UFLOW1D experiments with the "Squirrel"

[toakreon]

(This is in response to Larry’s earlier observations)

Hi Larry,

I've had a go at "tweaking" the Squirrel in UFLOW1D to try and (a) get the velocity node at 25% of the total engine length from the front and (b) try to ALSO get it in the middle of the combustion chamber at the same time - hope I understood the suggestion correctly!

I actually got pretty close with only a marginal change - just extending the inlet 2cm to 18cm.

This gave me:-

* An overall length of engine of 92cm.

* A Velocity Node at 24cm from the front (26%), which also happened to be right in the very middle of the combustion chamber ... :)

I then defined three output points:-

* Plotted RED - at 2cm, ie just inside the inlet.

* Plotted GREEN - at 24cm, ie the middle of the combustion chamber and velocity node.

* Plotted YELLOW - at 90cm, ie just inside the tail end of the tailpipe.

I then did a "temporal" plot of these three points over a period of 0.03seconds (which turns out to be almost exactly five periods). Attached!

Is this the sort of thing I should be looking for?

John

[larry cottrill]

John -

To me, this really looks pretty good. When I look at this, I am not so much interested in the first cycle (where your initial high pressure simulates the blast) but rather what happens after that. What I see there is a series of cycles that diminish very little over time. This just tells me that you have a good resonant pipe that can sustain.

What I usually do (this was suggested by Graham) is start with smoothly distributed LOW pressure, as described earlier, and look at this same kind of series, paying particular attention to the intake and exhaust velocity curves and how rapidly they decay in amplitude - the slower the better. Several of my earlier posts on the Lady Anne Boleyn, etc. illustrate this. It is very easy to set up the initial condition in UFLOW1D for this.

I have no doubt that your pipe will sustain. I think your temperature estimates are a little low, but that wouldn't change things much except that in real life your velocity node will probably be a little further forward, not right at the center of the chamber. No problem, really. Straight pipe "linear" designs are fairly forgiving of small variations.

L Cottrill

[toakreon]

Thanks Larry,

Now it seems I need to BUILD the thing, knock up a "Rosscojector" and give it a go ... :)

John

[larry cottrill]

Now it seems I need to BUILD the thing, knock up a "Rosscojector" and give it a go ... :)

John -

As Rossco himself has said, the problem with the Rosscojector is that it will make even a bad engine run! Wouldn't you rather see your first engine run by actually getting it reasonably well-tuned? I thought so ...

Try a "lemniscate nozzle" - it's about as easy to do as the Rosscojector, but gives good mixing with LOW pressure propane delivery. On a "linear" motor like this, try positioning it at about the "far" end of the straight intake section (rig it so you can play with the exact position a little). With one of these, you MIGHT even get halfway decent throttleability!

Good luck!

L Cottrill

[toakreon]

OK ... :)

A Lemniscate it'll be ...

John