This document discusses different types of internal combustion engines. It describes petrol engines as spark ignition engines with a compression ratio of 5-10.5 that use a spark plug, and diesel engines as compression ignition engines with a higher compression ratio of 12-25 that use a fuel injector. It also explains four-stroke engines go through intake, compression, power, and exhaust strokes, while two-stroke engines only have upward and downward strokes. Finally, it states the efficiency of an engine depends on its compression ratio, with higher compression ratios resulting in higher efficiency.