柴油汽车改用LNG燃料的实用技术及其经济性分析

攻克柴油汽车改用LNG燃料的技术难关，有助于推进清洁燃料汽车产业的发展进程。为此，指出了柴油汽车改用LNG燃料的技术关键在于对发动机（包括点火系统）、燃料供应系统以及相应控制系统的改装，提出了两种柴油汽车改用LNG燃料的实用技术：①将原车改装为柴油-LNG双燃料混合供应的掺烧汽车；②将原柴油发动机改装成专用的LNG发动机，使之成为单燃料供应的LNG汽车。在分析了柴油车改装技术的通用性，柴油改装车的适用对象及特点，天然气发动机动力性下降之原因，改装成本、改装技术的成熟度与改装效果，改装后汽车排放指标的变化等基础上，提出了提高柴油改装车动力性的举措：①利用稀薄燃烧技术增加动力性；②利用进气增压技术增加动力性。最后从技术层面和政策层面讨论了改装柴油车存在的问题。研究与实例分析结果表明：改装双燃料掺烧车较单燃料车相对来讲技术优势明显，其经济性也高一些，尽管这类改装车因为进入汽缸内的“天然气＋空气”混合气较原“柴油＋空气”混合气热值低、甲烷火焰传播速度也比柴油低而导致发动机最高功率、动力性和加速性能略有下降，但综合考虑认为，改装车排放效果有改善，发动机功率、扭矩等基本上能满足原车需要，车辆操作、行驶情况正常。经济分析结果则表明：单从燃料成本方面考虑，当LNG与柴油的比价低于0.75∶1.00时，柴油改装车具有经济性；而当比价低于0.50∶1.00时，柴油汽车改用LNG燃料的经济效益更显著。

Practical techniques and economic analysis of converting diesel-fueled into LNG-fueled vehicles

To tackle with technical difficulties in converting diesel-fueled into LNG-fueled vehicles will no doubt accelerate the development of clean-fuel automobiles.Herein this paper first points out that the key of this conversion technology lies in the modification of the engine(including the ignition system),the fuel feed system,and the corresponding control system.Then this paper presents practical techniques of converting the original diesel vehicles into diesel-LNG dual-fueled co-combustion vehicles or into LNG single-fueled vehicles.Furthermore,this paper analyzes the generality of the above two conversion techniques,suitable object and characteristics of the modified diesel vehicles,the reason of poor power performance in natural gas fueled engines,the modification cost,maturity and result,emission index difference between pre-and post-modified diesel vehicles,and so forth.On this basis,both lean combustion and boosting intake are put forward to improve the power performance of the modified vehicles.Finally this paper discusses the prevailing issues in the modification of diesel vehicles from the perspective of technology and policy.Through research and case studies,the dual-fueled co-combustion vehicles are better than the LNG-fueled vehicles in terms of technology and economical efficiency.Despite such disadvantages as the caloric values of the mixed natural gas and air are lower than those of the mixed diesel and air,or the maximum power,power performance and accelerating performance are all reduced to a low degree because the methane flume runs slower than the diesel,the modified dual-fueled vehicles in the end can not only meet any needs for operation and normal driving but get substantial emission reduction.In addition,the economic analysis shows that if only the fuel cost is considered,the economical efficiency will exist when the ratio of price between LNG and diesel is less than 3/4,and will be significantly obvious when less than 1/2.