Weâ€™ve built a big PJ (we expect over 100 lbf), and the closest thing to running we can get is what sounds like an idling nitro-burning funny-car engine (besides a really great boom) and of course, big billowy plumes of fire.
The dimensions are these:
- Combustion Chamber - 9 in. dia., 13 in. len.;
- Exhaust Tube - 6 in. dia., 36 in. len.;
- Reduction Cone - 16 in. len.
The fuel is propane; and is injected inside the chamber by two jets.
- .006, .008, and .010 in. thick spring-steel material for the valves;
- fuel in both gaseous and liquid forms;
- fuel pressure from 0 to 100 psi;
- with and without continuous (gas powered) leaf-blower air;
- extending the exhaust tube length with a "trombone" sleeve another 12 inches;
- shortening the exhaust tube length with metal cutters by 6 inches;
The best we get is by choosing a pressure, say about 20 psi, turn on the fuel, hit the spark, and give it the air blower. If we give it the air right away, we get something like, BbBbbbBBbBbbBBbbbBâ€¦ (though it only lasts for a few seconds). Or if we hold off on the air for a couple seconds, and when we give it we get a great BOOM! In any event, it just ends up an over-achieverâ€™s barbeque flame dispenser.
We figure there has to be something fundamentally wrong because there is such a wide margin of â€œas good as it getsâ€