RussianVolk

Hi all,

I am a student in engineering and as part of senior design project I need to know some information for my project model. Pretty much what it comes down to is I need to know the difference in temperature of exhaust gas before and after the turbo. Let's assume we are talking about cruising speed of 60 in overdrive in standard conditions (approximately 70 F), what ever that rpm may respond to. I know, it changes based on turbo and from truck to truck, but I just need a decent estimation to see if the project idea is worthwhile. So if some of you run gages pre-turbo, please let me know what kind of temperatures you are seeing. Same for post turbo. Also, do you guys happen to know if you would see similar temperatures in spark ignition engines?

The help is really appreciated. Thank you!

93flatbed

When I moved mine from down pipe to manifold with no other changes to the engine I saw a 250 to 300*. So for an example at 55 post turbo I would sit about 400* and pre turbo 750*. I give the range because it was different between hard accel and regular crusing. But that should get you in the ball park, good luck on senior project.
And gas engines......? don't have a pyro on my lawnmower.

RussianVolk

Awesome! That's what I expected, and agrees from what others have told me as well.

KD93

I don't think the type of turbo you're running affects rpm's. Weather conditions, (think headwind), ambient temperature, ground pressure, (load), tire pressure and gear ratios, yes. Turbo's? I'm not positive about that, but I don't see why it would affect rpm's.
AFAIK, gas engines run cooler than diesels, so the temps should be lower. I'd think gasoline would expand in a slightly different way so maybe the temperature range would be different too. I don't know beans about gasoline engines though, so maybe it's just the same. Come to think of it, I don't really know beans about diesels either. Don't listen to me, wait until someone who actually knows what they're talking about gives you an answer.

Douglas2

The gearing will change your operating conditions pretty radically. An early G56 with a 4.10:1 rear axle is going to be spinning its engine faster at 60 than any other trans, let alone a truck that has 3.07:1 gears. Of course, the 3.54:1 is somewhere in the middle... Also, a truck with a 21cm housing turning its engine slowly will have significantly lower boost pressure than one with a 12cm housing turning just a bit faster. This will change what sorts of EGT to expect, yes?
cheers,
Douglas

When I was in school, Senior Project was funded. If you're close, I'll let you instrument my 1990 and we can take measurements.

gman07

I'm pretty sure gas engines run considerably higher EGTs than a diesel. I think that's why there are more issues in getting a variable geometry turbo to work on a gas engine.

As for pre/post turbo EGTs, it'll depend on the work output from the compressor. Ignoring losses from drag on the shaft from the journal bearings, the work into the turbine = work out of the compressor, which depends on mass flow rate and the boost output from the compressor (and compressor efficiency). From reading around here, I've seen people claim anywhere from 250°F to 500°F.

RussianVolk

Thank you for the offer! I am still a junior actually, and I don't start senior design for another year . But! I am trying to come up with a project that will be fun, useful and worthwhile ahead of time.With that said, I am developing possible theoretical models, and this is one of them. My goal is to extract energy from exhaust enthalpy and convert it to electrical power (pretty much just a gas turbine). From what I am looking at now (and I am not putting much time into it due to finals next week - Thermo 2, fluids, controls and measurments!!! ahhhhh) is first seeing what kind of exergy I can get from exhaust. Then I can calculate how much power the compressor consumes (I know pressure in, temperature in and pressure out, probably around 5 psi gage, assuming I have reversible pump for now). By the way I am not boosting with this project, I just want to use turbine as well... turbine. I understand that there are a LOT more variables that go into this, but I am trying to keep it as simple as possibly for now. Once the finals are over I can sit down and go through everything that influences the results. But from my train of thinking for now if I can find power that compressor consumes, and I know what average temperature temp into turbine and temp drop, I should be able to estimate how much I loose due to heat, and can see what kind of electric power (power per flow rate for now) I can get get back. It's a lot of typing to do to describe what I want to do, and I am not positive I want to put it all here, if you know what I mean. Its one thing you are given a problem, but its a totally different monster trying to design one

Sorry for lengthy post, I dont know if you needed to know all that, but it is nice that here are still people out there that are willing to help . I am a student at Purdue (Indiana), and we don't get any funding as far as I know, unless you are working with a company.

RussianVolk

Thank you for the input as well. As some might now think so, I am actually writing it all down!

Again everyone's input is appreciated.

Douglas2

hey-Hey!!!,
Let me suggest getting your hands on a turbomachinery textbook. If Purdue is half as good as PennState you should have *NO* issues borrowing one from the Proff...

It is even more fun to do it at work...you get the problem and have to solve it completely( after deciding just exactly what needs solving ), and depending on the question it can get head-throbbing complex.

Let's see, pressure in, temp in, pressure out, temp out and flow rate will tell you *editable* near everything you wish to know about power.
cheers,
Douglas

d22019

I know this is a little off topic but why do 18 wheelers have the pyro probe post turbo. With an engine that expensive wouldn't you want the most accurate egt reading?

Purplezr2

Will be watching this thread closely, another engineering student(North Dakota State Unversity) Go Bison!

Douglas2

As if I needed any more proof that engineers are...ummmm...errrr...excentric...
cheers,
Douglas MS ME

KD93

Because it's possible for the pyro probe to come loose/break off. Any small chunk of metal going in to the turbine = . Like you said, big bore engines are really expensive, and if the wheels aren't turning, you ain't earning!

d22019

That makes sense I never thought of that. Thanks