Question 77Motor Plants - 1st Asst/Chief

The correct answer is A) the ignition of unburned fuel and air in the crankcase. Crankcase explosions in propulsion diesel engines occur when unburned fuel and air in the crankcase are ignited, usually due to a malfunction or improper operation of the engine. This can happen if there is a failure in the fuel system or if the engine is not running properly, allowing unburned fuel to enter the crankcase and mix with the air. The ignition of this fuel-air mixture can then cause a crankcase explosion. The other options are incorrect because they do not directly cause the ignition of the fuel-air mixture in the crankcase. Option B refers to the dilution of the crankcase oil, which can be a consequence of the explosion but not the cause. Options C and D describe conditions that may contribute to the buildup of fuel and air in the crankcase, but do not directly explain the ignition that leads to the explosion.