:wtf: why is it a diesel can't run as high of an EGT as a gas burner? over the years i have had many turbocharged vehicles (both car and motorcycles ) and have seen above 1800* EGT's AFTER the turbo sustained for long periods of time, and never had ANY melt-downs or problems

Just a guess, but I think it's a combination of the higher compressions and stress in the diesel and the size of components. Not only does the diesel have much higher pressures, but the pieces and parts are more massive, which leads to more heat "soak" and they can't shrug off heat as fast as the smaller and lighter gasser components.

anyone else?

Your "mass" issue works both ways.....Why can't we run a few seconds at highter temps since we have higher mass? I know that doesn't apply to hauling...but, is the metallurgy different in our stock diesels as compared to the best money can buy to build a race car? Something to think about....this guy has good point...

Mike

as mentioned above..might be because of the almost 20:1 compression ratio which makes it hot already, then add 30psi to the equation which adds even more heat. The rule of thumb in making power is low compression + boost..but diesels are high..

I could be wrong..Just my take on it. I'd be interested in seeing some hard data about this.

I thought it was for the turbo fins, so they don't melt. I thought they were made of aluminum, until I found out that Al melts at 660*. They must have some special alloy...

The compressor fins are aluminum...the turbine (hot section) fins are made out of a type of hastalloy that can withstand lots of heat.

---Ben

inconel

i still see no good reason as to why we need to keep such a low EGT compared to a gas burner...EGT is EGT.

i still see no good reason as to why we need to keep such a low EGT compared to a gas burner...EGT is EGT.

You know, on second thought, you're right. Go ahead and run that puppy up to 2200 degrees and let us know how that works out for you. ;)

You know, on second thought, you're right. Go ahead and run that puppy up to 2200 degrees and let us know how that works out for you. ;)

Oh boy.... :badidea: :funnypost :iamwithst :exactly:

metallurgy is the killer. In the lab we run about the same EGT's. For us it is simply the manifold will start to break down and eventually melt. They are just cast iron. Granted cast iron doesn't go completely liquid until 2200's if I remember correctly, but it gets real soft at 1800 degrees, and you start to recrystalize the iron at those elevated temps. You are essentially heat treating the material, and eventually it will harden, become brittle, and fail.

Seriously, it's the difference in the diesel compression ignition cycle versus the gasser spark ignition. Not only does diesel contain more btus/lbm than gas, but instead of squishing a fuel/air mixture to 8:1 compression and spark igniting it, we are smashing an air volume up to 20:1 compression (which generates a lot of heat doing that alone) and spraying in a more energetic and denser fuel that autoignites in the highly compressed and heated airmass. This results in a longer, hotter burn producing a lot more torque and stroke than the gasser before the exhaust valve finally pops open to vent out the remains. Although the gasser is exhausting hotter gases, it's actual power stroke is cooler and it's thinner cylinder walls, head and pistons can cool quicker once the power stroke is completed. It's also running hotter exhaust gases because it's a lot less efficient and there's an actual "afterburn" going on in the exhaust manifold.

If that doesn't do it for you, then go ahead with that 2200 thing I mentioned before.):h

i still see no good reason as to why we need to keep such a low EGT compared to a gas burner...EGT is EGT.

Good point, heat is heat no matter how it is created.

Good point, heat is heat no matter how it is created.

my point exactly, but it seems as though we have a smart ass who wants to go by the old school ways from what i gather from his posts, but IF the diesel created so much more heat in the engine than a "gasser" then would the engine coolant temp not sky rocket with such high (1800*) EGTs?

think about the gasser with ALOT of boost for a minute, you start off with say an 8.5:1 ratio, then add like 20 psi boost, i am willing to bet the relative C/R is geting on up around a diesels C/R.

i am just trying to figure out WHY this low EGT thing is so crutial on a diesel these days....

my point exactly, but it seems as though we have a smart ass who wants to go by the old school ways from what i gather from his posts, .

Well, if you mean physics and mechanics by "old school" you are right. But have no fear, I'm not going to play smart ass to your dumb ass any more. I was trying to give you some useful information with a bit of tongue-in-cheek, sorry if I offended you.

