Turbo Shaft Lawn Tractor Build

[Colin Heath]

Hello All,

Well after the first debacle and a turbo not worth using I am starting again and have a direction for the build.

My plan is to build a turbo shaft driven lawn tractor / Ride on mower.

Turbo has the following specs (Not checked them yet)

Turbine Trim: 78
Turbine Inducer Diamter /Exducer Diamter: 88 mm/77.5 mm
Turbine A/R: 1.05
Compressor Trim: 50
Compressor Inducer Diamter/Exducer Diamter: 69 mm/98 mm
Compressor A/R: 0.66

Not quite the 20% ratio required but at least it's 10% larger on turbine unlike my GT35 I was going to use

Be interesting to know what sort of thrust this might produce and in turn, what shaft HP from it.

I have had a little play on Jet Specs and it led me to a 138mm flame tube. I would like to reduce that 120mm but not at cost of being able to start the thing. It just means using a piece of 150mm stainless tube I have here.

Jet specs have the following and wondered how this looks:

- Inducer 69mm
- Primary holes 40 off at 6mm diameter 
- Secondary holes 5 off at 8mm
- Tertiary holes 10 off at 16mm
- Flame tube length 414mm

Now I'm not sure how hole size affects fuel and burn so those hole sizes I just picked at random. Is there a better way to size holes to ensure more even distribution, greater mixing or improved start/run please?

The flame tube will be CNC plasma cut then rolled and welded so no issue having square, diamond, star or any other shape if it's better.

I plan to machine out the centre section of turbine inlet if thats possible to reduce heat issues and risk of material flying through turbine. (Got that from Johns advice on another thread).

Plan is to run the engine on propane but I believe over 50mm inducer will make that difficult so may have to run on Kerosene.

Once engine is running I will then determine what second stage turbine housing I need to build for shaft power.

Thanks for reading and I will now be staying on this thread.

[azwood]

Welcome the rule for the holes is 30 20 50 percent of the turbo inducer volume starting at the primary holes

[Colin Heath]

Jan 10, 2020 14:06:53 GMT -5 azwood said:

Welcome the rule for the holes is 30 20 50 percent of the turbo inducer volume starting at the primary holes

Thanks Azwood,

I have been reading your thread with interest but still have plenty of pages to go. I used JetSpecs to get the areas you mention so the areas are correct but unsure if larger holes with less of them is better or smaller holes with more?

Reading a thread today it seems larger holes push the flame front further inside tube reducing walk heating of combustion chamber but still trying to get my head around it all.

[pitciblackscotland]

Hi welcome to JATO. I did a build thread on my jet mower project, but have scrap the project. Have a look it might give you some ideas jetandturbineowners.proboards.com/thread/600/turbine-rover-mower-project

[azwood]

Yes hole size does impact the burn I think my primary holes are 9mm with a 190mm tube but I use evap tubes so I get more air to the centre with those.im still learning myself but it's something you start to get a feel for after a while I made two flame tubes before I was happy

[racket]

A 77.5mm turb exducer is 26% LARGER in AREA than your 69mm comp inducer , its AREA thats important .

A 120 mm ID FT would come in at 3X inducer area , so OK

You should be able to get >50 lbs of thrust or 50HP

Your holes sizing in the Primary Zone will be greatly influenced by the fuel used and its injection , so you'll need to decide early in the build

Cheers
John

[dieselguy86]

John, the 30/20/50 rule of thumb, is that factoring before or after the vena contracta? The one book i have says a non radius'd hole will flow ~64% of its area. While one that is radius'd was ~81%, i could be off on the exact number, but didn't know if that played a role in how you figure out the ft hole area.

-Joe

[racket]

Hi Joe

LOL..........I've been waiting for this question for a long time :-)

I think its probably better if we just stick with plain holes because most guys will only use them as doing the bellmouthing is a bit hard with thicker wall material which will probably have the edge taken off the holes anyway and will end up half way between the two types.

Another "variable" is the actual flow that the turbo produces , some with "tight" hot sections will flow less than a more "open" one , so hole area/shape is going to need changing again if we want "perfection" .

