Optical Investigation Into Wall Wetting From Late-Cycle Post-Injections Used for Diesel Particulate Filter Regeneration

Wall wetting phenomena were investigated in a light-duty diesel optical engine, operating under typical diesel particulate filter regeneration conditions, through the use of liquid spray imaging during late-cycle post-injections. Three post-injection timings were explored: (1) an “early” timing (44.5 deg after top dead center (aTDC)) where high ambient temperatures and densities were expected to decrease the liquid penetration, (2) a “conventional” timing (78.5 deg aTDC) that is typically used to produce the necessary aftertreatment regeneration exhaust conditions, and (3) a “late” timing (133.5 deg aTDC) where in-cylinder flows generated by exhaust valve opening-induced blowdown can disrupt the liquid penetration. In addition to a 2007 U.S. certification diesel fuel, a palm-derived B20 biodiesel blend and a soy-derived B100 biodiesel were examined since liquid spray impingement is thought to worsen for biodiesel blends due to higher fuel distillation temperature, density, and viscosity. No significant wall wetting was observed for the early post-injection. However, considerable impingement occurred for the conventional and late post-injections. Liquid penetration and persistence of liquid fuel in the cylinder were found to increase with biodiesel content, while exhaust blowdown flows were ineffective in reducing the severity of wall wetting. Negligible distortion of jet structure was observed for the liquid spray at the late post-injection. Short pulse durations decreased the severity of liquid penetration with the soy-derived biodiesel during the early post-injection but were otherwise ineffective.