【作者】 张贵阳；

【导师】 乔信起；

【作者基本信息】 上海交通大学 ， 动力机械及工程， 2013， 博士

【摘要】 伴随着能源危机加剧和环境污染恶化，节能与减排已成为当今时代的主题。柴油机因热效率高、可靠性好等优点已成为交通运输和电力设施的主要动力，然而，其NO_x和soot排放对环境和人类健康具有重要影响，并且它们之间存在trade-off关系。本文从研究核心边界条件对柴油机燃烧的影响规律的角度出发，通过优化这些核心边界条件使混合气燃烧时尽量避开NO_x和soot生成区域，从而改善柴油机NO_x和soot排放的trade-off。针对煤直接液化柴油低十六烷值、低硫含量、低芳香烃含量和低蒸馏温度的特点，采用煤直接液化柴油替代石化柴油，并优化喷油参数和EGR率进一步改善柴油机NO_x和soot排放的trade-off关系，从而实现高效清洁燃烧。本文以一台批产CA6DL2-33E3F柴油机为原型机，采用电控共轨燃油系统替代直列泵燃油系统，对进排气系统、燃烧系统、缸盖等也进行了改造，并安装了关键参数测试设备，从而建立了柴油机燃烧测试系统。建立了喷油规律测试试验台，并测量了冲击喷油嘴和传统喷油嘴的喷油规律，试验结果表明：提高喷油压力可以提高最大喷油速率，当循环油量相同时，提高喷油压力可以缩短喷油持续期；最大喷油速率随喷油脉宽增大先升高然后基本保持不变；与传统喷油嘴相比，冲击喷油嘴具有高的喷油速率、短的喷油持续期，这增加了在混合气着火前将循环油量全部喷入缸内的可能性。建立了喷雾特性测试试验台并利用Matlab软件编程开发了喷雾照片处理程序，测量了冲击喷油嘴和传统喷油嘴的喷雾宏观参数，试验结果表明：随背压增大，两种喷油嘴的喷雾贯穿距离都减小、喷雾锥角都增大、喷雾投影面积和喷雾体积都减小。随喷油压力增加，两种喷油嘴的喷雾贯穿距离、喷雾锥角、喷雾投影面积和喷雾体积都增大。与传统喷油嘴相比，冲击喷油嘴的喷雾贯穿距离短、喷雾锥角大、喷雾投影面积和喷雾体积小。在建立的燃烧测试系统上研究了燃烧系统参数对柴油机燃烧的影响。试验结果表明：为降低NO_x到较低排放水平，必须采用较高EGR率；低压缩比敞口燃烧室比缩口燃烧室更有利于改善缸内混合气的形成质量，从而改善柴油机NO_x和soot排放的trade-off，并且有利于改善HC、CO排放以及BSFC性能；传统喷油嘴更有利于改善柴油机燃烧中NO_x和soot排放的trade-off，这是因为冲击喷油嘴的贯穿距离短于传统喷油嘴，与敞口燃烧室不完全匹配，造成其缸内油气混合相对不均匀；提高喷油压力可改善油气混合过程和缩短喷油持续期，然而，在低负荷时过高喷油压力可能导致缸内局部区域混合气过稀，从而引起不完全燃烧，因此，低负荷时喷油压力不宜过高，高负荷时可以适当提高喷油压力；采用上止点附近的晚喷油策略控制混合气燃烧相位，使柴油机在相对高负荷时可以避免粗暴燃烧。结合低压缩比敞口燃烧室和大量冷却EGR，以及最佳的喷油参数，可以实现较理想的柴油机高效清洁燃烧。在优化喷油嘴—燃烧室结构参数、喷油参数和EGR率实现了较理想的高效清洁燃烧以后，针对煤直接液化柴油具有低十六烷值、低硫含量、低芳香烃含量和低蒸馏温度等特点，本文采用煤直接液化柴油替代石化柴油，在柴油机燃烧测试系统上进行了喷油参数和EGR率对柴油机燃烧的影响规律，并优化喷油参数和EGR率来进一步改善柴油机NO_x和soot排放的trade-off。试验结果表明，与石化柴油相比，煤直接液化柴油可使柴油机在低EGR率下实现预混合燃烧模式；煤直接液化柴油的NO_x排放随EGR率的变化率与石化柴油接近，但前者的碳烟排放随EGR率的变化率远小于石化柴油；煤直接液化柴油可进一步改善柴油机NO_x和soot排放的trade-off。与原机相比，新机各试验工况NO_x和soot排放同时降低，尤其在25%和35%负荷，NO_x和soot排放下降幅度都超过50%，并且BSFC没有显著升高。而且原机最大增压比达到2.6，满足国Ⅲ排放标准。这可见效果显著。本文采用AVL-Fire软件模拟柴油机燃烧过程，计算结果进一步验证了敞口燃烧室更有利于缸内油气混合，从而改善NO_x和soot排放的trade-off。更多还原

【Abstract】 With the increased energy crisis and the deteriorated environmental pollution, theenergy saving and emissions reduction have become the theme of our times. Diesel engineshave become the main driving force for transportation and power facilities due to thehigher thermal efficiency and better reliability; however, the NO_xand soot emissions fromdiesel engines have an important impact on the environment and human health. Moreover,there is a trade-off relationship between NO_xand soot emissions in the conventionalcombustion mode of diesel engines. In this paper, while the effects of key initialboundaries on the combustion for vehicle diesel engine were investigated firstly, theincylinder mixture formation quality of vehiclediesel engine was improved by optimizingthe key initial boundaries, so that when the mixture burned, it could avoid the NO_xandsoot generation regionsandimprove the trade-off relationship between NO_xand sootemissions. Due to the lower cetane number, lower sulfur and PAH content andlowerdistillation temperature for the CTL (Coal to Liquid) fuel, it was used to substitute forpetroleum diesel fuel, and the fuel injection parameters and EGR rate were optimized tofurther improve the trade-off relationship between NO_xand soot emissions in order toachieve the clean and high-efficiency combustion.In this paper, a diesel engine combustion test bench has been established byreconstructing the key systems of a mass production CA6DL2-33E3F diesel