湍流对缸内存在催化燃烧的HCCI发动机燃烧与排放特性的影响

将发动机多维CFD程序KIVA-3V与化学动力学程序CHEMKIN Ⅲ及DETCHEM相耦合,模拟了湍流模型对缸内存在催化燃烧的HCCI发动机燃烧及排放特性的影响.发动机以甲烷为燃料,其表面和空间化学反应采用了详细的动力学机理.分析了两种湍流模型对缸内存在催化燃烧的HCCI发动机着火时刻、缸内温度场及HC、CO、NO浓度场的影响,结果表明当采用RNG k-ε模型时,与采用标准k-ε模型相比,HCCI发动机着火时刻会有所延迟,HC、CO排放有所升高,但Nox的排放将会有大幅降低.     

喷射参数对二甲醚PPCCI发动机燃烧与排放特性的影响

在一台6缸增压电控共轨二甲醚发动机上进行试验,研究了预喷时刻、预喷燃料量、喷射压力、主喷时刻等喷射参数对二甲醚部分预混合充量压缩燃烧(PPCCI)发动机燃烧与排放特性的影响。试验结果表明:随预喷时刻提前,缸内压力峰值降低,二甲醚发动机缸内燃烧由两阶段放热转变为PPCCI三阶段放热,氮氧化物(NOx)排放显著降低,HC和CO排放升高;随预喷射燃料量增加,缸内压力峰值及预混合燃烧的冷焰反应和热焰反应速率明显增大,NOx排放逐渐降低,HC和CO排放显著升高;随喷射压力降低,预混合燃烧热焰反应速率增加,主喷扩散燃烧始点推迟,扩散燃烧放热率峰值和NOx排放明显降低,HC和CO排放升高;随主喷时刻推迟,预喷预混合燃烧几乎没有变化,主喷扩散燃烧延后,缸内压力峰值和放热率峰值降低,NOx排放显著降低,HC和CO排放升高。     

冷起动首循环瞬态HC排放特性试验研究

从循环控制的角度，详细研究了LPG点燃式发动机冷起动首循环瞬态HC排放特性。试验在一台电控LPG进气道喷射单缸风冷四冲程、125mL发动机上进行。通过高速采集系统记录发动机首循环瞬态HC排放、瞬时缸压和转速，分析了瞬态HC排放与其他参数之间的关系。研究表明：随着过量空气系数的变化，首循环瞬态HC排放在一个较宽的混合气浓度变化范围内平缓变化，并稳定在较低的水平。首循环瞬态HC排放的最小值出现在缸内燃烧最好的燃空当量比附近。当首循环混合气浓度过浓或者是过稀时，瞬态HC排放迅速增加。首循环瞬态HC排放随点火角度的推迟，其变化规律为先增加再减少，随点火角度不断推迟，在膨胀行程中氧化的燃料不断增加，当点火角度推迟到一定限值，缸内燃烧不能进行，瞬态HC排放急剧增加。     

基于混合动力起动模式发动机起动过程HC排放试验研究

针对ISG型混合动力汽车发动机起动过程中HC排放问题,试验中采用了混合动力起动模式,研究了不同电机拖转转速和不同的冷却液温度条件下发动机起动过程HC的排放控制.不同的ISG电机拖转转速影响缸内混合气的混合与燃烧,合适的拖转转速可以减少HC的排放.试验证明:在常温起动阶段,发动机HC排放性能最佳电机拖转转速为1200r·min-1.试验分析了不同冷却液温度下起动过程HC生成的机理,为HC排放的优化控制提供了理论依据.     

均质压燃发动机燃烧与排放的多区模型模拟

应用一个有质量交换的6区模型模拟正庚烷在HCCI发动机中的燃烧和排放特性．通过把缸内划分为缝隙区、边界层区、外核心区和内核心区,加入Woschni传热模型计入了缸内的温度和浓度的不均匀分布．全部计算基于正庚烷燃烧的包含57种组分290个反应的详细机理,结果表明,该多区模型合理地模拟了HCCI发动机的燃烧过程,并可满意地预测出HC、CO和NO的排放．最后采用此多区模型分别讨论了缝隙容积、边界层厚度和壁面温度对HCCI发动机的燃烧和排放的影响．     

