Suppression of ethylene-induced carbon deposition in diesel autothermal reforming

Diesel has high-hydrogen density and well-developed infrastructure, which are beneficial properties for fuel cell commercialization. However, diesel reforming poses several technical difficulties, including carbon deposition, sulfur poisoning, and fuel delivery. Specifically, carbon deposition can cause catastrophic failures in diesel reformers. In diesel reformate gas, the concentration of ethylene, a carbon precursor, is higher than other shorter hydrocarbons (C₂–C₄). In this study, we examine the cause of ethylene formation in diesel reforming. Ethylene formation can be closely related to paraffins' decomposition from homogeneous reaction. A portion of the catalyst active sites can become occupied with aromatic compounds, degrading the activity of the catalyst. Thus, a portion of the paraffins is decomposed via non-catalytic, homogeneous reactions, accounting for much of the observed ethylene formation. In this study, reforming conditions and fuel delivery method are investigated with respect to ethylene formation. By using a diesel ultrasonic injector, reactant mixing was enhanced, resulting in suppression of ethylene formation. This subsequently inhibited the ethylene-induced carbon deposition and improved the long-term performance of diesel ATR (autothermal reforming).     

Performance,combustion and exhaust emissions characteristics investigation using Citrullus colocynthis L. biodiesel in DI diesel engine

The aims of this study is to investigate the performance, combustion and exhaust emissions of a single-cylinder, air cooled, direct injection (DI), compression ignition engine using biodiesel from non-edible feedstock. In this work, biodiesel (B100) used to lead this investigation is Citrullus colocynthis L. methyl ester (CCME) and its blends B30 with diesel fuel. The biodiesel is produced via alkaline-catalyzed transesterification process using methanol (6:1 M ratio), 1% of sodium hydroxide at the reaction temperature of 60 °C for 1 h. The important physical and chemical properties of CCME are close to those of diesel fuel. Fuels (diesel fuel, B100 and B30) were tested on a DI diesel engine at 1500 rpm for various power outputs. The results indicated that B100 and B30 exhibit the same combustion characteristics compared to diesel fuel. However, B100 and B30 display earlier start of combustion. At lower engine loads, the peaks of cylinder pressure and heat release rate (HRR) were higher for B30 than B100 and diesel fuel during premixed combustion period. At higher engine loads the peaks of cylinder pressure was higher for B100 than B30 and diesel fuel, but the HRR during diffusion combustion is more considerable than diesel fuel. The brake specific fuel consumption (BSFC) was higher for B100 than diesel fuel at all engine loads while B30 exhibited comparable trends. The thermal efficiency is slightly higher for B100 than B30 and diesel fuel at low loads and increase for B30 at full loads.B30 and B100 provided a higher reduction of hydrocarbons emissions up to 50% for B100. Nitrogen oxides and particulate matter emissions were also reduced.     

Integrated fuel cell APU based on a compact steam reformer for diesel and a PEMFC

This paper presents experimental results of a diesel steam reforming fuel processor operated in conjunction with a gas cleanup module and coupled operation with a PEM fuel cell. The fuel processor was operated with two different precious-metal based reformer catalysts, using diesel surrogate with a sulfur content of less than 2 ppmw as fuel. The first reformer catalyst entails an increasing residual hydrocarbon concentration for increasing reformer fuel feed. The second reformer catalyst exhibits a significantly lower residual hydrocarbon concentration in the reformate gas.     

Bio-fuel reformation for solid oxide fuel cell applications. Part 1: Fuel vaporization and reactant mixing

A new configuration of a mixing chamber integrated with a customized porous nozzle has been developed to completely vaporize heavy hydrocarbon fuels (e.g., diesel, biodiesel) and achieve homogenous mixing of fuel/air/steam. This proposed configuration suppresses hydrocarbon thermal pyrolysis and solid carbon formation in the fuel vaporization step. The porous nozzle promotes the micro-explosion of emulsified fuel and accelerates secondary atomization to reduce the droplet size. The mixing chamber with customized nozzle was integrated in a single-tube reformer system in order to analyze its effect on diesel and biodiesel auto-thermal reforming (ATR). It has been demonstrated that the customized nozzle not only improved the hydrogen production rate and the reforming efficiency, but it also stabilized the chemical reactions within the reformer and prevented the reactor inlet from high temperature sintering. For diesel ATR, this mixing chamber–reformer combination enabled operation at relatively low reformer temperature without forming solid carbon. This study is one component of a three-part investigation of bio-fuel reforming, also including biodiesel (Part 2) and biodiesel–diesel blends (Part 3).     

