Evaluating the Efficiency of a Conventional Diesel Oxidation Catalyst for Dual-Fuel RCCI Diesel-Gasoline Combustion 2018-01-1729

Reactivity controlled compression ignition (RCCI) combustion has demonstrated to be able to avoid the NOx-soot trade-off appearing during conventional diesel combustion (CDC), with similar or better thermal efficiency than CDC under a wide variety of engine platforms. However, a major challenge of this concept comes from the high hydrocarbon (HC) and carbon monoxide (CO) emission levels, which are orders of magnitude higher than CDC and similar to those of port fuel injected (PFI) gasoline engines. The higher HC and CO emissions combined with the lower exhaust temperatures during RCCI operation present a challenge for current exhaust aftertreatment technologies.

RCCI has been successfully implemented on different compression ignition engine platforms with only minor modifications on the combustion system to include a PFI for feeding the engine with the low reactivity fuel. Moving to the aftertreatment systems, the objective of this experimental work is to evaluate the potential of a conventional diesel oxidation catalyst (DOC) for light-duty diesel engines when operating under dual-fuel RCCI diesel-gasoline combustion. For this purpose, measurements of gas emissions have been done upstream and downstream the DOC under different conditions while keeping constant the combustion phasing (CA50). Under these conditions, the sensitivity of the DOC conversion efficiency to variations of the engine settings that govern RCCI combustion (gasoline fraction, EGR, diesel SOI and engine speed) has been addressed. The engine tests were done at 4 bar IMEP, where the DOC requirements are high. Later, a one-dimensional DOC model developed in GT-Power using the experimental data. After its calibration, the 1-D model was used to define the proper DOC geometry to achieve a suitable HC and CO conversion efficiency (95%-98%) for the RCCI combustion mode.