Well, if you mean physics and mechanics by "old school" you are right. But have no fear, I'm not going to play smart ass to your dumb ass any more. I was trying to give you some useful information with a bit of tongue-in-cheek, sorry if I offended you.

thank you jesus!, no need for a wealth of useless information

Careful guys, don't let this thread go the wrong way.

These are some good questions though...when a stock LLY can run 1300-1400 degree EGT's pulling up a mountain grade stock, it does make you wonder if the 1250 degree "safe limit" people talk about is no longer the case.

I could use some help. How or what do you do to get around the DTC's when a free flowing exhaust is installed? Is there any devices available that can trick the computer?

I heard that either a person or a product called "Finger Stick" might help with the EGR problem.

The "Finger Stick" corrects codes thrown by the computer when the computer does not see enough back pressure from a free flowing exhaust. The "Finger Stick" will do nothing for high EGT's (exhaust gas temps) or EGR (Exhaust Gas Recirculation) which are two totally different things.

Careful guys, don't let this thread go the wrong way.

These are some good questions though...when a stock LLY can run 1300-1400 degree EGT's pulling up a mountain grade stock, it does make you wonder if the 1250 degree "safe limit" people talk about is no longer the case.

...and this is the reason i ask this, like wassaid before, heat is heat, no matter how it is generated, and disapated in a "normal" operating range of the engine, i don't understand why ther is such a low set point and would like to see the REAL reason as to why....

I may be way off base on this so someone please correct me if I'm wrong, I just wish I could find my educational materials to back this up. Anyway here goes if I'm remembering correctly the combustion temperature of a compression ignition (i.e. Diesel) engine is way higher than that of a spark ignition. Something like 3000 degrees vs. 12-1800, what that means is you're far more likely to melt your piston on a compression ignition vs spark ignition, which is why you want lower EGT's on turbo'ed Diesel applications. Again take this with a grain of salt as my memory is a little flaky, I'm sure the numbers aren't exact but I do remember something along these lines from my edumactation, just dunt remember much else :Insane:

the aluminum inside the combustion chamber is the weak point for egt... your pistons are aluminum and on the dmax, the cylinder heads are too... if things get too hot, aluminum will melt on you. simple isn't it... now get a larger diesel engine with steel crown pistons and you can run hotter egt than the 1300-1400 where our aluminum components can start to fail at...

and even with the egt probe in the manifold, you will not see the full temptrature of combustion there.. with the valve overlap and the intake manifold pressure, you will get intake air charge air scavanging the cylinder into the exhaust manifold. you get cool intake air in the hot manifold, it will cool down the exhaust in the manifold...

sounds like a couple of good theorys, but still would like hard proof as to why

We are talking aluminum alloys here, and silicon content in the pistons. Turbo Buicks ran ridiculous boost pressures and egt's with aluminum heads and of course, aluminum pistons.

.

....would like to see the REAL reason as to why....
What do You believe is the REAL reason Why ? sounds like a couple of good theorys, ....but still would like hard proof as to why
What hard proof would you Understand?

What are you Realy looking for?

Idahofox

What are you Realy looking for?

Idahofox

hard proof as to why these are "limited" to a low EGT

do you have the answers?

oh, and re-read my origonal post

hard proof as to why these are "limited" to a low EGT
Please explain what hard proof is, I'm just a dumb O'l Idaho Potato Farmer.
do you have the answers?
No, do you ?
oh, and re-read my origonal post
Ok, I did that; what should I do now?

I'll bet that if you ran your EGT's @ 1800, no one would say a word.
.

whatever dude

So much for trying to get a good discussion on this, seems to be the way threads are headed on this board... :mad:

If you can't run past 1300-1400 degree EGT's without steel crowned pistons or what have you, then why do the thousands of stock LLY's towing across the country not melt down?? Many people have posted here that their stock LLY's can run some very hot EGT's. Surely not everyone installs an EGT gauge in their truck when they buy it. They buy the truck and tow their camper or whatever with it, without thinking about anything else...

