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Spark-ignition direct-injection (SIDI) gasoline engine, especially in downsized boosted engine platform, has proven to be one of the most promising concepts to improve vehicle fuel economy. SIDI engines are also getting a larger share of the gasoline engine market which is traditionally dominated by the port fuel injection (PFI) engines in the U.S., European and Chinese vehicles. However, higher particle number emissions associated with operating the engine at higher loads pose additional challenges for meeting future stringent emissions regulations. In this study, the potential of using multiple injection strategies (double injection and triple injection strategy during the intake stroke in homogeneous combustion mode) to reduce particle number emissions in a 2.0 liter boosted SIDI gasoline engine at 1000 rpm, 11 bar BMEP condition was investigated using Horiba MEXA SPCS1000 PN measurement instrument.

Spray atomization and evaporation are expected to be improved by injecting fuel at a superheated state. However, the breakup mechanism and evaporation processes of superheated sprays have not been clarified. In previous studies [1], the multi-hole spray flow-field on the vertical plane through the spray axis was investigated by using high-speed particle image velocimetry (PIV). The results showed that the spray plumes collapse to the spray axis under high superheat conditions. It's also proven that the superheat degree is the predominant factor influencing the structure and the flow-field of the spray. To further understand this process, the interaction among spray plumes on three cross-sectional planes under various superheated conditions is investigated. In this study, n-hexane sprays generated from an eight-hole DI injector were measured using a high-speed PIV system. The results provide insight to the spray-collapse processes and the interaction between the spray plumes.

The flash boiling phenomenon occurs at some operating conditions when fuel is directly injected into the cylinder of a homogeneous charge spark ignition direct injection (SIDI) engine due to the higher temperature of the injected fuel and lower back pressure. A flash boiling spray has significantly different characteristics from a conventional DI gasoline spray. In this paper, the planar laser-induced exciplex fluorescence (PLIEF) technique with two specially designed dopants of the fluorobenzene (FB) and the diethyl-methyl-amine (DEMA) in n-hexane was implemented to investigate the liquid and vapor phases of sprays from a multi-hole injector. A vapor phase calibration was carried out to quantitatively correlate the fluorescence signal with vapor concentration. The quantitative vapor concentration distribution is then obtained by applying the calibration.