二甲醚主机掺烧lpg喷雾.doc
约65页DOC格式手机打开展开
二甲醚主机掺烧lpg喷雾,摘要本文通过对内燃机理想工作循环进行理论分析，得出压燃式内燃机实现等压循环时热效率最高，同时运用数值计算的方法对二甲醚（dme）发动机中掺混液化石油气（lpg）燃料的燃烧过程进行了深入研究，揭示了预混合压燃式发动机混合气的形成与着火特点，并分析了喷油参数对实现预混合燃烧过程的影响。综合各方面因素，实现了dme发动机预混...
内容介绍
此文档由会员 违规屏蔽12 发布
摘 要
本文通过对内燃机理想工作循环进行理论分析，得出压燃式内燃机实现等压循环时热效率最高，同时运用数值计算的方法对二甲醚（DME）发动机中掺混液化石油气（LPG）燃料的燃烧过程进行了深入研究，揭示了预混合压燃式发动机混合气的形成与着火特点，并分析了喷油参数对实现预混合燃烧过程的影响。综合各方面因素，实现了DME发动机预混合等压燃烧过程，为进一步提高DME发动机效率提供参考。
理论研究发现：受机件强度的限制，压燃式内燃机必须限制其循环最高压力，为得到较高的热效率，需按定压加热循环工作，因此柴油机燃烧模式需遵循预混合近似等压燃烧理论。其燃烧方式要求燃烧放热在上止点附近，并且在着火前尽量将全部燃油喷入缸内，实现预混合燃烧以代替传统的空间雾化燃烧方式的扩散燃烧。
针对某机型进行了几何模型的建立和动态网格的划分及生成，之后对标定工况下掺混不同比例LPG燃料的DME发动机的气相流动过程、喷雾过程和燃烧过程等缸内过程进行了数值仿真研究，比较详细地展示了缸内流场、喷雾发展形态、及其燃烧的压力及放热率变化。研究表明：
（1）通过对DME发动机掺烧不同比例LPG后气缸内混合气浓度场、温度场及燃料蒸发率（量）曲线的比较发现，掺混LPG燃料后，燃油雾化程度有所提高，预混合气量增大，分布趋于均匀，缸内温度随LPG量增加而有所下降；
（2）通过其燃烧特性参数如着火始点、燃烧持续期、燃烧压力及放热率的计算比较发现：随混合燃料中LPG添加量的增加，其燃烧滞燃期延长，着火始点延后，燃烧持续期缩短。缸内燃烧压力略有升高，燃烧放热时刻和放热率峰值时刻推迟，同时放热率峰值大幅度增加。燃烧放热规律中扩散燃烧部分亦随LPG含量增加而减少；
（3）在研究喷油参数对预混合燃烧影响的基础上，通过选择合适的喷油参数，添加高热值的燃料LPG等措施，使燃烧放热规律实现近似等腰三角形燃烧模式，实现了预混合等压燃烧理论。对于提高压燃式发动机的效率具有重要意义。
关键词：等压燃烧；数值模拟；DME/LPG混合燃料；预混合气；燃烧特性
ABSTRACT
Diesel ideal motive cycle is theoretical analyzed in this dissertation and it is concluded that the heat efficiency is highest when compression-ignition engines realize equipressure cycle. Based on the theory, the combustion process of LPG-DME blends on the dimethyl ether (DME) engine is deeply investigated via the simulative calculation method. The mixture formation and inflammation characteristics are obtained and the injection parameters’ effects on the realization of premixing combustion process are also analyzed. In conclusion, synthesizing omnifaceted factors the premixing isopiestic combustion process of DME engine is realized. And the result provides certain reference for further improvement of DME engine efficiency.
By theoretical study, maximum combustion pressure of compression-ignition engine must be limited according to the restriction of parts’ force. To get high thermal efficiency, the engine should be operated according as constant-pressure heating cycle. Consequently, the combustion mode should be followed premixed approximate isostatic combustion theory. This mode requests combustion heat release in BDC nearly and most of fuel should be injected into the cylinder as far as possible before ignition. By this, the premixed combustion would be achieved in place of traditional diffusion combustion which adopts space atomization combustion mode.
By numerical simulation method, the moving mesh model of DME engine is built. And then in standard running condition the process of air fluid, atomization and combustion in cylinder with different LPG ration are investigated. Velocity distribution in-cylinder, spray development, pressure and heat release rate of combustion are shown in detail. The results are shown that:
(1) Through the comparison of Mixture concentration field, temperature field and fuel evaporation rate/volume curve, with the increase of LPG content not only the fuel atomization is improved but also the pre-mixed gas concentration is increased and more evenly distributed. On the contrary, the temperature in-cylinder is decreased with the increase of LPG content.
(2) Comparison of combustion characteristics parameters such as combustion duration, combustion pressure and heat release rate is investigated. With the increase of LPG content, ignition delay is prolonged; the time of ignition is delayed; the combustion duration of blend fuel is reduced. Combustion pressure in-cylinder is slightly higher and the time reaching peak of heat release rate is delay while the peak of rate is significantly increased. The diffusion combustion part of combustion heat release is decreased with the increase of LPG content.
