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Spray-guided Gasoline Direct Injection

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					         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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posted:11/16/2012
language:English
pages:2