Turbocharger Gas Turbine Design Equations

[britishrocket]

Hello all,

Hi my name is Carl. I have been a member here for a few years. I have also been running a very modest YouTube engineering channel for a couple of years now.

I have just made a film in which I try to present the design cycle calculations for my turbocharger to gas turbine project.

Essentially I have tried to make the film I wanted to watch when I first got interested in this topic. One that brings much of the pertinent information together. I hope you enjoy it. Moreover, I hope it becomes part of the great repository of information this site represents.

youtu.be/5M_FPAULPJI?si=_3FDBGZAVaZPNrpV

You are the experts so if I have made any errors please let me know!There will be another film to follow soon with further information. Thanks,

Carl.

[racket]

Hi Carl

Nice presentation :-)

A few minor things that I'd put differently.

The comp diffusion is mainly in the "plate" radial section , the scroll collector simply collects the air efficiently for easy plumbing .

Flametube losses at 12% might be a bit high for the usual sore thumb combustor , OK for small RC jet engines , but we should be able to get closer to 5% with a generously proportioned FT .

The turb exducer area is 28% bigger than the comp inducer , not 23% .........2577/2001 = 1.28

And I got a slightly different comp temp rise , heh heh , probably from using Imperial rather than SI 56.76 vs 58.4 C degs .............I'll have to see why .

Thanks for taking the time to put the video together , too much for me to do , I'll be looking forward to the next one :-)

Cheers
John

[britishrocket]

Hi John,

Thank you for your comments.I agree that I made a bit of a mess of the explanation of diffusion in the scroll. I will put that right in the next film. I often struggle to find the right words when the camera is running.

I don't put much stock in the slight difference in compressor temp equivalent of work that you got compared to mine. Slight differences in calculation method and rounding can account for this. Just using a figure of 1.4 for k instead of 1.418 makes a difference.

I use imperial measurements and metric quite interchangeably in my workshop, depending on what I'm working on. However, I only use SI when doing engineering calculations of this nature. I think that SI promotes clarity of purpose and is less error prone.

Imperial calculations involve too many unit conversions which to my way of thinking invite error. I also find Imperial thermodynamic units a total "Alphabet Soup".

I had tried to make sense of the information presented on this site and others, and bring it into a coherent whole, as well as including my own design cycle calculations.

My hope now is that people will find my treatment useful and that it will become a useful reference for anyone wanting an explanation of elementary gas turbine theory as applied to the turbocharger conversion.

[racket]

Hi Carl

LOL.............theres no way I'd attempt what you're doing , too many "traps" along the way .

Over the years I've tried to keep things as simple as possible with fairly rounded off "numbers" simply because theres so many variable with our engines that they virtually never perform "to design", the slightest change in the weather and their performance changes :-(

Then theres the turbos used .............a nightmare .............with thousands of configurations now available, and thats not including the chinese knockoffs , it becomes ever more impossible .

Add in the "corner cutting" that DIY builders invariably do with the combustor , fuel , oil , nozzles etc etc .............:-(

You'll find a lot of "holes"in Jetspecs , but they are intentional as they try to cover all of the above :-)

SI does make things easier in some ways , but I don't like working in 10 decimal placed calculations , too many opportunities for my fat fingers to hit the wrong button on my calculator.

My "bible" www.ebay.co.uk/itm/204363595652?hash=item2f9504ff84:g:oEYAAOSw-p5khDd3&amdata=enc%3AAQAIAAAA8IuLXn0Kysb9hU2Lf8Bsz7zJXICVX88cx5VFoTFOWIyb%2Fhx40OgTeziI%2BZaT6qvnw6JhRS0jKfImcp4R1aF%2F6mB4fOb4ZOrJZen7zxtEo80UTpr53iqD5JG5WQZsjXoLeqcvxPL5OICIILWUuZ0%2FZNCxWbm56%2BnJ8d03CBY7%2BqNJLrSL%2BaHJfxl%2BGAeBk3jkrja2NyfaM%2BFqIVrwLwApWoRXINMtsGIj84vFfOYGrc1ayufmFpzhuAa4IIgPS21DGRi93iVEOiCA%2BFtsFrKBl4ON0l5eOOL2G3qDq8fy1XmaP9L2futjtffio7gMNNqQcg%3D%3D%7Ctkp%3ABFBMruq_841j

Nice simple worked examples .

