The Performance Optimization And Experimental Research On Marine Diesel-LNG Engine

To adapt to the increasingly strict marine environmental protection regulation, many ships began to adopt the transformed diesel-LNG dual-fuel engine, trying to improve the economy and emission performance of the engine. However, some structural parameters of diesel engine do not fit the combustion mode of dual-fuel engine, which makes the economy and emission performance of the engine fail to meet the expectations. In terms of such a problem, this paper carries out the performance simulation study on the dual-fuel engine, proposes related optimization measures and verifies the optimization plan via test.The combustion process of dual-fuel engine is extremely complex. Current performance simulation software does not feature the sound dual-fuel combustion model. On the basis of the Hiroyasu Model in GT-power, this paper develops the complete machine model for the R6160 dual-fuel engine by making great efforts in the test data correction. The margin of error for marked performance parameters all fall in the section of 5%, which proves the reliability of the complete machine model.Based on the calibration model, the paper studies the influences of engine injection timing, natural gas air injection timing, express air coefficient and intake valve closing angle on the performance of dual-fuel combustion engine. The results turn out as follows: when the fuel oil injection timing is advanced by 3°CA, the engine’s comprehensive fuel consumption rate can be reduced; when the gas injection timing is between 24°CA ATDC(384°CA) and 38°CA ATDC(408°CA) of intake stroke, the NOx emission and the fuel consumption rate will be provide with the favorable performance; the excess air coefficient has the larger influences on the dual-fuel engine, especially in the low load conditions, the lower excess air coefficient is required to improve the engine combustion and reduce the comprehensive fuel consumption rate; if the intake valve closing angle is reduced by 30°CA from the original engine, the fuel economy and HC emission of the dual-fuel engine will be improved.Based on the above study, correlation between fuel oil injection timing/natural gas injection timing and the excess air coefficient has been analyzed, and the improvement plan for the dual-fuel engine R6160 has been proposed as follows: the fuel oil injection timing is-27°CA, the natural gas injection timing is 384°CA, the intake valve closing is reduced by 30°CA, and the excess air coefficient is reduced in the low load conditions. The simulation results have indicated that the comprehensive fuel consumption rate has been reduced by 7 g/(k W?h) and the engine economy has been promoted when the plan meets the Tier II emission standard.As for the unsatisfactory HC emission with the engine R6160, the three-dimensional flow model of engine has been built with AVL FIRE to analyze the reason for excessive HC. The following has been concluded through simulation: the intake air backflow is the major reason for high HC emission in the high load conditions of engine; in the case of 60% replacement and 100% load, HC emission caused by the intake air backflow accounts for 55.7% of the total HC emission; insufficient combustion of natural gas is the major reason for high HC emission in the low load conditions; in the case of 60% replacement and 25% load, HC emission caused by the insufficient combustion accounts for 77.4% of the total HC emissionThe test bed has been built to test and verify the simulation conclusions. According to the test, when the fuel oil injection timing is-27°CA, the engine’s comprehensive fuel consumption rate will be reduced and the NOx emission will be increased; when the natural gas injection timing is 384°CA, there will be no significant change with the engine’s comprehensive fuel consumption rate and the NOx emission and the HC emission will be reduced, compared with the cases of other timings; as the excess air coefficient is reduced, the engine’s comprehensive fuel consumption rate will decrease and the NOx emission will increase. The test results are the same with the simulation results, which proves correctness of the simulation conclusions and feasibility of the simulation plan.