85% throttable pulse jet engine.

[Rocket Man]

After 6 months of research I have determined the old style pulse jet engines are like running your car engine running wide open at 6000 RPMs. Your car engine will soon throw a rod and self distruct running wide open. Also it is like removing the round throttle disc from inside the car engine carburetor so the engine gets full air all the time and you attempt to throttle the engine by adjusting fuel flow only.

I have built several pulse jet engines over the past 6 months. Yesterday I fired up a 20 lb thrust engine. It is throttable from 3 lbs thrust to 20 lbs of thrust. It will run on propane, gasoline, alcohol or kerosene. I ran the engine in the test stand for 2 whole hours. After it cooled off I took it apart and the reed valve looks like it has never been used exxcept for the very tip end of one valve looks like it got slighty warm. I totally redesigned the reed valves, reed valve retainer, engine body and the engine is fuel injected. It starts extremely easy at low throttle and throttles up to full throttle easy too.

I am going to take a video I will post it here soon.

[Johansson]

Any pictures?

It would be interesting to find out how long it can run before a valve finally breaks, but the neighbours might not agree...

[Rocket Man]

Temperature is 13 degrees F outside I forgot and left my propane tank in the shop all night the propane is cold and I can not get enough fuel to throttle the engine up to full power. The engine is running at 40% throttle. This engine is throttable from 3 lbs to 20 lbs of thrust. It starts very easy at 3 lbs of thrust. The engine will run on propane, gasoline, alcohol or kerosene. I have run this engine 4 times at full throttle 7 minutes each time. I have also run the engine 6 or 7 times about 3 or 4 minutes each time. This is the 5th run for 6 minutes. The engine has about 1 hour of run time on it. The valves look good so far only 1 petal shows signs of getting a little hot it has a slight brown color about 1/32" of the very tip end. The petal valve only got hot when I ran the engine at very low thrust. The engine is throttled by adjusting the propane pressure from 2 psi to 8 psi.

http://www.youtube.com/user/Lowracerman ... UQqx2e2Eps

[tufty]

How are you adjusting the propane pressure?

[Rocket Man]

How are you adjusting the propane pressure?

I am using a pressure regulator. You can buy a pressure regulator at any industrial welding supply store. The pressure guage goes from 0 to 60 psi.

[tufty]

So all you're doing is adjusting fuel flow, then?

[Rocket Man]

So all you're doing is adjusting fuel flow, then?

Yes that is correct. The natural kenetic energy of the engine makes it suck in the amount of air it needs for the amount of fuel it has to burn through about 60% of its throttle range. The engine runs lean at low throttle and rich at high throttle. If the engine is put on an RC airplane ram air will keep the engine from running rich at full throttle. The engine starts extremely easy at low throttle, then throttle it up.

I have discovered all of my pulse jet engines can tolerate lean fuel but they do not like to run rich. Above about 90% throttle the engine starts to run rich up to 100% throttle for static tests. If I go over 100% throttle the engine stops running. If I use 150 mph ram air from a leaf blower on the engines air intake I can throttle it up to about 140% thrust. If I had more ram air I am sure the engine would do exactly as the German V1 engine did and keep producing more and more thrust as long as I keep turning up the fuel.

The math shows this engine will produce 30 lbs of thrust but I can only get 15.2 lbs of thrust on the test stand with no ram air. If I could get more ram air I should be able to get more than 20 lbs of thrust.

[tufty]

So all you're doing is adjusting fuel flow, then?

Yes that is correct.

So how does that gel with your first post in this thread, viz:

After 6 months of research I have determined the old style pulse jet engines … you attempt to throttle the engine by adjusting fuel flow only.

I'm a little stumped at what you mean by this:

The natural kenetic energy of the engine makes it suck in the amount of air it needs for the amount of fuel it has to burn through about 60% of its throttle range.

Kinetic energy is the energy of a mass in motion, defined by the amount of work required to accelerate the mass from a standstill to its current velocity, and is defined by (from wikipedia, as they have easily quotable equations)

The phrase "natural kinetic energy" makes absolutely no sense, especially when applied to an object at standstill. I *think* you're trying to say that your engine will only throttle up to 60% of your hypothetical 100% when static, and that running it further than that requires ram air or causes rich extinction. Am I correct?

