Need help designing engine
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dreadedmonky
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Need help designing engine
I have a wish to hit 80+ mph in a boat powered by ram jets. At 600 lbs with a tunnel hull design I estimated around 300 lbs thrust will be needed. My plan is to build two 150 lbs motors, I am having trouble with the math involved, help a fellow out?
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dynajetjerry
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Re: Need help designing engine
Hello, Dreadedmonky,
I can't supply much in the way of math but I can offer suggestions.
First of all, you will need pulse-jets, not ram-jets. P-js will operate at speeds from static to about Mach .6 while true ram-jets will not function below about Mach .5.
Your hoped-for thrust dictates an exhaust size of about 6 in. diameter for each with somewhat larger combustion chambers. Total length will be about 6 feet, gasoline consumption will be about 15 gal. per hour, and cycling will be about 80-100 cps. You can copy an enlarged version of the Globe/Solar 10P14 (PJ32,) but would be well-advised to inject much of the fuel into the air inlet at the front. (This can result in a fire hazard!) The 10P14 injectors are immediately downstream of the reed valves and provide very little cooling of the reeds. Therefore, statically and at low speeds, the reeds burn out within 10 minutes.
Aeromarine Co., in 1950, developed a 210 lb. thrust p-j that was 8 in in dia. along its full length of 8 ft. A 9.5 in.dia. flare at the rear added about 4 in. and helped low-speed operation. A draw-back was the need for lots of air being blown into the inlet for starting and much fire protection. Its reeds could last more than 2 hrs of continuous operation.
Eric Beck is working with all kinds of p-js and he may be able to help you. However, he is running a business and might need to charge for his help to you. He also mfrs. valveless p-js and, perhaps, valved types. He is on the Internet.
Jerry
I can't supply much in the way of math but I can offer suggestions.
First of all, you will need pulse-jets, not ram-jets. P-js will operate at speeds from static to about Mach .6 while true ram-jets will not function below about Mach .5.
Your hoped-for thrust dictates an exhaust size of about 6 in. diameter for each with somewhat larger combustion chambers. Total length will be about 6 feet, gasoline consumption will be about 15 gal. per hour, and cycling will be about 80-100 cps. You can copy an enlarged version of the Globe/Solar 10P14 (PJ32,) but would be well-advised to inject much of the fuel into the air inlet at the front. (This can result in a fire hazard!) The 10P14 injectors are immediately downstream of the reed valves and provide very little cooling of the reeds. Therefore, statically and at low speeds, the reeds burn out within 10 minutes.
Aeromarine Co., in 1950, developed a 210 lb. thrust p-j that was 8 in in dia. along its full length of 8 ft. A 9.5 in.dia. flare at the rear added about 4 in. and helped low-speed operation. A draw-back was the need for lots of air being blown into the inlet for starting and much fire protection. Its reeds could last more than 2 hrs of continuous operation.
Eric Beck is working with all kinds of p-js and he may be able to help you. However, he is running a business and might need to charge for his help to you. He also mfrs. valveless p-js and, perhaps, valved types. He is on the Internet.
Jerry
Louder is always better.
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Rocket Man
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Re: Need help designing engine
Engine shape and size math is easy. Designing the valves and making them fit in the available space on your engine is much harder.