The main housing of the combustor (grey) is a piece of steel pipe 100mm in diameter and 250mm long. On either end is a flat flange with six equally spaced holes to allow attachment of end plates. Between the combustor housing and the turbocharger exhaust inlet (brown) is an adapter plate (blue).

The adapter plate has two rectangular holes that exactly match the two rectangular inlets on the turbocharger. The plate has studs attached to either side. Four studs on the turbocharger side match up with the four mounting holes on the turbocharger exhaust inlet. Six studs on the opposite side of the plate match up with the six holes on the end of the combustor housing. The adapter plate also has a special fitting (pink) that couples the end of the flame tube (purple) onto the plate. This fitting matches the circular end of the flame tube to the rectangular holes in the adapter plate. The flame tube is a slide fit into the circular part of the fitting and this locates the flame tube centrally inside the combustor housing.

The flame tube will be made from 57mm diameter exhaust tube approximately 230mm long and it will contain holes along its length to allow air to enter the tube in a controlled manner. I haven't yet worked out what I think will be a suitable pattern of holes. The idea is to have three regions of holes. The primary zone, which is closest to the fuel injector and spark plug, is where you need to achieve the correct air/fuel mixture for combustion. After the primary zone is the secondary zone. Here extra air is added to complete the combustion. Finally, just before the hot gases enter the turbocharger, there is the dilution zone. Extra air is added to help cool the combustion gases before they impinge on the turbine wheel. The flame tube will need a lot of tinkering to get right so it is designed to be easily removed from the combustor housing. As a first attempt I will try having 15-20% of the air passing through the primary zone, 30% through the secondary zone and the rest in the dilution zone.

At the other end of the combustor housing is the end plate (blue/green). In the center of the end plate is a threaded hole into which the fuel injector is screwed. The injector consists of a brass hose fitting with a copper tube soldered to the inside of it. The copper tube is squashed almost flat at one end. The flattened end will spray the LPG fuel down the center of the flame tube. Next to the injector is another threaded hole for a normal automotive spark plug. The spark plug gap is opened up to around 3mm. The ignition system I am using will actually generate sparks over 10mm long.

On the side and at one end of the combustor housing is attached a short tube 50mm in diameter. This is the inlet where air from the turbocharger compressor is introduced into the combustor housing. My current plan is to have the air inlet positioned near the adapter plate end of the combustor. Air entering here should help cool the hot end of the flame tube and also, as the air is not blowing directly onto the holes in the flame tube, it should not affect the shaped of the flame. The combustor housing is symmetrical apart from the air inlet. The end plate and adapter plate may be attached to either end allowing me to have the air inlet positioned near the fuel injector. This seems to be the more usual way of doing things so I wanted the option of doing things this way if the need arises. A short piece of rubber hose will duct the air between the turbocharger compressor outlet and the air inlet on the combustor housing.