Steam reforming of commercial ultra-low sulphur diesel

Two main routes for small-scale diesel steam reforming exist: low-temperature pre-reforming followed by well-established methane steam reforming on the one hand and direct steam reforming on the other hand. Tests with commercial catalysts and commercially obtained diesel fuels are presented for both processes. The fuels contained up to 6.5 ppmw sulphur and up to 4.5 vol.% of biomass-derived fatty acid methyl ester (FAME). Pre-reforming sulphur-free diesel at around 475 °C has been tested with a commercial nickel catalyst for 118 h without observing catalyst deactivation, at steam-to-carbon ratios as low as 2.6. Direct steam reforming at temperatures up to 800 °C has been tested with a commercial precious metal catalyst for a total of 1190 h with two catalyst batches at steam-to-carbon ratios as low as 2.5. Deactivation was neither observed with lower steam-to-carbon ratios nor for increasing sulphur concentration. The importance of good fuel evaporation and mixing for correct testing of catalysts is illustrated. Diesel containing biodiesel components resulted in poor spray quality, hence poor mixing and evaporation upstream, eventually causing decreasing catalyst performance. The feasibility of direct high temperature steam reforming of commercial low-sulphur diesel has been demonstrated.     

Spray characteristics and controlling mechanism of fuel containing CO2

This paper presents studies of spray characteristics and controlling mechanism of fuel containing CO₂. Using diesel fuel containing CO₂ gas, experiments were conducted on diesel hole-type nozzles and simple nozzles. The steady spray and transient spray characteristics were observed and measured by instantaneous shadowgraphy, high-speed photography, phase Doppler anemometry (PDA) and LDSA respectively. The effects of CO₂ concentration in the fuel, the injection pressure, the nozzle L/D ratio, surrounding gas pressure and temperature on the atomization behavior and spray pattern were evaluated. The results show that the injection of fuel containing CO₂ can greatly improve the atomization and produce a parabolic-shaped spray; and the CO₂ gas concentration, surrounding gas pressure, temperature and nozzle configuration have dominant influences on spray characteristics of the fuel containing CO₂. New insight into the controlling mechanism of atomization of the fuel containing CO₂ was provided.     

Diesel fuel reformer for automotive fuel cell applications

Fuel economy and emission abatement are issues, which are highly prioritized areas in the automotive industry of today. The debate about climate change has in recent years even more emphasized the importance of these issues and has increased the search for finding sustainable technical solutions. This paper describes an effort to develop an innovative and environmentally-benign hydrogen generation system operating on commercial diesel fuel to avoid running the engine to supply electricity at stand-still. The use of a fuel cell-based auxiliary power unit (APU) has the potential of delivering electricity at high efficiencies independent of the heavy-duty truck engine. During the reformer development phase, spray formation and mixing of reactants proved to be crucial to obtain high reforming efficiencies and low diesel slip. The diesel is being injected through a nozzle creating a spray of fine droplets of a size which can establish rapid evaporation. Air and steam are being pre-heated and injected into the mixture chamber and subsequently mixed with the evaporated diesel fuel. Depending on the operating parameters, a part of the fuel is being oxidized and produces heat. Autothermal reforming was chosen to circumvent the heat transfer problem in catalytic steam reforming. By supplying heat directly to the catalyst surface by an oxidation reaction the heat demand of the strongly endothermic steam reforming reaction can be fulfilled. We employed CFD calculations, which revealed the importance of avoiding large recirculation zones leading to a prolonged residence time of the hydrocarbon molecules and causing auto-ignition and excessive temperatures in the catalyst. Five different reformer generations are being described and discussed in detail in this publication. The first one was based on a fixed bed reactor, while the other four all relied on catalytic monoliths enabling low pressure drops. The early reactor designs all suffered from auto-ignition and instability problems. The latter generations exhibited a considerably more stable temperature profile in the reformer. The conversion of diesel and the reformer efficiencies are significantly higher than the early generation diesel reformers.     

