A gas engine is an engine running on a gas, such as coal gas, producer gas, biogas, landfill gas, or natural gas.
A gas engine is an internal combustion engine which runs on a gas fuel, such as coal gas, producer gas, biogas, landfill gas or natural gas. In the UK, the term is unambiguous. In the US, due to the widespread use of "gas" as an abbreviation for gasoline, such an engine might also be called a gaseous-fueled engine or natural gas engine or spark ignited. Generally the term gas engine refers to a heavy-duty industrial engine capable of running continuously at full load for periods approaching a high fraction of 8,760 hours per year, unlike a gasoline automobile engine, which is lightweight, high-revving and typically runs for no more than 4,000 hours in its entire life. Typical power ranges from 10 kW (13 hp) to 4,000 kW (5,364 hp).
Source: Wikipedia - Gas engine