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The current trend toward more fuel efficient vehicles with lower emission levels has prompted development of new combustion techniques for use in gasoline engines. Stratified combustion has been shown to be a promising approach for increasing the fuel efficiency. However, this technique is hampered by drawbacks such as increased particulate and standard emissions. This study attempts to address the issues of increased emission levels by investigating the influence of high frequency ionizing ignition systems, 350 bar fuel injection pressure and various tumble levels on particulate emissions and combustion characteristics in an optical SGDI engine operated in stratified mode on isooctane. Tests were performed at one engine load of 2.63 bar BMEP and speed of 1200 rpm. Combustion was recorded with two high speed color cameras from bottom and side views using optical filters for OH and soot luminescence.

Gasoline and gasoline-ethanol sprays from an outward-opening piezo-injector were studied in a constant volume/pressure chamber using high-speed imaging and phase doppler anemometry (PDA) under stratified cold start conditions corresponding to a vehicle ambient temperature of 243 K (−30°C/−22°F); in-cylinder air pressure of 5 bar, air temperature of 350 K (−30°C/−22°F) and fuel temperature of 243 K. The effects of varying in-cylinder pressure and temperature, fuel injection pressure and fuel temperature on the formation of gasoline, E75 and pure ethanol sprays were investigated. The results indicate that fuel composition affects spray behaviour, but less than expected. Furthermore, varying the temperature of the fuel or the air surrounding the spray also had minor effects. As expected, the fuel injection pressure was found to have the strongest influence on spray formation under stratified conditions.

A Spray-Guided (SG) Direct-Injection (DI) Spark-Ignition (SI) engine is widely recognized to be a promising technology capable for substantially reducing fuel consumption and carbon dioxide emissions. Accordingly, there is a strong need for developing models of some effects specific to stratified turbulent burning under conditions of elevated and rapidly varying pressure. Two such effects were addressed in the present work by performing unsteady three-dimensional URANS simulations of stratified turbulent combustion in a SG DISI engine. First, a simple method of evaluation equilibrium combustion temperature, implemented into the CFD code OpenFOAM®, was improved in order to take into account the dissociation of the combustion products. Second, stratified turbulent combustion is affected by fluctuations in mixture composition. A widely used approach to modeling this effect consists of invoking a presumed Probability Density Function (PDF) for mixture fraction f.

This study investigated how the amount of dilution applied can be extended while maintaining normal engine operation in a GDI engine. Adding exhaust gases or air to a stoichiometric air/fuel mixture yields several advantages regarding fuel consumption and engine out emissions. The aim of this paper is to reduce fuel consumption by means of diluted combustion, an advanced ignition system and adjusted valve timing. Tests were performed on a Volvo four-cylinder engine equipped with a dual coil ignition system. This system made it possible to extend the ignition duration and current. Furthermore, a sweep was performed in valve timing and type of dilution, i.e., air or exhaust gases. While maintaining a CoV in IMEP < 5%, the DCI system was able to extend the maximum lambda value by 0.1 - 0.15. Minimizing valve overlap increased lambda by an additional 0.1.

The emissions from a parallel hybrid combustion engine and electric powertrain operated on a modified New European Drive Cycle (NEDC) was investigated in order to determine the relation between emissions and the road and engine load profile. The effect of simulated electric motor assistance during accelerations on emissions was investigated as a means to reduce particulate and gaseous emissions. The time resolved particulate number and size distribution was measured in addition to gaseous emissions. The combustion engine was a downsized, three cylinder spark ignited direct injection (SIDI) turbocharged engine fuelled with gasoline. Electric motor assistance during accelerations was simulated by reduction of the vehicle mass. This reduced engine load during accelerations. Fuel rich engine transients occurred during accelerations. NOx emissions were reduced with electric assistance due to a reduction in engine load.