Johanssons Jet-Cart

[Johansson]

Not yet but I will weld in stainless guide plates that will narrow the tube down to fit the turbine scroll entry.

I used Jetspecs to calculate the holes for the flame tube, and will count the cross sectional area of the narrowest part in the vapour tube as primary zone area. John has told me earlier in the pocketbike thread to measure the flow area through the vapour tubes and divide it by two to allow for flow losses in the bends and so on, so I will do just that.

Should I design the vapour tube with an increasing area further down the tube where the three J-hooks are welded to the main tube? Since I will have a spray nozzle inside the vapour tube that section will have the smallest area and should also be the area that I base the flame tube calculations on, right?

[racketmotorman]

Hi Anders

You want a minimum 10% of total FT hole area as the area of your evaporator's narrowest flow area , so for your 65mm inducer with ~3318 sq mms that equates to ~330 sq mms for the evap flow area , or ~20mm dia hole , but if you have the spray nozzle inside a "trunk" , you'll need to calculate the spray nozzle area then add on the 330 sq mms to get the final size of the trunk ID , if the spray nozzle is say 20mm dia -314 sq mms ,add on 330 gives us 643 sq mms , so a 28mm ID trunk required to get sufficient airflow around the embeded spray nozzle .

The micro RC gas turbine engines use that ~10-12 % figure for their straight evap tubes , with surface area of the evap tubes ~5 - 6 times inducer area , so say ~18,500 sq mms surface area of your evap system .

Hope this helps

Cheers
John

[Johansson]

It sure does, thanks a lot.

[Johansson]

Update: The all-stainless flametube is almost finished now, the secondary holes needs to be opened up from 8 to 10mm but I burned all 10mm drills trying to make holes in the thick SS flange so I have to get more drills first. The last flange holes were made with the plasma cutter instead.

I found a 25mm thin-walled stainless tube that I will use for the vapouriser, the L-pipes were scavanged from the jetbike combustor and cut to shape. One taketh what one findeth.

Btw, is there any gain in fitting the L-pipes to the main pipe at an angle so the exiting air/fuel mixture rotates in the FT or should I just point them straight up and make some rotation in the FT by bending the primary holes instead?

[racketmotorman]

Hi Anders

Probably easier to get swirl by modifying the air holes , they're on a larger radius so will be more effective )

Cheers
John

[Johansson]

Check!

I finally found out why cheap drills are cheaper than expensive ones, I probably went through 7 drills to get the final hole made and I still had to use the plasma cutter to finish it off. Once a drill had started to slip in the hole the stainless seemed to harden and no matter how much cutting oil or how many drills I used they just got blunt without even a chip coming lose from the material. It was some special stainless suited for ovens I got for free, it eats angle grinder discs for breakfast.

I am also reconsidering my idea of making the PT out of a single disc of stainless, if I cannot even drill a hole in the f*cking material I will most likely turn into a raging maniac if I try to make a turbine disc out of it. A SS tube cut to sections and welded to a disc sounds much more appealing now...

[Viv]

Check!

I finally found out why cheap drills are cheaper than expensive ones, I probably went through 7 drills to get the final hole made and I still had to use the plasma cutter to finish it off. Once a drill had started to slip in the hole the stainless seemed to harden and no matter how much cutting oil or how many drills I used they just got blunt without even a chip coming lose from the material. It was some special stainless suited for ovens I got for free, it eats angle grinder discs for breakfast.

I am also reconsidering my idea of making the PT out of a single disc of stainless, if I cannot even drill a hole in the f*cking material I will most likely turn into a raging maniac if I try to make a turbine disc out of it. A SS tube cut to sections and welded to a disc sounds much more appealing now...

Hi Johansson

You need a more aggressive cutting angle on the tip for stainless as opposed to ordinary steel, also you need to use a cutting fluid specifically for stainless steel not ordinary cutting fluid or it will you will still get galling (cold welding) and blunting of the cutting edges.

The other tip I would give is to use plenty of power (not speed) and and really get behind the drill and push! once you start the bit cutting don't let up or it will just slide and generate heat and blunt itself in seconds.

Sharpen often! don't be afraid to sharpen every time you drill, for thread taps only use them ten times in stainless then throw them away

Oh and a lot of tungsten based stainless will work harden as soon as you work it, use a centre tap to mark for drilling and you cant! the centre point work hardened the metal when it was struck so the drill cant penetrate it, lots of fun with that one if the drill slips or a lath tool rubs the steel it will work harden the surface then you cant cut it the only way around it is to start the cut from a fresh area and then cut under the work hardened area to lift it off as chips.

Viv

[Johansson]

Some good pointers there Viv, I´ve never worked with any thicker stainless than sheet before so this is all new to me. It is not helping either that my mill is 200km away so I have to use a next to worthless chinese pillar drill weighing in at aprox. 4kg...

[Johansson]

The vapour tree is finished and the holes are made to the right size, the primary row is directed counter-clockwise and four of the secondary holes points up to hopefully produce some recirculation in the upper end of the flame tube.

[racketmotorman]

Hi Anders

I notice you don't have a tapered funnel at the outlet end of the FT to blend the round FT to rectangular port , this can cause surge as the flow is restricted going into the scroll by the "vena contracta" effect over the sharp corner .

Cheers
John

[Johansson]

Hi Anders

I notice you don't have a tapered funnel at the outlet end of the FT to blend the round FT to rectangular port , this can cause surge as the flow is restricted going into the scroll by the "vena contracta" effect over the sharp corner .

Cheers
John

Hi John,

Look at the last picture, two D-shaped stainless plates are welded inside the flametube to direct the gasses into the rectangular port. I didn´t want to cut the flametube since it already had a nice flange on it so I decided to do it this way instead.

[racketmotorman]

Hi Anders

Now that you've pointed them out , that should do the job , an imaginative solution

Cheers
John

[Johansson]

Thanks, I figured that it should work. One thing I will do is to drill a small hole behind each plate to get some air in for cooling, don´t know if it is needed but it will certainly not do any harm so why not?

My idea is to fit the idle nozzle from the side of the combustor along with the spark plug, that way I think I will get better preheating of the vapour tree and I won´t have to drill more holes in the thick stainless plate.

A new oil tank will also have to be built since the old one is too high now that the turbo´s drain pipe is much lower than before, I will also try to move the oil pump and cooler to the front of the cart to get less weight around the rear axle.

[racketmotorman]

Hi Anders

Yep, a bit of cooling air won't hurt

Sounds like the build is proceeding nicely

Cheers
John

[Johansson]

Well it is moving forward at least, when the combustor is finished I have the oil tank to make along with new mounts for the pump, filter and cooler, new oil hoses and some simple throttle for the engine.

After that is done it is time for a test run, but since I am working on the jetkick, a friends pulsejet ice yatch and modifying my Hayabusa at the same time it might take most of the winter before I get to start it again.