压缩比对直喷天然气发动机燃烧与排放特性的影响

在缸内直喷火花点火天然气发动机上开展了压缩比为8、10、12和14的燃烧和排放特性研究。研究结果表明,压缩比对发动机性能、燃烧和排放有较大影响。压缩比增加,发动机充量系数增加,燃烧速率加快,热效率提高。缸内最高燃烧压力、最高燃气平均温度和最大压力升高率等燃烧参数随压缩比的增加而增加;HC和CO排放随压缩比的增加而降低,NOx随压缩比的增加而增加。压缩比过高会导致HC排放的增加,当压缩比大于12时,发动机在中高负荷出现轻微爆燃现象,NOx排放明显增加。综合考虑直喷式天然气发动机的动力性、经济性和排放性能,认为发动机的最佳压缩比设置在12比较合理。     

DN双燃料发动机掺H2燃烧的化学动力学分析

分别采用CFD耦合柴油/天然气/氢气(DNH)三燃料化学动力学机理以及CHEMKIN化学动力学分析的手段,对柴油/天然气(DN)双燃料发动机掺H_2的燃烧特性、重要组分及排放物生成过程进行数值模拟.研究表明:在保持引燃柴油量不变的条件下,将缸内燃料热值5%的天然气(NG)替换为H_2,燃烧过程中关键自由基OH的浓度峰值会增加了88%;而OH的强氧化性促使CH_4的氧化速率增加,HC排放下降为91.8%,CH_2O和CO的生成速率及峰值浓度增加,CH_2O排放减少为97.5%,CO排放降低为23%,碳烟排放下降为19.3%,由于缸内燃烧温度增加,导致NO_x排放增加为51%;掺H_2之后,缸内压力升高率增加,燃烧持续期缩短,累积放热量及瞬时放热率峰值增加,缸内温度峰值增加,温度峰值相位提前.     

缝隙区催化燃烧影响HCCI发动机燃烧与排放特性的多维数值模拟

将发动机多维CFD程序KIVA-3V与化学动力学程序CHEMKIN Ⅲ及DETCHEM相耦合,模拟了缝隙区催化燃烧对HCCI发动机燃烧及排放特性的影响.发动机以甲烷为燃料,其表面和空间采用详细的化学反应动力学机理.利用此模型分析了活塞顶部及侧面催化剂铂涂层对HCCI发动机着火时刻、缸内温度场及HC、CO、NO浓度场的影响.结果表明,当仅活塞顶存在催化剂涂层时,HCCI发动机着火时刻提前,HC、CO排放降低;当活塞顶及缝隙区同时存在催化剂时,HC、CO的排放更低,但NOx排放略有升高.     

不同喷射时刻下缸内直喷天然气发动机的燃烧特性

开展了天然气高压缸内直喷发动机不同喷射时刻时的燃烧特性研究。研究结果表明：燃料喷射时刻对发动机性能及排放有较大影响,喷射太迟会导致天然气和空气混合时间短,混合效果差,燃烧持续期长,放热速率慢。喷射过早会导致充量系数下降,燃料容易进入燃烧室狭缝间隙处,造成较高的HC排放。对于给定转速,发动机存在一个最佳燃料喷射提前角,此时缸内最高压力值最大,最大压力升高率和最大放热率最大,放热速率快,燃烧过程等容度好,火焰发展期、快速燃烧期和燃烧持续期短,发动机热效率高,HC、CO排放也维持较低水平。     

预喷对重载柴油机燃烧与排放影响的试验

基于内窥镜测量技术,在一台6缸高压共轨重载柴油机上研究了预喷正时、预喷油量与EGR率等对燃烧放热、排放物生成的影响作用.对柴油机缸内燃烧过程中的火焰图像进行了采集,并且通过双色法计算得到了碳烟颗粒场分布图像.结果表明:随预喷正时延迟,缸内峰值压力升高,预喷燃烧的两阶段放热现象消失,预喷燃烧的火焰亮度加强,NOx和碳烟排放均降低;随预喷油量增加,预喷燃烧的放热率和火焰亮度升高,NOx和HC排放增大,而碳烟和CO排放降低;随EGR率提高,预混燃烧强度变弱并且开始呈现两阶段放热现象,主燃烧始点滞后,NOx排放显著降低,但碳烟、HC和CO排放升高.采用内窥镜测量可以更方便准确地了解发动机实际运行工况下缸内燃烧特性.     

