【作者】 冷先银；

【导师】 隆武强；

【作者基本信息】 大连理工大学 ， 动力机械及工程， 2010， 博士

【摘要】 随着国际海事组织(IMO)关于船舶NOx排放的Tier II法规实施日期的日益临近,船用柴油机低NOx排放技术成为当前的研究热点,而保持柴油机良好的燃油经济性和降低技术改造成本一直是船用柴油机低NOx排放研究的重点任务。论文以陕西柴油机重工有限公司的6PC2-6／2L型船用中速柴油机为研究对象,开展了通过供油系统的技术革新降低NOx排放的相关模拟和试验研究。为了以较低成本降低6PC2-6／2L柴油机的NOx排放并改善其燃油经济性,论文提出船用柴油机新型供油系统,它主要包括调压孔式喷油泵和交叉喷孔油嘴。调压孔式喷油泵通过加大油泵柱塞直径并在柱塞套上设置调压孔,使初期燃油喷射率降低,后期燃油喷射率升高,以实现靴型喷射规律,从而降低柴油机的NOx排放；交叉喷孔油嘴的喷孔由多个子喷孔交叉汇聚而形成,能够产生扇状喷雾,促进混合气形成,改善混合气的空间分布,进而改善柴油机的燃烧和排放。为认识交叉喷孔的喷雾特性,在高压容器内进行了交叉喷孔喷雾的高速摄影试验研究。研究发现交叉喷孔的结构会影响喷雾的形状、贯穿距和锥角,子喷孔中心线交于油嘴球头表面时,喷雾贯穿距最大,喷雾的正面锥角比侧面锥角小；子喷孔中心线交于针阀体内部时,喷雾贯穿距较小,喷雾的正面锥角比侧面锥角大；子喷孔中心线交于针阀体外部时,喷雾贯穿距最小,喷雾的正面锥角比侧面锥角大。为深入认识和解析柴油机缸内工作过程,应用三维CFD软件AVL FIRE对缸内流动、喷雾、燃烧和污染物生成等过程进行了模拟计算。利用6PC2-6/2L柴油机E3循环4个工况的缸内压力和NOx排放的试验结果验证了模型的可信性。然后计算了调压孔式喷油泵所产生的两种靴型喷射规律Bootl和Boot2,以及原机喷油泵的喷射规律Base,柴油机按推进特性运行的100%和50%负荷工况5种不同喷油定时下的缸内流动和燃烧过程。计算结果表明：采用两种靴型喷射规律时都可以获得比原机更低的NOx排放,Boot1规律在100%和50%负荷时可以获得最好的NOx-Soot折衷关系,而Boot2规律在这2种负荷下可以获得最好的NOx-bi折衷关系。综合考虑柴油机在高负荷和中低负荷下的油耗和排放,选定Bootl规律-8°CAATDC喷油定时为最佳的喷油规律和定时匹配：在100%负荷工况下,柴油机的NOx排放比原机降低17%,Soot排放比原机降低24%,bi比原机增加2%；在50%负荷工况下,其NOx排放比原机降低20%,Soot排放比原机降低2%,bi比原机增加0.3%。为验证新型供油系统对于降低船用中速柴油机NOx排放和改善其燃油经济性的效果,开展了6PC2-6／2L柴油机的燃烧和排放试验。试验结果表明,作者设计的18x0.65mm规格的交叉喷孔油嘴可以使柴油机的NOx排放下降9%左右,同时有效油耗率降低约1%；采用18x0.65mm规格的交叉喷孔油嘴和调压孔式喷油泵相结合而得到的新型供油系统,可以使6PC2-6／2L柴油机E3循环所有工况下的有效燃油消耗率和NOx排放同时降低,试验研究中所得的最佳结果是加权平均NOx排放率降低14.3%,同时有效油耗率降低1.5%。更多还原

【Abstract】 With the coming of implement of International Maritime Organization (IMO) Tier II regulation on harmful emissions from ships, the research activities on reducing NOX emissions from marine diesel engines are drawing more and more attention. To keep the advantages of low BSFC and to reduce the costs for equipment retrofits are of vital important for NOχemission control of marine diesel engines. In this dissertation, the 6PC2-6/2L type diesel engine was selected as the research object to investigate the practical and inexpensive methods of reducing NOx emission. Comprehensive numerical and experimental researches on the fuel injection and combustion processes relating to the reduction of NOχemission were performed.To reduce the NOX emission and improve the fuel economy of 6PC2-6/2L diesel engine, a new fuel supply system, including a new fuel pump with a pressure modulating hole and intersect hole nozzle, was developed. In the new fuel pump, the enlarged plunger and the configuration of pressure modulating holes lead to lower initial fuel injection rate and higher fuel injection rates at medium stage. By this way, the boot-type injection rates, which will be profitable for decreasing NOχemission, are achieved. The holes of intersect hole nozzle are formed by the intersection and convergence of child holes at inner side. Each hole has only one outlet. The sprays of intersect hole nozzle are fan-shaped, which will improve mixture formation and mixture distribution, thus improve the combustion and emissions of the diesel engine.To clarify the spray characteristics of intersect hole nozzles, high speed photography of the spray in high pressure constant volume vessel was conducted. The analysis of spray images indicates that the structure of intersect hole has strong influences on the shape, penetration and spread angle of the spray. When the center line of the children holes intersect on surface of the nozzle tip, the spray penetration is longest, and the front spray angle is less than the side spray angle; when the center line of the children holes intersect in the nozzle valve body, the spray penetration becomes shorter, and the front spray angle is larger than the side spray angle; when the center line of the children holes intersect out of the nozzle tip, the spray penetration is shortest, and the front spray angle is much larger than the side spray angle. To understand the working process of 6PC2-6/2L type diesel engine, the 3D CFD package AVL FIRE was employed to simulate in-cylinder air motion, fuel injection, combustion and emission formation processes. The simulation model was validated by the pressure trace and NOχemission data of the E3 work cycle experiment of 6PC2-6/2L diesel engine. The performance of two kinds of boot-type injection rate curves produced by the two fuel pumps with pressure modulation hole, named as Bootl and Boot2, and the injection rate produced by the primary fuel pump, named as Base, were investigated for 100% and 50% load working conditions of 6PC2-6/2L diesel engine. And for each kind of injection rates, five injection timings were studied. The computational results indicate that, both of boot-type injection rates can obtain lower NOχemission than the primary engine. Particularly Bootl can get better NOχ-Soot trade-off relationship in both loads, whereas Boot2 can get better Soot-ISFC trade-off relationship in two loads working conditions. To balance the fuel consumption and emissions at high load and low load, the Bootl injection rates with an injection timing of-8°CA ATDC were selected as the optimized matching. Compared with the base engine, the engine with new injection system and optimized injection strategy has NOχemission reduction of 17% at 100% load and 20% reduction at 50% load; the Soot emission reduction of 24% at 100% load and 2% at 50% load; the relating ISFC increases 2% at 100% load and 0.3% at 50% load.To validate the effects of the new fuel supply systems on reducing NOχemission and improving fuel economy of marine diesel engines, performance test of 6PC2-6/2L diesel engine was carried out on test bench. The experiment results show that, with the application of the intersect hole nozzles with a specification of 18×0.65 mm, NOX emission was reduced by 9%, while the BSFC reduced by 1%. Moreover, by the use of these nozzles and new fuel pump, the NOX and BSFC are simultaneously reduced under all loads of the E3 work cycle. The best experiment results were 14.3% of NOX emission reduction together with 1.5% BSFC reduction.更多还原