What types of emissions do gasoline, LPG and natural gas engines produce?
The major emissions from spark-ignited gasoline, LPG and natural gas engines are carbon monoxide (CO), hydrocarbons (HC), and oxides of nitrogen (NOx). Unlike diesel engines, particulate emissions are very low. For spark-ignited engines, emissions depend heavily on engine tune-up and air-fuel ratio. In engines tuned overly rich, carbon monoxide levels can far exceed those found in diesel engines. Carbon monoxide levels in rich tuned spark-ignited engines can exceed 2% CO at the tailpipe, a potentially dangerous level if the engine operates in a poorly ventilated confined space. Starting in 2004, many spark-ignited engines over 25 hp for off-road machinery came factory equipped with a three-way catalyst and closed loop air-fuel ratio control. For older vehicles operating in confined spaces, retrofit of an oxidation catalyst or three-way catalyst with air-fuel ratio controller is worth considering.