Your videos will be very helpful , heh heh , especially to me, as I'll be able to recommend them to Members rather than having to answer those difficult questions :-)

Keep up the good work, its not an easy task , any comments I make aren't meant as a criticism, just robust debate :-)

Cheers
John

[jetmanjoe]

Thanks for the video Carl, watching it right now. I'm sure alot of beginners will appreciate this.

Ahh John another book I have to buy now 😁

Cheers

Joe

[racket]

Hi Joe

Yep , another book , that early edition assumed, " nobody knew nothin' ", which was the case in the 1950s , just the right level for me ;-)

The many later editions start getting a bit complicated for me with SI units , though the Second Edition from the 70's www.biblio.com/book/gas-turbine-theory-2e-cohen/d/987391976?aid=frg&gad_source=1&gclid=Cj0KCQiAj_CrBhD-ARIsAIiMxT87EzWPwbA3-QdS_0lB8Pm9PNhI8pfGqr5LLhuWV_WmCJU9pKxhIQUaAlmQEALw_wcB isn't too bad , and if you prefer SI units then this is a better Edition than the '50's book .

Cheers
John

[britishrocket]

The thing is that we can characterise any scenario as long as we understand where we are at with it in terms of losses and how the system behaves in practice. What I'm trying to do is to observe actual units that people have built and that run - like the ones you have built - and then get a handle on them using the theory. The thermodynamics are real and not just numbers on a board.

I'm not trying to design the perfect gas turbine based on a turbocharger - far from it. I'm just trying to get a handle on what is going on using the principles to model it.

I made my video as the video I wanted to watch about this subject, or at least I tried to. Personally I found the documentation on here impenetrable. No real explanation of what all the numbers are and being told to press this or that button on a calculator really doesn't explain to the reader that you are trying to calculate the work required by the compressor to see if your turbine can produce enough to drive it.

SI units I used because it is a consistent set of units that is easy to work in and does not require any intermediate conversions as in imperial calculations. To my mind that is massively prone to error.

I'm not looking at doing calculations to an accuracy of 6 dp, that is pointless in almost any field of technical endeavour. What I'm doing is characterising the process that is going on inside these little engines by using the very principles that is making the process happen.

The calculations aren't enormously accurate, but they aren't bad, they certainly give us a good idea of what is going on and put us in the same room as the problem, not just in the same house.

I will be very pleased indeed if you send people with questions to my film, that is why I made it, my horrendous production values to one side. What matters to me is the content.

Thanks again for all your kind words and encouragement.

[britishrocket]

By the way, I thoroughly approve of your recommending people to look to Cohen and Rogers. My dog eared copy is in front of me as I write this!

[racket]

Hi Carl

Good old C&R , they've been at it a long time , sorta in the same league as Thomas Kamps book www.abebooks.com/servlet/BookDetailsPL?bi=30903769679&searchurl=an%3Dthomas%2Bkamps%26sortby%3D17%26tn%3Dmodel%2Bjet%2Bengines&cm_sp=snippet-_-srp1-_-image2 for being a handy reference .

One of my engines pretty much performed as the theory said it should jetandturbineowners.proboards.com/thread/78/garrett-gt6041-powered-kart , thankfully I had both a comp and turb map for the GT6041 turbo which made life very easy, when I made the 2 shaft kart jetandturbineowners.proboards.com/thread/40/2-shaft-turbine-kart-build I had to bypass/dump a portion of the gases exiting the gas producer because of the undersized freepower turbine , theory came in very handy in calculating the required diameter of the dump jetnozzle so as to maintain the correct backpressure on the gas producer .

