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Soot emissions from direct-injection engines are sensitive to the fuel-air mixing process, and may vary between combustion cycles due to turbulence and injector variability. Conventional exhaust emissions measurements cannot resolve inter- or intra-cycle variations in particle emissions, which can be important during transient engine operations where a few cycles can disproportionately affect the total exhaust soot. The Fast Exhaust Nephelometer (FEN) is introduced here to use light scattering to measure particulate matter concentration and size near the exhaust port of an engine with a time resolution of better than one millisecond. The FEN operates at atmospheric pressure, sampling near the engine exhaust port and uses a laser diode to illuminate a small measurement volume. The scattered light is focused on two amplified photodiodes.

In direct-injection engines, combustion and emission formation is strongly affected by injection quality. Injection quality is related to mass-flow rate shape, momentum rate shape, stability of pulses as well as mechanical and hydraulic delays associated with fuel injection. Finding these injector characteristics aids the interpretation of engine experiments and design of new injection strategies. The goal of this study is to investigate the rate of momentum for the single and post injections for high-pressure direct-injection natural gas injectors. The momentum measurement method has been used before to study momentum rate of injection for single and split injections for diesel sprays. In this paper, a method of momentum measurement for gas injections is developed in order to present transient momentum rate shape during injection timing. In this method, a gas jet impinges perpendicularly on a pressure transducer surface.