Reciprocating engines are highly efficient.
Technology enhancements such as better combustion chamber design and controls that constantly optimize the air-fuel ratio increase engine efficiency. There have been many technical improvements that have improved engine reliability as well as extended the equipment life. Improvements in ceramic valve seat materials can easily double the life of engine valves between overhauls. This extends engine cylinder thus reducing maintenance costs and engine downtime. However, these emissions vary primarily with combustion technology and fuel.