droping frequency

[i ride sand]

hello, ive built a few pulsejets, first 3 failed, and most have suceeded since the first runner.
all of them have been built out of mild steel, and were hacked on untill they ran. so i decided to build one more out of stainless, and have proceeded to test run it.

i was running on acetylene (easiest fuel source at the time) and found that the frequency would drop as the throttle increased, then the engine would flame out. so, before i cut the exhaust and modify it, could it possibly run right on propane? i know the flame speed is different, as well as the temp. but i was not achieving very high throttle at all. it would throttle down very well, right down to the point of being able to yell over it. but the frequency dropped the whole time. my thoughts/experiance say the exaust needs to be shortened just a tad, but im not sure. i will post exact demensions a bit later, im on lunch break at the moment

[metiz]

Just like engines have a minimum size to run of off propane, Small engines have a maximum required size to run of off acetylene. There may be an "intermediate" size but we'll need some pics, dims and stuff to access that.

Most engines drop in frequency a bit when they're throttled up. nothing to worry about (not a clue why btw, maybe due to higher temps)

[i ride sand]

Just like engines have a minimum size to run of off propane, Small engines have a maximum required size to run of off acetylene.

that would make sense, the higher burn rate would mean that the gasses inside the engine would have to be accelerated throught the exhaust and intakes much faster than propane, therefore (in my mind) the lengths would have to be modified to properly resonate and "breath".

quote="metiz"]Most engines drop in frequency a bit when they're throttled up. [/quote]
thats my experiance too, but this is dropping vastly. several hundred hertz. im currently working on getting a propane fueling system going, ill test run it again once thats done. the last rig i had is 100 miles away and was very leaky... made for an interesting fireball one time... at least my engines are in a good solid vice so they cant go flying! (just teasing)... but i did make a rather large escoppette and ran it at the high school, after that everyone knew me as "the kid that tried to blow everyone up". when all the tough guys in the class are backing away, and your just standing there, people tend to look at you a wee bit different...