Comparative study of engine control strategies for particulate emissions from direct injection light-duty vehicle fueled with gasoline and liquid phase liquefied petroleum gas (LPG)

To evaluate the potential of a dedicated direct injection liquefied petroleum gas (LPG-DI) vehicle, we investigated several engine control parameters that are closely related to the characteristics of mixture preparation and nano-particle emissions. The fuel supply circuit for the direct injection of LPG in liquid form was modified into a return-type system comprised of a three-way high pressure pump, a low pressure regulator, a brushless direct current (BLDC) pump, and an LPG tank. Particulate number (PN) and size distribution measurements were performed in FTP-75 and HWFET modes, and also using an engine test bench. The experimental results showed that significant PN emissions were produced during the cold start and the transient warm-up operations of the gasoline direct injection (GDI) vehicle; this production of particle emissions was due to application of split injection and catalyst heating function. A bimodal particle size of 10 < dp < 100 nm was formed in the GDI vehicle, whereas a sub 30 nm nuclei mode was mainly formed in the LPG-DI vehicle. Excessive particle formation during sudden acceleration of the GDI vehicle in the HWFET mode was improved with LPG fuel. The reduction rate of the PN concentration with LPG application reached approximately 98% (FTP-75 mode) and 99% (HWFET mode) compared to the GDI vehicle. The total PN concentration in the LPG-DI vehicle was significantly improved to 1.6 × 1010 (N/km) for the FTP-75 mode and 3.4 × 109 (N/km) for the HWFET mode.

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