuel. Larger volume without increased pressure is what I think you would want.

Is it correct to say, if I have cooler air temps going into the turbo that I will get lower EGT's. for example, will my EGT's be lower early in the morning when the air it cold than in the afternoon when its 30* hotter out?

hmm, probably not since your grid heaters heat up the air to a more optimum temperature when it is cold out. If you disable them you may see cooler EGT's but the ignition of the fuel may not be as efficient, thereby reducing power



hope it helps and I hope someone chimes in if I have made any incorrect assumptions.

 

[Bobalos]

thanks Gary,



Nobody else have a comment?



Bob

 

[NoSeeUm]

Im fairly new to this Diesel thing so be gentile. LOL.

Where is my hammer.



I think you got the idea, but keep in mind for complete combustion no matter what fuel and air will only burn efficiently to a maximum fuel-air ratio. With a diesel, being lean has little adverse effect as it does with gas engines. This is because diesel readily ignites when under compressoin and heat. But a rich mixture is not efficient. It results in incomplete combustion and soot.

Is it correct to say, if I keep everything else constant, & add more fuel, that I will make more HP than I was a second ago & get higher EGT's?

Fuel is heat is Hp.



Most of the time. There is a point where you can actually overfuel so much that it can detract from proper combustion. But not something to really be concerned with generally.

Is it correct to say, if I keep everything else constant, & add more boost, that I will not make any more HP than I was a second ago, but get lower EGT's? ?

You are mostly right but it depends. Often more boost will net more Hp. The break over point would be when no more air can find any more fuel to combust with. As I said earlier diesel engines can burn lean, but still require and optimum mixture for complete combustion. More air present just gives the whole process a better chance of succeeding at a more efficient level.



Keep in mind that boost is not free. There is actually pressure in the exhaust that drives the turbo. Generally speaking, more boost equals more exhaust pressure. As you raise the exhaust pressure you drop the Hp output. It is a give and take. So there is a point where, depending upon the turbo design, you could lose Hp after a certain value of boost.



Additionally concerning EGT's, with higher boost there is just excess air present. Think about the same amount of heat essentially spread over a larger area and there is less temperature rise.



Then as some one above stated, to make boost you must compress the air. When air is compressed its temperature rises. If the turbo compressor is operating outside of its efficient pressure and flow range the temperature can really dramatically rise. So with over increased boost comes over increased temperature.

Is it correct to say, if I have cooler air temps going into the turbo that I will get lower EGT's. for example, will my EGT's be lower early in the morning when the air it cold than in the afternoon when its 30* hotter out? ?

The number that sticks in my head is 1F for 1. 5F. That is, lower IAT by 1F and the EGT will drop around 1. 5F. I have never tested this, just seems to be common knowledge to some people.

I realize that there are exceptions to every rule, but Im talking about general terms with a relatively stock truck. ?

Seems there are always exceptions. But yeah I think you get it.



Jim

 

[Bobalos]

Right on Jim, thanks a bunch. I am going to play with it a bit & see what I find out.



thanks again

bob