共查询到20条相似文献,搜索用时 62 毫秒
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针对预混合氢气的柴油机,在AVL Fire软件上建立了计算模型,并与试验结果进行对比,验证模型的准确性。在此基础上改变了喷射策略,对发动机缸内工作过程及相应的燃烧和排放性能进行数值模拟和分析。研究结果表明:随着预混合氢气质量分数的增加,缸内压力和温度升高,NOx 排放恶化,Soot排放改善;随着预喷射油量和预喷间隔角的增加,NOx 质量分数升高,Soot质量分数降低;随着后喷射喷油量的增加,缸内压力和放热率稍微减小,NOx 和Soot质量分数降低;随着后喷间隔角的增加,缸内压力、放热率、NOx 和Soot排放均未发生明显变化。 相似文献
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预喷射对生物柴油发动机燃烧及排放特性影响研究 总被引:3,自引:0,他引:3
研究了不同预喷条件下满足国Ⅴ排放的高压共轨柴油机燃用混合燃料BD20(含80%体积分数的国Ⅴ柴油和20%体积分数的餐饮废油制生物柴油)的燃烧及排放特性。结果表明:采用预喷射后滞燃期有所缩短,燃烧持续期有所增大。相比于预喷间隔,预喷油量对滞燃期及燃烧持续期的影响更为显著;预喷射显著减小了主燃烧的压力升高率,改善了燃烧的剧烈程度,且低负荷取较小预喷间隔、高负荷取较大预喷间隔效果较优;采用预喷射后NO x 排放均有所降低,大部分预喷射条件下PM 排放有所增加,各负荷均存在着较佳预喷射方案,可以同时改善NO x 及PM 排放。 相似文献
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基于柴油机排气热管理的喷油策略控制试验研究 总被引:3,自引:0,他引:3
为有效满足柴油机中低转速、中小负荷工况下颗粒捕集器(DPF)主动再生时的工作温度需求,利用发动机台架试验研究了中低负荷稳态工况下主喷正时、近后喷及次后喷参数等排气热管理主动控制措施对缸内燃烧过程、排气热状态及排放性能的影响规律。稳态试验结果表明:推迟主喷提前角缩短了滞燃期,燃烧持续期延长,缸内最高燃烧压力及峰值温度下降,瞬时放热率峰值减小且燃烧重心后移,同时燃油消耗率及烟度略有增加,DOC入口温度提升也不明显;引入近后喷使得缸内最高燃烧压力降低,但放热率第二峰值及后燃期有所增加,近后喷油量与主-近后喷间隔角的合理匹配能适当提高DOC入口温度,最高增幅可达19.3%,同时也能有效改善NOx排放和烟度;次后喷油量的增加能显著提升DPF入口温度,最大增幅达70%,但会导致燃油消耗率及HC逃逸量增加。依据样机全工况排温分布状态提出各区域升温喷油控制策略:低负荷区域采用"近后喷+次后喷"的喷油组合,并且采用较大喷油量;中大负荷区域逐渐减少近后喷,直至无近后喷,同时将主喷适当提前。 相似文献
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文章研究了预喷正时对柴油发动机燃烧和排放特性的影响,通过调整一台高压共轨直列四缸柴油发动机预喷时刻,进行相关台架试验。分析了预喷时刻对压力升高率、瞬时燃烧放热率、有效压力循环变动系数、缸内温度等燃烧特性的影响,以及对超细颗粒物、NOx比排放和大颗粒物数目比排放等排放特性的影响。试验结果表明,随着主预喷间隔的增大,峰值压力升高率降低,瞬时放热率峰值提前,超细颗粒物浓度下降,大颗粒和NOx比排放持续降低。因此可以在不改变柴油机整体结构的前提下,通过调整预喷时刻,有效改善发动机的燃烧性能,减少污染物的排放。 相似文献
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《汽车工程》2015,(10)
本文中对比分析了某四缸轻型车用柴油机喷射正时、废气再循环(EGR)率和喷射压力对燃烧过程和污染物排放的影响规律。结果表明:采用适时早喷或者晚喷策略均能延长滞燃期而改善可燃混合气的均匀性,以实现部分预混合燃烧,抑制碳烟排放。适时早喷策略相对晚喷策略更有利于降低碳烟排放,但将受到NO_x排放恶化的限制。引入EGR后,适时早喷不但可降低缸内燃烧温度抑制NO_x排放,还可有效解决因早喷带来的燃烧相位过早的问题,从而提高燃烧效率,改善燃油经济性,在高EGR率区域可兼顾有效燃油消耗率、NO_x和碳烟排放。而晚喷条件下,引入EGR后会进一步加重后燃现象,使有效燃油消耗率和碳烟排放有所恶化。随着喷射压力的提高,适时早喷时,燃烧放热过程变缓,瞬时放热率峰值和缸内平均温度降低,从而可同时降低NO_x和碳烟排放,而晚喷则相反,NO_x排放随着喷射压力的提高而有所上升。而不论适时早喷还是晚喷,有效燃油消耗率受喷射压力的影响很小。 相似文献
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T. Fang R. E. Coverdill C. -F. F. Lee R. A. White 《International Journal of Automotive Technology》2008,9(5):551-561
An optically accessible single-cylinder high speed direct-injection (HSDI) Diesel engine equipped with a Bosch common rail
injection system was used to study low temperature Modulated Kinetics (MK) combustion with a retarded single main injection.
