Experiments were conducted to compare the mixing and combustion properties of natural gas jets issuing from elliptical and round nozzle holes within an optically accessible combustion bomb. High speed images of combustion events were captured and analyzed along with cylinder pressure and heat release data. Hydrocarbon measurements of the combustion products were used to calculate combustion efficiencies. The elliptical nozzle holes were found to produce a more evenly distributed heat release profile, with a smoother transition from premixed to diffusion burning. The elliptical nozzle jets also produced far more luminous flames. Ignition delay and combustion efficiency were not found to vary significantly with nozzle design. The use of elliptical nozzles as a method of mixing enhancement for gaseous engine fuels remains potentially viable, although further work is necessary to fully quantify the performance and emissions impacts.

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