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indicator diagram & rpm limit

by Mark Hills in 2 Stroke Technical Questions 7 years ago

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Re: indicator diagram & rpm limit

by Glenn Martin » 7 years ago

Glenn Martin

3 281 798

Hi Mark,
generally manufacturers do not develop indicator diagrams for engines. You can grab a standard 2 stroke indicator diagram and scale the area under the curve to match the continuous torque. This would give you and indication of the peak.

However this is not what you actually need. The torque is modified by the inertia of all the moving components from the pistons, rings, con rods, cranks, bearings crankshaft windage, gear train etc. to the peak and trough of the output on the output shaft is far less that the peak would indicate.

I once measures instantaneous cylinder pressure at each degree of rotation and went through the exercise of calculating the resultant based on all of the above. Interesting exercise...

However If I really wanted to know the peaks for design purposes it gets even more complicated.

A designer I worked with when working for one of the major aircraft engine manufacturers said the drive train was designed for a worst case of a backfire pulse at the worst rpm then they added a 100% margin.

Most people seem to base the size on experience and testing.

Naturally torsionally soft couplings in the drive train decrease the peak loads enormously

As to RPM limit there are several very good and cheap aftermarket 2 stroke ignition systems you do not need to develop your own.

The rotax one is perfectly adequate.

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