生物柴油醛、酮类污染物的排放特性与分析

采用2,4-二硝基苯肼(DNPH)衍生法和高效液相色谱(HPLC)技术,对柴油机排气中的醛、酮污染物进行了捕集和分离测定,考察了柴油机燃用BD100、BD50、BD0时,不同负荷下的醛、酮污染物排放规律,分析了燃料组分、缸内温度、压力、排气温度等对醛、酮污染物排放的影响。研究结果表明,该方法可实现微量醛、酮污染物的准确、快速测定;柴油机排气中含量较高的羰基物有甲醛、丙醛、丙烯醛、乙醛、丙酮、丁酮和丁醛,其排放水平均随负荷增大而呈下降的趋势;高负荷时,高温区域的滞留时间延长,醛、酮类被再次氧化、转化几率增加;较高的排气温度会促使排气中的醛、酮类物质和HC燃料再次氧化生成CO和CO2。     

Influence of biodiesel on engine combustion and emission characteristics

This paper discusses the influence of biodiesel on the engine combustion characteristics. The considered fuel is neat biodiesel from rapeseed oil. The considered engine is a bus diesel engine with injection M system. The engine characteristics are obtained by experiments and numerical simulation. The results obtained with biodiesel are compared to those obtained with mineral diesel under various operating regimes. In this way, the influences of biodiesel usage on the injection pressure, injection timing, ignition delay, in-cylinder gas pressure and temperature, heat release rate, exhaust gas temperatures, harmful emissions, specific fuel consumption, and on engine power are analyzed. Furthermore, the relationships among fuel properties, injection and combustion characteristics, harmful emissions, and other engine performance are determined. Special attention is given to possible explanations of higher NO_x emission in spite of lower in-cylinder gas temperature.     

Numerical investigation and Pareto optimization on performance,emission and in-cylinder reforming characteristics for two cylinder reciprocating engine with COx free fuel

The main objective of this study is to introduce the applicability of ammonia to the downsized compression ignition diesel engine for power generation or range extender. For this research objective, the two cylinder engine, which was the result of the previous study, fueled with diesel-ammonia blends was considered and the performance and NOx emission tendency were identified using the numerical method. Ammonia was mixed with diesel via injection at a specific fuel energy fraction (0%, 5%, 10%, or 15%) to evaluate the engine performance and emission characteristics. In addition, concept of “in-cylinder reforming” was introduced adopting negative valve overlap (NVO) by advancing the exhaust valve closing time to investigate the effect of adding ammonia as a hydrogen carrier. Subsequently, the primary variables affecting the brake-specific fuel consumption and NO_X are determined via multi-objective Pareto analysis. The optimal Pareto front confirms that exhaust valve timing exerts a greater effect on the performance and emissions than injection timing. Moreover, in-cylinder reformed hydrogen was increased under negative valve overlap strategy.     

EGR对生物柴油/异丁醇混合燃料燃烧与排放的影响

在一台四缸四冲程水冷高压共轨柴油机上研究了生物柴油/异丁醇混合燃料在不同EGR率下的燃烧及排放特性.试验结果表明:随EGR率的升高,缸内压力和放热率峰值降低,燃料滞燃期延长,燃烧持续期先缩短后延长,NO排放与核模态颗粒物数密度降低;当EGR率小于6%时,CO和HC污染物的排放都保持在较低水平.相较于生物柴油,燃用混合燃料降低CO污染物的排放;随异丁醇掺混比例的增加,缸内压力与放热率峰值逐渐升高,CO排放降低,但HC与NO的排放逐渐升高,核模态颗粒物数密度升高,积聚态颗粒物数密度和颗粒物质量浓度有不同程度的下降.     

