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Visualization of transient single- and two-phase jets created by diesel engine injectors Chepakovich, Alexander C.

Abstract

Propagation of single- and two-phase transient jets for direct injection of natural gas and natural gas with pilot (liquid) into diesel engines has been investigated experimentally by optical methods. The jets created by three (diesel, gas, and gas-diesel) electronically controlled injectors, were observed in a constant-volume chamber charged with air, the pressure of which varied from atmospheric to 3.5 MPa. The injection (gas-to-chamber) pressure ratio varied from 1.5 to 8 for gas injection. The liquid-gas mass ratio of the injected mixture for the dual-fuel injection varied from 0 to 0.9. The liquid injected with the gas was finely atomized by the gas due to the acceleration of the gas within the nozzle. Schlieren and laser sheet systems were used for flow visualization. A single-shot video camera was used for image acquisition. Series of pictures of a jet at different time intervals from the beginning of injection were taken to determine the jet penetration rate. The jet penetration rate was observed to be independent of the chamber pressure as long as the injection pressure ratio was constant and was proportional to the square root of time from the virtual beginning of the jet (defined as the beginning of an equivalent impulsively started jet) for continuous injection. The jet penetration rate was found to depend weakly on the liquid-gas mass ratio of injected two-phase mixture. The experimentally observed penetration rate of a methane jet was compared with that of a carbon dioxide jet, and no significant difference was detected. The jet penetration rate was compared with calculations done using an integral model of the jet. The model proved to be fairly accurate in predicting the round jet propagation rate if the experimental data was plotted relative to the virtual beginning of the jet. The model was not as accurate in predicting the conical sheet jet propagation.

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