engine. Somedevelopments are as follows:the mechanical in-line fuel system was replaced by the highpressure common rail fuel system. The cylinder head with the intake air swirl ratio of2.1was replaced by the one with the intake air swirl ratio of1.3.The EGR system with theintake air throttle valve was developed to ensure that enough exhaust gas could be inducedinto the intake manifold, and the shell-and-tube heat exchanger was developed to ensurethe induced exhaust gas could be cooled to the target temperature.An exposure portcombustion chamber of low compression ratio and large throat diameter was alsodeveloped. Also, the key parameters test equipments have been installed in the dieselengine combustion test system. The fuel injection rate testing bench has been established, and the fuel injection rateof both the impingingspray nozzle and the conventional spray nozzle were measured. Thefuel injection test results showed that the maximum fuel injection rate was increased withthe increased fuel injection pressure, which meant that the fuel injection duration could beshortened by increasing the fuel injection pressure at the same cyclic fuel quantity. Themaximum fuel injection rate first increased and then remained unchanged with theincreased fuel injection pulse width. Compared with the conventional spray nozzle, theimpinging spray nozzle has a higher fuel injection rate and shorter fuel injection duration,which increased the possibility of injecting the cyclic fuel into the cylinder completelyprior to the ignition.The spray characteristics testing bench has been established and the spray photoprocessing program has been developed using Matlab codes. The spray photos of both theimpinging spray nozzle and the conventional nozzle wererecorded in the spraycharacteristic testing bench, and the spray photos were processed by the spray photoprocessing program. The spray characteristics test results showed that the spray tippenetration, the spray projected area and the spray volume decreased, and the spray coneangle increased with the incrased back pressure for both the impinging spray nozzle andthe conventional spray nozzle. The spray tip penetration, the spray cone, the sprayprojected area and the spray volume increased with the increased fuel injection pressure forboth the impinging spray nozzle and the conventional spray nozzle. Compared with theconventional spray nozzle, the impinging spray nozzle had shorter spray tip penetration,larger spray cone angle, smaller spray projected area and spray volume.The effects of combustion system parameters on combustion for vehicle diesel enginehave been investigated on thenewly-built combustion test bench. The test results showedthat the heavy EGR is necessary to significantly reduce the NO_xemissions. Compared withthe reentrant combustion chamber, the exposure port combustion chamber of lowcompression ratio and large throat diameter can improve the trade-off relationship betweenNO_xand soot emissions, and even improve the HC and CO emissions as well as the BSFC.The conventional spray nozzle was more beneficial for improving the trade-off betweenNO_xand soot emissions than the impinging spray nozzle, because the spray tip penetrationof the impinging