Johansson´s Pocketbike

[Fricke]

Nice work Anders!

And congratulations to the new license!! =)

[Jmitchell]

Wait a second, I thought that it was going to be mechanically powered, not jet-exhaust powered.

[Johansson]

Correct, but first I have to get the turbine sorted out. I will measure the pressure and temp after the turbine when I have found the right exhaust nozzle area, and after that I can start calculating on the power turbine. I also needed to know how much space there would be left in the frame before building the PT...

At the moment it seems like the only solution is to make an axial power turbine from scratch along with a gear box, 321 stainless will do just fine since I won´t let the exhaust temp rise above 650C. Anyway, I will save that problem until later since I have to get it running on pure thrust first.

The calculated max thrust is 12.6 kg so it will be interesting to find out how much it differs from reality.

Fricke: Thanks! It feels great to have the license, big bikes can also be fun! ;-)

//Anders

[Johansson]

I forgot to tell you that the main fuel system is almost finished, I have soldered together the main parts and only need to make the piece that connects the nozzles and the fuel pressure gauge to the system. I will have that along with connecting the switches and gauges done before next week if nothing gets in the way.

After that there is nothing left to do before attempting to start it. I will use my trusty 230V transformer to provide ignition, a car battery for the pumps and an external fuel tank for the first tests so I won´t have to wait for that damn lid to arrive. Since I am going to run it without exhaust nozzles the idle will be higher than "normal" due to the higher pressure drop over the turbine, but the 1.5 GPH nozzle should not get it spinning faster than the steel bearings can handle.

Since the bearings are standard ones I won´t run it at pressures above 1 bar, if I find that the bearings are getting good cooling and lubrication I will then get hybrid bearings and do tests at higher P2:s.

I have a rev-counter that I modified to IR for the gocart, but the signal was too weak for bouncing off the compressor nut so I gave it up. I am thinking about fitting the diodes on the bearing house so they reflect off a point on the shaft between the bearings, that way the distance for the signal to travel is short and I won´t have any restricive parts in the intake. I can paint one side of the shaft black after the rear bearing has been fitted and make it reflect off the metal. Then I can move the display up to the instrumentation and mount the counter box out of the way.

//Anders

[Johansson]

At last! The lid arrived yesterday after 4 months of waiting. The good looks outweighs the long delivery time though...

I finished the fuel system today and have started to connect everything with hoses, the transparent ones are used mostly because of a smaller bend radius and so I can see if any fuel is flowing through them to the bearings. They are super-glued to the nipples so they won´t come off.

//Anders

[racketmotorman]

Hi Anders
Getting close :D
I'm a little concerned about your hoses on top of the combustor, they'll probably be OK at low P2's but at higher P2's with T2's approaching 200 degrees C and heat rising off the combustor , they're going to soften significantly .
I'd be thinking of changing to all metal once you get the engine running and things a little more sorted . When I first got my engine running I had other than metal lines and there were "problems." :(
Cheers
John

[Johansson]

Yup, a few tweaks here and there and it is ready for its first run. The question is if I am ready... ;-)

I will have to check the hoses while running so they won´t soften and come loose. I am a bit worried about the transparent fuel hose I used for the bleed air to the bearings, but at the pressures I will be running at the first tests they should be fine.

Do you think that I will get an accurate P2 reading the way I have done it with both the bleed air hose and the pressure gauge hose connected with a T-fitting to just one nipple on the combustor? The bleed air could perhaps cause a pressure drop in the line messing with the pressure reading, but since the air flow through the bearings is quite low and the ID of the hoses is 4 mm it should be of minor importance.

//Anders

[Fricke]

Looking good Anders!

I´m looking forward to hear about the first start!

And that fuelcap is sooooo nice... =)

[Johansson]

Thanks!

Since the hoses on top of the combustor will be filled with fuel all the time it should provide some cooling, but I guess only time can tell if it is enough...

//Anders

[Fricke]

I´m a bit concerned about the clear hose... It´s not rated for high pressure...

But I hope that it will atleast hold for a first test...