Is it possible the 1250 "limit" on EGT's was due to older turbo's that weren't water cooled?? I duno...someone must. Doesn't Edge default the fuel down at 1350 degrees EGT with the attitude?? Wonder why they don't go for the 1250?? Again, just trying to think outside the box.

3k oil changes have been proven to be a waste, why is this one so hard to discuss without panties getting wadded up??? :confused:

So much for trying to get a good discussion on this, seems to be the way threads are headed on this board... :mad:

If you can't run past 1300-1400 degree EGT's without steel crowned pistons or what have you, then why do the thousands of stock LLY's towing across the country not melt down?? Many people have posted here that their stock LLY's can run some very hot EGT's. Surely not everyone installs an EGT gauge in their truck when they buy it. They buy the truck and tow their camper or whatever with it, without thinking about anything else...

Is it possible the 1250 "limit" on EGT's was due to older turbo's that weren't water cooled?? I duno...someone must. Doesn't Edge default the fuel down at 1350 degrees EGT with the attitude?? Wonder why they don't go for the 1250?? Again, just trying to think outside the box.

3k oil changes have been proven to be a waste, why is this one so hard to discuss without panties getting wadded up??? :confused:

one thing i DO know is that the older (i mean OLD) like first turbochargers could not take much heat before the melted (non inconel) and that was the reason they where first used on aircraft and where a LOOONG way from the source of heat, then they where put on diesels (due to a lower EGT compared to a gasser)...other than that, i am miffed as to why all the worry over keeping such a low EGT in check :confused:

Metals will fatigue when exposed to and beyond their respective melting points without immediately causing the part in question to 'melt down'

Typically the structure of the metal will start to crystallize and become brittle with each high heat cycle. This damage takes time before a part fails. In most failures the Aluminum alloy will not melt so much as it tends to dissolve out of the forging. Forging Aluminum or any other metal aligns the grain .. exposure to high heat (similar to forging results in the material crystallizing and falling out of alignment with the rest of the forging's grain. Result is a weak area where the metal has changed to a crystalized structure.) However even in high heat situations of a gas or diesel engine, there is a 'boundary layer' where combustion is not directly acting on the head or piston. Unfortunately in a Diesel engine's piston design (bowl) the boundary layer is much less than on a gasoline engine.

That's all i know on the topic. JE Pistons, Ray Barton, Arias, or someone in the industry would be better qualified to answer the question.

Ti Pistons would be the answer! 4000F Melting Point (alloyed!) Unfortunately the 11% expansion rate might prove impossible to use in a piston engine application. But WOW... talk about no EGT issues!

Nicely put Juice.

Turbo-max, if you would stop flaming everyone for throwing out ideas and solutions you would be able to see that this has been answered. The real "Proof" comes from several things. High compression, Metallurgy, Heat soak, Turbocharger spinning 90krev, more energetic fuels.

All of the above factors play their own little part in temp limits for diesels. Even with a gasser being turbocharged, they still only hit low teens for CR. Diesels live close to 20:1 the Dmax's I believe are around 18:1. For the most part Diesel engines struggle to run below 15:1.

Also generally anytime a Gasser is force fed air, the bottom end is beefed up considerably with forged parts and special alloys. All the engines here at work are big diesels and most run steel pistons and cast iron heads, and even they can't handle more than 1300 degrees for long periods of time. It's all physics, heat may be heat, but throw extremely high pressures in there, and things change dramatically.

The weak spots for EGT's are the exhaust valves, turbo, and piston.

The exhaust valves benfit from the aluminum heads by getting cooled my the highly heat conductive aluminum surrounding the valve seat.

The turbo, as has been said before, sees the actual EGT that your guage reads. On turbine engines, they actually pass bleed air through the tubine blades to cool them and generate a boundry layer. I don't think we are there yet. So we are limited by the turbines heat and thermal cycle tolerence.

Lastly, the pistons. The huge amount of oil cooling being squirted into the underside of the piston is the only thing keeping these puppies from total melt down. In theory, with enough cooling, these will take as much, if not more heat than the heads.

Something that has shown up on people that run there turbos very hard is cracking in the scroll. None have failed yet, but some of the cracks have been severe.