Cold-start hydrocarbon emissions in port-injected gasoline engines

An analysis is made of the sources of the high engine-out hydrocarbon (HC) emissions during cold starting of port-injected gasoline engines. A cycle-by-cycle analysis of the different parameters, which affect engine-out HC emissions, is made during the startup process. The contribution of each cylinder of a four-stroke V6, 3.3 l production engine in the total HC emissions is investigated. The HC emissions were measured in the exhaust port using a fast response flame ionization detector (FID). The effect of the initial startup position of the piston and valves in the cycle on combustion and HC emissions is examined. The mass of fuel injected, burned and emitted was calculated for each of the first 120 cycles. Different approaches to reduce engine-out and tailpipe HC emissions during cold-start are discussed.     

汽车催化剂快速起燃技术

汽车排气中大部分的CO和HC是在汽车冷起动期间 1～ 2min内排放的 ,但是由于冷起动时催化剂未达到工作温度而不能起转化作用 ,使冷起动排放超标。本文介绍了车用催化剂的快速起燃技术 ,它们包括电加热催化剂、燃烧器、前置主催化剂、碳氢收集器、排气点火器、前级催化器及二次空气技术等。快速起燃技术能使催化剂在冷起动时加快起燃 ,达到其工作温度 ,从而有效转化污染物     

Combustion-chamber crevices: the major source of engine-out hydrocarbon emissions under fully warmed conditions

This article presents a critical review of the studies performed to investigate combustion-chamber crevices as sources of hydrocarbon (HC) emissions, and an evaluation of potential technologies for reducing these emissions. Of the combustion-chamber crevices, the piston upper crevice volume is the main contributor to engine-out HC emissions. Chamfering the piston crown or reducing the top-land height and/or the volume behind the top compression ring may result in significant reductions in HC emissions. Modest reductions may also be achieved by reducing the central-electrode crevice of the spark-plug. However, reducing the head gasket crevice of current production engines appears to have little effect on engine-out HC emissions. In general, the sensitivity of the HC emissions to the combustion-chamber crevices is influenced strongly by the in-cylinder flow field and combustion, which influence the concentration of burned gases in the crevice gases.     

Effects of reformed exhaust gas recirculation on the HC and CO emissions of a spark-ignition engine fueled with LNG

Reformed exhaust gas recirculation (REGR), which can generate onboard hydrogen-rich gas (i.e., the reformate including H₂, CO, unreformed hydrocarbon, etc.) via catalytic reforming of fuel and engine exhaust gas, is an attractive way to improve the performance and emissions characteristics of the engine fueled with liquefied natural gas (i.e., NG engine). However, the leakage during the valve overlap period and incomplete burning of the added reformate may lead to extra HC and CO emissions from the engine with REGR. In the present study, a multi-dimensional computation fluid dynamics model coupled with a detailed chemical kinetic mechanism was developed to investigate the effects of the ratio of reformate addition (R_ref) and exhaust valve closed (EVC) timing on the total emissions characteristics as well as the sources of HC and CO emissions from the engine. The emissions from the combustion and the leaking were included to calculate the total emissions. Moreover, the unburned CO from the added reformate was distinguished from the total CO emissions by adding marked-species. Results show that the unburned CH₄ in the cylinder is the main component of the total CH₄ emissions. Due to the increase of the concentrations of OH, O and H radicals during the combustion process, the oxidization of CH₄ is promoted with the increase of R_ref at high load, and therefore the total CH₄ emissions decrease. However, the total CO emissions increase with the increase of R_ref, and it is demonstrated that the unburned CO from the added reformate increases and turns to be the main sources of the total CO emissions. At R_ref of 10%, the total CH₄ and CO emissions firstly remain nearly constant and then increase dramatically with the delay of EVC timing. Therefore, low concentration of CO in the reformate and short valve duration are recommended to achieve low HC and CO emissions for the NG engine with REGR.     

汽油/乙醇双燃料复合喷射对发动机排放性能的影响

通过在一台汽油气道喷射(GPI)的单缸、四冲程发动机上增加一套乙醇缸内直喷(EDI)系统,将其改装成为双喷射发动机,研究了汽油/乙醇复合喷射对发动机排放性能的影响,并建立了发动机计算流体动力学(CFD)模型,详细分析了缸内各区域的温度和组分分布特点.结果表明:加入乙醇直喷可以有效降低CO、NOx和soot排放,提高乙醇...     