High-speed liquid fuel Mie-scattering was employed to investigate the liquid distribution and evolution. By carefully setting
up the optics, three-dimensional images of fuel spray were obtained from both the bottom of the piston and the side window.
The NOx emissions were measured in the exhaust pipe. The influence of injection pressure and injection timing on liquid fuel
evolution and combustion characteristics was studied under similar fuel quantities. Interesting spray development was seen
from the side window images. Liquid impingement was found for all of the cases due to the small diameter of the piston bowl.
The liquid fuel tip hits the bowl wall obliquely and spreads as a wall jet in the radial direction of the spray. Due to the
bowl geometry, the fuel film moves back into the central part of the bowl, which enhances the air-fuel mixing process and
prepares a more homogeneous air-fuel mixture. Stronger impingement was seen for high injection pressures. Injection timing
had little effect on fuel impingement. No liquid fuel was seen before ignition, indicating premixed combustion for all the
cases. High-speed combustion video was taken using the same frame rate. Ignition was seen to occur on or near the bowl wall
in the vicinity of the spray tip, with the ignition delay being noticeably longer for lower injection pressure and later injection
timing. The majority of the flame was confined to the bowl region throughout the combustion event. A more homogeneous and
weaker flame was observed for higher injection pressures and later injection timing. The combustion structure also proves
the mixing enhancement effect of the liquid fuel impingement. The results show that ultra-low sooting combustion is feasible
in an HSDI diesel engine with a higher injection pressure, a higher EGR rate, or later injection timing, with little penalty
on power output. It was also found that injection timing has more influence on HCCI-like combustion using a single main injection
than the other two factors studied. Compared with the base cases, simultaneous reductions of soot and NOx were obtained by
increasing EGR rate and retarding injection timing. By increasing injection pressure, NOx emissions were increased due to
leaner and faster combustion with better air-fuel mixing. However, smoke emissions were significantly reduced with increased
injection pressure. 相似文献
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T. Fang R. E. Coverdill C. -F. F. Lee R. A. White 《International Journal of Automotive Technology》2009,10(3):285-295
In this paper, the influence of injection parameters on the transition from Premixed Charge Combustion Ignition (PCCI) combustion
to conventional diesel combustion was investigated in an optically accessible High-Speed Direct-Injection (HSDI) diesel engine
using multiple injection strategies. The heat release characteristics were analyzed using incylinder pressure for different
operating conditions. The whole cycle combustion process was visualized with a high-speed video camera by simultaneously capturing
the natural flame luminosity from both the bottom of the optical piston and the side window, showing the three dimensional
combustion structure within the combustion chamber. Eight operating conditions were selected to address the influences of
injection pressure, injection timing, and fuel quantity of the first injection on the development of second injection combustion.
For some cases with early first injection timing and a small fuel quantity, no liquid fuel is found when luminous flame points
appear, which shows that premixed combustion occurs for these cases. However, with the increase of first injection fuel quantity
and retardation of the first injection timing, the combustion mode transitions from PCCI combustion to diffusion flame combustion,
with liquid fuel being injected into the hot flame. The observed combustion phenomena are mainly determined by the ambient
temperature and pressure at the start of the second injection event. The start-of-injection ambient conditions are greatly
influenced by the first injection timing, fuel quantity, and injection pressure. Small fuel quantity and early injection timing
of the first injection event and high injection pressure are preferable for low sooting combustion. 相似文献
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