The new combustor

After my initial trials with the old HR-1 engine on the go kart, I decided to start from scratch and build a whole new combustion chamber and call it the HR-1A engine.

The new engine design should be capable of producing more thrust so that it will propel the go kart faster. I also have the benefit of everything I have learned so far to help me along the way, although I am sure that I will learn even more during the experience.

I recently purchased a band saw and it has been helpful in cutting all of the parts for the new combustor. I also have been using Auto Cad to layout templates for parts to make sure that bolt holes fit where they should and that things just line up generally. I think the next purchase I make will be a plasma cutter though, as using a jigsaw for inside cuts is very time consuming and not a lot of fun.

Turbo flange

This is the turbo flange. It will bolt to the turbine inlet housing and provide the passage for air from the combustor. I cut the mild steel using the band saw, and made the inside cuts with the jigsaw. Four holes were drilled in the inside corners and the jigsaw just had to connect the areas between them. It is 1/8 inch mild steel plate and should hold up pretty well.

End rings and combustor caps

The end rings weld on to the end of the combustion chamber and provide a secure mounting point for the end caps. I used Auto Cad to layout a pattern for the rings and caps and to provide for an even bolt hole spacing all around. After using the pattern to scribe the circumference and center punch the bolt holes, I cut them out using the band saw. By marking the dead center of each cap, I could drill a pilot hole which the steel could be rotated about. I then inserted a pin into the hole and turned the blank around while using my bandsaw to cut away the material around the outside edge. Inside cuts on the rings were then completed with a jigsaw as before on the turbine flange. After cutting, the bolt holes were all drilled to size and the parts were cleaned up.

If you do not have a plasma torch or other means to cut the circles, using the band saw can be very effective. It sure beats trying to freehand all of the cuts with a jigsaw alone.

Combustor housing

I could not find a tube in the diameter that I wanted for the combustor. Most tubing in larger diameters has a very thick wall, or even worse it is not tubing at all but pipe. Pipe is measured by inside diameter, and the wall thickness is referenced by a strength number, whereas tubing will be measured via outside diameter and has a wall thickness that is measured in thousandths of an inch. Since the project requires specific dimensions I had to have the tube rolled to shape for me. I could have searched and found a tube in the size that I need , but I am trying to use stainless steel for the combustor and it is much harder to source stainless tube in larger diameters. To roll a tube, a piece of rectangular steel is passed through heavy steel rollers which slowly arc the metal until it finally makes a full circle. Once rolled the length of the tube is seam welded to make it one solid piece. The tube I had rolled was 8 inches in diameter, and 15 inches long. Let me tell you that it was not an inexpensive part to have fabricated.

End ring flange

The end rings were welded on to the combustor housing to provide a means to bolt on the end caps. After welding, a flap disc was used to smooth out the welds and make a flush seating area for the caps themselves. After grinding the welds smooth, the whole combustor can was buffed out to make it shine.

Top of combustor

With all of the welding done, the fit of the end caps was tested. Nuts were welded on the underside of the ring flange to make the unit easier to assemble. You can clearly see that the use of the Auto Cad program makes layout very nice and everything fits together like a glove. The end cap will fit into place no matter which way it is rotated. This was the first time I had ever welded with stainless steel, and I can assure you that it is not the same as welding mild steel.

Finished combustor

The next step on the combustor was to fabricate the exhaust flange. Four pieces of steel were cut in a trapezoidal shape and welded to create a square funnel that tapered from a 5 inch square opening, to a 2 x 3 inch opening for the turbine flange. A 5 inch square hole was then cut into one of the combustor end caps and the funnel was welded in place between the end cap and the turbine flange. The funnel can be seen at the far right of the combustor can in the picture above.

Exhaust funnel

The exhaust funnel is viewable more clearly in the photo above. You can make out the shape of the trapezoidal pieces in the side view, and see how the hot gasses will funnel down into the turbine flange.

Inside the combustor

Looking down from inside the combustor housing, you can see the exit funnel which should help the exhaust gasses to escape freely. This is the path the hot gasses will see as they roar through the combustor at high speed, of course if you were in the combustor you probably wouldn't see much with all the flames in there.

Laser wrap

The final combustion chamber is kept in the protective paper covering the stainless was wrapped in, until further assembly takes place. The paper is actually a backing for laser cutting, since a laser would reflect off of the stainless if it weren't present. This just happened to be the brand of stainless that was used to roll the tube, even though no actual laser cutting was done or was ever planned for this piece.

Check back soon, as there is much more work to be done on the new HR-1A engine.

Gary Richards

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