If I had more ram air I am sure the engine would do exactly as the German V1 engine did and keep producing more and more thrust as long as I keep turning up the fuel.

There are limits to this, and ram air can be your enemy as well as your friend. The Argus engines would "blow themselves out" above a certain speed, and even before then, you may well find "speed of sound" problems with your valves leading to valve destruction or sudden extinction.

The math shows this engine will produce 30 lbs of thrust but I can only get 15.2 lbs of thrust on the test stand with no ram air. If I could get more ram air I should be able to get more than 20 lbs of thrust.

To quote my old math teacher, "Please show your working calculations".

All that said, sounds like you're getting some impressive valve life. Howsabout some photos?

[Kool]

Do you have some photo's of the valve system?

[Rocket Man]

There is not a good way to explain some of this with words. There is no easy way to draw a graph either and post it here. I don't have exact figures anyway because I don't have a lot of good test equipment. This is what I have learned. Lets assume you build a pulse jet engine and built 2 sets of reed valves, 1 set of reed valves are 50% of the cross sectional area of the exhaust pipe the other set of reed valves is 40% of the cross sectional area of the exhaust pipe. The engine will start much easier with the small reed valves. The 50% reed valves will throttle up to a much high thrust than the smaller reed valves. The larger reed valves allow too much air into the combustion chamber for the engine to start at a low thrust.

You are correct at a certain high speed ram air can hold the reed valve open and the engine will flame out. There is a way to stop this from happening. After WWII the USA did its own research on pulse jet engines. The USA version of the German V1 engine was called the JB-2 Loon it also had another name and it was 900 lbs thrust. The Loon research data shows a speed of 950 mph then after some more improvements it reached a speed of 1200 mph. The Loon research data tells how to over come the flame out problem at high speed. It is very simple.

The Germans made several improvements on the V1 and they increased the speed from 400 mph to 440 to 460 then 500 mph.

The way most people run a pulse jet engine would be like running your car engine with no carburetor. You try to adjust the speed of your car engine by changing how much fuel the engine gets and all the time the engine suck in all the air it wants. If the reed valves on a pulse jet engine are designed to be 50% of the exhaust cross sectional area the engine sucks in too much air at low thrust and not enough air at high thrust. The engine needs a throttle body to restrict air flow at low speed just like a car carburetor. If air flow is restricted to about 20% then the engine can be started extremely easy on 10% thrust. If the throttle body opens and allows more air to enter at the same time fuel is increased too the fuel/air mixtures stays closer to 15/1 ratio then the engine runs perpect at all thrust ranges and there is no lean fuel burn at low thrust and no rich fuel burn at high thrust.

Here is something very cool I learned by experementing. You build a pulse jet engine so about 33% of the reed valves are made of .010" thick blue spring steel, about 33% are make of .012" thick blue spring steel, and the last 33% are made of .014" blue spring steel. The .010" reed valve open first and the engine sucks in a small amount of air with a small amount of fuel and the engine starts very easy at 10% thrust and can be throttled up to full thrust. As the fuel is increased at some point the .012" reed valves will open and supply the engine with more air, and at high thrust the .014" valves open and give the engine more air at full throttle. This works the same as a throttle body.

If the exhaust pipe is made about 20% longer than it needs to be it sucks a much stronger vacuum in the combustion chamber and it sucks the flame away from the reed valves. This keeps the reed valve from getting hot.

Also the reed valves should not open more than 3/16" and should never be more than 1" long. This keeps the reed valves from hammering themself to death. I have run pulse jet engine at full throttle in a test stand for several hours and after inspecting the reed valves they look like they have never been used. Also the port hole the reed valve is covering should be no larger than 10 mm to keep the reed valve material from cracking. As the reed valve hammers themself on the holes they cover the metal tends do bow down into each hole every time the valve slams shut this causes the metal to bend and crack.

The reed valve retainer should NEVER be made flat, it should be curved with a very smooth flowing radius with no shape corner at the bottom where the curve starts. You can do a test on your desk with a 12" wooden ruler. Hold the ruler down with 1 finger and lift up the other end of the ruler and let it go. The ruler will slam down on the desk hard and go BAM. You never want your reed valve to go BAM on the retainer and you don't want the reed valve to open far enough it goes BAM on the engine head. It is a bit of a disadvantage to restrict the opening of the reed valves to keep them from self distructing you just have to have MORE reed valves to get all the air flow the engine needs.

