IMPACT OF FUEL, INJECTION TYPE AND AFTER-TREATMENT SYSTEM ON PARTICULATE EMISSIONS OF LIGHT-DUTY VEHICLES USING DIFFERENT FUELS ON FTP-75 AND HWFET TEST CYCLES

The characteristics of particulate emission, in relation to factors such as fuel, injection type, after-treatment system and test cycle, were investigated. Five light-duty vehicles with different fuel, injection types and after-treatment systems - Compressed Natural Gas (CNG), Gasoline (Port Injection/Direct injection), and Diesel (with/without Diesel Particulate Filter (DPF)) - were tested on Federal Test Procedure (FTP) -75 and Highway Fuel Economy Test (HWFET) cycles. Particulate emissions were measured using a TSI 3090 Engine Exhaust Particle Sizer (EEPS) and Horiba Solid Particulate Counting system (SPCS). For the FTP-75 cycle, the DPF-equipped diesel vehicle showed the lowest particulate emission for the EEPS system, while CNG showed the lowest emission for the SPCS system due to the difference between the two measurement systems. However, the DPF-equipped diesel showed the least PN emission for both EEPS and SPCS method on the HWFET test cycle. Except for the DPF-equipped diesel, fuels with lighter molecular weight generated fewer particulates. Aside from fuel-type, the status of the engine was the most important factor determining particulate emission. When the engine was cold, a large number of particulates is formed regardless of engine-operating conditions. In contrast, warm engines form particulates only if the load on the engine is high enough, and the absolute magnitude is also lower than during the cold-start condition.