Abstract
An experimental investigation was carried out to investigate Particulate Number (PN) emissions from a modern, small-capacity Gasoline Direct Injection (GDI) engine. The first part of the study focused on improving measurement repeatability using the Cambustion DMS-500 device. Results showed that sampling near the exhaust valve – while dampening the pressure oscillations in the sampling line – can significantly improve the repeatability. It was also found that uncontrolled phenomena such as deposition in the exhaust system from earlier engine operation can undermine the accuracy of measurements taken at tailpipe level. The second part of the work investigated PN emissions from three types of gasoline fuel, Pump-grade, Performance and Reference. Fuel chemical composition was found to have an appreciable impact on PN, but the magnitude of this effect differs in various operating points, being more pronounced at higher engine load. The Reference fuel was found to have the lowest PN emission tendency, conceivably because of its lower aromatics, olefins and heavy hydrocarbons content. A sweep of operating parameters showed that higher injection pressure reduces PN, but the extent of the reduction depends on fuel physical properties such as volatility.
Highlights
Gasoline Direct Injection (GDI) engines offer higher efficiency and lower CO2 emissions compared to PortFuel Injection (PFI) gasoline engines,[1] but with the drawback of higher particulate matter (PM) emission.[2,3,4,5,6] Considering the stringent regulations on particulate mass and particulate number (PN), the need for developing and deepening the knowledge around the complexities of PM formation and measurements in GDI engines is evident
Part 1: Repeatability of particulate mass/number measurements. It has been suggested in literature[29,30] that soot particles and liquid hydrocarbon droplets/vapours might deposit/condense in the after-treatment system and be released later, when for instance the exhaust temperature is high enough to re-vaporise and release them, causing unexplained variations in PM measurements, which affect repeatability. This issue was examined in the current study by observing the effect of preconditioning the engine at two different running points (High and Low pre-conditioning) on subsequent PN measurement taken at the baseline condition
This could be attributed to the fact that the majority of particles in this size range may be in liquid phase.[30]
Summary
Gasoline Direct Injection (GDI) engines offer higher efficiency and lower CO2 emissions compared to PortFuel Injection (PFI) gasoline engines,[1] but with the drawback of higher particulate matter (PM) emission.[2,3,4,5,6] Considering the stringent regulations on particulate mass and particulate number (PN), the need for developing and deepening the knowledge around the complexities of PM formation and measurements in GDI engines is evident. Such knowledge is necessary to reduce PM emission tendencies at design level, and to develop simulation models for predicting PM emission accurately and inexpensively. Once the combustion starts the chemical composition of the fuel is decisive in setting the kinetics and chemical pathways through which PM is formed
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