In short, indications are that the turbo is the weak spot and is limited by the metals being used there. 1500 IMO is below the what these metals can tolerate.

Nicely put Juice.

Turbo-max, if you would stop flaming everyone for throwing out ideas and solutions you would be able to see that this has been answered. The real "Proof" comes from several things. High compression, Metallurgy, Heat soak, Turbocharger spinning 90krev, more energetic fuels.

All of the above factors play their own little part in temp limits for diesels. Even with a gasser being turbocharged, they still only hit low teens for CR. Diesels live close to 20:1 the Dmax's I believe are around 18:1. For the most part Diesel engines struggle to run below 15:1.

Also generally anytime a Gasser is force fed air, the bottom end is beefed up considerably with forged parts and special alloys. All the engines here at work are big diesels and most run steel pistons and cast iron heads, and even they can't handle more than 1300 degrees for long periods of time. It's all physics, heat may be heat, but throw extremely high pressures in there, and things change dramatically.

don't recall "flaming" anyone per say, mearly debating what they said
and FYI turbos spin WAAAAAAAAAAY more than 90k rpms, thanks for your input

The weak spots for EGT's are the exhaust valves, turbo, and piston.

The exhaust valves benfit from the aluminum heads by getting cooled my the highly heat conductive aluminum surrounding the valve seat.

The turbo, as has been said before, sees the actual EGT that your guage reads. On turbine engines, they actually pass bleed air through the tubine blades to cool them and generate a boundry layer. I don't think we are there yet. So we are limited by the turbines heat and thermal cycle tolerence.

Lastly, the pistons. The huge amount of oil cooling being squirted into the underside of the piston is the only thing keeping these puppies from total melt down. In theory, with enough cooling, these will take as much, if not more heat than the heads.

Something that has shown up on people that run there turbos very hard is cracking in the scroll. None have failed yet, but some of the cracks have been severe.

In short, indications are that the turbo is the weak spot and is limited by the metals being used there. 1500 IMO is below the what these metals can tolerate.

gas turbine engine use "bleed air" to cool them, as that is it's only means for cooling (other than a small amount of oil cooling).

from my past experience with turbos, what normaly cracks the housing is rapid heat/cool cycles, not so much the amount of heat.

from my past experience with turbos, what normaly cracks the housing is rapid heat/cool cycles, not so much the amount of heat.

That appears to be the case here too.

ok so here's a bit more info for you to chew on...

“...Whether a spark plug is installed in a lawn mower, boat, truck, or race car, the plug tip temperature must remain between 450° C and 850° C. If the tip temperature is below 450°C (yada yada it's a gasser who cares :D ), the insulator area surrounding the center electrode will not be hot enough to burn off carbon and combustion chamber deposits. These deposits will accumulate and foul the plug gap, leading to a misfire. When the tip temperature exceeds 850°C (ok so this means it don't get much hotter in a gasser combustion chamber than this), the ceramic around the tip will blister and the electrodes will melt...”

"This figure shows the temperature during combustion in the diesel cylinder. Note the near adiabatic flame temperature in the bowl just above the piston face. This is where the fuel becomes almost completely atomized after being injected from the cylinder head down towards the piston face."

Now I'm still searching for exact temps for spark ignition engines but I'm sure the area surrounding the spark plug is gonna be pretty damn hot, but as you can see from the attached pic no where near as hot as the Diesel engine... 2766 K Yikes that's a hot meatball!

sweet info, Enigma..thanx

Wow, Enigma, that's cool!!

On a side note, I thought I remember reading something that Mackin stated a while ago that the DMAX was tested at 13XX degree EGT continuously during testing. I tried a search, but can't find the actual number he stated, I thought it was in the high 1300's though. Might just PM him and see if he still has that info available...oh MAC!!! :D

Its not the turbo which you have to worry about melting down but your pistons, which stay hot longer after combustion due to slow burn rate of diesel. The cooler the intake temp, the hotter you can run egts without hurting the pistons. This is what Ive noticed with heavy equipment. I could be wrong too.

Turbo, In regards to turbo speed, I was refering to engines here at work with similar displacements. Most of them do not excede 110krev. Out of curiousity what do these Honeywell's spin at?