Experimental and numerical study on the combustion characteristics of partially premixed charge compression ignition engine with dual fuel

The objective of this work is to investigate the effect of premixed fuel ratio on the combustion and emission characteristics in diesel engine by the experimental and numerical method. In order to investigate the effect of various factors such as the premixed ratio, EGR rate, and equivalence ratio on the exhaust gas from the premixed charge compression ignition diesel engine, the injection amount of premixed fuel is controlled by electronic port injection system. The range of premixed ratio between dual fuels used in this study is between 0 and 0.85, and the exhaust gas is recirclulated up to 30 percent of EGR rate.     

Pilot ignited premixed combustion of dimethyl ether in a turbodiesel engine

This paper describes combustion studies of dimethyl ether in a common rail turbodiesel engine wherein the dimethyl ether was fumigated into the intake air and the conventional diesel injection was used with the intention of igniting the premixed DME-air charge. This combustion process is referred to here as a “mixed mode” process and is similar in some respects to what is commonly referred to as “dual fuel” combustion. In contrast to “dual fuel” combustion, however, in which the gaseous fuel is often natural gas or biogas, in this process with DME the gaseous charge ignites largely independently of the diesel injection. The diesel injection was accomplished with a single, main injection. The engine was operated at a single speed and load. Gaseous and particulate emissions were monitored and heat release analysis was performed to examine how the fuels burn and the impact on emissions formation at various levels of substitution of diesel fuel with fumigated DME, at as high as 44% of the fuel energy from DME. Reductions in NO_x emissions and increases in particulate matter emissions are observed with DME fumigation. The increase in PM emissions is attributed to enrichment of the diesel fuel spray, due to displacement of intake oxygen by the fumigated DME, despite the widely observed soot suppressing effect of DME.     

Parametric investigations of premixed methane-air combustion in two-section porous media by numerical simulation

Motivated by detailed designs of industrial porous burners published in patents, the combustion of methane-air mixtures in a two-section porous burner has been studied numerically. The software FLUENT is used to solve a two-dimensional transient mathematical model of the combustion. In order to reveal the reality of the combustion in porous media, the user defined function (UDF) is used to extend the ability of FLUENT and enable two-dimensional distributions of temperature and velocity to be obtained. Some operating or property parameters, which mainly affect the functions and quality of the industrial burner design, such as the inlet velocity of the reactants, the equivalence ratio, the extinction coefficient and the thermal conductivity of porous media, have been investigated. The results show that the contours of temperature and velocity change considerably at the interface of the porous media and near the wall, the gas temperature at the low inlet velocity limit is higher than that for the high velocity limit, the thermal conductivity in the upstream section has more influence on the temperature than that in the downstream section and finally, the temperature profiles of both the gas and the porous skeleton vary considerably with changes of the radiative extinction coefficient of the large-pore porous media.     

Pulverized coal combustion characteristics of high-fuel-ratio coals

It is strongly desired for coal-fired power plants in Japan to utilize not only low-rank coals with high moisture and high ash contents, but also high-rank coals with high fuel ratio for diversifying fuel sources and lowering cost. In this study, pulverized coal combustion characteristics of high-fuel-ratio coals are experimentally investigated using an approximately 100 kg-coal/h pulverized coal combustion test furnace. The combustion characteristics are compared to those for bituminous coal. The coals tested are six kinds of coal with fuel ratios ranging from 1.46 to 7.10. The results show that under the non-staged combustion condition, the minimum burner load for stable combustion rises as fuel ratio increases. To improve the stability, it is effective to lengthen the residence time of coal particles in the high gas temperature region close to the burner outlet by using a recirculation flow. The conversion ratio of fuel nitrogen to NOx and unburned carbon fraction increases with increasing the fuel ratio. In addition, as the fuel ratio increases, NOx reduction owing to the staged combustion becomes small, and unburned carbon fraction increment becomes significant. The numerical simulations conducted under the staged combustion condition show that although the numerical results are in general agreement with the experimental ones, there remains room for improvement in NOx reduction model for high-fuel-ratio coals.     

Multistage catalytic combustion systems and high temperature combustion systems using SiC

Multistage catalytic combustion systems for commercial applications using noble metal catalyst were investigated at conditions under 1000°C. Also, the high temperature combustion systems using SiC material were investigated at conditions up to 1400°C.     

