Assessment on the Impacts of Vehicle Speed and Slope on Tailpipe Emissions Using Desirability Function Analysis

Abstract

Pollutant emissions from vehicles can significantly increase when driving on a road with a positive slope, according to previous studies. In internal combustion engines, minimizing tailpipe emissions like carbon monoxide (CO) and hydrocarbon (HC) by using different strategies increases carbon dioxide (CO₂). This likely contributes to global warming through the greenhouse effect. This study aimed at determining the effect of road slope and vehicle speeds on tailpipe emissions, such as CO, HC, and CO₂. Full factorial analysis was employed for the design of the experiment. An experiment was conducted in Addis Ababa, Ethiopia, using a portable emissions analyser and Global Positioning System (GPS) to collect emissions data from passenger vehicles at a speed of 10, 20, 30, 40, and 50 km/h and road slopes of -2, 0, 2, 4, and 6 degrees. The regression models developed for CO₂, CO, and HC were acceptable, with R-squares of 98.0, 92.9, and 84.9 %, respectively. Finally, desirability function analysis was employed to simultaneously optimize the responses to identify optimum points that minimize CO, HC, and CO₂ formation. The most preferable speed to simultaneously reduce CO, HC, and CO₂ emissions was found to be 40 km/h on a level road and 30 km/hr on a 2-degree road slope with composite desirability of 0.83 and 0.72, respectively. As a conclusion, it is shown that the use of desirability function analysis can effectively be used to identify the optimum driving speed at which CO, HC, and CO₂ emissions are minimized simultaneously for the given road slope.