The QD-88 lives!!

hinote · Post by **hinote** » Fri Apr 23, 2004 12:22 am

hinote wrote:
mk wrote:Congratulations again to you, Bill and Milsavljevic!!
REALLY impressive work!
Hearing (or rather reading) such "good news" in pj developement just makes these "fire pipes" more and more interesting...
The QD series is a single-inlet design, and owes its heritage to the SNECMA Ecrevisse.

My experience with the 4-tube Kentfield, although positive, would lead me to recommend a single-inlet design if possible--to avoid the complications of construction and fuel feed.

Geezo-Pete guys--I KNOW I'm getting old now!

I was sure the referenced post said something about "five pipes".

Sorry 'bout that!--I looked through the wrong part of my bifocals.

Yes--these things are definitely FIRE-pipes.

Bill H.
Acoustic Propulsion Concepts

Post by **Mike Everman** » Fri Apr 23, 2004 1:21 am

Bill, that's a good one!

milisavljevic · Post by **milisavljevic** » Fri Apr 23, 2004 11:02 am

DELETED.

Rossco · Post by **Rossco** » Fri Apr 23, 2004 12:55 pm

Guys, im honoured!

This is of course going to be straight then hey!
I am looking foward to seeing your adaptation and even more so, the thrust comparison. You gotta get it in an wind tunnel! Thats where i think this intake has potential!
Keep me posted.

Rossco.

PS, Ross Gordon, but i get it around either way so much i get confused!

Post by **Mike Everman** » Fri Apr 23, 2004 1:47 pm

Ahhh. Tis a beautiful thing!

sam · Post by **sam** » Fri Apr 23, 2004 2:05 pm

milisavljevic,
your results are very impressive. What exactly is this Cronje score that you use? It ceratinly cant be a thermal efficiency. I think I've read Cronje's thesis and I dont remember him deriving a performance parameter as you describe. Was it from a different publication? Can you explain it to the rest of us because without a physical meaning the numbers dont really have any meaning to me (and probably others).
Thanks,
Sam

Pieter van Boven · Post by **Pieter van Boven** » Fri Apr 23, 2004 2:51 pm

Bill and M,

Beautiful work!
Congratulations with these results!

Pieter van Boven.

Anthony · Post by **Anthony** » Fri Apr 23, 2004 3:00 pm

The first pic looks like it was taken with thermal imaging hehe.

153 pounds LPG bottle? Isn't that big? Anyway, the fuel consumption looks good to me. Congrats!

hinote · Post by **hinote** » Fri Apr 23, 2004 3:35 pm

Avenger wrote:The first pic looks like it was taken with thermal imaging hehe.

153 pounds LPG bottle? Isn't that big? Anyway, the fuel consumption looks good to me. Congrats!

No--the engine looked pretty much like that to the naked eye.

The bottle IS big--BTW you can see it in the second shot--it stands about 5 feet tall and holds 20 gallons. I'm using it because it doesn't have the restrictor in the shutoff valve that all the small "barbecue"-sized 5-gallon tanks have.

BTW max flow to the engine is achieved through the smallest commonly available ball valve--it's 1/8 NPT.

Also BTW (in the 2nd photo) you can see the engine starting to sag off to one side (not aligned vertically) as the combustion chamber metal is softening and deforming around the 2 hard mount points.

Bill H.
Acoustic Propulsion Concepts

hinote · Post by **hinote** » Fri Apr 23, 2004 3:43 pm

sam wrote:milisavljevic,
your results are very impressive. What exactly is this Cronje score that you use? It ceratinly cant be a thermal efficiency. I think I've read Cronje's thesis and I dont remember him deriving a performance parameter as you describe. Was it from a different publication? Can you explain it to the rest of us because without a physical meaning the numbers dont really have any meaning to me (and probably others).
Thanks,
Sam

As an experiment (to see if I'm correct) I'm going to attempt an explanation:

As I understand it, the Cronje score is the ratio of achieved combustion efficiency to its theoretically optimized maximum. That is, divide achieved by theoretical, to get a percentage.

As to the actual math involved in getting the 2 numbers, I'll let M. handle that portion.

BTW there's apparently some concern that we may approach (or even exceed!) the magic 100 score--which would debunk the formulas used.

But at least it creates a value that's useful for comparison.

Bill H.
Acoustic Propulsion Concepts

Anthony · Post by **Anthony** » Fri Apr 23, 2004 3:44 pm

hinote wrote:
Avenger wrote:The first pic looks like it was taken with thermal imaging hehe.

153 pounds LPG bottle? Isn't that big? Anyway, the fuel consumption looks good to me. Congrats!
No--the engine looked pretty much like that to the naked eye.

The bottle IS big--BTW you can see it in the second shot--it stands about 5 feet tall and holds 20 gallons. I'm using it because it doesn't have the restrictor in the shutoff valve that all the small "barbecue"-sized 5-gallon tanks have.

BTW max flow to the engine is achieved through the smallest commonly available ball valve--it's 1/8 NPT.

Also BTW (in the 2nd photo) you can see the engine starting to sag off to one side (not aligned vertically) as the combustion chamber metal is softening and deforming around the 2 hard mount points.

Bill H.
Acoustic Propulsion Concepts

I guessed it was real, it's only that the color of the pulsejet is weird.

I didn't see the tank first; that's almost an industrial one!

hinote · Post by **hinote** » Fri Apr 23, 2004 4:31 pm

Rossco wrote:Guys, im honoured!

This is of course going to be straight then hey!

Heck no--it doesn't make any real difference whether it's bent or not, performance-wise.

The current engine (the QD) is bent so we can measure total thrust conveniently--without the need to develop an efficient flow rectifier. Plus, it's easier to mount the shorter overall length.

It's easy to use a thrust plate to measure the flows from the separate ends of the engine--if you need to know.

Bill H.
Acoustic Propulsion Concepts

P.S.: The SNECMA patent on the Ecrevisse says the best place to bend the engine (if you're going to) is in the transition cone behind the combustion chamber--because the outflow velocitiy is lower there. Of course, we've bent the QD aft of that point--we should ask M. how much performance is being lost due to flow rectification at the u-bend.

Mark · Post by **Mark** » Sat Apr 24, 2004 1:00 am

Nice colors and nice scenery of the mountains in the distance.
Mark

hinote · Post by **hinote** » Sat Apr 24, 2004 3:42 am

Hello again to fellow PJ enthusiasts:

It's my turn to beat M. to this post.

I ran the QD-88 today at a low power level, and carefully measured thrust and fuel consumption to get as accurate a TSFC number as is possible with the current equipment. The thrust stand was double-checked for accuracy before and after the run.

Here's the numbers:

Run time: 10:00 minutes

Fuel consumption: 5.0 lb, plus or minus .5 lb.

Indicated steady thrust output: 17.5 lbf, plus or minus 1 lbf.

Using the numbers as recorded, I get a TSFC number of 1.71 lb/lbf/hr.

Now isn't THAT special!!

I have gone over the numbers several times to try and find any errors, but I sure can't find any. A number like this indicates very high efficiency for a pulsejet, IMHO.

I have an opinion about this, which is that the first-generation MFI injectors are showing their promise at the lower power levels, where the pressure-sensing modulation of fuel delivery is more effective.

I'm hoping M. will chime in on this. I'm also hoping I haven't made some stupid mastrake in the math to get this great TSFC number.

Holding my breath, until somebody else verifies.

Bill H.
Acoustic Propulsion Concepts

milisavljevic · Post by **milisavljevic** » Sat Apr 24, 2004 4:38 am

DELETED.