PISTON FAILURE BY PREIGNITION AND DETONATION

Operation of a CFR and a Wright G-200 single-cylinder engine with excessive spark advance under high load and temperature conditions led to characteristic preignition-type piston failures and permitted study of the factors and mechanism involved. It is shown that the local peak piston temperature determines whether and where piston failure takes place. This temperature is determined by the general temperature level and temperature distribution on the piston, and by the effects of local blow-by and scuffing.

In these laboratory tests made with new and clean engine parts under closely controlled operating conditions, the piston failure could be produced or averted at will by adjustment of two blow-by controlling factors: piston-cylinder clearance and ring gap position. It is likely that in field operation other factors may have similar effects, for example, sticking of the rings, scuffing due to foreign particles or faulty lubrication, or irregularities in the power or temperature control of the engine.

The progress of the piston burning mechanism is illustrated by photographs and compared with the quite dissimilar detonation type piston failure.