Emissions test results from diesel buses, with and without oxidation-catalyst and regenerating particle-trap, and CNG buses with three-way catalyst in India

Eight Euro II compliant buses, using diesel with different levels of sulphur, and with and without emission control devices, and two Euro II compliant CNG buses with three-way catalyst were tested on a chassis dynamometer using Mumbai Driving Cycle. Emissions of PM from buses using ultra-low sulphur (50 ppm maximum) diesel and fitted with particle traps and those from CNG-powered buses were comparable; CO and HC were lower from diesel buses and NO_x was lower from CNG buses. Although progressive reduction of sulphur lowered PM emissions, their levels were significantly lower when coupled with appropriate emission control devices.