增压中冷车用柴油机EGR率阶跃工况响应

利用实时EGR率测量系统及瞬态工况测控平台对增压中冷柴油机废气再循环(EGR)阶跃工况下的EGR率、进气量、发动机转矩、燃烧过程特征参数、排气烟度及气态有害排放物的响应历程进行了试验研究.试验结果表明:在1 600 r/min5、0%负荷工况,EGR率从0分别阶跃到3%、5%、13%和28%时,EGR率、进气流量及发动机有效转矩响应速度较快且相近,均为0.5 s左右;排气烟度和以最高燃烧压力表征的缸内燃烧过程趋于稳定状态历时较长且时间相近,不同EGR率阶跃时均为2.5 s左右;以气态有害物排放表征的柴油机排放响应历时最长为6 s左右.这说明在EGR阶跃工况下,当EGR率达到稳定时,由于燃烧边界条件存在迟滞效应,从而会导致燃烧过程、有害物排放存在较长的延迟.     

Experimental investigations of performance,emission and combustion characteristics of Karanja oil blends fuelled DICI engine

Vegetables oils are simplest route of biofuel utilization in direct injection compression ignition (DICI) engines however several operational and durability problems are encountered while using straight vegetable oils in CI engines due to their high viscosity and low volatility. Reduction of viscosity by blending or exhaust gas heating leads to savings in chemical processing cost incurred on transesterification. In this experimental study, performance, emission and combustion characteristics of Karanja oil blends (K10, K20, K50 and K100) with mineral diesel were investigated in unheated conditions in a direct injection CI engine at different engine loads and constant engine speed (1500 rpm) vis-à-vis baseline data from mineral diesel. Analysis of performance parameters such as brake specific fuel consumption (BSFC), thermal efficiency, and exhaust gas temperature; mass emissions of various gaseous pollutant species; combustion parameters such as in-cylinder pressure rise, instantaneous heat release and cumulative heat release etc. were carried out. Detailed combustion analysis revealed that the combustion duration increased significantly even with smaller concentration of Karanja oil in the fuel blend. HC, CO and Smoke emissions were found to decrease for 20–50% (v/v) Karanja oil content in the fuel blends.     

Soot processes in compression ignition engines

While diesel engines are arguably superior to any other power-production device for the transportation sector in terms of efficiency, torque, and overall driveability, they suffer from inferior performance in terms of noise, NO_x and particulate emissions. The majority of particulate originates with soot particles which are formed in fuel-rich regions of burning diesel jets. Over the past two decades, our understanding of the formation process of soot in diesel combustion has transformed from inferences based on exhaust measurements and laboratory flames to direct in-cylinder observations that have led to a transformation in diesel engine combustion. In-cylinder measurements show the diesel spray to produce a jet which forms a lifted, partially premixed, turbulent diffusion flame. Soot formation has been found to be strongly dependent on air entrainment in the lifted portion of the jet as well as by oxygen in the fuel and to a lesser extent the composition and structure of hydrocarbons in the fuel. Soot surviving the combustion process and exiting in the exhaust is dominated by soot from fuel-rich pockets which do not have time to mix and burn prior to exhaust valve opening. Higher temperatures at the end of combustion enhance the burnout of soot, while high temperatures at the time of injection reduce air entrainment and increase soot formation. Using a conceptual model based on in-cylinder soot and combustion measurements, trends seen in exhaust particulate can be explained. The current trend in diesel engine emissions control involves multi-injection combustion strategies which are transforming the picture of diesel combustion rapidly into a series of low temperature, stratified charge, premixed combustion events where NO_x formation is avoided because of low temperature and soot formation is avoided by leaning the mixture or increasing air entrainment prior to ignition.     

