20 replies to this topic

[Robbie414]

Hmmm......Pulse jets are a different beast entirely. For a start off they take in Air at the front and expel at the back. The process of Induction occurs in either of two ways.
The fuel can be drawn in using the difference in pressure between the Atmospheric pressure in front of the valve plates and the combustion chamber. A pulse jet engine still has a combustion cycle and is nothing like a rocket engine which does not. This is why you need an air source to get a pulse jet started, giving you an airflow over your fuel head and into the combustion chamber, once the engine is started the fuel is drawn in by the airflow on the induction stroke. The vacuum created in the combustion chamber is caused by the hot gases only being able to flow out of the engine via the exhaust due to the one way petal valve at the front. The decrease in pressure as a result of the gases expansion and then exit sucks in fuel and air for the next stroke through the petal valve which is then compressed using a wave effect.

The other option is to have a compressed fuel source (ie propane gas) which is INJECTED straight into the combustion chamber this allows the engine to be throttled. The air source (oxidiser) is still drawn through using atmospheric pressure.

Rockets do not use difference in pressure to draw fuel, IE they must have a compressed fuel/oxidiser source. This is why they work in the vacuum of space!!!! And zero gravity!!!

Gravity feed may work for very low thrust and pressure systems but will certainly not lift the motor off the ground. I would have thought that V.B'r fuel cells where pressurised.

[smpip]

When the combustion chamber momentarily ceases to function (due to fuel starvation and pressure drop) the valves are then released from the closed position, the fuels are able to flow again, combustion occurs the valves seal against the expansion of gases, etc etc etc, the faster the unit the greater the "G" force acting on the fuel, ergo it would/could function in a vacuum, I would say that without actual models to assume that (at onset) a low pressure unit would remain so during any firing period, is a bit premature, and also who's to say this would be a low pressure system?
I grant you (at onset) only the fuel delivery is low pressure.
Do you have any relevent fuel reaction info so that we could at least come up with a few mathematical models.

I've put this web address in, if your not familiar with the lockwood / hiller "pulsejet", you might get some mileage out of it, click on the Hiller 5.25 link,the information on the web link is all worth reading, 150lbs thrust from a 15lb unit!! (fuel weight not included)
But first check out the site before going to the link, it has a few interesting photo's

http://blastwavejet.com/

Edited by smpip, 24 August 2003 - 01:31 AM.

[Robbie414]

My 'model and experience' is a first class degree in Aerospace Engineering (Bristol University) and my current role as a design engineer for Rolls-Royce Aero Derby. Speed has nothing to do with what you call 'G's. One could be travelling at 18,000MPH and not experience any G's...I think you are talking about acceleration! If what you are saying is correct (which I am afraid it is not) then the engine would have never worked on a test bed (1g). As an engineer I can tell you that if it does not work on the test bed it does not get anywhere near an airframe!
You are still talking about pulse jets in your post, they are nothing like and function nothing like rocket engines, thrust is a mere fraction of that of a good rocket engine. The lockwood hiller engine you talk about is a valveless design that was proven to be incredibly ineffcient, low power and with such high fuel consumption and heat output (as you can see by the glowing exahust) totally useless in practical aplications..other than crop spraying!
PLEASE DO NOT PAY FOR PULSE JET PLANS ON THE NET!!!! they are often merely copied from other sites where you may obtain them free!
however if you want a more informative and well built site click here. http://www.aardvark.co.nz/pjet/ Bruce has to be one of the best 'ameature' propulsion engineers on the web, and his valveless p-jet designs are nothing short of awesome!

If you want mathematical models I can give you them, but I think they would only bore you and everyone else on this forum and unless you are of degree level maths? We are here to learn the applied theory not the boring bit that people like me spent hours trying to stay awake during aweful lectures to learn.

Another good article http://www.popsci.co...73272-1,00.html

Can we get back to Rocket engines now please!

[Gor]

How is Derby?
I spent my first 17 years there before escaping to Uni in London. I haven't been back in years.

Don't be too hard on this topic, it has been an interesting diversion.

[mrpyromx]

I tried to make a rocket once out of a house and 14 pounds of flash poweder, it didnt work well, the walls were to weak. just kidding

[Robbie414]

Lol Mrpyro!!! Now that would be one hell of a rocket!! You should consider using a longer burn composition next time, I still reckon the KNO3/sugar comp would be most suitable....just need to make sure you keep all the doors and windows locked otherwise you could be looking at a rocket sled for a house...now that could be dangerous!!

Gor...

Derby is Derby lol.....in otherwords SH*te... I live in a little village past Burton called Barton-under-needwood, which is great...just love the drive to Sinfin everyday...not! Maybe moving back down to Bristol to work on the defence side of things as Derby is mainly commercial engines, and I am more into the defence and weaponry element. Bristol is a great city.