System Approach for Compliance with Full Load Targets on a Wall Guided Diesel Combustion System 2008-01-0840

Low temperature combustion concept as HCCI is one of the most promising research ways to comply future emission regulations of Diesel passenger vehicles. IFP promoted this concept with NADI^™ (Narrow Angle Direct Injection) combustion design whose original approach lies on a fuel spray guided by the bowl central tip to the re-entrant. For full load operating range, one of the key issue for success is to use as much as possible available air in the combustion chamber in order to reach low value of air fuel ratio, and therefore high value of specific power and specific torque. In this study, engine tests on a single cylinder engine with NADI^™ concept are performed at full load; 3-D calculations as well as air/fuel mixing process visualizations in a constant volume vessel with optical access allowed to establish criteria for helping future combustion system design for full load operation. Accordingly, at low engine speed, a large bowl with a thin re-entrant is recommended because this configuration implies a weak interaction between fuel jets and the bowl central tip. At high engine speed, a large bowl with a thin re-entrant as well as a dedicated configuration to guarantee a strong interaction between fuel jets and the bowl central tip; this design promotes the fuel spray momentum conservation in order to get a well homogenized fuel vapor within piston bowl but also a good use of the air available in the squish area.