A Study on Reduction of Heat Loss by Optimizing Combustion Chamber Shape
Challenge - A method to improve fuel consumption in diesel engines is to enhance their theoretical thermal efficiency by increasing their compression ratio. This results in an increase in heat loss due to the elevation of the concomitant in-cylinder temperature and the expansion of the impingement area between fuel spray and chamber wall. Therefore, reducing heat loss to the chamber wall is important to effectively benefit from a high compression ratio.
Solution - To meet this challenge, in this study, we optimized the combustion chamber shape using the three-dimensional computational fluid dynamics (CFD) simulation software, CONVERGE, and integrated it with modeFRONTIER. Input variables were coordinates of the five points defining the chamber shape and spray angle. Constraints were added to these coordinate values to prevent the edge of chamber shape. Evaluation criteria consisted of heat loss minimization and cumulative heat release and cumulative work maximizations. The multiobjective genetic algorithm MOGA-II was used in this study.
Benefits - The combustion chamber optimized with modeFRONTIER improved fuel consumption under high load and advanced injection timing conditions. A weak premixed combustion was observed, as predicted by the CFD calculation. The thermal balance analysis also revealed that heat loss from the cylinder decreased while exhaust loss increased. The optimized chamber improved fuel consumption by 3.2% compared with the baseline design.