An efficient approach to improve thermal efficiency on a low-speed two-stroke marine diesel engine

Abstract

To increase the intensity of the swirl motion and further optimize the combustion characteristics, an efficient approach named cylinder gas recirculation (CGR) is proposed in this study. The effects of the CGR strategy on the swirl motion, process of fuel/air mixing, combustion characteristics, and energy distribution are investigated. Compared to the original case, the simulation results show that the CGR strategy can increase the swirl ratio with a 131.8 % increase at TDC, and the mass of cylinder recirculated gas only accounts for 3.65 % of the total mass of the charge in the cylinder. The enhanced swirl motion can improve the fuel/air mixing effect, and further optimize subsequent combustion characteristics. On the one hand, the STD value of the cases using the CGR strategy becomes smaller compared to the original case, showing the better mixing process of the fuel and surrounding charge in the cylinder. On the other hand, the enhanced swirl motion accelerates the combustion rate, specifically, the duration of CA50 ∼ CA90 of the CGR case and CGR-optimal case is reduced by 42.96 %, and 51.96 %, respectively. In the end, compared to the original case, the gross indicated work under the CGR and CGR-optimal case is increased by 0.61 % and 2.4 %, and the effective power output increases by 1.24 % and 4.84 %, respectively, which proves that the CGR strategy has great potential in improving thermal efficiency and reducing fuel consumption.