Biodiesel combustion in an optical HSDI diesel engine under low load premixed combustion conditions

An optically accessible single-cylinder high-speed direct-injection (HSDI) diesel engine was used to investigate the spray and combustion processes for biodiesel blends under different injection strategies. The experimental results indicated that the heat release rate was dominated by a premixed combustion pattern and the heat release rate peak became smaller with injection timing retardation. The ignition and heat release rate peak occurred later with increasing biodiesel content. Fuel impingement on the wall was observed for all test conditions. The liquid penetration became longer and the fuel impingement was stronger with the increase of biodiesel content. Early and late injection timings result in lower flame luminosity due to improved mixing with longer ignition delay. For all the injection timings, lower soot luminosity was seen for biodiesel blends than pure diesel fuel. Furthermore, NO_x emissions were dramatically reduced for premixed combustion mode with retarded post-TDC injection strategies.     

Kinetics of PdO combustion catalysis

The kinetics of the catalytic combustion of methane by supported palladium oxide catalysts (2 wt.-% Pd/La₂O₃·11A1₂O₃ and 5 wt.-%Pd/ γ-A1₂0₃ were examined for several oxygen partial pressure levels over the temperature range from 40–900°C using temperature-programmed reaction and slow ramp and hold temperature-time transient techniques. Combustion rates were measured by differential reaction in a fixed bed of powdered catalyst at lower temperatures (200–500°C). Also, by preparing the catalysts as thin (ca. 10 μm) coatings on an alumina tube and conducting the experiments with very high flows of dilute methane and oxygen in helium, the rate measurements were extended up to 900°C without significant contribution from gas phase reactions. The specific combustion activity of supported PdO shows a persistent hysteresis between 450 and 750°C, i.e., the rate of combustion between these temperature limits depends strongly on whether the catalyst is cooling from above 750°C or heating from below 450°C. This region is also notable for negative apparent activation energy in the rate of methane oxidation, i.e., the rate increases with decreasing temperature during reoxidation of the Pd metal and decreases with increasing temperature (especially with low oxygen partial pressure) prior to decomposition of the bulk oxide. Detailed time-temperature transient kinetic analyses were performed for supported PdO catalysts within the 450–750°C temperature range. The hysteresis in methane combustion rate is caused by a higher activation energy for reduction of oxygen chemisorbed on metallic Pd and by suppressed reoxidation of Pd metal relative to PdO decomposition.     

Catalytic combustion reactor design and test results

Engelhard Corporation has been investigating catalytic combustion for low NO, applications since the 1970s [ 11. Reactor systems have been developed for various applications including, gas turbines, boilers and automobiles. This paper will discuss the generic reactor system, its design and chemistry. An overview which shows the temperatures within the catalyst bed and the design parameter flexibility will be presented. The window of operation of the various reactors will be discussed as will life test data. Finally, the effect of fuel and temperature turndown and pressure will be discussed which demonstrate the feasibility of catalytically supported thermal combustion for natural gas fueled gas turbines.     

Evidence of PAH production under lean combustion conditions

While it is common knowledge that PAH formation can be expected at rich combustion conditions, this paper presents experimental and computational evidence that PAH formation can also be expected under lean, or cool, combustion conditions. Experimental evidence for diesel engine operation at lean conditions, as well as the literature references related to waste tire and coal combustion, are cited as supportive evidence of conclusions drawn here. A computational model based on reaction mechanisms for three surrogate fuels: C₂H₂, C₇H₁₆ and C₁₄H₂₈, was validated against the available diesel engine data, and projected to both lean and rich combustion conditions. The finding was that for the adiabatic case, minimum production of PAHs occurs at equivalence of unity and increases as equivalence becomes either lean or rich; the latter observation being consistent with the common knowledge.     

