【作者】 刘建龙；

【导师】 付建勤； 王健；

【作者基本信息】 湖南大学 ， 动力工程（专业学位）， 2019， 硕士

【摘要】 近些年来,随着石油资源的过度开发以及环境污染问题的加剧,寻找清洁替代燃料已经迫在眉睫。天然气具有排放低、价格低、储量丰富、辛烷值高等众多优点,是一种很好的替代燃料。柴油引燃天然气发动机由于具有经济性好、排放低、压缩比高等众多优点,在国内外受到了广泛的应用。目前国内对柴油引燃天然气发动机的研究起步较晚,还有很多的技术问题没有解决,因此开展对柴油引燃天然气发动机的研究具有重要的意义。本课题基于柴油引燃天然气发动机的台架试验数据和几何参数建立了CFD（计算流体动力学）三维仿真模型并验证了模型的可靠性。基于验证后的CFD仿真模型,分别开展了进气迟闭角、过量空气系数（λ）以及天然气能量替代比对双燃料发动机燃烧与排放影响的研究。本课题的主要研究内容和结果如下:（1）在全负荷工况下,当进气迟闭角提前10°CA时,缸压和放热率峰值均高于原正时,CO浓度明显降低,NOx浓度变化不明显。CH₄的浓度在1600r/min时出现了先减后增的情况,主要原因是缸内的气流运动加剧。（2）在部分负荷工况,随着λ的增加,指示功和指示热效率增加,改善了双燃料发动机的燃烧性能。而在全负荷工况,在λ增加的过程中,指示功与指示热效率出现了先增后减的趋势,并在λ=1.3时取得最大值。另外,随着λ的增加,NOx浓度受氧浓度的影响出现了先增后减的趋势;CO浓度迅速降低;CH₄的浓度呈现出先减后增的趋势,当λ>1.3时,CH₄浓度有所增加。（3）随着天然气替代比的增加,缸压峰值和放热率峰值均降低。这是因为喷入柴油变少,降低了初始放热率,延长了滞燃期。燃烧持续期随着替代比的增加先增后减,在60%替代比达到最大值。在替代比从50%增加到90%的过程中,由于缸内温度、天然气浓度以及氧浓度的升高,NOx和CH₄的浓度增加;CO的浓度先增后减,在60%替代比达到最大值。当替代比大于60%时,缸内温度的增加有利于CO氧化成CO₂,CO浓度降低。本文的研究内容揭示了进气迟闭角、过量空气系数以及天然气能量替代比三个参数下柴油引燃天然气发动机的燃烧与排放特性,为优化柴油引燃天然气发动机的燃烧和排放性能提供了理论指导。更多还原

【Abstract】 In recent years,with the overexploitation of petroleum resources and the intensification of environmental pollution problems,it is urgent to find clean alternative fuels.Natural gas is a good alternative fuel which has many advantages such as low emissions,low price,abundant reserves and high octane number,etc.Because diesel-ignited natural gas engines have many advantages such as good economy,low emissions,high compression ratio etc.,they have been widely used at home and abroad.Researches on diesel-ignited natural gas engines in China started late,and many technical problems have not been solved now.Therefore,it is significance to carry out research on diesel-ignited natural gas engines.Based on the bench test data and geometric parameters of diesel-ignited natural gas engine,a three-dimensional simulation model of CFD（Computed fluid dynamics）was established and the validity of the model was verified in this topic.Based on the verified CFD simulation model,the effects of intake retardation angle,excess air coefficient（λ）and natural gas energy substitution ratio on combustion and emissions of dual-fuel engine were studied.The main research contents and results of this topic are as follows:（1）Under full load conditions,when the intake retardation angle was advanced by 10°CA,the peak values of cylinder pressure and heat release rate are higher than the original angle and the CO concentration was reduced significantly,while the NOx concentration was almost not change at all.The concentration of CH₄ decreased first and then increased at 1600r/min,mainly reason was the intensify airflow in the cylinder.（2）Under partial load conditions,asλincreases,the indicated work and indicated thermal efficiency increase,combustion performance of the dual-fuel engine has been improved.While in the full load conditions,in the process of increasingλ,the indicated power and the indicated thermal efficiency appear to increase first and then decrease and the maximum value is obtained atλ=1.3.In addition,with the increase ofλ,the concentration of NOx increases first and then decreases with the influence of oxygen concentration;the concentration of CO decreases rapidly;the concentration of CH₄ showed a trend of decreasing first and then increasing.Whenλ>1.3,the concentration of CH₄ increased.（3）As the natural gas replacement ratio increases,both the peak value of cylinder pressure and heat release rate reduced.That is because less diesel fuel is injected,which reduces the initial heat release rate and prolongs the retardation period.The duration of combustion increase first and then decrease with the increase of the substitution ratio,and reached the maximum at the 60%substitution ratio.The duration of combustion reduced when the replacement ratio excess 60%because the flame propagation speed increased.In the process of increasing the substitution ratio from 50%to 90%,the concentration of NOx and CH₄ increased due to the increase of the temperature in the cylinder,the concentration of natural gas and the concentration of oxygen;the concentration of CO increases first and then decreases,reaching a maximum at 60%substitution ratio.When the substitution ratio is greater than 60%,the increase in the in-cylinder temperature is good for the oxidation of CO to CO₂,and the CO concentration decreases.The research content of this paper reveals the combustion and emission characteristics of diesel-ignited natural gas engines under three parameters:intake retardation angle,excess air ratio and natural gas energy substitution ratio.It provides a theory guide for optimizing the combustion and emission performance of diesel-ignited natural gas engines.更多还原