Surgery on a
Microturbo Couguar 022
Turbojet Engine!

Last updated on 10/23/06 18:30 AST

These pages document the process I undertook to clean the injectors on the engine of my BD-5J.

The reason for the cleaning? Refusal to start. Itty bitty "Foom!" and then... nothing. After having determined there's proper fuel flow, RPM and a heck of a blue flame coming from the igniter, and checking all systems, a determination was made that the injectors need to be cleaned. The engine was removed from the aircraft and I brought it home with me to work on it.

These images are VERY LARGE. These are thumbnails. Clicking on them will show the large images. If you have a slow connection to the Internet it will take time for these to download.

That said, enjoy!

After coming home I set up in the balcony on a nice table. Plenty of newspaper to absorb any spills, but there really weren't any, that was taken care of when I removed the engine from the airframe (a job that took me several hours and convince me I need to replace a LOT of screws with small bolts).

Looking inside the business end of the engine, it looks in excellent condition. Not a single nick that I can see on any of the blades. The engine has eight burners inside the back cover, you can see the outline of the places where the burners go.

The engine picks up and returns fuel from these two fittings on the back of the case. These pictures are of the front wheel blades. The focus is not great but the blades are in new condition.

More blades.

This is the place for the engine speed magnetic pickup. The pickup generates a pulse every time the accessory gear box puts a tooth in front of it. I use a custom N1 indicator that picks up the pulses and does the math. Nice programmable indicator.

On the left, the fuel control box. Fuel goes into the box, through filters, and then to the injectors, then back to the fuel box, to the pump and out to the wings, then around again. The small box on the left with the lever is the throttle, it's actually a spill valve. On the right is the solenoid valve that controls fuel to the engine. It's operated electrically from a switch in the cockpit. Below that the tube is the impingement air start. Behind that is the oil pump.

Closeup of the solenoid valve and the blades on the back.

More blades. These are also in perfect condition.

Some twenty small bolts later, the back end comes out in one piece. The interior condition looks very clean and the blades are in excellent condition. The wheel turns freely with no binding, very smooth.

Another view of the wheel and blades. On the right, the back of the case with the burner assembly and exhaust pipe.

Inside of the burner assembly, and on the right you can barely see an injector. The goal is to get to those by removing the integral exhaust/burner assembly from the back case where the injectors are instaled.

This is the combustion chamber. I guess this is why they call it "annular"?

The exhaust pipe and integral bullet.

The burner injectors are installed inside the back plate. Fuel flows inside the plate, through the channels to the burners, where it is atomized and delivered to the combustion chamber. These are dirty, I can see the gunk and carbon in plain sight. I wasn't sure if I should remove them individually or have the entire backplate, injectors and all, dunked into the ultrasound. Answer below.

This is the best I can do to show what the injector looks like. My Nikon Coolpix doesn't do in-your-face closeups very well... but that third one on the right looks pretty good, eh? All three pictures are of the injector closest to the igniter. The hole to the right of the injector is where the igniter pokes through into the combustion chamber.

And these are closeups of the injectors, after I decided to take them out. Actually, this is just one injector, the acceptance manual mentions more than one type, so just in case, I am keeping them separate and labelled as I clean them, with the number matching a wax pencil mark on the hole in the case. (I later found they are all the same, but they have serial numbers, so I recorded each serial number and where it came out of, so I can put them back in the same place.)

It isn't Saturday, but it's bath time! That's my ultrasound cleaner I bought more than a decade ago to clean crusty coins. I hadn't used it for a very long time and had thought of selling it, but now I'm glad I kept it. An hour in there and the fluid gets hot! Kinda reminds me of tequila and that weekend in Tijuana with... hmm... on second thought, I better keep that one to myself for now... Yes, I think that would be a good idea.

After cleaning and reassembly. Looks better, doesn't it? I haven't safety wired yet because I want to take it to a place where I can test the flow and spray pattern.

Indeed, they look at lot better after an hour-long bath in hot LP-1 penetrating lubricant (I wound up using this at the recommendation of the aviation supply shop because I couldn't find denatured alcohol) in the ultrasound machine and a good wipedown. Turns out my ultrasound is a heater too! I had no idea.

I sent off the injectors to Hugh Syme in Idaho, who offered to test them for me to verify a good spray pattern. While that takes place, I took off the fuel distribution block to give it a good cleaning as well in the ultrasound. At the left is the block, bottom facing left. The big holes on the right hand side picture are for the fuel filters (the aircraft has three fuel filter stages: two fuel injection filter cans for the intakes from the tanks, another filter in the electric boost pump and these two in the distribution block.

This is the spill valve. It originally had an electric actuator, similar to the setup on the TRS-18, but since Quentin forgot to get the computer with engine, the actuator was removed and replaced with a manual throttle. When the throttle is closed, the spill valve opens and allows fuel to return to the distribution block and back to the tanks. When the throttle is opened, the spill valve closes, the fuel return is blocked, pressure increases in the system and more fuel is fed into the burners.

This is one of the fuel filters on the distribution block. There are two, and they are identical. The filtering medium is made of some kind of finemetal mesh.