Performance of a diesel oxidation catalyst under diesel-gasoline reactivity controlled compression ignition combustion conditions

Abstract

Reactivity controlled compression ignition is a promising combustion strategy due to the combination of excellent thermal efficiency with ultra-low nitrogen oxides and particulate matter raw emissions. However, very high levels of unburned hydrocarbons and carbon monoxide emissions are found. It limits the reactivity controlled compression ignition use at very low loads and presents an additional challenge for the diesel oxidation catalyst. The low exhaust temperature and high carbon monoxide and hydrocarbon concentration can penalise the catalyst conversion efficiency. The objective of this work is to evaluate the response of an automotive diesel oxidation catalyst when used for reactivity controlled compression ignition combustion combining experimental and modelling approaches. For this purpose, dedicated tests have been done using diesel-gasoline as fuel combination in a single-cylinder engine. This way, the catalyst conversion efficiency has been determined within a wide operating range covering hydrocarbon adsorption conditions and the pollutants abatement dependence on the mass flow and temperature. The experimental results in the full-size catalyst has been analysed by modelling. A lumped diesel oxidation catalyst model has been applied to extend the results to multi-cylinder engine conditions and to determine the light-off curves for both carbon monoxide and hydrocarbons. These tests evidence the penalty in light-off temperature due to high pollutants mass fraction, which promotes inhibition limitations to the reaction rate.