Don´t forget to wear your Superman pyjamas when your testing it! =)

[Johansson]

I had a great day testing the fuel system today with water, it works almost flawlessly with a linear throttle range from 0.5 bar to 7.5 bar. While doing some high-pressure tests I found some solderings that leaked, but they are fixed now. I am pretty wet right now since a hose came off at 7 bar and gave me a quick shower before I could close the throttle...

The only less good thing was that the metering jet for bearing lubrication flows massive amounts of water at higher pressures, the jet I used for the test was a 50 idle jet from a carburator. At a system pressure of 1 kg (just below the opening pressure for the pressure valve) it gave a good flow of a few drops per second but as soon as I opened up the throttle a bit more it flowed way too much water. It would have flooded the engine in no time...

Tomorrow I will do some more test with a pressure regulator before the metering jet and see if I can get a stable flow throughout the entire throttle range.

//Anders

[multispool]

With that high fuel supply pressure, a pressure reducer would be definatelynecessary.

Or to avoid great complication you might consider the old method of lubrication. This idea uses case pressure to pressurise a separate oil tank, it's much easier then to meter the lube flow through a restrictor. Of course, if your using ceramics, then instead of just lube in the tank, it could have a 3% blend of turbo oil and kero...

[Johansson]

The pressure regulator didn´t work properly either, at higher pressures it could be adjusted down to a low and steady pressure but at idle fuel pressures it didn´t regulate at all and sent a stream of fuel out of the metering jet.

Anyway, I hooked everything up for a quick test without the lubrication system working. I squirted a 50/50 mix of 2-stroke oil and diesel into the bleed air line before the test and tried to start the engine with the leaf blower, but I couldn´t get the fuel to ignite despite a good spark. After some thinking I realised that I gave the engine way too much air before starting the fuel pumps, so I tried to start the pumps with the shaft spinning at only a couple of 1000 rpm and it ignited instantly. I had some troubles with flame-outs while starting but when I started to remove the blower earlier that problem was gone.

I also found out that the engine can be started with shop air, the video shows the last test when I used the air nozzle in the compressor housing to spool up the engine. That is great since I won´t be able to use the leaf blower once all the plastic covers are in place on the bike.

The EGT at idle is 420ºC so I can make the thrust nozzles quite small before reaching 650ºC. I didn´t bother to check the P2 gauge since it will idle at a lower pressure than now when the thrust nozzles are in place.

I will have to dismantle the combustor and rearrange the primary holes a bit since the engine flamed out very easy once it was running, I made the holes just below the spray nozzles quite large so I will probably have to close them and make two rows of smaller holes instead to avoid this...

Overall, I am very satisfied with the first test. I am thinking about how to solve the lube problem without filling up more space in the frame, perhaps if I could use the combustor pressure to pressurise the fuel tank and draw the fuel through the metering jet it could work. I dont see any dangers in a couple of psi in a tank full of diesel.

//Anders

[racketmotorman]

Hi Anders
Congratulations :D
Please don't pressurise your fuel tank , I shudder when I think of possible consequences :shock:
Your lubrication will need to be supplied at combustor pressure ( P2) otherwise it won't be able to get into the engine.
You should be very proud of your achievement, getting her to spoolup and idle so quickly is a great job .
Congratulations again
Cheers
John

[Johansson]

Thank you for your kind words, we will see how it performs at higher P2´s as soon as I get the combustor problem sorted out and have fitted the thrust nozzles.

Hmm, if I use a separate oil tank I would not have to mix the fuel with 2-stroke oil and it would be easier to see that the bearings are getting oil from a transparent tank. I guess that 1 dl of oil would be enough to run the engine for quite a while. I will have to go through the garage and try to find a suitable tank...

Here is a pic of the combustor, don´t read anything out of the heating pattern since I forgot to polish it after the atmospheric test. I think that I am getting too much primary air, so closing the upper row of holes and drill a couple of rows with smaller holes to get the total hole area down a bit would prevent the flameouts.

I would really like some comments about the flametube so I can get it right the first time.

//Anders