HX35W Turbojet Build Thread

[turbinenjoe]

Hi,

lately I work on my newest engine. It is a turbojet based on a Holset HX35W. If everything works out fine I will possibly start another attempt to convert this engine into a freeshaft engine. But thats far from now.



The wheel sizes on the compressor side are 54 mm inducer and 82 mm exducer.

on the turbine side 70 mm inducer and 60 mm exducer.

Unfortunately the turbo is wastegated but I will fix the wastegate in a closed position.

The combustor will be arranged in a „sore thumb design“.

I am not completely sure what components I will use for my oil system but as soon as I figured it out I will post it here.

The fuel system will consist of an automotive fuel pump that pressurizes diesel fuel or kerosene to 3 bar above combustor pressure with a boost referenced pressure regulator. To control the fuel flow i will use an automotive fuel injector valve with a high cc/min value and after that the fuel is injected through an oil furnace nozzle into an evaporator.
A separate oil furnace nozzle with a lower GPH will serve as a pilot burner. Ignition will be done with a spark plug and some kind of NE555 timer circuit. In the past this setup worked out fine for me on my previous engines.

To evenly space the three trunks of the evaporator i drew three equally sized cylinders inside of the fame tubes inner diameter.



The evaporator can be seen below:



Most of the parts for the combustor are already finished. 











For the flame tube I used a 101,6x2 mm stainless steel tube. The length of the cylindrical portion is 250 mm. The outer can will have an inner diameter of 130 mm.

I now have to cut the outer can to length, fabricate a delivery tube and then weld it all together. 

On my way along the build I will post the progress here. Please feel free to ask and comment.

[turbinenjoe]

Hi,

I made some progress on the combustion chamber.



I tack welded the cone and flametube together




This is a look down into the flametube and combustion chamber




I cut the sleeve for the combustion chamber a few cm longer than it has to be. After installing the gasket between the end cap and the sleeve I will measure again and cut it to the right length. Usually i use a pretty thick gasket of around ~ 2 mm at first and if the cones at the end of the flametube and combustor get hot during the initial run they settle a little bit and I can use a lightly thinner (1 - 1,5 mm) gasket.




Something that i still have to figure out is how I can achieve a reliable rpm-pickup on the compressor nut. On my turbo it is a Bi-hexagon nut that has only a small flat surface where I can point my fiber optic rpm sensor to. I am thinking about fabricating my own nut with a larger surface that i can paint black and white but I am concerned about material strength. Holset mentions a tightening torque of 124 lb. in which would require a pretty high grade of steel. Something like 4140H or similar. Typical hexagonal rods are made of lower grade steel or stainless steel which both seem to be not strong enough. Online I can only find hexagonal 4140H in 13 mm wrench size. Ideally I want it a little bit smaller. Does somebody already have experience in manufacturing a compressor nut? Is a weaker material propably okay, too?



Thank you in advance


Best regards

Matthias

[racket]

Hi Matthias

I normally paint the whole wheel hub snout including the nut to get a larger surface area .

Cheers
John

[turbinenjoe]

Jan 8, 2023 15:41:58 GMT -5 racket said:

Hi Matthias

I normally paint the whole wheel hub snout including the nut to get a larger surface area .

Cheers
John

Hi John

probably I will do that, too. I was just thinking about an alternative way by fabricating a - maybe even more streamlined - nut.


I made a small excel sheet which helps me with calculating the parameters of my engine.



It is in German but I translated the following calculations with Google Lens. To start I divided a pressure ratio of 3.0 in 3 equal pressure ratios. Those single ratios are then 1.44. Two of those three parts (1.44 x 1.44 ~ 2.1) will be "consumed" by our gas producer volute & turbine stage. This leaves us with another PR of 1.44 for the jet nozzle or free shaft turbine stage. For my inital parameters of 650°C (~ 1202°F), PR 1.44 and a mass flow of 0.3 kg/s (~ 0.66 lb/s) I get a thrust of about 28 lbs with a nozzle diameter of 47 mm (~ 1.85 in).



Basically it is just a very crude version of the jetspecs turbo analysis software but with it I am able to calculate different pressure ratios or efficiency levels more flexibly.
Right now I am working on a version that can also calculate typical parameters for a free power stage but this is in a very early state. For example I get the max. theoretical power output of the given temperature drop and combined with the efficiency factors I get the power output that can be expected by that free shaft turbine. So a PR of 1.45 and a temperature of 650°C (~ 1202°F) combined with an efficiency of 0.72 gives me around 21 hp.





Regards

Matthias

[turbinenjoe]

Hi,

i cut the combustor gasket out of 2mm NBR/PARA sheet:




After a quick cleaning pass:




On the combustor flange:




After installing the gasket I was able to cut the outer can of the combustor to the right length and I tack welded the cone to it. This is how the combustor assembly looks when it is mounted to the turbine housing.




The next step will be the discharge tube.


Regards,
Matthias

[turbinenjoe]

Hi,

I found the time to build the discharge tube and to tack weld it to the combustor.








I also spent some time modifying the shaft of my FoMoCo oil pump. After shortening the shaft I also drilled and tapped iit M8 left hand so that I can screw it onto my MY1020:







Best regards

Matthias

[turbinenjoe]

Hi,

I spent some time working on the oil pump.

On the left is the gasket. In the middle you can see the flange and on the right is the pump:




I added a shaft seal because the pump is not sealed and oil could leak out along the shaft.




On this picture the pump is mounted to the flange. I still have to weld in the ports for the oil inlet and outlet into the two large holes.




I was not happy with my previous idea to couple the pump and motor rigidly. So I bought a flexible coupling to allow for heat expansion.





Another topic:

Eventually after the turbojet is finished I want to convert it to a turboshaft with a turbine of a turbocharger. For that purpose I want to use another turbo that I have sitting around.






It has a 96 mm turbine inducer & a 86 mm turbine exducer and should fit my gas producers turbine exducer (60 mm) very well. One thing that I am uncertain about is what kind of rpms I have to expect from that power turbine. I am not familiar with the velocity triangles on radial turbines. I just about understand the explanation of the axial DIY turbine that can be found in the basics here on the forum.

I will appreciate every help regarding that topic.


Regards

Matthias

[racket]

Hi Matthias

The freepower could be rotating up to 60,000 rpm

Cheers
John