eli5 What’s happening when an engine stalls from low RPM?

Question

eli5 What’s happening when an engine stalls from low RPM?

In: 21

Answer 1

After the spark fires, it has to produce enough momentum to return the piston for the exhaust stroke, then the intake stroke, and finally, and most difficultly, the compression stroke. At lower speeds it won’t have enough stored energy to complete the cycle.

Tiny motors in things like RC cars are nearly weightless, which is why they can’t run below 1500 rpm or so, as soon as they hit the compression stroke they lose all momentum.