Turbojet Riding Mower Build

[barnyard]

Hi guys, I’ve been working on a new project and though I’d share. A few years ago I build a engine using a 71/94mm turbo, see  ( jetandturbineowners.proboards.com/thread/875/turbine-noob-surge-question ). Since then I’ve put it on a ice sled to play with on the pond in the winter.


Now that it’s approaching spring it’s time to change platforms to a riding mower! The mower is a old John Deere 165.



Exhaust from the turbine will feed into the exhaust side of a second turbo, the free power turbine, hanging under the mower. The free power turbine will drive the mowers hydrostatic transmission via a 25:1 gear reduction and belt drive.  


Drive turbine and gearbox. Gearbox is from a gas ice auger. 25:1 reduction, but I’m unsure how it will hold up to the high rpms. The bearings on the turbine shaft are suppose to be rated for 20,000rpm, but I can’t see them lasting long with rubber seals. Either way they were cheap and easy to upgrade if needed. 






my goals with this project are to have the mower drive with at least the same amount of power it had with the 16Hp IC engine, and have similar control. The challenge will be matching up throttle with transmission control. I plan to use a dump valve on the inter stage ducting so that in neutral the free power turbine won’t over speed. I know the FPT is undersized for the gas producer, another reason to use a dump valve to control the back pressure. If I can link that valve to the foot pedal that runs the throttle and transmission speed, then we are in business! 

I’ll be putting up more pictures as progress happens. And of course advice is always welcome. 

James 

[racket]

Hi James

Your freepower stage might be a bit small for the gas producer , you will need to "dump" a fair chunk of the interstage gases to prevent your gas producer from surging and overtemperaturing , or worse :-(

Currently your gas producers turb exducer is >50% greater in area than your comp inducer , this will create some problems to start with as the comp will try to flow in the high flow/low efficiency region of its map , this will exacerbate the mere 25% greater exducer area of the freepower over the gas producer exducer area , it needs to be closer to 100% bigger in area . ................your gas producer has 30 lbs./sq in of pressure going in , the freepower only 7 psi , the resulting gas velocities will be lower in the freepower , as well the gas densities will be only a fraction of the gas producers , the two combined mean the freepower needs to be a lot bigger.

A 3" dia butterfly valve required on the interstage .

As for the freepower bearings , why not do what I did with my 2 shaft kart , jetandturbineowners.proboards.com/thread/40/2-shaft-turbine-kart-build , remove the bearing seals and have some lube drip feed and some bleed P2 air going through the bearings and dumping into the freepower wheel area .

You've already done a lot of the hard work , I'll be interested to see how it performs :-)

Cheers
John

[barnyard]

Mar 17, 2021 23:17:03 GMT -5 racket said:

Hi James

Your freepower stage might be a bit small for the gas producer , you will need to "dump" a fair chunk of the interstage gases to prevent your gas producer from surging and overtemperaturing , or worse :-(

Currently your gas producers turb exducer is >50% greater in area than your comp inducer , this will create some problems to start with as the comp will try to flow in the high flow/low efficiency region of its map , this will exacerbate the mere 25% greater exducer area of the freepower over the gas producer exducer area , it needs to be closer to 100% bigger in area . ................your gas producer has 30 lbs./sq in of pressure going in , the freepower only 7 psi , the resulting gas velocities will be lower in the freepower , as well the gas densities will be only a fraction of the gas producers , the two combined mean the freepower needs to be a lot bigger.

A 3" dia butterfly valve required on the interstage .

As for the freepower bearings , why not do what I did with my 2 shaft kart , jetandturbineowners.proboards.com/thread/40/2-shaft-turbine-kart-build , remove the bearing seals and have some lube drip feed and some bleed P2 air going through the bearings and dumping into the freepower wheel area .

You've already done a lot of the hard work , I'll be interested to see how it performs :-)

Cheers
John

John, thanks for the advice, the drip lube and no seals is the next thing I’ll try if I have any problems with these bearings, I’ve already considered where the ports would be. As for how undersized the free power is, I hadn’t realized it needed to be that much larger, 100%. That gives me some number to think of next time I’m in a salvage yard and see a turbo. For right now I’ll run with the dump valve partly open and watch my temperatures. 👍

James

[racket]

Hi James

Yep , it needs to be a lot bigger unfortunately , generally once past a gas producer with a 2" inducer we need to start thinking about using aero turbine wheels for freepowers, or "dumping" a part of the gas producerts exhaust .

