Effect of the valve timing and the coolant temperature on particulate emissions from a gasoline direct-injection engine fuelled with gasoline and with a gasoline-ethanol blend

Variable-valve-timing technology and ethanol addition to gasoline are both considered to be effective strategies for better performance and potential improvement in the fuel economy in gasoline engines. In this study, a Jaguar V8, naturally aspirated spray-guided direct-injection engine was operated with four different valve-timing combinations using an unleaded gasoline and a gasoline-10 vol% ethanol blend. The internal exhaust gas recirculation rate and the in-cylinder gas temperature were modelled for different valve-timing strategies. The results showed that a high valve overlap led to high internal exhaust gas recirculation and a high charge temperature, which evidently improved the fuel spray atomization and reduced the particulate matter emissions. Adding 10 vol% ethanol led to a rise in the total particle number and the total particle mass in emissions by a factor of up to 2 under warm-engine conditions (with a coolant temperature of 90 degrees C) but led to a reduction in the total particle number and the total particle mass in emissions by up to two-thirds under cold conditions (with a coolant temperature of 20 degrees C). Thermogravimetric analysis tests were conducted to analyse the compositions of filter-borne particulate matter emissions, and more than 75 mass % organic material was always present. All measurements are reported for both pre- and post-three-way-catalyst samples, the latter always showing a significant reduction (a factor of about 2) in the particulate matter emissions.