An experimental assessment of simultaneous reduction in vehicle tailpipe emissions employing desirability function analysis

In vehicles powered by fuel, the effort to minimize CO and HC emissions through various strategies leads to an increase in CO₂, contributing to global warming. This study aimed to experimentally assess the simultaneous reduction of vehicle tailpipe emissions of CO, HC, and CO₂ using desirability function analysis (DFA). On predetermined routes in Addis Ababa city, two vehicles were tested for on-road emissions at five various speeds and on five various road slopes using a portable emissions tester. Surface plots were used to display how the tailpipe emissions of CO₂, CO, and HC vary with changes in vehicle speed and road gradient. The DFA results revealed that the optimal speed for simultaneous reduction of CO, HC, and CO₂ emissions was 40 km/h on a flat route and 30 km/h on a 2-degree uphill, with composite desirability of 0.83 and 0.72, respectively. This study found that a speed of 30 km/h on a flat road increased CO₂ by 2.82%, CO by 18.97%, and HC by 5.28% compared to an optimized vehicle speed of 40 km/h. On a 2-degree gradient, a vehicle traveling at 20 km/h exhibited a 4% increase in CO₂ emissions, a 23.92% increase in CO emissions, and a 1.26% decrease in HC emissions compared to the optimized speed of 30 km/h. Adjusting speed limits according to road gradients is recommended to minimize vehicle tailpipe emissions simultaneously using DFA. This approach contributes to lowering air pollution by reducing pollutant emissions from vehicles through optimized speeds.