Theres info here jetandturbineowners.proboards.com/thread/680/diy-turbines just click on the icons

Cheers
John

[barnyard]

A quick update. From a scrap yard I managed to pick up a larger turbo for the free power unit. Turbine exducer is 103mm diameter, which should be around 100% larger in area than my gas producers turbine exducer (94mm). It’s a few steps backwards but my plan now is to use the 103mm turbine and housing, without the gear reduction, to drive the mower transaxle. I’ll build a new bearing tunnel, and use a air/oil drip to lubricate the bearings. Quick question, what rpm should I expect to take this free power turbine to? 

James 

[racket]

Hi James

The 103 mm exducer wheel might be a tad small , currently your 71/94 gas producer has a grossly oversized turb stage which would normally have created some problems with the gas producers performance as the comp would have flowed in the inefficient choke region .

Normally a well matched 94 turb exducer would have a ~80-84 comp inducer and your freepower would need an exducer of ~130 mm.

I'd be fitting a buttefly dump valve in the interstage duct to allow "tuning"

Cheers
John

[barnyard]

May 17, 2021 17:33:57 GMT -5 racket said:

Hi James

The 103 mm exducer wheel might be a tad small , currently your 71/94 gas producer has a grossly oversized turb stage which would normally have created some problems with the gas producers performance as the comp would have flowed in the inefficient choke region .

Normally a well matched 94 turb exducer would have a ~80-84 comp inducer and your freepower would need an exducer of ~130 mm.

I'd be fitting a buttefly dump valve in the interstage duct to allow "tuning"

Cheers
John

Ok John I’ll stick with the dump valve then. I also like the idea of using it to free up torque on the free power unit at idle, so it won’t over speed the transaxle when in neutral.
Ive picked up 2 bearings and hope to find material for the bearing tunnel this week.

James

[barnyard]

It’s been a while since I’ve posted anything, still this project has been making good progress. I’ll try to add pictures and document the build so far. 

From the old jet sled I moved the jet engine, oil pump, and oil reservoir over to the mower. 



The fuel pump this time is a knockoff 044 pump, feeding the hollow cone fuel nozzle in the engine. Thankfully I was able to use the fuel tank from the lawnmower, complete with low level sensor! 




I’ve mounted the larger free power turbine, built a new bearing tunnel for it with drip lube and bleed air to it. It is chain drive from the turbine to an intermediate shaft, where it powers a belt driving the rear hydrostatic transmission. This is a 103mm turbine. 







Per John’s advice I’ve added a 2” bypass valve to the interstage ducting, so that I can tune the back pressure and temperature.
Unfortunately the interstage ducting is fairly restrictive, due to lack of space to make smooth bends, and also not having tubing to work with. The actual flow area through the ducting is large enough I believe, it just doesn’t have any real radius’s. For now it will have to work. 






lastly gauges and the electrical have been fitted. Oil pressure has a low pressure light, but no shut down. Boost, EGT, and battery volt gauges are installed. Oil pump switch, fuel pump switch, and master On/Off key all working. For throttle control, the fuel pump is ran on a speed controller, and the throttle position sensor is connected to the lawnmower throttle handle. 





Things fit well under the hood. A oil cooler is mounted to the front grill, where it should get plent of air being drawn through by the turbo inlet. Cooling under the hood is going to be the real challenge. I have done one test run and quickly melted any plastic wire loom near the turbo. I plan to wrap the turbo and ducting, though I am concerned about fire potential with the wrap. 




Still more to come, including some test videos and data. 

James 

[slittlewing]

Awesome work slotting that all in there! Look forward to videos

For heatshielding I find the best things to be:
-Thin stainless sheet ideally polished
- ceramic insulation or similar on “cold side” (or you could use a turbo blanket but I haven’t tried one)
-gold foil reflective tape by 3M
-raychem RW200 heatshrink for wiring, if you can’t re route it to a cooler area
-textalu over the top of wiring if required

Cheers

Scott

[barnyard]

Scott thanks for the advice. I will do some stainless heat shield, and I like the idea of having the cloth wrap on the outside of that. Electrical wise re routing will fix most of the heat issue. Otherwise Amazon had some sleeves similar to that textula.

