The effect of the shape of the EOI was investigated through a pressure-modulated injection system in order to improve the understanding of the last portion of the traditional diesel diffusion combustion process. Here, the combustion recession at EOI is when the combustion of a mixing controlled diesel jet recedes backwards toward the fuel injector nozzle orifice.
Combustion recession was observed using combustion luminosity imaging filtered at 309 nm to capture OH* chemiluminescence and 430 nm to capture CH* chemiluminescence, although soot Natural Luminosity (NL) will also be visible in these measurements. Experimental spray vessel results show that for relatively slow EOI decelerations below 1 ×106 to 2 ×106 m/s2, combustion strongly recesses completely back to the nozzle in both OH* and CH*/NL imaging. 1-D jet mixing calculations add support that this strong recession is indeed fuel rich. Ambient temperature (860 to 915K range) and dilution (18.5 to 20.9% O2 range) influence the weaker combustion recession, mainly for OH* chemiluminescence imaging. The influence of temperature variation is stronger than the influence of dilution variation over the present ranges. Weak combustion recession under high EOI deceleration conditions shows only OH* recession, as characterized by temporal LOL analyses, with an absence of significant CH*/NL combustion recession. Additionally, the strength of the combustion recession can be inversely ordered by EOI deceleration for a given ambient condition. Rate shape and EOI deceleration had a stronger influence on combustion recession behavior than ambient conditions. The link between combustion recession at EOI and engine emissions is further discussed with multiple hypotheses proposed.
