Effects of EGR and Injection Strategies on the Performance and Emissions of a Two-Stroke Marine Diesel Engine

摘要

Clean combustion is critical for marine engines to meet the Tier III emission regulation. In this paper, the effects of EGR and injection strategies (including injection pressure, injection timing as well as multiple injection technology) on the performance and emissions of a 2-stroke, low speed marine diesel engine were investigated by using computational fluid dynamics (CFD) simulations to reach the IMO Tier III NO_x emissions target and reduce the fuel consumption rate. Due to the large length scale of the marine engine, RANS simulation was performed in combination with the CTC-SHELL combustion model. Based on the simulation model, the variation of the cylinder pressure curve, the average temperature in the cylinder, the combustion heat release rate and the emission characteristics were studied. The results show that, on the basis of the Tier II-level prototype engine, 30% EGR rate can effectively reduce the NO_x emission to the Tier III target, while it also causes the deterioration of fuel consumption rate; appropriate matching injection pressure and injection timing can obtain better fuel consumption rate at different EGR rates; pilot injection has the potential for simultaneously reducing NO_x and fuel consumption, a small PMF (2%) with SOMI-SOPI (10°CA) has the lowest fuel consumption rate, while the pilot injection strategy with 5% PMF+10° CA (SOMI-SOPI) has the best potential to reduce NO_x emission. In the contest of using EGR, through synergistic optimization of pilot-injection, injection pressure and injection timing, the IMO Tier III target can be met while remaining a relatively good fuel consumption rate.