Then another variable is where the air delivery tube is positioned and how it'll affect the airflow speed along the gap betwee FT and outer can .

Theres probably more I could think of , so lets just stick with plain holes and wear the slightly higher pressure drop across the FT wall in some scenarios.

I settled on the 30/20/50 ratio as it seemed to provide working engines for guys , but as with any engine it'd need fine tuning if we wanted the best outcomes

Cheers
John

[Colin Heath]

Jan 10, 2020 16:51:03 GMT -5 pitciblackscotland said:

Hi welcome to JATO. I did a build thread on my jet mower project, but have scrap the project. Have a look it might give you some ideas jetandturbineowners.proboards.com/thread/600/turbine-rover-mower-project

Thanks for the welcome and will take a look as all inout is very welcome at the moment

[Colin Heath]

Jan 10, 2020 18:12:32 GMT -5 racket said:

A 77.5mm turb exducer is 26% LARGER in AREA than your 69mm comp inducer , its AREA thats important .

A 120 mm ID FT would come in at 3X inducer area , so OK

You should be able to get >50 lbs of thrust or 50HP

Your holes sizing in the Primary Zone will be greatly influenced by the fuel used and its injection , so you'll need to decide early in the build

Cheers
John

Thanks John,

I was thinking diameter and not area so it seems this should be a good turbo with regard to proportions and 50HP will certainly be tasty on a lawn mower! Thats providing I get it running first. I mean the 12hp engine is enough really so should be great fun even with losses.

I am going to run with kerosene as found a supplier just round the corner from my workshop for heating and they do the 20l containers. So I will need to base me flame tube design on that. I will have the flame chamber flanged though so I can change out flame tubes with relative ease as I'm sure it's going to take a few revisions to get things right.

Injection method I think it would be good to start with the least troublesome and something forgiving / easy to source parts. No problem fabricating the parts as I have a fabrication and machining business so fortunate there.

Thanks for the help so far, this forum really is a very helpful place.

[Colin Heath]

Jan 10, 2020 20:40:23 GMT -5 racket said:

Hi Joe

LOL..........I've been waiting for this question for a long time :-)

I think its probably better if we just stick with plain holes because most guys will only use them as doing the bellmouthing is a bit hard with thicker wall material which will probably have the edge taken off the holes anyway and will end up half way between the two types.

Another "variable" is the actual flow that the turbo produces , some with "tight" hot sections will flow less than a more "open" one , so hole area/shape is going to need changing again if we want "perfection" .

Then another variable is where the air delivery tube is positioned and how it'll affect the airflow speed along the gap betwee FT and outer can .

Theres probably more I could think of , so lets just stick with plain holes and wear the slightly higher pressure drop across the FT wall in some scenarios.

I settled on the 30/20/50 ratio as it seemed to provide working engines for guys , but as with any engine it'd need fine tuning if we wanted the best outcomes

Cheers
John

That's interesting as I will be CNC Plasma my holes out of flat sheet then rolling. I will go for 1.5mm 304 sheet as it's light enough to work easily and 304 is what I work with daily so have stock laying around.

I'm wondering if I should machine up a forming punch for my press brake so i can bell mouth the holes? Maybe thats one for later once I know I have configuration right?

Think I need to buy a good book on the subject and do some reading.

[Colin Heath]

Jan 10, 2020 16:51:03 GMT -5 pitciblackscotland said:

Hi welcome to JATO. I did a build thread on my jet mower project, but have scrap the project. Have a look it might give you some ideas jetandturbineowners.proboards.com/thread/600/turbine-rover-mower-project

I have checked out the thread but all the pictures have gone which is a real shame.

[azwood]

If you have a fab shop I don't see you haveing to much problems with the build.enjoy

[pitciblackscotland]

Mmmm i just had a look at my old build and i also can not get any photos up. OK here is some photos that may give you some sort of idea.

[Colin Heath]

Jan 11, 2020 7:41:58 GMT -5 azwood said:

If you have a fab shop I don't see you haveing to much problems with the build.enjoy

Thanks, it will make it easier but then everything seems to throw up challenges which is why I have never got bored being an engineer