Comparative study of regulated and unregulated toxic emissions characteristics from a spark ignition direct injection light-duty vehicle fueled with gasoline and liquid phase LPG (liquefied petroleum gas)

In this study, to evaluate the potential of a dedicated liquefied petroleum gas-direct injection (LPG-DI) vehicle, regulated and unregulated emissions from a light-duty gasoline direct injection (GDI) vehicle were compared. The vehicle tests were performed on a chassis dynamometer with constant volume sampler (CVS) over the federal test procedure (FTP)-75, highway fuel economy test (HWFET), and new European driving cycle (NEDC), which include the engine starting, transient and warm-up operation. The emissions of total hydrocarbon (THC) as well as nitrogen oxides (NOx) and nano-particles from the LPG-DI vehicle showed significantly superior performance relative to gasoline with excellent gaseous mixture preparation and low carbon fuel. The CO₂ emission of the LPG-DI vehicle decreased approximately 4-6% compared to the GDI vehicle. Aldehydes formation was influenced by vehicle test modes, such as the proportions of vehicle low speed patterns as well as long idle duration and the inclusion of engine warm-up periods. Formaldehyde, acetaldehyde, and acrolein compounds significantly increased with the LPG-DI vehicle, and this increase was related with partial oxidation during the combustion process of butane and propane. Except for the slightly increase in the HWFET mode, strong decreases in BTEX were observed with the application of LPG fuel in the FTP-75 and NEDC mode. It was found that the regulated and unregulated emissions were closely related to both the vehicle driving patterns and fuel compositions.