Natural gas engine uses natural gas as the fuel source. This is used for vehicles, water pumping systems, compressors and chillers. This engine requires maintenance just like a car engine. These are louder than an electric motor and require sound attenuation. These can be naturally aspirated or turbocharged. In naturally aspirated engines, air is drawn into the engine at atmospheric pressure. Turbocharged engines use the exhaust to drive a small turbofan that compresses the intake of air. The turbofan compresses the air fuel mixture so more molecules are squeezed into the cylinder. When the mixture is ignited, more energy is released. Thus a turbocharged engine will provide more shaft work out than a naturally aspirated engine of the same size.