| Depending on high efficiency and excellent operational reliability, the low-speed two stroke diesel engines becomes modern ship’s main propulsion power source. But the shortage of fuel resources, international emission legislation becomes increasingly rigorous. Therefore, energy conservation and emission reduction has become a significant research topic on marine diesel engine. The performance of power and fuel economy of marine diesel engine has affected by many factors, finally emission performance determined by the quality of combustion. But the spray(fog) in process of diesel engine combustion has a decisive and important influence. Therefore, the critical data have been acquired, according to the actual experimental platform, research the influence of fuel injection characteristics on the comprehensive properties of marine diesel engine by means of numerical simulation, optimized and ameliorated the combustion procedure of diesel engine, the target is to reduce the harmful emissions of diesel engine and can meet the requirements of the performance and fuel economy.In this paper, the research object is based on a marine low-speed and two strokes diesel engine. First of all, the geometric model of the combustion chamber is established, which is assembled by the exhaust valve, cylinder head, consisting of the piston and the cylinder wall. Then, using the ES-ICE module which is a general CFD fluid simulation software STAR-CD, in order to complete the division of the grid about surface and body, define dynamic grid in cylinder, set up the base parameter. Pre-treatment settings, calculation and post-processing work need applied software which is Pro-star. Contrast the results of simulation with experiment, including dynamometer diagram and heat release rate, the match degree is higher, the relative error rate of the highest combustion pressure and maximum rate of heat release were 0.84% and 1.73% respectively, simulation of weighted average about NOX compared with experiment result, the change trends are basically identical, it can provide certain reference for the generation and emissions of actual NOX.Establishment of a high pressure fuel pipe, one dimensional system calculation model of fuel injector by AMESim which is multi-domain simulation software, getting on the different simulation curve of injection regular pattern. The initial conditions and boundary conditions are provided with one dimension performance analysis results, completed the three different fuel injection law(rectangular, boots and double injection) on diesel engine combustion process and emissions of the simulation calculation, the results show that: Multiple injection makes the emissions of NOX decrease by nearly 23.9%, there was a decrease of 3% of work capacity, the rate of fuel consumption is slightly elevated. Considering the comprehensive performance of diesel engine, multiple injection is an ideal fuel injection solution. In order to improve the power capability decline caused by the multiple injection need to find a reasonable adjustment of injection timing.Research pre-injection rate and pre/main injection interval angle in single variable factors, found that with the increase of pre-injection rate and pre/main injection interval angle, the emissions of NOX and combustion noise will be significantly reduced, the power of engine comes down and fuel consumption is increased, pre/main injection interval angle is more obviously effects on the performance of engine than pre-injection rate. To acquisition an optimum combination, Numerical simulation the effect of parameters orthogonalized of multiple-injection, selecting a multiple injection scheme which is most suitable for diesel engine in this paper, the pre-injection rate is 15% and pre/main injection interval angle is 3°CA. Comparing with the original model, the emissions of NOX has reduced by 17.2%, Achieved the purpose that is to effectively lower the emissions of NOX and noise, and ensure the power performance and fuel economy of diesel engine. |
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