The Opacity Test as a Tool to Determine Combustion Efficiency in Diesel Engines and the PM2.5 Emission Rate

Objective: To evaluate the relationship between exhaust gas opacity and PM2.5 particulate matter emission rate in diesel engines, in order to determine whether the opacity test can be used as an indirect indicator of pollutant emissions. Theoretical framework: Combustion in diesel engines generates particulate matter, especially PM2.5, which poses a significant risk to human health. In the city of Quito, the Vehicle Technical Inspection (RTV) uses opacity measurements to assess combustion efficiency, without directly measuring PM2.5 emissions. Although previous studies have explored the correlation between opacity and particulate matter, the influence of injection pressure on this relationship has not been addressed. Method: Static tests (according to NTE INEN 2202:2000) and dynamic tests (Lug Down) were performed on a diesel engine with a mechanical injection system, varying the injection pressure at 10, 12, 14, 15.5, and 18 MPa. During each test, opacity levels and PM2.5 concentrations were simultaneously recorded. The data were analyzed using simple linear regression to determine the correlation between the two variables. Results and Discussion: An inverse relationship was observed between injection pressure and both opacity and PM2.5 levels, with a strong correlation between the latter two. These findings suggest that opacity may serve as a reliable indirect indicator of fine particulate matter emissions. Research Implications: The results may contribute to more effective environmental regulations and to the optimization of vehicle maintenance programs, thereby reducing the environmental impact of the diesel vehicle fleet. Originality/Value: This study provides an innovative approach by correlating opacity and PM2.5 levels as a function of injection pressure, offering a more efficient method for monitoring emissions in diesel engines.