Bringing the pulse jet engine into the 21st century
Last Updated: 9 April, 2001
100 Pounds Of Thrust
The vast majority of pulse jets currently in operation or circulation are
the smaller type originally designed for model airplanes.
Pulse jets such as the Dynajet, OS or Tiger are relatively small and produce comparatively little power -- between 3-10 lbs maximum. Always looking to push the boundaries, I have developed a significantly larger engine that provides an honest 100 lbs of thrust, more than enough to propel a gokart or small a reasonably efficient microlight aircraft. This engine is not a toy -- it is a seriously powerful source of thrust which, is capable of lifting a small kart right off the ground if not properly controlled. Another thing to be aware of is the fact that large amounts of highly flammable air/fuel mixture are used to create the thrust in this engine. For this reason, extreme care should be taken when starting it because it is quite easy for this explosive mixture to build up very quickly before ignition occurs. See this page for an explanation and pictures of what happens if you're not careful.
The Valving The valves on this engine are in the form of a double-V shaped seat with no less than eight individual valves and movement limiting plates. If I had been building this engine for an episode of the excellent Scrapheap TV program (that's Junkyard Wars in the USA) I'd have just used a series of simple spring-steel flaps seated against holes bored in the front plate (much like the petal valves of smaller engines). However, as a prototype for the production engines, it is built to be solid, reliable and powerful rather than just to last for half an hour or so.
This is the heaviest and most complex part of the engine and in the production
version it will be made from a casting rather than welded from individual parts.
A cast aluminum version will be cheaper and, because aluminum is a much better
valve-seat material than steel, provide longer valve-life and more reliable
operation.
See It Run! The files below are in the RealVideo format and have been rendered in 56Kbps and 200Kbps formats. Note that they won't stream, you'll have to download the entire file before it starts to play.
I am very pleased with the quite even burning within the combustion zone which shows that the injector is doing a good job of evenly distributing the fuel into the incoming airstream.
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After building this engine I find it easy to see why so many people are
increasingly drawn to the idea of a valveless engine.
There are a total of more than 60 individual parts in the valving and fuel-jet
part of the engine. Most of this is made from 3mm steel plate and much of the
time building it was spent creating the 32 rectangular slots in the seats
through which the airflow passes.
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