I have built a lot of different types of fuel systems. Fuel injection works best. I have built several types of fuel injection and their is a right way and wrong way to do it. Another thing I learned is and engine is much easier to start and throttle if it has 2 fuel systems. The engine has a START fuel system that is preset and it allows the engine to start very easy at low thrust and warm up the engine for about 60 seconds. Then the other fuel system is used to throttle the engine up to full thrust. The cool thing about the RUN fuel system is it can be any fuel you like even motor oil, kerosene, gasoline, alcohol, and any mixture of fuels you like, anything that will burn. Once the engine warms up for 60 seconds on the start fuel system the other fuel system can be turned on and throttled up to full thrust. The start fuel system can stay on all the time if you want.

The typical Hobby pulse jet engine like the Dyna Jet engine is designed to run at full throttle all the time. If you push the gas pedal to the floor on you car engine and hold it there it won't run screen wide open like that for very long it will throw a rod and self distruct. If you want a pulse jet to produce 70 lbs of thrust you need to design the engine to produce 100 lbs of thrust at full throttle then you throttle it down to 70% to get 70 lbs of thrust. The pulse jet engine will run at 70% throttle all day long.

Here is a video of my 20 lbs thrust engine. http://www.youtube.com/user/Lowracerman ... VNyTsUT2Xg

[PyroJoe]

Thanks for sharing your experience with the engines. Any preference on the number of openings that should be used to achieve the 40% to 50% cross sectional area intake?

One thing to keep in mind of the Dyna-Jets and some of the versions that arose over past decades, is they where/are designed to achieve fast lap times on the back of a control line craft. Super light, need just enough static thrust to get off the ground, quickly picking up the ram effect. More like formula one cars than sunday drivers. Race engines often are only built to last a very short time, but milk as much performance out of what is there. I doubt anything I have built would come close to these types.

Most of the V-1 footage shows a launching device was needed, haven't found any instances of a V-1 taking off on its own power. Is the Loon research data available somewhere? 950 mph to 1200 mph sounds kind of fast, that would really be haulin'!

Joe

[Mark]

"The USA version of the German V1 engine was called the JB-2 Loon it also had another name and it was 900 lbs thrust. The Loon research data shows a speed of 950 mph then after some more improvements it reached a speed of 1200 mph. The Loon research data tells how to over come the flame out problem at high speed."
Was this a theoretical speed of 1200 mph, or did they do it? Would you site your source on this? I recall reading of a capped front end to block ram air but I didn't ever come across actual 1200 mph test runs in my readings. That's a fast pulsejet.
Thanks,
Mark

[ace_fedde]

Very interesting information about throtling, Rocketman! Thanks for sharing.
Seems like technicians and scientists/physicists have both there own kind of input! (this one is for you Simon )

Fedde

[Mark]

Thanks for sharing your experience with the engines. Any preference on the number of openings that should be used to achieve the 40% to 50% cross sectional area intake?

One thing to keep in mind of the Dyna-Jets and some of the versions that arose over past decades, is they where/are designed to achieve fast lap times on the back of a control line craft. Super light, need just enough static thrust to get off the ground, quickly picking up the ram effect. More like formula one cars than sunday drivers. Race engines often are only built to last a very short time, but milk as much performance out of what is there. I doubt anything I have built would come close to these types.

Most of the V-1 footage shows a launching device was needed, haven't found any instances of a V-1 taking off on its own power. Is the Loon research data available somewhere? 950 mph to 1200 mph sounds kind of fast, that would really be haulin'!

Joe

I remember Foa in the book "Elements of Flight Propulsion" mentioning increasing forward air speed is in effect equivalent to increasing the valve area.

[Rocket Man]

There is a book at the University Library that contains all the research data done by the USA after WWII. It is a pretty large book with fold out blue prints. I read all the information about the engine and made some photo copies of parts of it. That is where I got the information about the actually speed and how it was done. I know 900 mph sounds fast but they claim they did it using a shroud to block ram air. I don't recall exactly what changes were made to increase the speed to 1200 mph.