Browse Publications Technical Papers 2019-01-0294
2019-04-02

An Optical and Numerical Characterization of Directly Injected Compressed Natural Gas Jet Development at Engine-Relevant Conditions 2019-01-0294

Compressed natural gas (CNG) is an attractive, alternative fuel for spark-ignited (SI), internal combustion (IC) engines due to its high octane rating, and low energy-specific CO2 emissions compared with gasoline. Directly-injected (DI) CNG in SI engines has the potential to dramatically decrease vehicles’ carbon emissions; however, optimization of DI CNG fueling systems requires a thorough understanding of the behavior of CNG jets in an engine environment. This paper presents optical and numerical characterizations of DI gaseous jets, using methane as a surrogate for CNG. Experiments are conducted in a non-reacting, constant volume chamber (CVC) using prototype injector hardware at conditions relevant to modern DI engines. The schlieren imaging technique is employed to investigate how the extent of methane jets is impacted by changing thermodynamic conditions in the fuel rail and chamber. Post-processing of these optical results presents challenges because of the similarity between the density of methane and the background nitrogen, therefore a methodology to interpret the jet extent in the high-speed movies is proposed and used to quantify methane jet propagation and structure. The processed experimental results are compared against predictions by 1D gas dynamics and previously established jet penetration correlations. Exploiting the theory of underexpanded gas jets and using simple arguments, the experimental trends are qualitatively captured by the 1D model.

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