Particulate Characterization of CNG Fuelled Public Transport Vehicles at Traffic Junctions

Compressed natural gas (CNG) is considered as cleaner fuel compared to gasoline and has emerged as an important alternate transport fuel in view of its abundant availability globally. CNG has been implemented in mass transport sector globally. This study explores the emission characteristics of two different classes of CNG operated vehicles used for public transportation in Indian Cities. One is a heavy-duty CNG bus and the other one is a light-duty CNG tempo. Both are very popular commuting vehicles in Indian cities. The number of such CNG vehicles is quite large therefore their emissions affect the health of traffic policemen, who are responsible for regulating the traffic during their long duty-hours. They are continuously exposed to harmful regulated and unregulated pollutants from such vehicles. Regulated gaseous emissions and particulate bound polyaromatic hydrocarbons (PAHs) were determined for both vehicles at different engine speeds at no load, which simulates typical traffic junction scenario. For the heavy-duty CNG operated bus, particulate number-size distribution and mass-size distributions were also evaluated. Carbon monoxide (CO), Hydrocarbons (HC) and nitric oxide (NO) emissions were found to be higher for the CNG operated bus compared to the CNG tempo. Particle bound PAHs were quite significant for CNG fuelled vehicles however they reduced at higher engine speeds. Particulate number emissions increased with increasing engine speed, especially in the accumulation mode (50-250 nm) for the heavy-duty CNG bus. Despite moderate increase in particle number emissions, particulate mass contributions of the accumulation mode particles increased significantly with increasing engine speed.