Over the past decade, improved performance has given advanced gas engines a special role in numerous applications. High-density gas engines with BMEP values exceeding 2MPa and power generation efficiency exceeding 45% are now widely available. The performance parameters of advanced lean burn gas engines such as thermal efficiency and BMEP now nearly equal those of diesel engines. Despite higher thermal efficiency, these designs have successfully maintained low emissions, particularly NOx emissions. Nevertheless, problems associated with knocking, misfires, and spark plug service life have grown more serious with increasing BEMP. Micro pilot engines offer the advantage of fast and stable combustion over conventional spark ignition systems and represent a technical solution for such problems. They also provide long maintenance intervals. Niigata Power Systems has already introduced the 22AG series and 28AG micro pilot gas engines to the Japanese market. The five models in the 22AG series (namely 6, 8L and 12, 16, 18V) cover the power range from 1 to 3MW. The output of the 18V28AG is 6MW. The first delivered 8L22AG has operated daily and continuously from 2002, with no serious issues encountered to date over a total time of operation of roughly 60,000 hours, with minimum engine stops for scheduled maintenance every 4,000 hours. Environmental issues, cost effectiveness, energy conservation, and the ability to use waste alternative fuels are major concerns worldwide. Micro pilot gas engines can contribute in these areas by using refuse and synthesis gas—very low heat energy sources—as fuel. Synthesis gas contains hydrogen and carbon monoxide as combustible components. Micro pilot engines offer major potential advantages, making an examination of their NOx emission characteristics worthwhile. This paper discusses issues related to the NOx emissions of micro pilot gas engines.

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