Abstract

The present paper investigates the effect of triple injection strategies on aftertreatment thermal management of a diesel engine both experimentally and computationally to reduce cold start emissions. The experiments were performed using a 1.9 L four-cylinder, turbocharged compression ignition engine with diesel fuel. The injection strategy made use of a late post injection to reduce catalyst light-off time. The pilot and main injection are fixed, and the post injection timing is swept later into the expansion stroke to increase exhaust enthalpy available to heat the aftertreatment. To further understand the source of hydrocarbon (HC) emissions from late injections, equivalent experiments were conducted with a mixture of n-heptane and iso-octane that matched the reactivity of the diesel fuel. The increased volatility of PRF~34 suppressed liquid fuel impingement on the cylinder liner, which isolated liner impingement as a possible source of HC emissions. Simulations were also performed for the present engine configuration and operating conditions in a sector mesh using CONVERGE. The chemical kinetics of the diesel fuel were modeled with a reduced n-heptane model. Experimental and computational studies find HC emissions increase for both fuels as the post injection timing is retarded. Overmixing of fuel and air is found to be the cause of the increase in HC emissions and moderate levels of exhaust gas recirculation (EGR) intensifies the increase.

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