Johanssons Jet-Cart

[Johansson]

Then I´ll get busy making a jet nozzle for the engine, 680C seems like a good compromise between performance and endurance since the turbine is relatively new and never overheated. A power turbine for a gocart won´t run at full power for very long so shorter bursts at 680C ITT won´t stress the turbine much.

If I was to build a completely new cart I should have used a 2-stroke chainsaw engine to power the oil- and fuel pump, but as I am "recycling" the old jetcart I will restain myself and use the old 12v pumps.

I will build a new flame tube following RC-Don´s method with evenly spaced holes since my previous attempts to visualise flame behavour in the combustor and drill holes following my gut feeling haven´t turned out to be the best way...

The next decision to make is whether I should use propane preheating for the vapourisor or a spray nozzle as I did in the jetbike combustor. An all-out diesel fuelled combustor seems like the best choice since I won´t have to bring a propane bottle with me.

[racketmotorman]

Hi Anders

680 C for an ITT is "modest" compared to the temps I was experiencing with the PJ turboprops turbine wheel , its ITT was off the end of my 1700 F - (925 C ) gauge yet still sort of survived >20,000 rpm , even if the blades were a bit twisted and burned at the end of the "destruction test"

Most of that homemade freepowers structual problems were caused by only using ~2mm thick tubing to make the blading (it was all I could source) and from my poor welding of them to the disc leaving a weak point at the blade root , the blades were also very long , much longer than you'll need to use , I'd recommend using 3mm thick SS for the blading

With your hole spacing for the FT have you tried using the Jetspecs program , available over on the Yahoo DIY Turbine Site , also on Sals Site , it'll give you a workable set of parameters , Jesse the creator of Jetspecs and myself worked on it some years ago so as to provide an easy to use guide for builders .

If you can get a spray preheat sorted , it'd certainly be the way to go , having to carry propane is only another added cost/problem .

There are available small minibike engines (chinese) ~50cc that are both relatively cheap and come with electric starter/generator and gearbox giving a perfect APU to power pumps with .

If you need some help with things , do a posting and we'll work something out

cheers
john

[Johansson]

I haven´t built a flame tube from the Jetspecs yet, I´ll give it a try when I make the new FT for the cart turbine. I have a working FT already but since I will have to rebuild it for the vapouriser I might as well build an entirely new one from SS sheet instead of the old thick walled steel tube.

I can´t see that spray preheating should cause any problems, I can use some leftover parts from the jetbike combustor. I have a 2GPH nozzle that perhaps flows enough to keep it idling, it´s worth a try at least before I order a larger one.

The jetcart is ready for testing so I can gather some numbers, but I haven´t time to run it before next week. I´ll aim for a TOT of 700C and measure jet pipe pressure, jet pipe temp, nozzle area, comp outlet pressure and possibly turbine rev if my friend has finished his tachometer.

I have been staring on the cart for quite a while trying to figure out how to fit the turbo, combustor and power turbine to get a compact looking cart and still being able to fit the chain drive.

John, do you think that I am up for a Darwin award if I fit the power turbine behind the seat (with a thick walled burst shield around the turbine disc) with myself perfectly alligned with the spray of broken off turbine blades in case of a turbine failure? It is the best (only?) way to fit everything with the turbocharger to the left looking at the cart from behind, combustor above the turbo, power turbine to the right of the turbo and chain drive/reduction directly to the right of the driver seat.

[racketmotorman]

Hi Anders

LOL....I'd be more worried about the turbocharger bits hitting me than relatively low speed freepower stuff , this was the reasoning behind the positioning of parts with my kart build http://www.racketmotorman.turbinebuilde ... hp?album=4 , I wanted all of the planes of rotation away from my position.

The high speed turbo stuff was hung well to the rear with the freepower besides me in the "normal" kart engine position , this allowed mounting the heavy turbo to the "strong??" axle bearings mounts and the freepower to a standard kart engine mount for simplicity and ease of mounting with chain alignment/adjustment as per normal .

Theres no reason why you couldn't mount the freepower behind you , a bit of plate steel between it and you will give some security )

I had considered a similar setup if using an axial turbine wheel fitted to a shaft mounted gearbox http://www.davidbrown.com/geared-motor-series-j.php , and would have placed a kevlar scatter shield behind the seat for protection .

The main thing is to have any "heat " behind or off to the side of you so there's minimal risk of harm if there's a fire at high speed , cold stuff in front , hot behind )

Cheers
John

[Johansson]

It is difficult to fit the power turbine like you did on your cart since my frame design won´t allow me to have the axle sprocket that far in on the rear axle, if the sprockets are to allign the free power turbine will be sticking out several decimeters to the right of the cart.

