FWE IV - the 'Smooth Lady' runs and runs well.
However - the Smooth Lady is not perfect ...
First successful run was around dusk on Saturday, 03 Sep 2005. Air was about 80 degF and moderately humid. Propane delivered at 20 PSIG (flow adjusted via needle valve), starting air at 30 PSIG, spark ignition. The engine was held in my new vise, clamped about halfway along the tailpipe.
MAIN PROBLEM ENCOUNTERED -
I finally had to add a 3-inch pipe extension to get it to sustain, making the total length 24.5 inches.
There is a strange 'sputtering pulsation' mode with starting air and low fuel levels. Sustaining operation is not possible until you allow enough fuel flow to smooth this out - as soon as you have that level of fuel flow, you can add just a little more, kill the starting air and the engine is running.
Perfectly smooth running was observed over a wide range of fuel flows. I never did reach rich extinction with my regulated setup (20 PSIG max. available pressure and needle valve wide open). I have never been able to kill an FWE engine with too much fuel. This leads me to think that either the regulator, the needle valve and/or the 1/8-inch copper fuel line is too restrictive.
Very high temperature all over the chamber, and it comes to red heat very quickly (due, no doubt, to the thin steel used). The front dome is very hot - even the spark plug shell reaches red heat after a minute or two! (I thought this would ruin the little CM-6 plug for sure, but apparently not!) There is no visible tailpipe radiation anywhere along the pipe (remember, though, that I'm getting pretty effective heat sinking from that vise).
There is very heavy flame ejection from the intake, due to the orientation of the intake pipe. Good internal and ejected flame colors, indicative of good lean combustion. Unlike what was seen in the 'Short Lady', there is no 'cold spot' observable anywhere on the chamber. 'White hot' spark plug electrode and rim observable through the intake (not through the tailpipe, due to the weird orientation of the chamber cone).
COOLING DOWN -
The chamber shell cools down quickly, as would be expected with such thin material. Amusingly, the heavy oval-shaped weld all around the intake tube stays hot a long time as a sort of stretched-out, red-hot 'halo' (no doubt to symbolize the purity of this design ;-) I'll try to get a picture of this, just for fun. After cooldown, there was no distortion of the chamber noted, and a uniform blue-black oxidation covered the entire cone and dome. The vise was hot for a pretty long time after the run.
The Smooth Lady started easily and ran well after the embarrassing 3-inch length adjustment. I think the front dome of the chamber is running too hot, and I believe I should have used the severe turndown of the intake 'spout' as I showed in the intake detail plan. I would rather have a cold zone in the front than a red-hot spark plug (of course, the plug could be relocated elsewhere in the chamber and would still work, I'm sure).
Bruno - Did you observe anything like the 'sputtering pulsation' mode when starting the Fo Mi Chin II out at Burning Grape? I'm asking since the intake geometry / orientation of the Smooth Lady is somewhat similar. If not, perhaps this too is a symptom of the minimal intake 'spout' that I used. Does anyone know if a small Thermojet will demonstrate this effect during starting?
I will post photos here after I receive my next (mid-month) paycheck.