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Spark Ignited Engine Vibration Signal

Spark Ignited Engine Vibration Signal

(OP)
Hello All,

I've got accelerometer data from a running engine and the signal is confusing me. I'm looking at time domain vibration data and I'm seeing some very high impulse spikes that seem to line up with firing frequency. I normally would expect this however these spikes are all positive, there is no negative g bounce back in the signal at all...it's possible I'm missing something obvious but I can think of a situation where an impulse signal from an accelerometer does not have an up and down portion to it...it spikes up to say 10G's, then comes back down to zero, then spikes up again to 10G's and comes back down to zero again...it never does a 10G's up and neg 10G's down and quick decay like I'd expect for an impulse signal. I've attached a picture of some of the time data.

I'm looking to see if anyone would have a physical explanation for how that signal could be created on a running engine. Is this normal? Am I just over thinking this? Any help would be useful, thank you.

Tyler

RE: Spark Ignited Engine Vibration Signal

can you post a picture of the engine, and the location and orientation of the sensor(s) ?

I picture if the sensor is oriented somewhat tangentially, it will be responding to torque variations on a flexibly mounted engine.

The torque jumps pretty high right around when the plug fires.
http://i260.photobucket.com/albums/ii3/cdcracing/t...

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