应用双脉中激光全息术对柴油机喷雾运动的研究

本文介绍利用双脉冲激光全息术研究柴油机喷雾油束的宏观运动瞬时速度和喷雾粒子的微观运动速度。得到了节流轴针式油嘴雾油束在喷射开始１ｍｓ内宏观速度分布规律的新认识，并给出了喷雾粒子微观运动轨迹照片，讨论了喷雾粒子场的微观速度分布规律。     

闪急沸腾喷雾速度场的LDA研究

为探索代用燃料液化石油气LPG和二甲醚DME的喷雾机理,采用LDA技术测量了喷雾粒子的速度分布。为安全起见,用制冷剂R12作试验液体,它与LPG和DME有相似的物理特性。为做比较,在相同试验条件下对传统柴油喷雾进行了测量。考察了喷雾模式对速度分布的影响。结果表明,R12喷雾的速度分布比传统柴油喷雾均匀得多,前者的平均径向速度远大于后者。这被认为归因于闪急沸腾大大改善了雾化和液气混合。     

Performance improvement of diesel autothermal reformer by applying ultrasonic injector for effective fuel delivery

Technology for the reforming of heavy hydrocarbons, such as diesel, to supply hydrogen for fuel cell applications is very attractive and challenging due to its delicate control requirements. The slow reforming kinetics of aromatics contained in diesel, sulfur poisoning, and severe carbon deposition make it difficult to obtain long-term performance with high reforming efficiency. In addition, diesel has a critical mixing problem due to its high boiling point, which results in a fluctuation of reforming efficiency. An ultrasonic injector (UI) have been devised for effective diesel delivery. The UI can atomize diesel into droplets (∼40 μm) by using a piezoelectric transducer and consumes much less power than a heating-type vapourizer. In addition, reforming efficiencies increase by as much as 20% compared with a non-UI reformer under the same operation conditions. Therefore, it appears that effective fuel delivery is linked to the reforming kinetics on the catalyst surface. A 100-W_e, self-sustaining, diesel autothermal reformer using the UI is designed. In addition, the deactivation process of the catalyst, by carbon deposition, is investigated in detail.     

溶有甲烷柴油稳态喷雾特性的试验研究

对溶有甲烷柴油的稳态喷雾特性进行研究。喷雾特性和形状分别由激光粒度分析仪LDSA1300A和数码照相机记录。试验使用了六个不同长径比L／D的直圆孔喷嘴。溶解压力和喷射压力范围分别是0．1MPa到10MPa和5MPa到10MPa。研究了甲烷溶解度、测量位置、喷射压力和喷嘴参数对喷雾特性的影响。结果表明：在柴油中溶入甲烷,出现了减压沸腾喷射现象;与纯柴油相比,喷雾形状和锥角产生了很大变化;流量系数随着溶解度和L／D值的增加而减小;甲烷溶解度和L／D的共同作用对雾化有正反两方面的影响。     

GC-MS determination of low hydrocarbon species (C1–C6) from a diesel partial oxidation reformer

