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Lean operation of natural gas fired reciprocating engines has been the preferred mode of operation as it allows low NOx emissions and simultaneous high overall efficiencies. In such engines, the operation point is often close to where the ignition boundary and the knock limiting boundary cross-over. While knocking is, to a large extent, limited by engine design, ignition of lean-mixtures is limited by the mode of ignition. Since significant benefits can be achieved by extending the lean-ignition limits, many groups have been researching alternate ways to achieve ignition reliably. One of the methods, laser ignition, appears promising as it achieves ignition at high pressures and under lean conditions relatively easily. However, most of the current knowledge about laser ignition is based on measurements performed at room temperature. In this paper, ignition studies on methane-air mixtures under in-cylinder conditions are presented.

Reduction in NOx in light and medium duty diesel engines, without the requirement for Catalyst Converter or Exhaust Gas Recirculation (EGR) and meeting the U.S. emission standards is an important challenge. This paper shows how injection rate shaping should be performed to reduce NOx while engine performance and soot formation remain almost constant. Effects of intercooler with and without rate shaping on NOx reduction will be investigated. Results indicated that the rate shaping was an effective technique to reduce NOx at some operating condition. Combined effects of intercooler and rate shaping have shown a reduction of NOx by 50% for some operating conditions. At idle condition a split injection was found to be a good solution for NOx reduction. A combustion-simulation computer program was used in this analysis for six different operating conditions.