Otto cycle in the context of "Six-stroke engine"

The Diesel cycle is a combustion process of a reciprocating internal combustion engine. In it, fuel is ignited by heat generated during the compression of air in the combustion chamber, into which fuel is then injected. This is in contrast to igniting the fuel-air mixture with a spark plug as in the Otto cycle (four-stroke/petrol) engine. Diesel engines are used in aircraft, automobiles, power generation, diesel–electric locomotives, and both surface ships and submarines.

The Diesel cycle is assumed to have constant pressure during the initial part of the combustion phase (${\displaystyle V_{2}}$ to ${\displaystyle V_{3}}$ in the diagram, below). This is an idealized mathematical model: real physical diesels do have an increase in pressure during this period, but it is less pronounced than in the Otto cycle. In contrast, the idealized Otto cycle of a gasoline engine approximates a constant volume process during that phase.

Engine efficiency of thermal engines is the relationship between the total energy contained in the fuel, and the amount of energy used to perform useful work. There are two classifications of thermal engines-

1. Internal combustion (gasoline, diesel and gas turbine-Brayton cycle engines) and
2. External combustion engines (steam piston, steam turbine, and the Stirling cycle engine).

Each of these engines has thermal efficiency characteristics that are unique to it.

The Otto engine is a large stationary single-cylinder internal combustion four-stroke engine, designed by the German Nicolaus Otto. It was a low-RPM machine, and only fired every other stroke due to the Otto cycle, also designed by Otto.