The partial oxidation (POx) reforming of Ultra Low Sulphur-Diesel (ULSD), rapeseed methyl ester (RME) - biodiesel and Fischer–Tropsch synthetic diesel fuels (SD) were studied by using a fixed-bed reactor. The ease of reforming the three fuels was first examined at different O/C feed ratios at constant gas hourly space velocity (GHSV) of 35 k h⁻¹ over a prototype monolith catalyst (1%Rh/CeO₂–ZrO₂). The hydrocarbon species (C₁–C₆) produced in the reformer were analyzed using direct gas injection gas chromatography mass spectrometry (GC-MS). Under the same O/C ratios for 35 k h⁻¹ the fuels conversion and process efficiency was dependent on the fuel type, and followed the general trend: SD > biodiesel > ULSD. The GC-MS analysis shows that both, biodiesel and ULSD diesel produced significantly higher amounts of alkenes compared to SD fuel. Fuel with relatively high aromatics content such diesel can be efficiently reformed to syngas over the catalyst used in this study but the reformer operating range (e.g. O/C ratio and space velocity) is limited compared to paraffinic fuels such as FT-SD. At increased GHSV of 45 k h⁻¹ and O/C = 1.75, the diesel fuel conversion efficiency to syngas (H₂ and CO) was improved significantly and the formation of intermediate species such as methane, ethylene, and propylene was reduced considerably as a result of the increased peak reaction temperatures. The reduced HC species and increased H₂ concentration in the reactor product gas from the reforming of FT-SD fuel can provide significant advantages to the IC engine applications.     

Performance comparison of autothermal reforming for liquid hydrocarbons,gasoline and diesel for fuel cell applications

This paper discusses the reforming of liquid hydrocarbons to produce hydrogen for fuel cell applications, focusing on gasoline and diesel due to their high hydrogen density and well-established infrastructures. Gasoline and diesel are composed of numerous hydrocarbon species including paraffins, olefins, cycloparaffins, and aromatics. We have investigated the reforming characteristics of several representative liquid hydrocarbons. In the case of paraffin reforming, H₂ yield and reforming efficiency were close to thermodynamic equilibrium status (TES), although heavier hydrocarbons required slightly higher temperatures than lighter hydrocarbons. However, the conversion efficiency was much lower for aromatics than paraffins with similar carbon number. We have also investigated the reforming performance of simulated commercial diesel and gasoline using simple synthetic diesel and gasoline compositions. Reforming performances of our formulations were in good agreement with those of commercial fuels. In addition, the reforming of gas to liquid (GTL) resulted in high H₂ yield and reforming efficiency showing promise for possible fuel cell applications.     

燃料设计改善发动机燃烧和排放的研究(1)--燃料参数设计与喷雾特性研究

研究了通过含氧燃料与柴油相互掺混来改变燃料的成分与输运参数、改善燃料的喷雾特性，从而降低了柴油机的排放。选择了几种典型的含氧燃料一乙醇、碳酸二甲脂(DMC)、甲缩醛(DMM)，测量和分析了它们以不同比例与柴油互溶后燃料的输运参数变化。为了考察混合燃料的喷雾特性，以不同比例的DMM柴油混合燃料为例，运用激光相位多谱勒(PDA)技术测量它们的索特平均直径(SMD)，并与柴油进行了比较。研究结果表明：通过含氧燃料与柴油的互溶互混，重新设计了燃料的输运参数和成分后，显著改善了燃料的喷射雾化特性。     

Study of the characteristic of diesel spray combustion and soot formation using laser-induced incandescence (LII)

In this paper, the planar images of diesel spray combustion flame and soot formation were measured and analyzed by using LII, in a constant volume combustion vessel. The effects of combustion flame and fuel–air mixing characteristics on soot formation and distribution of soot concentration were studied at different conditions. The result indicates that, with increase in ambient temperature and pressure, the ignition delay of diesel fuel is shorter. The increase of ambient temperature and pressure and the reduction of injection pressure shorten the diesel flame lift-off length. The lower the ambient temperature and pressure, the weaker LII signal intensity. At the same ambient temperature and pressure condition, the higher the diesel injection pressure, the smaller the soot production in diesel jet spray, and soot particles are primarily produced in the relative fuel-rich region, which is encompassed by the flame surface front at the downstream of the diesel jet.     

