Optimization of combustion chamber geometry for the improved-double swirl combustion system based on the sensitivity analysis method

Based on the well-established double swirl combustion system (DSCS) for direct-injection diesel engines, a novel improved-double swirl combustion system (I-DSCS) has been proposed. Previous visualization experiment has verified the superiority of the I-DSCS in enhancing impinging spray diffusion and impinging flame propagation. To advance I-DSCS development from theoretical principle analysis toward engineering application, in this study, simulation research is conducted to investigate the effects of combustion chamber geometry on the fuel–air mixing and combustion performance of the I-DSCS. A sensitivity analysis method is adopted to evaluate the significance of various combustion chamber geometries on I-DSCS combustion performance. As the critical combustion chamber geometries that influence the I-DSCS performance considerably, the outer chamber diameter D O , inner-to-outer chamber diameter ratio D I / D O , and inner chamber volume ratio V I / V are optimized. In addition, the characteristic values of D I / D O , V I / V , and the inner chamber fuel mass fraction Φ are obtained. Accordingly, a method for designing the I-DSCS combustion chamber geometry and matching the optimal spray angle is proposed. Experimental research is conducted on a single-cylinder diesel engine to validate the simulation results. The experimental results reveal that, compared to the mature DSCS and baseline I-DSCS, the optimized I-DSCS achieves the lowest fuel consumption rate and soot emissions, as well as the highest in-cylinder pressure and heat release rate during the diffusion combustion process. More specifically, compared to the mature DSCS, the optimized I-DSCS reduces the fuel consumption rate and soot emissions by 10.2–16.8 g/kWh and 0.23–2.09 FSN, respectively.