汽油替代物组分对缸内直喷和进气道喷射汽车性能影响的试验研究

采用3种研究法辛烷值相同的汽油替代物在一辆缸内直喷(gasoline direction injection,GDI)和进气道喷射(port fuel injection,PFI)汽车上研究了不同汽油替代物组分对整车性能的影响。试验结果表明:相比异辛烷,添加甲苯会导致CO_2排放升高,而添加二异丁烯会降低CO_2排放,甲苯和二异丁烯均使体积油耗降低。添加二异丁烯和甲苯使GDI汽车的CO排放升高并使THC排放降低,使PFI汽车新欧洲驾驶循环(new European drive cycle,NEDC)前100s的瞬态CO和THC排放升高。二异丁烯会使NOx排放降低而甲苯会导致NOx排放升高。在颗粒排放方面,添加甲苯使GDI汽车排放的颗粒物质量(particle mass,PM)和数量(particle number,PN)增加,添加二异丁烯会降低GDI汽车PM和PN排放;添加甲苯和二异丁烯会降低PFI汽车的PM排放,但会导致其PN增加。在加速性能方面,二异丁烯和甲苯的加入会缩短GDI汽车的加速时间,而甲苯会使PFI汽车的加速时间增加。     

On the capabilities and limitations of predictive,multi-zone combustion models for hydrogen-diesel dual fuel operation

Compared with traditional hydrocarbon fuels, hydrogen provides a high-energy content and carbon-free source of energy rendering it an attractive option for internal combustion engines. Co-combusting hydrogen with other fuels offers significant advantages with respect to thermal efficiency and carbon emissions.This study seeks to investigate the potential and limitations of multi-zone combustion models implemented in the GT-Power software package to predict dual fuel operation of a hydrogen-diesel common rail compression ignition engine. Numerical results for in-cylinder pressure and heat release rate were compared with experimental data. A single cylinder dual-fuel model was used with hydrogen being injected upstream of the intake manifold. During the simulations low (20 kW), medium (40 kW) and high (60 kW) load conditions were tested with and without exhaust gas recirculation (EGR) and at a constant engine speed of 1500 rpm. Both single and double diesel injection strategies were examined with hydrogen energy share ratio being varied from 0 to 57% and 0–42 respectively. This corresponds to a range in hydrogen air-equivalence ratios of approximately 0–0.29.The results show that for the single-injection strategy, the model captures in-cylinder pressure and heat release rate with good accuracy across the entire load and hydrogen share ratio range. However, it appears that for high hydrogen content in the charge mixture and equivalence ratios beyond the lean flammability limit, the model struggles to accurately predict hydrogen entrainment leading to underestimated peak cylinder pressures and heat release rates. For double-injection cases the model shows good agreement for hydrogen share ratios up to 26%. However, for higher energy share ratios the issue of erroneous hydrogen entrainment into the spray becomes more accentuated leading to significant under-prediction of heat release rate and in-cylinder pressure.     

基于CFD的增压柴油机不同喷油提前角的排放影响分析

在考虑进气涡流比的情况下,对某490增压直喷柴油机不同喷油提前角下的缸内喷雾及燃烧过程进行了三维CFD模拟,给出了4种不同喷油提前角时的缸内火焰、NOx和Soot的时空分布.计算和分析了不同的喷油提前角下,上止点前后喷入缸内的油量比例、着火时刻、上止点温度、最高燃烧温度等对燃烧与排放物的影响.结果表明上止点前后的油量比例对排放有较大影响,对于该机型在喷油提前角较小的情况下,应考虑适当减小喷油锥角以充分利用燃烧室底部的空气.仅靠喷油提前角的变化并不能同时降低NOx和Soot的排量,并通过性能与排放试验进行了验证.     

CA6DL1—30柴油机燃烧室改进的模拟与实验研究

为研究燃烧室形状对柴油机燃烧和排放性能的影响,应用大型通用CFD软件STAR—CD程序对3种不同形状的燃烧室内燃烧过程进行了多维数值模拟计算,研究了不同的燃烧室形状对缸内气流运动以及缸内燃烧温度和排放的影响,并通过实验验证了计算模型的正确性。     