焦炉煤气低NOx燃烧技术研究进展

介绍了焦炉煤气燃烧NOx排放情况和NOx生成机理,总结了废气循环、空气分级、燃料分级、高温贫氧、浓淡偏差燃烧、低NOx燃烧器、催化燃烧等低NOx燃烧技术的研究进展,指出实现焦炉煤气低NOx排放燃烧是以后的研究重点。低NOx燃烧技术与传统的焦炉、锅炉等燃烧方式相结合,可望实现焦炉煤气的高效、低污染排放燃烧。     

Effect of fuel composition on NOx formation in high‐pressure syngas/air combustion

In this study, an experimental investigation of lean premixed syngas/air flames with H₂/CO ratio of 1.0 and equivalence ratio of 0.5 has been conducted in a high‐pressure burner facility to investigate the effects of pressure and the presence of hydrocarbons on NO_x speciation. Detailed NO_x speciation measurements in the post‐flame region were conducted for various pressures up to 1.5 MPa (15 bar) using Fourier transform infrared (FTIR) spectroscopy. When the pressure is increased, NO concentration decreases while NO₂ increases due to pressure dependence of NO to NO₂ conversion. For a given pressure, the presence of hydrocarbons in syngas leads to an increase in NO_x concentrations possibly due to prompt NO formation. Comparison of NO concentrations in presence of CH₄ at different pressures shows that the effect of CH₄ due to prompt NO formation is more dominant than the effect of pressure on NO. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3134–3140, 2018     

水煤浆MILD燃烧数值模拟研究

为解决水煤浆常规燃烧存在的运行稳定性差等问题,以IFRF炉为研究对象,采用数值模拟方法尝试对水煤浆燃料进行了MILD燃烧研究。结果表明,在燃料输入功率不变的条件下,水煤浆MILD燃烧相对于常规旋流燃烧,流场的回流区域更大,烟气循环更加强烈,整体的炉膛温度更低,分布更加均匀,峰值温度最高降低了227 K,燃烧反应速率更慢,燃烧反应区面积存在区域更大,整个炉膛基本处于低氧氛围下,尾部烟气中的NO_x排放降低了50%以上。此外,水煤浆浓度的改变对炉膛流场几乎没有影响,但可以降低炉膛整体温度以及尾部烟气中NO_x排放。     

自由堆积多孔介质内预混燃烧火焰传播

为了解多孔介质内预混燃烧火焰前沿的传播特性,对不同化学当量比（=0.7～1.0）的甲烷/空气预混气体在不同孔隙率（ε为0.37和0.42）的多孔介质内的火焰前沿传播特性进行了研究,多孔介质采用3 mm和6 mm直径的Al₂O₃小球在陶瓷管中堆积而成。结果表明,预混气体在多孔介质中能够形成低速燃烧的稳定燃烧波;其火焰传播速度随化学当量比增大而加快,最大的火焰传播速度为3.52×10^-3 cm·s^-1;多孔介质的结构对火焰前沿传播速度影响很大,即使在孔隙率差别不大的情况下,大球堆积而成的多孔介质比小球具有更高的火焰前沿传播速度。     

天然气燃烧中NOx减排的数学模型

在燃烧过程氮氧化物生成的基元反应和反应动力学基础上,推导并建立了新的NOx生成化学动力学模型,并利用流体力学计算软件及湍流模型分析手段,对天然气燃烧过程NOx生成进行了模拟计算,预测结果与实验结果吻合良好。研究表明,新模型比平衡模型和部分平衡模型预测更加接近实验结果,实现了对NOx生成数学模型的优化。     

微型燃烧器内甲烷预混催化燃烧的数值研究

微尺度燃烧存在热量损失大、易熄火、燃烧不完全、转化效率不高等问题,因此对微型燃烧器内甲烷的燃烧采取预混催化燃烧方式来提高燃烧的稳定性和转化效率,为微型发动机碳氢燃料燃烧技术奠定基础。采用连续介质层流有限速率模型和二阶离散方法对微型燃烧器微流道内的催化燃烧、流动和传热进行了三维数值模拟。结果表明,甲烷质量流量和过量空气系数对催化转化效率有一定影响,壁面温度是影响催化转化效率的主要因素。甲烷质量流量、壁面温度与最佳过量空气系数之间具有一定的变化关系。可根据催化温度选择富燃料或富氧燃烧方式来提高微尺度催化转化效率。恒壁温边界条件下,催化燃烧主要发生在燃烧腔的下壁面。     

高海拔对煤粉燃烧特性的影响研究

为掌握高海拔低气压环境下煤粉燃烧特性,指导高海拔地区大型燃煤锅炉设计,在试验台上模拟高海拔低气压环境,利用一维火焰炉、着火炉研究了煤粉在不同海拔高度下的着火、燃烬及NO_x排放特性。结果显示随着海拔的升高,煤粉的着火温度升高,燃烬性能有一定下降,而NO_x生成量变化不大。与低海拔地区类似,试验煤样煤粉变粗会使着火温度升高,但对燃烬率影响较小,氧含量对燃烬率和NO_x影响较大。综合考虑,高海拔地区锅炉设计应采用较细的煤粉细度、适当提高燃烬空间。     

