Carbon monoxide: the new emission challenge for diesel passenger cars

This article concerns the emissions of carbon monoxide (CO) from diesel engines, the measurement of these emissions and calibration-based measures to reduce them. CO is formed in hydrocarbon fuel combustion and oxidised to carbon dioxide. A diesel oxidation catalyst (DOC) is employed in passenger cars to reduce CO and hydrocarbon emissions using exhaust-gas residual oxygen. Thermal aging and contamination reduce DOC activity during use. This study tested a diesel engine with two-stage turbo-charging, with an auxiliaries management system to reduce fuel consumption. The cut in consumption resulted in increased emissions. Two separate approaches to reduce CO emissions were based on engine calibration methods. CO raw emissions can be reduced by optimising pilot injection quantities and shortening injection intervals, optimising rail pressure and increasing air mass. CO conversion can be improved through increasing exhaust gas temperature, by retarding main injection and reducing rail pressure, splitting main injection into two events, and activating the throttle valve and exhaust gas recirculation (EGR) while coasting. The preferred measure was a combination of splitting the main injection and activating the EGR in coasting.