Studies on alternative fuels are being pursued actively in the Engines and Unconventional Fuels laboratory of Indian Institute of Technology, Delhi. Use of gaseous fuels such as compressed natural gas and hydrogen have been elaborately investigated. Tests have been carried out in various engine configurations using specially designed injection system. Tests conducted on existing spark ignition engine fuelled with compressed natural gas exhibited better thermal efficiency and lower levels of NO_x with respect to baseline gasoline operation. Since CNG-fuelled engines often result in slow flame propagation, hydrogen which has fast burning characteristics was added to the existing system to improve the combustion characteristics. This was reflected in drastic improvement in emission characteristics and increase in lean burn limit. The emissions of HC, CO,CO₂
decreased with increasing percentage of hydrogen but NO_x
was found to increase. Efficiency values vary with hydrogen amount, equivalence ratio.The experiments clearly indicate that addition of hydrogen to existing CNG operated engine improves the combustion and emission characteristics.