Question about v band clamps, I didn’t have a mating flange for the gas producer turbo to interstage ducting, so I’ve made one from sheet metal. Problem is it leaks, worse than I’d like. When I’m look to buy a pre made flange, will a generic 5” Vband flange and clamp fit, or does the flange need to be specific to my turbo brand/model? 

James

[noshell]

Have you considered a kart clutch on your freepower?
Im also planning to use a turbo housing as my freepower unit, so im intrigued to see how yours goes.

I was thinking of using a big angle grinder gearbox or something as a freepower reduction drive on my next build. Some of those motors rev to like 30k with just a bit of grease lobbed on the gears. I rekon with them bathed in oil you could spin them up to 40k easy peasy.

[barnyard]

Jan 18, 2023 13:14:15 GMT -5 noshell said:

Have you considered a kart clutch on your freepower?
Im also planning to use a turbo housing as my freepower unit, so im intrigued to see how yours goes.

I was thinking of using a big angle grinder gearbox or something as a freepower reduction drive on my next build. Some of those motors rev to like 30k with just a bit of grease lobbed on the gears. I rekon with them bathed in oil you could spin them up to 40k easy peasy.

I have wondered about clutches, though I thought of using a clutch system from a snowmobile. They use two variable pulleys with a belt drive, basically a CVT system. I expect the losses would be to much. Your grinder gearbox idea sounds good to me, if you can find a large enough one. The I bet the disk output shaft is strong enough it would directly support a sprocket.

[racket]

Theres a "problem" when using a gearbox with less than ~6:1 Ratio , the chain drive from it, because of the relationship between power output , chain size and its RPM limits .

Lets use karting chain as an example , its good for 20,000 rpm at the "engine", but has a horsepower limit of maybe 25 hp before it stretches , 25 hp at 20,000 rpm equates to ~6 ft lbs of torque , but if we have our freepower capable of 60,000 rpm and use a 3:1 gearbox to bring it down to 20K our torque has multiplied by 3 to start with , then because of the higher rpm the horsepower has increased substantially over the ungearboxed engine limited to 20K , we end up with too much torque for the karting chain , a heavier strength chain will be rpm limited to <10K .

Cheers
John

[turbinenjoe]

I like the looks of the combustion chamber sticking out of the hood.

[barnyard]

A quick update. I was able to re route some of the electrical out of the high heat areas. The remaining wiring still near the turbo is now lined with heat shrink, and then protected in aluminized fibreglass sheath. 





I’m still waiting for the high heat manifold wrap and turbo blanket to arrive. Once I get that I can design a stainless heat shield as well. In the mean time I removed the hood for another test drive. My camera helper didn’t last very long with all the loud noises before he ran away, but he did manage to film a short run. The run is cut short when I throttled down to fast and flamed out, but you get the idea. 

youtu.be/1sSsdw7NsH8

Findings from testing:
- bypass valve helps with a quicker startup. Temps at low-moderate idle are 475’C, and didn’t seem to change much with the valve open or closed. 

- with bypass valve open the power from the drive turbine is definitely reduced, but provides a nice “neutral” zone where the drivetrain isn’t spinning, or not as fast anyways. 

- test run with the bypass valve closed showed 650’C egt at full throttle. Needs further testing to get complete comparison. 

- on startup, fuel is pooling at the bottom of the outer combustion liner, where it burns right against the outside liner and base bolt flange. It gets hot enough to glow the outer liner, but doesn’t last long. The only fix I can think of is to do a propane pre heat and start, so the fuel doesn’t get a change to pool before igniting. 

- drive chain is not up to the task. On a high speed run the chain blew apart. It’s a W35 chain, so not to suprised. From the discolouration on the chain I’d say it was over reeved. Either I find a better chain, or change sprockets so it doesn’t need to spin so fast to get my desire riding speed. I think I’ll go the sprocket route first. 

James