Question 38Motor Plants - Assistant Engineer

The correct answer is B) 12:1. The theoretical minimum compression ratio necessary to ensure compression ignition in a direct injection diesel engine is 12:1. This is because the high compression ratio in a diesel engine is required to generate enough heat and pressure to ignite the air-fuel mixture without the need for a spark, as in a gasoline engine. A compression ratio of at least 12:1 is typically needed to achieve this in a direct injection diesel engine. The other answer choices are incorrect because 10:1 would not provide sufficient compression, while 16:1 and 20:1 are higher than the minimum required for compression ignition in a direct injection diesel engine.