What causes hydraulic lock in large radial engines?

Hydraulic lock in large radial engines is primarily caused by oil accumulation in the combustion chamber. This phenomenon occurs when oil from the crankcase leaks past the piston rings, particularly during engine shutdown or when the engine is not running. When oil collects in the combustion chamber, it can create a situation where the piston is unable to compress the liquid, leading to a locked condition where the engine cannot turn over.

In radial engines, where the design involves a complex arrangement of cylinders and a unique ignition process, this issue is particularly critical. If oil collects excessively, it can prevent the pistons from moving, which can lead to severe engine damage when an attempt is made to start the engine.

While factors such as fuel vaporization, fuel mixture richness, and piston wear do affect engine performance, they are not directly linked to the hydraulic lock condition. Fuel vaporization typically concerns issues related to combustion efficiency, excessively rich mixtures can lead to fouling but not hydraulic lock, and piston wear, while it can impact engine function, does not directly contribute to the oil accumulation that results in hydraulic locking. Thus, oil accumulation is the definitive cause of hydraulic lock in this context.