(3) Injection parameters’ effects on premixed combustion are also investigated. Based on the above conclusion, pre-mixed constant pressure combustion theory is able to realized by the way of selecting applicable Injection parameters, the content of LPG and other measures which make the combustion model similar to premixed combustion of isosceles triangle of heat release. The above conclusion has important significance to improve the efficiency of compression ignition engine.
Key word: isobaric combustion, numerical simulation, DME/LPG fuel combination, premixed gas, combustion characteristics -..
本文通过对内燃机理想工作循环进行理论分析，得出压燃式内燃机实现等压循环时热效率最高，同时运用数值计算的方法对二甲醚（DME）发动机中掺混液化石油气（LPG）燃料的燃烧过程进行了深入研究，揭示了预混合压燃式发动机混合气的形成与着火特点，并分析了喷油参数对实现预混合燃烧过程的影响。综合各方面因素，实现了DME发动机预混合等压燃烧过程，为进一步提高DME发动机效率提供参考。
理论研究发现：受机件强度的限制，压燃式内燃机必须限制其循环最高压力，为得到较高的热效率，需按定压加热循环工作，因此柴油机燃烧模式需遵循预混合近似等压燃烧理论。其燃烧方式要求燃烧放热在上止点附近，并且在着火前尽量将全部燃油喷入缸内，实现预混合燃烧以代替传统的空间雾化燃烧方式的扩散燃烧。
针对某机型进行了几何模型的建立和动态网格的划分及生成，之后对标定工况下掺混不同比例LPG燃料的DME发动机的气相流动过程、喷雾过程和燃烧过程等缸内过程进行了数值仿真研究，比较详细地展示了缸内流场、喷雾发展形态、及其燃烧的压力及放热率变化。研究表明：
（1）通过对DME发动机掺烧不同比例LPG后气缸内混合气浓度场、温度场及燃料蒸发率（量）曲线的比较发现，掺混LPG燃料后，燃油雾化程度有所提高，预混合气量增大，分布趋于均匀，缸内温度随LPG量增加而有所下降；
（2）通过其燃烧特性参数如着火始点、燃烧持续期、燃烧压力及放热率的计算比较发现：随混合燃料中LPG添加量的增加，其燃烧滞燃期延长，着火始点延后，燃烧持续期缩短。缸内燃烧压力略有升高，燃烧放热时刻和放热率峰值时刻推迟，同时放热率峰值大幅度增加。燃烧放热规律中扩散燃烧部分亦随LPG含量增加而减少；
（3）在研究喷油参数对预混合燃烧影响的基础上，通过选择合适的喷油参数，添加高热值的燃料LPG等措施，使燃烧放热规律实现近似等腰三角形燃烧模式，实现了预混合等压燃烧理论。对于提高压燃式发动机的效率具有重要意义。
关键词：等压燃烧；数值模拟；DME/LPG混合燃料；预混合气；燃烧特性
ABSTRACT
Diesel ideal motive cycle is theoretical analyzed in this dissertation and it is concluded that the heat efficiency is highest when compression-ignition engines realize equipressure cycle. Based on the theory, the combustion process of LPG-DME blends on the dimethyl ether (DME) engine is deeply investigated via the simulative calculation method. The mixture formation and inflammation characteristics are obtained and the injection parameters’ effects on the realization of premixing combustion process are also analyzed. In conclusion, synthesizing omnifaceted factors the premixing isopiestic combustion process of DME engine is realized. And the result provides certain reference for further improvement of DME engine efficiency.
By theoretical study, maximum combustion pressure of compression-ignition engine must be limited according to the restriction of parts’ force. To get high thermal efficiency, the engine should be operated according as constant-pressure heating cycle. Consequently, the combustion mode should be followed premixed approximate isostatic combustion theory. This mode requests combustion heat release in BDC nearly and most of fuel should be injected into the cylinder as far as possible before ignition. By this, the premixed combustion would be achieved in place of traditional diffusion combustion which adopts space atomization combustion mode.
By numerical simulation method, the moving mesh model of DME engine is built. And then in standard running condition the process of air fluid, atomization and combustion in cylinder with different LPG ration are investigated. Velocity distribution in-cylinder, spray development, pressure and heat release rate of combustion are shown in detail. The results are shown that:
(1) Through the comparison of Mixture concentration field, temperature field and fuel evaporation rate/volume curve, with the increase of LPG content not only the fuel atomization is improved but also the pre-mixed gas concentration is increased and more evenly distributed. On the contrary, the temperature in-cylinder is decreased with the increase of LPG content.
(2) Comparison of combustion characteristics parameters such as combustion duration, combustion pressure and heat release rate is investigated. With the increase of LPG content, ignition delay is prolonged; the time of ignition is delayed; the combustion duration of blend fuel is reduced. Combustion pressure in-cylinder is slightly higher and the time reaching peak of heat release rate is delay while the peak of rate is significantly increased. The diffusion combustion part of combustion heat release is decreased with the increase of LPG content.
(3) Injection parameters’ effects on premixed combustion are also investigated. Based on the above conclusion, pre-mixed constant pressure combustion theory is able to realized by the way of selecting applicable Injection parameters, the content of LPG and other measures which make the combustion model similar to premixed combustion of isosceles triangle of heat release. The above conclusion has important significance to improve the efficiency of compression ignition engine.
Key word: isobaric combustion, numerical simulation, DME/LPG fuel combination, premixed gas, combustion characteristics -..
