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The spray characteristics is the key to achieve the clean combustion in diesel engines and the in-cylinder conditions are one of the factors affecting the spray process. In this work, the diesel spray characteristics were studied over a range of injection pressures and ambient pressures in a constant volume chamber and a single-hole common rail diesel injector was used. The present work is to decouple the effects of ambient pressure and ambient density on near-field spray processes by using different ambient gas (N2, and CO2). The spray processes were captured by a Photron SA X2 camera with speed of 300,000 fps and resolution of 256 by 80 pixels. The spray processes were analyzed in terms of penetration length and spray tip velocity. Difference in penetration length and tip velocity were found at the same ambient density and/or ambient pressure when different ambient gases were used.

Spray atomization, spray-wall impingement, and mixture formation are key factors in affecting the particulate matter (PM) emission in gasoline direct injection (GDI) engines. Current knowledge of wall-wetting phenomenon and mixture formation are mostly based on the studies that the fuel is injected at ordinary temperature and various ambient conditions. In the real GDI engine, the fuel pipe and injector are always heated up by the pump and the engine body, especially at hot engine conditions, thus the fuel temperature is always higher than the ordinary temperature, and the relevant research is still limited. The aim of this study is to numerically investigate the spray, spray-wall impingement, and mixture formation characteristics under different fuel temperature conditions, so as to provide theoretical support in optimizing the combustion performance and further reducing the PM emission of GDI engines.

Low-temperature heat release (LTHR) in spark-ignited internal combustion engines is a critical step toward the occurrence of auto-ignition, which can lead to an undesirable phenomenon known as engine knock. Hence, correct predictions of LTHR are of utmost importance to improve the understanding of knock and enable techniques aimed at controlling it. While LTHR is typically obscured by the deflagration following the spark ignition, extremely late ignition timings can lead to LTHR occurrence prior to the spark, i.e., pre-spark heat release (PSHR). In this research, PSHR in a boosted direct-injection SI engine was numerically investigated using three-dimensional computational fluid dynamics (CFD). A hybrid approach was used, based on the G-equation model for representing the turbulent flame front and the multi-zone well-stirred reactor model for tracking the chemical reactions within the unburnt region.

The near-field diesel spray process in diesel engines is the intermediate one that connects the in-nozzle flow with far field spray process and high-speed imaging techniques with high-quality temporal and spatial resolution are required in order to record this short process (< 300 μs). In this study, a high-speed charge-coupled-device (CCD) camera with the speed of up to 1,000,000 fps was used to study the near-field spray process for a diesel injector with different nozzle diameters. The tests were carried out in a constant volume vessel over a range of injection pressure and ambient pressure in non-evaporating conditions. The observed zone of the spray was where penetration length is less than 18 mm. The development of spray penetration length against time after start of injection (ASOI) was used to evaluate the spray process. The significant difference on spray penetration length development is found when the nozzle diameter varied.