Uncooled EGR as a Means of Limiting Wall-Wetting under Early Direct Injection Conditions 2009-01-0665
Collision of injected fuel spray against the cylinder liner (wall-wetting) is one of the main hurdles that must be overcome in order for early direct injection Premixed Charge Compression Ignition (EDI PCCI) combustion to become a viable alternative for conventional DI diesel combustion. Preferably, the prevention of wall-wetting should be realized in a way of selecting appropriate (most favorable) operating conditions (EGR level, intake temperature, injection timing-strategy etc.) rather than mechanical modification of an engine (combustion chamber shape, injector replacement etc.). This paper presents the effect of external uncooled EGR (different fraction) on wall-wetting issues specified by two parameters, i.e. measured smoke number (experiment) and liquid spray penetration (model). Experiments performed in a dedicated heavy-duty direct injected (HDDI) diesel engine suggest that the elevation of intake temperature caused by delivery of external uncooled exhaust gases led to significant reduction in wall wetting. This is combined with IMEP improvement. In-house spray- and ignition modeling was used to gain insight into the measured trends.