Combination of High EGR Rates and Multiple Injection Strategies to Reduce Pollutant Emissions

This paper describes mid-load experimental tests combining massive EGR rates and multiple injection strategies. Influence of very high EGR rates on combustion has been reviewed, and a response-surface-modeling tool has been used to present main results. Outputs from this empirical model did highlight a dramatic soot increase when oxygen concentration is reduced. The empirical model based on experimental results model was also used to define more precisely the EGR rate needed to reach US 2010 NOx target. This EGR rate being defined, some investigation has been made on dual-injection strategies combining a main injection with an early pilot injection. Both quantity and timing of pilot injection were varied, and experimental results showed large benefits of this strategy to reduce soot emissions without significant increase of NOx emissions or fuel consumption. Better results were also experienced with the addition of a close post-injection. However, the use of early pilot injection with a wide spray angle has major drawbacks for the durability of cylinder liners, piston rings and oil. These drawbacks have been experienced during the tests and presented with the other mechanical issues induced by massive EGR rates.