摘要随着社会的进步，人们更加注重环境问题。而传统柴油机因为其排放污染大，人们决定研究出一种新型发动机取代他。天然气储量大,是新能源一个合适的选择。但因为其燃烧困难，CNG发动机充气效率低，于是引出了柴油LNG双燃料发动机这个概念。目标是在保证传统柴油机的性能功率基础上，尽可能地降低排放。因为较传统柴油机加入了另外一种燃料，所以喷油策略的选择是一个重要的研究课题。87027

本文运用AVL-FIRE软件。以L21/31中速船舶柴油机改装的双燃料发动机为研究对象，建立了数值计算模型，验证了建立的模型是否合理之后，分别在缸内平均温度、缸内平均压力、NOx的排放、SOOT的排放四个方面对两种喷油策略进行对比。选择更加合理的喷油策略：第一种喷油策略是先喷入主燃料LNG，待其与缸内空气混合形成均匀混合气之后，喷入引燃柴油，开始燃烧；第二种喷油策略是先喷入引燃柴油，待形成稳定着火源之后，喷入主燃料LNG，开始燃烧。

最后通过模拟分析，在缸内平均压力方面第二种喷油策略压力峰值出现时刻和峰值更加接近原柴油机。在缸内平均温度方面第二种喷油策略温度峰值出现时刻和峰值大小更加接近原柴油机，而且温度分布更加均匀燃烧充分。在NOx排放方面，第二种喷油策略的排放量仅为原柴油机的7。9％，满足了降低NOx排放的目标。在SOOT排放方面，第二种喷油策略SOOT排放量，满足了降低排放的要求。综上所述，LNG柴油双燃料发动机的喷油策略要选择现象缸内喷入引燃柴油，待形成稳定着火源之后，喷入主燃料LNG。

毕业论文关键词：柴油LNG双燃料发动机；喷油策略的选择；数值模拟计算；NOx的排放

Abstract With the progress of society, people pay more attention to environmental problems。 The traditional diesel engine because of its heavy pollution, people decided to study a new type of engine to replace him。 Natural gas reserves are large, is a suitable choice for new energy sources。 But because of its combustion difficulties, CNG engine inflation efficiency is low, so it leads to the concept of diesel LNG dual fuel engine。 The goal is to reduce emissions as much as possible on the basis of ensuring the performance of conventional diesel engines。 The selection of fuel injection strategy is an important research topic because of the addition of another kind of fuel to the traditional diesel engine。

In this paper, the use of AVL-FIRE software。 After the modifications to the L21/31 medium speed marine diesel dual fuel engine as the research object and establishes a numerical calculation model, validate the model established is reasonable, respectively in cylinder mean average temperature, in cylinder pressure, NOx emissions, soot emissions four aspects of two fuel injection strategies were compared。 Choose more reasonable injection strategy: the first injection strategy is to spray white LNG fuel, until the air mixture in the cylinder and form homogeneous mixture was injected into the pilot diesel, began to burn; the second injection strategy is first injected into the pilot diesel, until the formation of a stable source of ignition, spray white LNG fuel and began to burn。

Finally, through the simulation analysis, in the cylinder average pressure aspect second kinds of fuel injection strategy pressure peak time and peak value is more close to the original diesel engine。 In the cylinder average temperature, the peak value of the second fuel injection strategy appears to be more close to the original diesel engine, and the temperature distribution is more uniform。 In terms of NOx emission, the emission of the second fuel injection strategies is only 7。9% of the original diesel engine, which meets the goal of reducing the NOx emission。 In the SOOT emissions, second kinds of fuel injection strategy SOOT emissions, to meet the requirements of reducing emissions。 In summary, diesel LNG dual fuel engine fuel injection strategy to choice phenomenon in cylinder spray into the pilot diesel, until the formation of a stable source of ignition, spray white fuel LNG。