Spray-guided Gasoline Direct Injection Objectives • Assess the scope and limitations of spray-guided Gasoline Direct Injection combustion system concepts • Investigate the aspects of different suitable fuel injectors Establish design criteria for the geometry and operational parameters of such systems. • Investigate the potential to reduce cold start emissions by utilizing stratified charge combustion Potential A stable, misfire free lean operating spray-guided Gasoline Direct Injection combustion system have an estimated fuel consumption reduction potential of about 20% in the new European driving cycle (NEDC) which means 20% reduction in CO2 emissions. In fact for typical highway driving (low load) the fuel consumption reduction in (lean) mode can be up to 40% higher than the same engine operating in homogeneous mode. Cold start emissions is a well known problem in the automotive industry. However, by utilizing stratified cold starts the engine out emissions of unburned fuel prior to catalyst light-off can be dramatically reduced. Stratified cold starts give us a bonus thanks to the improved vaporization rate; it also enables cold starts on alternative fuels such as alcohols. This is good since alcohol fuels need much more energy to vaporize than gasoline. Why does this combustion system give a fuel The challenge: consumption reduction? Why is it difficult to design a spray-guided stratified The fuel consumption reduction is obtained in stratified combustion system which runs stable and without (late injection combustion mode) and is due to: misfires? The challenge lies in how to create a suitable stratified fuel cloud which must meet the following • Much lower heat losses requirements: • No pump losses • Higher thermodynamic efficiency due to: • Good stratification • Higher compression ratio • Fuel/air ratio within ignitibility limits at spark • Lean burn (lambda > 1) • Not too small and not too steep fuel gradients • Higher volumetric efficiency • Good mixing ability • Fast burn • Low cycle-to-cycle variations • Low sensibility to in-cylinder motion • Low sensibility to back pressure • Not too high cross-flow velocities at the spark • Not too low and not to high turbulence levels at the spark • Not too sensitive to flash-boiling Fuel distribution with laser spectroscopy (LIF) in optical engine. Spray formation from a fuel injector. Photograph from a spray chamber.
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