Question 80Motor Plants - Assistant Engineer

The correct answer is C) method of igniting fuel. The main operating characteristic that distinguishes diesel engines from other internal combustion engines is the method of igniting the fuel. In a diesel engine, the fuel is ignited by the heat generated through the compression of air, rather than by a spark as in a gasoline engine. This compression ignition is the defining feature of diesel engines, which sets them apart from other types of internal combustion engines. The other answer choices are incorrect because they do not represent the primary distinguishing characteristic of diesel engines. The method of air supply, cooling system, and valve operating mechanism are important features, but they are not the fundamental difference between diesel and other internal combustion engines.