A numerical study on a hydrogen assisted diesel engine

This work aims to numerically study the performance, combustion and emission characteristics of a hydrogen assisted diesel engine under various operating conditions. Simulations were performed using multi-dimensional software KIVA4 coupled with CHEMKIN. The Kelvin–Helmholtz and Rayleigh–Taylor hybrid break up model was implemented to accurately model the spray development. A detailed reaction mechanism was constructed to take into account the chemical kinetics of diesel and hydrogen, and it was validated against the experimental results with 0% of hydrogen induction. Simulation results showed that at low engine speeds, the indicated thermal efficiency, in-cylinder pressure and apparent heat release rate increased significantly with the induction of hydrogen. On the other hand, at high engine speed and high load conditions, no tangible changes on the engine performance, combustion characteristics were observed. In terms of emissions, CO and soot emissions were shown to be reduced under most of the engine operating conditions. Whereas for NO_x emissions, a slight increase was observed at low engine speed of 1600 rpm.     

低压EGR对GDI增压汽油机外特性下性能和排放影响

通过一款涡轮增压汽油直喷(gasoline direct injection,GDI)发动机低压废气再循环(exhaust gas recirculation,EGR)的试验,研究了EGR率和点火提前角的综合作用对增压GDI发动机的燃烧、缸压、排放和油耗等方面的影响。结果表明,在GDI增压发动机中加入EGR后,由于废气的稀释和热容作用,使缸内燃烧持续期增大,排气温度下降,燃烧相位也发生了改变。这对发动机外特性的有利影响是油耗减少,CO和NO_x排放也明显减少;不利影响是EGR的加入提高了增压发动机的排气压力,导致泵气损失增加。此外,总碳氢(total hydro carbons,THC)排放也有所增加。在GDI增压汽油机中使用EGR系统并配合点火角的调节能够有效提高热效率,降低NO_x排放。     

An experimental and modelling study of dual fuel aqueous ammonia and diesel combustion in a single cylinder compression ignition engine

The ability of ammonia to act as a hydrogen carrier, without the drawbacks of hydrogen gas-storage costs and low stability-renders it a potential solution to the decarbonisation of transport. This study combines both modelling and experimental techniques to determine the effect of varying the degree of aspiration of ammonium hydroxide (NH₄OH) solution, at different engine loads, in the combustion of a compression ignition engine. Ignition delay was extended as ammonia injection increased, causing an increase in peak in-cylinder temperature, but generally lower combustion quality-increasing incomplete combustion products, while decreasing particle size. The higher peak in-cylinder temperatures generally correlated with higher nitrous oxide (NO_x) emissions in the exhaust, though a fuel-bound nitrogen effect was apparent. Chemical kinetic modelling at equivalent conditions found increasing levels of unburnt ammonia with greater aspiration. Moreover, the ignitability of NH₄OH was found to improve in simulations substituting diesel with hydrogen peroxide direct injection.     

直喷式柴油机排放的机内控制研究

不同的油气混合和缸内燃烧过程的组织．对直喷式柴油机污染物的排放有较明显的影响,从而找到了降低直喷式柴油机排放的方法．     

Experimental study of combustion and emission characteristics of ethanol fuelled port injected homogeneous charge compression ignition (HCCI) combustion engine

The homogeneous charge compression ignition (HCCI) is an alternative combustion concept for in reciprocating engines. The HCCI combustion engine offers significant benefits in terms of its high efficiency and ultra low emissions. In this investigation, port injection technique is used for preparing homogeneous charge. The combustion and emission characteristics of a HCCI engine fuelled with ethanol were investigated on a modified two-cylinder, four-stroke engine. The experiment is conducted with varying intake air temperature (120–150 °C) and at different air–fuel ratios, for which stable HCCI combustion is achieved. In-cylinder pressure, heat release analysis and exhaust emission measurements were employed for combustion diagnostics. In this study, effect of intake air temperature on combustion parameters, thermal efficiency, combustion efficiency and emissions in HCCI combustion engine is analyzed and discussed in detail. The experimental results indicate that the air–fuel ratio and intake air temperature have significant effect on the maximum in-cylinder pressure and its position, gas exchange efficiency, thermal efficiency, combustion efficiency, maximum rate of pressure rise and the heat release rate. Results show that for all stable operation points, NO_x emissions are lower than 10 ppm however HC and CO emissions are higher.     

