International experience with compressed natural gas (CNG) as environmental friendly fuel

Environmental concerns relating to gaseous emissions from transport have led to growth in the use of compressed natural gas (CNG) as transportation fuel worldwide with over 19 million natural gas vehicles (NGVs) currently in operation. This paper reviews the environmental advantages of natural gas fuel, presenting laboratory and real world comparative emission performance of NGVs with diesel and gasoline fueled vehicles. The aim is to clarify the worldwide experience of NGVs in terms of various emission factors i.e. CO$$_{2}$$2, CO, NO$$_\mathrm{x}$$x, NMHC and PM. The paper provides a critical analysis of information collected and draws general conclusions on the world-wide NGVs experience. The results reveal that CNG in public transportation can contribute to the improvement of urban air, reduce adverse health effects and social costs of air pollution. It was observed that on a well-to-wheels basis, CNG produce less greenhouse gases as compared to conventional gasoline and diesel vehicles. The results showed that there is large variation in the resulted NMHC emission data of CNG fuel. Some studies reveal that CNG can significantly reduce NMHC emission while other concluded that CNG increase the NHMC emission.