Quantifying start emissions and impact of reducing cold and warm starts for gasoline and hybrid vehicles

Abstract

In this study, a portable emissions measurement system (PEMS) was used to measure trip emissions of a gasoline vehicle (2020 Hyundai Tucson Preferred) and a hybrid vehicle (2020 Ford Fusion Hybrid Titanium) under various soak times (12 h–1 min) along two driving routes in Toronto, Canada (highway and city core). A new method was proposed to identify start emissions in a PEMS test, employing confidence intervals (CIs) of hot-running emission rates, and distributions of hot-running coolant and catalyst temperatures. In addition, GPS data reflecting one-week of travel for 82 drivers in Toronto were used to quantify the contributions of start emissions under realistic trip schedules and to estimate the benefits of reducing cold and warm starts. In Toronto, over 95% of the trips have a soak time over 1 h, and over 33% of the trips are within 5 km. Compared to the Tucson, the Fusion Hybrid generates approximately 43.4% less carbon dioxide (CO2) and 77.7% less nitrogen oxides (NOx), but 183.6% more carbon monoxide (CO) and 15.8% more ultrafine particles (measured in particle number, PN), on a representative Toronto drive schedule. For soak times greater than 12 h and trip distance less than 5 km, the contributions of starts to total trip emissions for CO2, CO, NOx, and PN are in the ranges of 13.4%–70.0%, 93.5%–99.9%, 22.3%–73.9%, and 80.3%–99.3%, respectively, for the Tucson. For the Fusion Hybrid, these contributions are in the ranges of 31.4%–95.6%, 25.1%–73.2%, 58.7%–95.9%, and 25.6%–87.7%. With engine and catalyst preheating, total trip emissions for CO2, CO, NOx, and PN decrease on average by 5.1%, 81.3%, 20.2%, and 48.1%, respectively, for the Tucson. For the Fusion Hybrid, these reductions are 10.4%, 16.3%, 40.8%, and 7.9%.