某四缸乘用车柴油机燃烧系统的设计优化

介绍了长城汽车研发的一款高性能"2.0VGT"柴油发动机燃烧系统的设计优化过程,通过模拟计算发动机整个工作过程,对进排气系统和进气道形状、气流运动形式、喷油器喷雾特性、燃烧室形状进行多方案优化选型。研究不同工况下,喷油规律(次数、喷油间隔、每次喷油量、喷油时刻)、喷油器特性(喷孔数量、喷孔直径、喷油压力、喷油锥角)的喷雾特性(油滴细化程度、贯穿度)对发动机性能、排放和油耗的影响规律。并对发动机实现国Ⅴ排放要求,对所需要的喷油系统特性及燃烧室形状进行研究。     

Combustion performance and emission reduction characteristics of automotive DME engine system

This article is a condensed overview of a dimethyl ether (DME) fuel application for a compression ignition diesel engine. In this review article, the spray, atomization, combustion and exhaust emissions characteristics from a DME-fueled engine are described, as well as the fundamental fuel properties including the vapor pressure, kinematic viscosity, cetane number, and the bulk modulus. DME fuel exists as gas phase at atmospheric state and it must be pressurized to supply the liquid DME to fuel injection system. In addition, DME-fueled engine needs the modification of fuel supply and injection system because the low viscosity of DME caused the leakage. Different fuel properties such as low density, viscosity and higher vapor pressure compared to diesel fuel induced the shorter spray tip penetration, wider cone angle, and smaller droplet size than diesel fuel. The ignition of DME fuel in combustion chamber starts in advance compared to diesel or biodiesel fueled compression ignition engine due to higher cetane number than diesel and biodiesel fuels. In addition, DME combustion is soot-free since it has no carbon–carbon bonds, and has lower HC and CO emissions than that of diesel combustion. The NO_x emission from DME-fueled combustion can be reduced by the application of EGR (exhaust gas recirculation). This article also describes various technologies to reduce NO_x emission from DME-fueled engines, such as the multiple injection strategy and premixed combustion. Finally, the development trends of DME-fueled vehicle are described with various experimental results and discussion for fuel properties, spray atomization characteristics, combustion performance, and exhaust emissions characteristics of DME fuel.     

掺混比例和喷射定时对二甲醚-乙醇发动机燃烧和排放的影响

在一台电控共轨发动机上,试验研究了乙醇掺混比例和喷射定时对二甲醚-乙醇混合燃料燃烧及排放的影响。结果表明:随乙醇比例的增加,滞燃期延长,燃烧持续期缩短,最大压力升高率上升。随喷射推迟,滞燃期延长,燃烧相位延后,燃烧持续期在纯二甲醚时延长,而在掺混乙醇时则先延长后缩短,最大压力升高率先下降后上升。掺混乙醇和推迟喷射使预混燃烧比例增加。随喷射推迟,混合燃料的排气温度升高,喷射推迟到上止点后,排气温度随乙醇比例的增加而升高,排气温度高,则废气能量高,增压器增压比大,进气流量大,导致缸内压缩压力升高。在上止点前喷射时,掺混乙醇能使HC和CO排放保持在较低范围的同时,一定程度降低NO_x排放,掺混15%的乙醇较纯二甲醚最大降低约11%NO_x排放。随推迟喷射,NO_x排放降低,最大降幅达52%,在过分推迟燃料喷射时,因热效率低,循环喷射量增加,含15%乙醇混合燃料的NO_x排放会高于纯二甲醚。HC和CO排放随喷射推迟而升高,且升高幅度增大。     

车用汽油机有害排放物的形成、影响因素及危害

本文详细地论述了车用汽油机排放的特点,分析了车用汽油机有害排放物的形成、影响因素及危害,并指出降低车用汽油机排气污染,改善人类生存环境已是当务之急。