Fuel Line Pinch for throttle control effectiveness vs Butterfly valve

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Fuel Line Pinch for throttle control effectiveness vs Butterfly valve

Post by Car6on14 » Mon Aug 06, 2018 6:11 pm

Greetings all,
I am planning my first pulsejet powered craft and have been doing much research on throttling. I had thought my simple servo controlled fuel line pinch would be effective, but recently read rocket mans thread on reducing air flow. This thread seems to make good sense and I just would like to know some opinion on both. The pinch seems the easier of the 2 and I have the parts for it now, but I can keep my eye out for a simple throttle body if this would be better and allow my pulse just to throttle better and last longer... I am planning to run white gas, as it seems mine is jetted for this, and it sounds like its tolerant of running lean? but in the future Id like to try running E85 gas, which would require a 1.6mm jet...?

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Re: Fuel Line Pinch for throttle control effectiveness vs Butterfly valve

Post by Tegra » Mon Oct 22, 2018 1:06 pm

Hello Car6on14,

Belatedly, I'm willing to share the little I have, in the hope that it'll provoke some debate!

I'm not (yet) a pulse-jet builder, but have worked on 2-stroke, 4-stroke petrol/alco/gas/diesel engines on the dyno - back in the day.


Assuming that the throttled engine is still pulsing (which is not guaranteed) your decision needs to account for the fuel/air mixture ratio and its consequences.

The spark-ignition (petrol/gas/alcohol) engines usually run hotter when leaned out - the leaner mixture is usually slower-burning, so the piston is further down the bore and the flame then washes the walls of the cylinder as well as the combustion chamber, so more heat needs to be dissipated by the cooling system.

This may shift the hot-spots on either type of pulse-jet - the glow pattern on a valveless is indeed worth watching - but there is at least one reference in this forum to the blueing of valve reeds due to lean mixture, which would fit. Am I right that you are working with a valved motor? What configuration, please?

Carburettors and other fuel systems (eg petrol injection) usually aim to control the fuel/air mixture, so my suggestion would be that you might attempt both fuel and air control to get the throttle range you need.

I did that stuff as a grad student back in the 1960s, even got a quasi-closed loop system going with vacuum tubes (valves) and relays in the feedback loop from the exhaust gas sensor! Drift was a problem, oh yes.

Modern solid state electronics could sample the exhaust gas and provide feedback to a very simple electro-mechanical system using mostly off-the-shelf automotive hardware.

HTH, Ben

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