Influence of cold-start time reduction on scooter emissions and fuel consumption over WMTC cycle

Abstract

Scooters with small displacement air-cooled engine which is technically mature and low cost have been widely used nowadays. Compared to water-cooled engines, the air-cooled engines have nothing like thermostat to speed up warm-up duration. The crankshaft of the air-cooled engine drives the cooling fan coaxially. Thus it starts cooling even at the cold start, which extends the warm-up duration. It harms THC emissions. Many studies have shown that speeding up engine warming up can reduce THC emissions. For a 2-wheel motorcycle of category L3e, in the face of the EURO5 emission standard that was implemented in 2020, the current THC emission of 380 mg/km will be revised down to 100 mg/km, with a reduction ratio of 73.68%, which is the most significant reduction among all polluting gases. Thus, the purpose of this study is to develop a low-cost double-layer fan cover with a function of automatic open and shut. It was installed in a commercially available motorcycle with a raw catalyst for WMTC test. The cooling air was blocked during the cold start, which results in the reduction of 20 s of cold-start time, a period of time from the vehicle starting from ambient conditions to the moment when the engine goes into closed loop mode. Also, the cold phase is reduced by 18.8%, which reduced 12.8% of THC raw emissions and achieved 1.6% fuel economy improvement.