NOX EMISSIONS FROM A DIESEL-ENGINE FUELED WITH NATURAL-GAS

The performance and emission characteristics of a single-cylinder two- stroke diesel engine fueled with direct injection of natural gas entra ined with pilot diesel ignition enhancer have been measured. The therm al efficiency of the optimum gas-diesel operation was shown to exceed that of the conventional diesel at full load, but to be less at part l oad where the ignition delay was excessive. At high load, where the NO x emission problem is most serious, substantial reduction in NOx emiss ion rate was obtained with delay of injection timing and also with use of exhaust gas recirculation. Measured cylinder pressures were used w ith a three-zone combustion model to determine ignition delay and the temperatures of the burned gas. The predicted NOx emissions based on e quilibrium concentration of NO at the maximum burned gas temperature w ere found to correlate closely with exhaust pipe measurements of NOx.