共查询到19条相似文献,搜索用时 171 毫秒
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对柴油机选择性催化还原(SCR)系统的研究,主要集中在催化器出口测量系统的整体氮氧化物(NO_x)转化效率。为了进一步提高系统的效率,在柴油机试验台架上,调整不同的排气工况及尿素喷射参数,研究了SCR催化器出口截面的NO_x转化效率分布特性。结论表明:催化器出口截面的NO_x转化效率分布呈现中心高而边缘低的规律,随着排气流量的增加,NO_x转化效率降低,在排气流量较大时,由于弯管对排气流场的作用,NO_x转化效率的高效区偏向一侧;提高氨氮比可以提高NO_x转化效率,当排气温度为250和350℃、氨氮比为1.0时就可以达到比较高的效率,进一步提高氨氮比NO_x转化效率的增幅不明显;当排气温度为450℃时,提高氨氮比对NO_x转化效率的增加比较有利。 相似文献
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未来的排放标准对汽车工业是一个很大的挑战,要达到这些要求,在排气系统中安装废气催化器是一个有效的措施。由于汽油车排放大部分是在发动机冷态和暖机运转过程中生成的,所以要尽可能地改善催化剂的低温活性以降低催化剂的起燃温度,提高其反应速率;另外还要对催化器进行预热处理,优化催化剂的激化环境,使其尽快投入反应。本文描述了近年来为满足未来排放要求而在汽油机废气催化剂上所采取的激化措施和在催化器上所采取的预热措施。 相似文献
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《内燃机与动力装置》2017,(2):1-4
本文针对一款国五SCR催化器,采用发动机台架试验的方法研究了SCR样件温度场的关键特征,包括SCR催化剂前后温度、催化器外壳温度、喷嘴处温度等,比较了SCR催化剂温度传感器与发动机台架上催化器进出口排气温度测试结果的差异。研究表明:SCR催化器外壳体温度较高;稳态工况下,该样件的SCR入口温度测量值明显比台架的入口温度测量值偏小,在SCR出口处,二者的偏差很小;瞬态循环中SCR样件的温度传感器与台架温度传感器测量值偏差更为明显,由于动态响应的原因,样件的前温传感器测试结果滞后于台架测试结果;尿素不喷射条件下,尿素喷嘴处可以达到很高的温度,可能出现尿素管接口失效。 相似文献
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采用进气节流降低排气氧浓度的方式,试验研究了柴油机氧化催化器(diesel oxidation catalyst, DOC)入口氧浓度对柴油机颗粒捕集器(diesel particulate filter, DPF)主动再生时的入口温升特性、载体峰值温度、有效再生时间和再生过程燃油消耗的影响。结果表明:随着排气氧浓度降低,DPF温升速率增大,入口温度上升时间缩短;在所有氧浓度下,载体峰值温度均出现在DPF轴线后端位置。随着氧浓度降低,载体峰值温度先增后减,最大径向温度梯度先减后增,有效再生时间先缩短后延长,再生过程燃油消耗先减后增。在恒定DPF碳烟负载量和再生温度的前提下,当排气氧体积分数为11.0%时DPF主动再生时间最短,再生过程燃油消耗最少。 相似文献
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The conversion efficiency of three way catalyst (TWC) depends on chemical reaction and transport limitations. This paper reports a quantitative analysis of the relative importance of these limiting processes based on experimental data obtained under real world vehicle operating conditions. The main conclusions are as follows: (i) above light-off temperature the mass transport phenomena overlaps the kinetic limitation but pure external mass transfer control is hard to attain in TWC operating under real world automotive conditions, even when both space velocity and operating temperature are very high; (ii) above light-off temperature the automotive TWC operates in a mixed regime with both internal and external mass transfer playing important roles; (iii) the internal mass transfer limitation is more important to control conversion in the TWC than the external mass transfer limitation but the relative importance of the external mass transfer increases as the temperature rises; (iv) the internal mass transfer limitation cannot be disregard in TWC modeling studies and (v) the results show that the current generation of TWC is over designed from an external mass transport viewpoint so that future improvements of these devices can be achieved with porous washcoat with improved transport proprieties. 相似文献
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基于三效催化转化器内部化学反应机理以及化学动力学模型,使用大型通用计算流体力学软件FLUENT进行数值仿真.首先,建立2种三维单孔道模型;其次,通过数值模拟得到尾气各组分的质量分布、组分分布随孔道长度变化的关系以及反应过程中孔道温度的变化关系.结果表明:净化器中单孔道内催化反应主要发生在孔道前端,前端载体的利用率高于后端载体,孔道边缘比孔道中心有更高的转化率以及孔道的形状对组分边缘处的转化效率影响较大.以上研究为净化器的性能分析提供了有效的计算依据. 相似文献
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利用GRACE重力卫星反演得到陆地水储量变化受数据低空间分辨率的限制,目前仅应用于大尺度的空间范围内,为此提出一种简易的降尺度方法将GRACE陆地水储量变化精度提高了16倍。借助全球水文模型模拟的陆地水储量变化数据,在中国九大流域上进行分区对比分析,发现高分辨率数据基本保持了原始数据的时空变化趋势,同时又增加了水文模型模拟的水储量变化信息。此外,利用全国455个地下水位监测站的水位数据,验证了降尺度后的陆地水储量变化数据,可知高分辨率陆地水储量变化数据与实测地下水变化值的相关系数最高达0.847,普遍高于低分辨率GRACE陆地水储量变化值与实测地下水变化值的相关系数,证明降尺度后的数据更加准确有效。进而基于降尺度数据,利用EOF方法分析了2005年1月~2012年12月中国各地陆地水储量变化的时空变化特征,即在总体趋势上,长江流域及以南地区春夏两季的陆地水储量有明显增加,华北地区的地下水超采及南方流域的极端气候事件为影响该区域陆地水储量异常的重要因素。 相似文献
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通用小型汽油机尾气后处理技术研究 总被引:1,自引:0,他引:1
分析某通用小型汽油机在各工况下的排放规律,探究三元催化器在小型汽油机上的应用效果,建立比排放因子的计算公式,提出了通用小型汽油机的尾气后处理方案. 相似文献