Fundamentals‐based low‐dimensional combustion modeling of spark‐ignited internal combustion engines

A four‐mode low‐dimensional model for the in‐cylinder combustion process in an internal combustion engine is developed. The lumped parameter ordinary differential equation model is based on two mixing times that capture the reactant mixing limitations inside the cylinder and mixing limitations caused by the input and exit stream distribution. For a given inlet and operating conditions, the model predicts the exhaust composition of regulated gases (total unburned HCs, CO, and NO_x) as well as the in‐cylinder pressure and temperature. The model is able to capture the qualitative trends observed with change in fuel composition (gasoline and ethanol blending), air/fuel ratio, spark timing, engine load, and speed. The results show good qualitative and fair quantitative agreement with the experimental results published in the literature and demonstrate the possibility of such low‐dimensional model for real‐time control. Improvements and extensions to the model are discussed. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Large Eddy simulation for lean premixed combustion

In comparison to previous numerical studies interested in the ORACLES benchmark (One Rig for Accurate Comparisons with Large Eddy Simulations), the present study demonstrates the advantages of LES‐WALE model in both inert and reacting flows using the Fluent‐CFD. So, the confirmation is based on the experimental research effort that was involved in the European Union‐funded research program MOLECULES (Modelling of Low Emissions Combustors Using Large Eddy Simulations), for three parameters: longitudinal velocity, longitudinal velocity fluctuation, and length of recirculation zone. In line with what was observed by the experimental reference study, the dynamic model (LES‐WALE) predicts, respectively, as well as the asymmetry and the symmetry, for both inert and reacting flows. In addition, the simulation succeeds to predict the zones of recirculation and shows the differences between the two cases, inert and reacting flows. Moreover, results have been compared with those of the k–ε model performed by Kurenkov and Obserlack [Kurenkov and Obserlack, Flow Turbulence Combustion 74, 387–407 (2005)] study. © 2012 Canadian Society for Chemical Engineering     

配风方式对部分预混燃烧系统燃烧振荡的影响

部分预混燃烧系统是燃气热水器的常用燃烧系统,研究这种燃烧系统中配风方式和燃烧工况的关系十分重要。通过搭建实验台,研究了一个具有三次风的部分预混燃烧系统在不同过量空气系数下的燃烧振荡区域。发现该系统存在一个介于两正常工作区域之间的燃烧振荡区域,该区域的界限随着配风方式的变化发生偏移,减小一次风量时其正常工作范围扩大。通过分析,认为其燃烧振荡范围与一次过量空气系数值有直接关系,该范围具有一个上限,对应一次过量空气系数为0.80～0.95;具有一个下限,一次过量空气系数为0.40～0.50,此范围内发生燃烧振荡的概率较大。     

位移钝体稳燃的旋流预混燃烧污染物生成特性

石化炉、加热炉等设备中燃烧过程的污染物控制具有重要意义。旋流预混燃烧过程具有低NO _x 排放的潜力,引发了学术界和工业界的广泛关注。结合钝体燃烧和旋流燃烧各自的优势,本文设计了带有位移钝体的旋流预混燃烧器。首先研究了不同钝体结构下的污染物的生成情况,确定了最优的钝体结构,在此基础上进一步研究了在不同旋流数下污染物生成、火焰形态和温度场分布情况。研究发现,钝体角度为30°、体积较小的倒锥形钝体具有较低的NO _x 和CO生成量。NO _x 生成量随着旋流数从0增加到0.83呈先减小后增加的趋势,并且当旋流数为0.25时,NO _x 生成量最低。在同一热功率下,火焰高度随着旋流数的增加而减小。在同一旋流数下,火焰宽度随热功率增大呈增大趋势。NO _x 生成量变化规律与其火焰温度分布规律一致,即NO _x 生成量最低的工况下火焰温度也比较低。由此推测旋流引发的温度变化是NO _x 生成量变化的主要影响因素之一。本文的研究结论对旋流预混燃烧器的设计提供了理论基础。