Can a belt stand high rpm´s? If so I am tempted to gear down the power turbine from, lets say 30.000rpm to 15.000 or what a normal cart engine revs. I´ll have lots (yeah right) of space to the right of the seat so there is enough room for a reduction drive.

omega_hp.jpg (6.34 KiB) Viewed 9296 times

//Anders

[Johansson]

I´ve been going through my old metal caches at my parents house for any sign of stainless and have managed to fill the entire car with both sheet and tubing, among the tubes were a couple of 4" 90 degree bends that are going to be useful in the future.

A spray nozzle holder was also found which is great since I´ve managed to lose the special thread tap for them, I will build a new stainless flame tube for the engine with a flange that bolts on to the bottom of the combustor can so the FT is fixed inside the CC and still can expand freely, another benefit from this is that air can flow through the vapour tubes without the need of specially made air channels in the lid.

I am eager to get the testing done so I can take the cart apart and start working on refitting the engine to the frame.

[racketmotorman]

Hi Anders

The only problem with belts are they require accurate alignment at all times otherwise they break easily , a "flexible" kart chassis isn't the best setup for a belt drive especially if centres are fairly close , chain is a better bet , its got flexibility .

If you are going to use some form of gearbox on the freepower I'd go for a minimum 5:1 redux so a heavier drive chain can be used , something stronger than kart chain which probably is only good for ~30 hp .

You could always use an axle mounted gearbox , this way theres no alignment or mounting problems, the axle simply slips thru the hollow main gear shaft with its keyway providing drive , a simply torque arm is all the mounting required )

Looking forward to developments

Cheers
John

[Johansson]

I tried to get the engine running an hour ago to collect some pressure and temp readings but alas, no success.

I had to remove the propane preheat coil when I rebuilt the jetpipe and without it the engine didn´t run very well in this cold weather, I could hear that the combustion was very rough and the engine was unable to spool higher than 0.4kg P2 even after I opened up the jet nozzle a centimeter so I decided to abort the test.

Now I will take the cart apart and start to convert it to diesel, I can take the measurements when that is done instead.

I don´t think that I will build a gearbox for this engine, to much work considering the old design and tiny mass flow of the turbo so I will save the cash and effort for the next free power project instead.

[racketmotorman]

Hi Anders

How big is this turbo's inducer ??

Cheers
John

[Johansson]

The comp inducer is 65mm and the turbine exducer is 86mm, the turbo is a predecessor to the Holset HX series and I measured a PR of 2.2 at max revs a couple of years ago. Not much to start with but I ain´t aiming for any hp records, I just want to build something fun out of the cart since I have no use of a pure jet cart.

Since I won´t run it on propane any more I can fit spikes to a set of rain tyres and run it on a lake in the winter, should be great fun!

[Johansson]

Here are some mock-up pics of the cart with the turbo aprox. where it will be, I think that there will be enough space to build a power turbine and still have room left for the chain drive.

[Johansson]

After 7 straight hours in the workshop the turbo is in place and the combustor is rebuilt for a new SS flametube, next up is to scavange some stainless tubing for the vapourisor and drill the flametube holes.

I had to make some modifications to the engine mount to fit the turbo, it is fitted with one plate held in place by the compressor housing bolts and one welded to the turbine outlet pipe.

Lunchtime!

The flame tube without its cap, there will be a space of 5cm between the cap (which holds the vapour tube) and the combustor lid so air can flow through the vapour tube. The main spray nozzle will reach down the vapour tube and the preheat nozzle will heat the VT through a hole in the cap next to it.

[racketmotorman]

Hi Anders

What diameter is your flametube , it looks a little on the skinny side in that nice big fat combustor can , with a 65mm inducer on the comp , you'd be needing probably at least a 100mm, preferably 125mm, dia flametube for running liquid fuel to minimise the chances of combustion difficulties at high power/fuel loading settings.

Cheers
John

[Johansson]

Hi John,

It is 105mm ID and will be 260mm long when the endcap is fitted. The combustion can was made that large since the turbo had to sit upon it before.

[racketmotorman]

Hi Anders

LOL......So thats why it looks skinny

Do you have a "funnel" on the outlet end of the FT to blend the round tube into the rectangular scroll port , without one the engine can surge due to a "vena contracta" at the sharp edged scroll inlet .

Cheers
John