Theres certainly a place for the theory , but generally guys aren't interested, they just wanna have fun .

LOL............as the guy who Posted all those "impenetrable" calculations , there was a very good reason for it, they were written up quite a long time ago for the Yahoo DIY Gas Turbines Group , at that time a DIYér building a turbo based turbine engine had no info available and there were some horrible mistakes being made, the average builder had trouble working out the inducer area let alone doing thermodynamic calcs or even wanting to know the reasoning behind the calcs , they just wanted to burn fuel and make noise , one needed to satisfy ones audience , so I kept to "KISS".

Anyone who was/is theory orientated joined the GTBA , as I did in the '90s, I recommend the GTBA to everyone whos interested in more than just making noise .

I would have found your video exactly what I needed 30 years ago , but alas no internet back then , new builders have it so easy these days , just hit YouTube and watch your vid/s :-)

How long before the next one ??

Cheers
John

[britishrocket]

Thanks.It means a lot to me.Although I have a background in this I'm far from an expert in these devices. I'm using my knowledge and experience to get a handle on it. What you do here with this site is inspirational.

I found the calcs on here hard to follow (yahoo group ones) but they are totally sound.

Thanks again for all your encouragement, over the past few years and now.

[andym]

Hi Carl

nice work.... like john said a good referance for new members,

looking forward to seeing your next video

If you need any help give me a shout.

Have shared your video on Diy Gasturbine facebook page and Diy Jet engine

[britishrocket]

Thanks so much Andy I really appreciate that.

[monty]

Hi Carl,

Thanks for doing that. I don't even know where to start trying to explain the theory behind this. I've spent years studying it, and have a background in thermodynamics and math....how to even start?? Hand someone a pile of text books on calculus, physics, fluids and thermo? Get back to me in a few years. None of the math is that hard (once derived!), but the concepts are daunting for a newb. Most of the texts are over-written on the difficult side. Typical academic approach. Not what's needed. The older texts are better. But most of the papers and texts have assumptions, simplifications, or approaches which don't work for someone trying to assemble an engine from a pile of parts. One of the reasons these things are fascinating is the theoretical complexity which reduces to such (seemingly) simple hardware.

Monty

[racket]

Hi Monty

LOL............they're only a couple of fans on a shaft ;-)


Why do I have so much trouble making them get along with each other , I'm starting to feel like a Marriage Councillor with a waring couple :-(

Cheers
John

[britishrocket]

Hello Monty,

Thanks for your kind words. I am very glad you enjoyed my film and I hope others will find it useful.

I'm glad you felt that my explanations and the calculations were digestible. I find that quite often people are put off by the theoretical side, they see themselves as purely practical. I wasn't taught that way and I don't think it either. The two go hand in hand and that is the way I was taught in the Royal Air Force. I had some excellent tutors at DCAE which is the Defence College of Aeronautical Engineering here in the UK.

Our tutors were from Cranfield University and our Supersonic Wind Tunnel facilities were so good that Cranfield used to come to use it. The lecturers were experts in their fields - Engineering Maths, Engineering Science and Aero/Thermodynamics.

They were also expert in making seemingly complex concepts easily understandable and digestible.

I try to emphasise the fact that the theory and mathematics are just another tool. Like a spanner or a lathe or a milling cutter. They are tools to help us to achieve an objective.

I generally find that people who are practically minded have an instinctive understanding of how things work. Taking them that little bit further in their understanding is a joy.

One of the things I have noticed about this turbocharger/gas turbine community is that it is riven with misunderstanding and half truth. The most common example of this is the regularity with which people recommend others to have a tangential entry of the compressor air into the combustor liner. Swirl is the last thing you want in there!

The people on this forum have done so much over the years to correct these misapprehensions and to get builders on the right track. My film is nothing in comparison to their efforts.