Investigation of the effects of liquefied nitrogen on performance and emissions of a spark ignition engine operated with different fuels

Engine researchers work intensively to improve the performance and to reduce environmental damages of gasoline engines. When the desired performance and emission values cannot be achieved in the case of gasoline use, studies are being made to determine the availability of alternative fuels that can replace gasoline. Hence, it is difficult to get out of standards in gasoline-powered engines and to meet performance requirements with alternate fuels; researchers evaluate the performance characteristics and environmental effects of mixtures of fuels with different additives. In this study, effects of liquid nitrogen addition on performance and NO formation of a single-cylinder four-stroke SI engine using different alternative fuels (methane, methanol, toluene, iso-octane, propane, hexane, ethanol, benzene) and gasoline are examined and compared. A zero dimensional two-zone simulation model which was validated on previous experimental studies is used to define the effects of nitrogen addition. Results showed that nitrogen addition increased power output, power density and torque while decreasing thermal efficiency and NO emission with all fuels. The maximum power output increment is about 33% for methanol, minimum increment is about 21% for benzene and toluene. Maximum thermal efficiency decrease is about 8,5% for benzene and toluene and minimum decrease is less than 1% for methanol. In addition, NO emissions for all fuels used in the study have been reduced significantly by nitrogen addition. After examining the effects of nitrogen addition, effects of changing engine design and operation parameters has been investigated in case of running the engine with 50% mass of nitrogen addition for different fuels.