The effect of spray angle on the combustion and emission performance of a separated swirl combustion system in a diesel engine

To improve air efficiency in the center and squish areas of the combustion chamber, a new separated swirl combustion system (SSCS) was developed. It became necessary to find the optimal spray angle for the SSCS. This study aims to bridge this gap. It was found there were two peaks in the indicated power of the SSCS that occurred as a result of changing the spray angles. One peak occurred when the lower spray angle was 105°CA and the upper spray angle was 165°CA (herein referred to as spray angle scheme one). The other peak occurred when the lower spray angle was 75°CA and the upper spray angle was 165°CA (herein referred to as spray angle scheme two). To find the optimal spray angle, the combustion and emission performance of the two schemes was tested under different speeds, loads and excess air coefficients in a single-cylinder engine. The experiment results show that the SSCS experiences a greater reduction in fuel consumption and soot emission under spray angle scheme one: fuel consumption decreased by approximately 1.6%–8.3% and soot emission decreased by approximately 16.16%–36.64%. Therefore, it can be concluded that the optimal lower spray angle in the SSCS is 105°CA, and the optimal upper spray angle is 165°CA. The simulation results show that the lower spray colliding with the first circular ridge benefits the fuel/air mixture in the cylinder, such that the equivalence ratio is smaller under spray angle scheme one. Therefore, spray angle scheme one creates a more uniform fuel/air mixture, consumes less fuel, improves thermal efficiency and reduces soot emission.