Misfire, Knock and NOx Mapping of a Laser Spark Ignited Single Cylinder Lean Burn Natural Gas Engine

Abstract

Evermore demanding market and legislative pressures require stationary lean burn natural gas engines to operate at higher efficiencies and reduced levels of emissions. Higher in-cylinder pressures and leaner air/fuel ratios are required in order to meet these demands. The performance and durability of spark plug ignition systems suffer as a result of the increase in spark energy required to maintain suitable engine operation under these conditions. Advancing the state of the art of ignition systems for these engines is critical to meeting increased performance requirements. Laser-spark ignition has shown potential to improve engine performance and ignition system durability to levels required meet or exceed projected requirements. This paper discusses testing which extends previous efforts [1] to include constant fueling knock, misfire, thermal efficiency, and NO x emissions mapping of a single cylinder lean burn natural gas engine. Tests are conducted using an open beam path laser spark ignition system and a conventional spark plug based system for contrast. Under the conditions tested, the laser-spark ignition system increased the total operating envelope of the engine by 46% when compared to the conventional ignition system. Due to a wider misfire margin using the laser spark system, NO x emissions were half the minimum value of the spark plug ignition system with no appreciable degradation in thermal efficiency. Hydrocarbon emissions were comparable for both systems. The results of the testing are discussed in detail.