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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.

Experimental studies have been undertaken on a single-cylinder HPCR diesel engine with a compression ratio of 15.5:1 to explore the effect of fuel injection strategy on cycle by cycle stability. The influence of the number, separation and quantity of pilot injections on the coefficient of variation of IMEP has been investigated at -20°C, 1000 rev/min, post-start idling conditions. Injection strategy and glow plug temperature trade-off has also been investigated at a range of soak temperatures. Up to four pilot injections have been used. For timing of the main injection near to the optimum, CoVIMEP values of 10% or better can be achieved. Closer spacing of injections improved stability and extended the range of timings to meet target stability. The best combinations of pilot number and pilot quantity varied with total fuel delivered.

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.

U.S. federal vehicle emission standards effective in 2007 require tight control of NOx and hydrocarbon emissions. For light-duty vehicles, the current standard of Tier 2 Bin 5 is about 0.07 g/mi NOx and 0.09 g/mi NMOG (non-methane organic gases) at 120,000 mi. However, the proposed future standard is 0.03 g/mi for NMOG + NOx (~SULEV30) at 150,000 mi. There is a significant improvement needed in catalyst system efficiencies for diesel vehicles to achieve the future standard, mainly during cold start. In this study, a less than 6000 lbs diesel truck equipped with an advanced urea Selective Catalytic Reduction (SCR) system was used to pursue lower tailpipe emissions with an emphasis on vehicle calibration and catalyst package. The calibration was tuned by optimizing exhaust gas recirculation (EGR) fuel injection and cold start strategy to generate desirable engine-out emissions balanced with reasonable temperatures.

Soot formation and distribution inside the cylinder of a light-duty direct injection diesel engine, have been predicted using Kiva-3v CFD software. Pathlines of soot particles traced from specific in-cylinder locations and crank angle instants have been explored using the results for cylinder charge motion predicted by the Kiva-3v code. Pathlines are determined assuming soot particles are massless and follow charge motion. Coagulation and agglomeration have not been taken into account. High rates of soot formation dominate during and just after the injection. Oxidation becomes dominant after the injection has terminated and throughout the power stroke. Computed soot pathlines show that soot particles formed just below the fuel spray axis during the early injection period are more likely to travel to the cylinder wall boundary layer. Soot particles above the fuel spray have lesser tendency to be conveyed to the cylinder wall.

This paper studies the effect of cooled EGR on fuel consumption and anti-knock performance of a boosted port fuel injection (PFI) SI engine. Experimental results show that the cooled EGR increases the thermal efficiency by 2%∼18% depending on the operation conditions. Compared to low load operations, more improvements of the thermal efficiency are obtained at higher loads, primarily owing to the enhanced anti-knock performance, advanced combustion phasing, elimination of fuel-rich operations as well as reduced heat transfer loss with cooled EGR. The anti-knock performance of cooled EGR provides further potential to improve the thermal efficiency by increasing the compression ratio. To this end, a 1-D thermodynamic model of the engine is built and calibrated using the GT-Power code. A knock prediction correlation considering EGR is developed and validated with the experimental data.

Diesel combustion and emissions is largely spray and mixing controlled. Spray and combustion models enable characterization over a range of conditions to understand optimum combustion strategies. The validity of models depends on the inputs, including the rate of injection profile of the injector. One method to measure the rate of injection is to measure the momentum, where the injected fuel spray is directed onto a force transducer which provides measurements of momentum flux. From this the mass flow rate is calculated. In this study, the impact of impingement distance, the distance from injector nozzle exit to the anvil connected to the force transducer, is characterized over a range of 2 - 12 mm. This characterization includes the impact of the distance on the momentum flux signal in both magnitude and shape. At longer impingement distances, it is hypothesized that a peak in momentum could occur due to increasing velocity of fuel injected as the pintle fully opens.