| The global requirements for Marine engine emissions are increasingly strict,and high efficiency and low emissions have become the main development direction of the industry.Natural gas has become the mainstream alternative fuel because of its low price and environmental protection.And because natural gas is not easy to ignite and diesel is easy to be combusted,the engine which only uses diesel as ignition fuel attracts people’s attention.In this paper,the combustion and emission of micro diesel injection ignition natural gas engine under the influence of different parameters are investigated.Firstly,the combustion chamber model was established by PRO/E and imported into FIRE software to divide the grid.Then,the calculation sub-model was determined.Finally,the accuracy of the model was verified by comparing the simulated cylinder pressure curve with the actual cylinder pressure curve.The effects of initial conditions and injection strategy on combustion and discharge process were calculated by simulation.In addition,a set of optimal matching schemes were obtained by orthogonal experimental design with NO quality score as evaluation index.The results are as follows,（1）With the increase of the amount of diesel fuel ignited,the peak pressures are 12.90 MPa,13.48 MPa,13.99 MPa,14.48 MPa and 15.02 MPa,respectively.Appear at 732.2°CA,730.2°CA,729°CA,728.2°CA,727°CA;Compared with R=5%,the peak temperature in cylinder is increased by 3%,5.6%,7.2%and 8.5%respectively.（2）When the initial pressure is 0.16 MPa,the peak value of the heat release rate is the largest.Compared with this value,the peak value of the other four conditions decreases by 5.49%,12.33%,20.86%and 29.47%,respectively.Compared with the initial pressure of 0.16 MPa,the CO mass fraction under other conditions decreased by 12%,22%,28%and 36%,respectively.（3）When the excess air coefficient is 1.2,the maximum values of the cylinder pressure and CO mass fraction are 16.97 MPa and 9.2×10-4,respectively.When the excess air coefficient is1.6,the minimum values of the peak values are 11.37 MPa and 1.9×10-4,respectively.（4）When the injection advance Angle is 14°CA,the peak cylinder pressure is 16.21 MPa,but only 12.50 MPa when the parameter is 6°CA.Compared with the injection advance Angle of 14°CA,the peak temperature of the other four injection conditions decreased by 1.7%,3.4%,5.3%and 6.6%,respectively,and the peak phase lagged by 2°CA,5°CA,7°CA and 8°CA,respectively.（5）Compared with the cylinder pressure and peak phase of the injection duration of 4°CA,the cylinder pressure peaks of the other four conditions decreased by 11.5%,16.1%,23.3%and27.5%,respectively,and the peak phase lagged behind 4°CA,6°CA,8°CA and 10°CA,respectively.When the injection duration was 4°CA,the maximum in-cylinder temperature reached 2713 K at 730.2°CA.Compared with this,the maximum in-cylinder temperature at the other four dura decreased by 1.3%,1.8%,2.9%and 3.8%,respectively.（6）The best matching scheme obtained by orthogonal experimental design is A2B4C4D1E4,under which the mass fraction of NO is 9.6×10-5.In this paper,through the simulation analysis of the micro-injection diesel ignited natural gas engine,its change rule under the influence of different variable parameters is obtained,and the law is consistent with the actual,the research results have a certain reference value for the subsequent development of this type of engine. |
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