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汽油机颗粒物数量排放及粒径的分布特性 总被引:3,自引:0,他引:3
采用 DMS500快速颗粒取样分析仪对一台气道喷射国Ⅲ汽油机进行了颗粒物粒径分布特性的试验研究.结果表明,汽油机排气中颗粒物以核态为主,仅部分工况存在积聚态.怠速时呈现包括核态和积聚态的双峰分布;低转速时表现为核态的单峰分布;中等转速时粒径分布范围扩大,既存在核态颗粒物,也存在积聚态颗粒物.相同转速下,随负荷的增加核态颗粒物数密度峰值先降低后增加;相同负荷下,随转速的升高核态颗粒物数密度峰值和峰值粒径均降低,积聚态颗粒物数密度峰值有增加的趋势.催化器对核态颗粒物的净化效果较好,对积聚态颗粒物的净化效果较差,对低转速下的粒径分布有明显影响 相似文献
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《Applied Thermal Engineering》2007,27(11-12):1904-1910
A 3-cylinder port fuel injection engine was adopted to study engine power, torque, fuel economy, emissions including regulated and non-regulated pollutants and cold start performance with the fuel of low fraction methanol in gasoline. Without any retrofit of the engine, experiments show that the engine power and torque will decrease with the increase fraction of methanol in the fuel blends under wide open throttle (WOT) conditions. However, if spark ignition timing is advanced, the engine power and torque can be improved under WOT operating conditions. Engine thermal efficiency is thus improved in almost all operating conditions. Engine combustion analyses show that the fast burning phase becomes shorter, however, the flame development phase is a little delay.When methanol/gasoline fuel blends being used, the engine emissions of carbon monoxide (CO) and hydrocarbon (HC) decrease, nitrogen oxides (NOx) changes little prior to three-way catalytic converter (TWC). After TWC, the conversion efficiencies of HC, CO and NOx are better. The non-regulated emissions, unburned methanol and formaldehyde, increase with the fraction of methanol, engine speed and load, and generally the maximum concentrations are less than 200 ppm. Experimental tests further prove that methanol and formaldehyde can be oxidized effectively by TWC. During the cold start and warming-up process at 5 °C, with methanol addition into gasoline, HC and CO emissions decrease obviously. HC emission reduces more than 50% in the first few seconds (cold start period) and nearly 30% in the following warming-up period, CO reduces nearly 25% when the engine is fueled with M30. Meanwhile, the temperature of exhaust increases, which is good to activate TWC. 相似文献
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《International Journal of Hydrogen Energy》2020,45(39):20491-20500
The unburned H2 can be used to reduce NO emission in conventional TWC (three-way catalyst) for a hydrogen internal combustion engine when it works at equivalence ratio marginally higher than the stoichiometric ratio. To explore the effects and feasibility of this reaction, a Perfectly Stirred Reactor simulation model of TWC has been built with simplified mechanisms. Experiments on a 2.3 L turbocharged hydrogen engine are used to verify the conclusion. It shows that rising initial temperature accelerates the reduction of NO and the maximum reaction rate occurs at 400 °C temperature. The conversion efficiency of NO remains approximately 0 when temperatures below 300 °C. The efficiency reaches a peak value of approximately 98% with 400 °C and declines gradually. The unburned H2 to NO mixing ratio greater than 1.5 in TWC guarantees 100% NO conversion efficiency. The experiments indicate that the NOx concentration decreases from 2056 ppm to 41 ppm at the stoichiometric ratio after the treatment of TWC and NOx reaches 0 ppm with a rich ratio. Results also demonstrate that the suitable reaction temperatures for TWC locate in the range of 400 °C–500 °C. Therefore, if the temperature and the mixing ratio are appropriate, it can achieve zero emissions with NOx reduction by unburned H2 in conventional TWC for a hydrogen engine. 相似文献