Water Injection

[Pyrotec99]

Hi, I am interested in experimenting with water injection to a vpj. Additional mass to rapid expansion = thrust???
I was wondering if anyone else has experimented with this. Is this something that is viable?
Thanks,

[Dang911]

read the forum

[Johansson]

Don´t be so hard on the new guy. Besides, there is not THAT much written here about actual testing of a water injection system, some general thoughts here and there is what I can remember that I have read.

At the bottom of this page is an explanation of water injection:
http://www.pulse-jets.com/phpbb2/viewto ... &highlight

Happy reading and remember to keep the forum updated if you do any experimentation in the future!

//Anders

[Eric]

I have been doing a lot of water injection over the past year or so, I have mentioned a few times the advantages of injecting water but only a few people even showed remote interest in doing it on their own, and other than my own comments I cant really remember much else on water injection.

I have done quite a bit of work perfecting the water injection on my chinese designs especially, there are huge gains to be had in increasing efficiency and thrust.

If the engine is running on propane, you can feed up to 12 times more water into the engine than the volume of liquid fuel it would need directly into the intake, and that is with a basic venturi that does not adaquately atomize the water.

With an advanced setup you can easily inject 35 x the liquid fuel flow volume into the engine over its length with no ill effects. Though the optimum volume is much less, how much less is a closely gaurded secret. :)

Eric

[Mike Everman]

I've been quiet on the subject, but it's been central to my recent designs. I just wanted to get some testing in before I show.

Thanks for bringing it up some time ago, Eric. I think it's one of the most faaascinating ways to get a neat effective SFC. I've got a different spin on it, I'm hoping.

[Dang911]

Well, I am getting ready to start messing with water injection, and possibly an afterburner on my lockwood. I have asked the question for more detail on water injection before without many answerers...SOOO lets start up this topic.....

Where is the best place to inject water on a lockwood. I was thinking in the center of the U shape, or at the beginning of the exhaust cone. Also does the water need to be sprayed, or because of the intense heat, could it just be injected though an open tube. I would preheat the water in order to build some pressure and start the expansion process.

[Daz Man]

Dang 911, Can I ask if your "solid brass high precision aerodynamic radial cryogenic fuel injector" is mounted through the Combustion Chamber or plumbed via a pipe through the inlet tube? (I ask because one of your pics shows a bend in the pipe close to the brass injector)

[Dang911]

Its on the end of a pipe through the end of the intake. It is clamped to the top of the intake till about 5" before the brass injector, there I made a Z bend so the injector is centered in the pipe, but still doesn't rattle around.

The benefit to this rig, it allowed me to move the injector all over, tweaking the engine, and learning valuable info about injection.

Further down the road, I might plumb the injector thought the combustion chamber and up the intake backwards, and than weld it in place...

[Eric]

The best place to inject water is not in the middle of the tailpipe. That is a great place to inject it if you want to make a nice warm cloud of water vapor, but does jack for performance.

Mike hopefully your design is pretty radical, I have done some pretty wild stuff..... Including an engine for the "chinese contest" which fully takes advantage of all the rules :)

Eric

[Mike Everman]

Mike hopefully your design is pretty radical, I have done some pretty wild stuff..... Including an engine for the "chinese contest" which fully takes advantage of all the rules :)

Eric

Eric, if you've already done what I'm doing, then, damn! And, nice work. and Damn! I will be posting the results sometime soon.

Can you tell us how much thrust you got within the contest rules? Set the bar!

[Dang911]

so where is the best place to inject water?

[Eric]

Mike you would be very surprised at some of the stuff I have been doing :)

Keep in mind that these numbers are for a system that could be used to power something at the same speed (or greater) than the base engine, not some super enormous augmented space heater that will max out at 3 mph. Even though that might be allowed in the rules im not going to put a lot of time into something like that which I am not going to really get anything useful out of.

These figures could be beat pretty easily with the space heater from hell approach provided you dont care about the power to weight part.


With the current rig, which doesnt fully implement all the things I want:

19 from a non tuned stock 4.5 lb thrust classic chinese

27.5 from a tuned "classic" chinese

The semi-advanced "radical" design engine caused a failure of the primary extraction system at around at around 40+/- lbs, and needs a new system built around it to fully harness the engines potential.

I am working on getting a carbon fiber fan and am making a fiberglass annular wing duct for the semi-adv system, both should greatly increase performance. With a bigger extraction system and some better bearings, the fan and the annular wing I am expecting, conservatively, 90 lbs.

My budget is really the limiting factor, If I had $20,000 and access to some really top end equipment I could make something with 1000 lbs thrust from a 32" pulsejet. I will leave it to you guys to ponder how I am packing anywhere near that much thrust in a 32" engine without detonations, and dont guess diesel fuel :)

Eric

[Eric]

Dang your going to have to be more specific, there are various methods that increase different things such as:

maximize thrust

maximize fuel efficiency

ballanced thrust and efficiency

reduce noise

increase noise (yes you can make your engine even louder!)

or use the engine to create a massive cloud of water mist on a freezing cold day which then freezes into a nice evenly distributed layer of ice.

I can imagine Jerry must have some fun winter time dynafog testing stories.

Eric

[Mike Everman]

27.5 from a tuned "classic" chinese

Fantastic! The rest, well, I can't wait to see. It's really quite phenominal how much wasted heat there is to use!

Congratulations, Eric. That's some amazing results. Don't tell me any more, I should test mine by Monday. Not like you'll be publicizing this yet anyway.

What though is the effective sfc, considering water mass expended?

[Eric]

Are you thinking along the lines of having the water counted as fuel?

From a price standpoint the water is a lot cheaper :) but on the propulsion side the volume and mass would be a factor.

Maybe we could make up a unit like the fuel cost-pound per pound thrust per hour. Or maybe something more scientific if people use different fuels....

maybe the fuel btu-pound-cost-density-availability at walmart per pound thrust per hour.

I think I was telling Bill that things can be tuned so that you have a "water based fuel additive" to have the same fuel flow and add extra water for max thrust, or a "water based fuel substitute" where you reduce the throttle but achieve the same overall thrust by adding water. The two require slighly different approaches and consumption rates.

There is a ton of waste heat, the trick is to convert the most efficient way to produce heat into the most efficient way to produce thrust.

Eric