spray nozzle was shorter than that of the conventional spray nozzle,which was not well matched with the exposure port combustion chamber, resulting in the heterogeneous mixture in the cylinder.The increased fuel injection pressure can promotethe fuel-air mixing process and shorten the fuel injection duration; however, theexcessively high fuel injection pressure may result in the over-lean fuel-air mixture in thelocal areas at low load, which can lead to the incomplete combustion. Thus, there exists anoptimum fuel injection pressure at low load, and the fuel injection pressure can be raisedappropriately at high load.Thenear TDC late fuel injection strategy was used to control themixture combustion phase, which could prevent the violent combustion of diesel engine atthe relatively high load. The relatively ideal clean and high-efficiency combustion modecan be achieved by combining the exposure port combustion chamber of low compressionratio and heavy EGR as well as the optimal fuel injection parameters.After the relatively ideal clean and high-efficiency combustion mode has beenachieved by optimizing the injector-combustion chamber parameters, fuel injectionparameters and EGR rate, when vehicle diesel engine was fuelled with petroleum dieselfuel. Due to the lower cetane number, lower sulfur and PAH content and lower distillationtemperature for the CTL fuel, petroleum diesel fuel was replaced by the CTL fuel.And theeffects of fuel injection parameters and EGR rate on the combustion for vehicle dieselengine have been investigated in the newly-bulit combustion test bench.Moreover, the fuelinjection parameters and EGR rate were optimized in order to further improve thetrade-offrelationship between NO_xand soot emissions.The experimental resultsshowed that thepremixed combustion mode could be realized with lower EGR rate when vehicle dieselengine fuelled with CTL fuel, comparaed to petroleum diesel fuel. The gradient of NO_xemissions with EGR rate for the CTL fuel was nearly the same with that for petroleumdiesel fuel. However, the gradient of soot emissions with EGR rate was much smaller thanthat for petroleum diesel fuel. Moreover, the CTL fuel could indeed improve the trade-offrelationship between the NO_xand soot emissions while petroleum diesel fuel had no sucheffects.Compared to original vehicle diesel engine with petroleum diesel fuel, the NO_xandsoot emissions of new vehicle diesel engine fuelled with the CTL fuel were simultaneouslyreduced in all the tested operation conditions. Especially in the25%and35%loads, theNO_xand soot emissions decreased more than50%, while the BSFC was not obviouslydeteriorated. Moreover, the maximum supercharging ratio of original vehicle diesel enginewas2.6, which meets national stage Ⅲ emission standard. Thus, there is a remarkable improvement for the new vehicle diesel engine compared to original vehicle diesel engine.AVL-Fire software was used to simulate the combustion process of the vehicle dieselengine, the simulation results validated that the exposure port combustion chamber of lowcompression ratio was beneficial forimproving the mixing quality of the cylinder mixture,thus contributing to solving the trade-off between the NO_xand soot emissions.更多还原