(I) The simplest type of engine classification is doubtless by reference to the kind of fuel used. (II) Nevertheless, reciprocating engines may be divided more fundamentally into those running on the Otto cycle (spark ignition) and those running on Akrody's and Diesel's cycles (compression ignition). (Ill) The former are usually used for small scale power generation. (IV) The latter, which burn heavy oil are of two types, slow speed for ships and high speed for motor vehicles. (V) Subsequently, improvements in engine design appeared at an amazing speed.