减少柴油机暖机阶段HC排放的控制策略研究

柴油机在起动后的暖机过程中排出大量含有未燃碳氢(HC)的蓝烟，给人类健康和社会环境都带来极大的危害。本研究提出降低柴油机暖机阶段未燃HC排放的控制策略，并在试验基础上对不同转速与负荷时柴油机的HC排放浓度和HC排放总量进行了比较与分析，找到一种HC排放浓度和HC排放总量都较小的工况作为柴油机的暖机工况，证实了优化控制的可行性。     

Effects of intake air temperature on SI engine emissions during a cold start

This paper presents the concept of preheating the intake air to reduce cold-start emissions from gasoline engines. The effects of intake air temperature on emissions from a gasoline engine were studied by using an air heater based on spark ignition. A light-duty vehicle test of cold-start emissions was carried out at an ambient temperature of?7°C according to New European Driving Cycle for Euro 3 and Euro 4 exhaust emission legislations. The results showed that preheating the intake air could effectively reduce both hydrocarbon (HC) and carbon monoxide (CO) emissions and improve fuel economy during a cold start. During idling conditions, the key phase of the HC and CO emissions was the first 40 s. With the aid of the air heater, cold-start HC and CO emissions from the vehicle were lower than the limit values in the Euro 3 and Euro 4 regulations.     

A review on emissions and mitigation strategies for road transport in Malaysia

The emissions from road transport are serious threats to urban air quality and global warming. The first step to develop effective policies is to determine the source and amount of emissions produced. This paper attempts to review emissions from road transport using COPERT 4 model and examined possible emission mitigation strategies. In road transport, results have show that passenger cars are the main cause of CO₂, N₂O and CO emissions, while motorcycles are main source of hydrocarbon (HC) emissions. However, light duty vehicles and heavy duty vehicles are the main contribution of particulate matters. The total CO₂ equivalent emissions for road transport in Malaysia are 59,383.51 ktonnes for year 2007. Further results show that CO₂ emission is the primary source of greenhouse gas pollution which is 71% of the total CO₂ equivalent. A parametric study was conducted to estimate the potential emission mitigation strategies for road transport by taking the emissions in 2007 as a reference year. It was observed that promoting the public transport is an effective strategy to reduce emissions and fuel consumption from the technical view point. It can totally save up to 1044 ktonnes of fuel consumption and total CO₂ equivalents emissions can be decreased by 7%. It was noted that, fleet renewal and promoting natural gas vehicles will significantly contribute in the reduction of emissions in Malaysia.     

降低汽油机起动及暖机过程中HC排放的探讨

根据实测的催化器入口、出口 HC排放浓度及排气管不同位置的温度 ,结合示功图对电喷汽油机冷起动时 HC排放量在台架上进行了模拟分析 ,将起动过程以节气门突开为界划分为 3个阶段 ,其中HC的主要排放量发生在开始起动到节气门开这一段时间内。通过控制点火提前角使缸内发生不完全燃烧 ,将燃烧延续到排气管内 ,即可降低 HC排放量 ,也有助于加速催化器起燃。     

Factors affecting emissions from diesel fuel and water-in-diesel emulsion

The purpose of this research is to investigate the effect of addition of surfactant and water in diesel and to make an emulsified fuel considering the needs for vehicle performance and its cleanest possible operation. The total surfactant concentration in each of the diesel-water emulsion samples studied (span 20, span 80, tween 20, tween 80) is fixed at 1% w/w. The water content is variable at 5–15% w/w and the diesel content is varied from 84 to 94% w/w. Among all the tested nonionic surfactants, tween 80 is found to prominently reduce the carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOx) emissions. Tween 20 reduced the NOx emission to a greater extent. Diesel emulsion with a fixed ratio of span 80 and tween 80 (1:1) efficiently reduced the overall emissions as compared to diesel alone. The developed diesel emulsion employed with nonionic surfactants clearly reduced the harmful engine emissions such as CO, HC, and NOx, signifying them as a future potential emulsifier in diesel fuel emulsion.