Natural Gas Vehicles - A Review of the State of the Art

This paper reviews the present state of the art in natural gas vehicles, focusing on engine technology and emissions. Natural gas engines generally show very low emissions of reactive hydrocarbons, carbon monoxide, and particulate matter, but NOx emissions can be fairly high. Approaches to NOx control include stoichiometric operation using a three-way catalyst and air-fuel ratio feedback, and «lean-burn/fast-burn» engines with NOx controlled through reduced flame temperature