利用气体模拟技术研究直喷式柴油机的燃油喷雾特性

本文利用气体模拟技术研究了直喷式柴油机的燃油喷雾特性。研究结果表明,瞬态燃油喷雾的前端存在一个强烈的紊流混合前锋区,其后是浓度分布处于平衡状态的雾锥。雾锥轴线上的浓度随贯穿距离的增加而线性衰减;雾锥的径向浓度分布与剖面至喷孔的距离有关,对于充分发展的雾锥,径向浓度不同于稳定自由射流的浓度分布,而服从指数型分布规律。当喷雾与壁面撞击时,可观察到紊流混合过程出现一个从强化到减弱的有利于混合的过渡过程,但过量壁喷会在壁面上出现浓混合气层的堆积,恶化混合。     

Steam reforming of shale gas in a packed bed reactor with and without chemical looping using nickel based oxygen carrier

The catalytic steam reforming of shale gas was examined over NiO on Al₂O₃ and NiO on CaO/Al₂O₃ in the double role of catalysts and oxygen carrier (OC) when operating in chemical looping in a packed bed reactor at 1 bar pressure and S:C 3. The effects of gas hourly space velocity GHSV (h^?1), reforming temperatures (600–750 °C) and catalyst type on conventional steam reforming (C-SR) was first evaluated. The feasibility of chemical looping steam reforming (CL-SR) of shale gas at 750 °C with NiO on CaO/Al₂O₃ was then assessed and demonstrated a significant deterioration after about 9 successive reduction-oxidation cycles. But, fuel conversion was high over 80% approximately prior to deterioration of the catalyst/OC, that can be strongly attributed to the high operating temperature in favour of the steam reforming process.     

气流扰动对含氧混合燃料喷雾的影响

内燃机缸内空气运动对混合气的形成和燃烧过程有重要的影响。为了更好地研究气流扰动对燃料喷雾体的影响,我们设计了在高压共轨试验台上一系列的实验,且在横向气流扰动下,使用频闪摄像系统,对柴油、黄连木籽生物柴油B30,B50和B100等不同类别的含氧混合燃油的喷雾进行拍照实验。结果发现,在气流扰动条件下,每种燃油喷雾的雾化效果都得到了增强;对于相同的气流扰动情况下,随着燃油粘度的增大,其喷雾投影面积均呈现出先增大后减小的趋势。     

Monolithic flat tubular types of solid oxide fuel cells with integrated electrode and gas channels

A new monolithic solid oxide fuel cell (SOFC) design stacked with flatten tubes of unit cells without using metallic interconnector plate is introduced and evaluated in this study. The anode support is manufactured in a flat tubular shape with fuel channel inside and air gas channel on the cathode surface. This design allows all-ceramic stack to provide flow channels and electrical connection between unit cells without needing metal plates. This structure not only greatly reduces the production cost of SOFC stack, but also fundamentally avoids chromium poisoning originated from a metal plate, thereby improving stack stability. The fuel channel was created in the extrusion process by using the outlet shape of mold. The air channel was created by grinding the surface of pre-sintered support. The anode functional layer and electrolyte were dip-coated on the support. The cathode layer and ceramic interconnector were then spray coated. The maximum power density and total resistance of unit cell with an active area of 30 cm² at 800 °C were 498 mW/cm² and 0.67 Ωcm², respectively. A 5-cell stack was assembled with ceramic components only without metal plates. Its maximum power output at 750 °C was 46 W with degradation rate of 0.69%/kh during severe operation condition for more than 1000 h, proving that such all-ceramic stack is a strong candidate as novel SOFC stack design.     

Impact of gas-phase reactions in the mixing region upstream of a diesel fuel autothermal reformer

The use of diesel fuel to power a solid oxide fuel cell (SOFC) presents several challenges. A major issue is deposit formation in either the external reformer, the anode channel, or within the SOFC anode itself. One potential cause of deposit formation under autothermal reforming conditions is the onset of gas-phase reactions upsteam of the catalyst to form ethylene, a deposit precursor. Another potential problem is improper mixing of the fuel, air, and steam streams. Incomplete mixing leads to fuel rich gas pockets in which gas phase pyrolysis chemistry might be accelerated to produce even more ethylene. We performed a combined experiment/modeling analysis to identify combinations of temperature and reaction time that might lead to deposit formation. Two alkanes, n-hexane and n-dodecane, were selected as surrogates for diesel fuel since a detailed mechanism is available for these species. This mechanism was first validated against n-hexane pyrolysis data. It was then used to predict fuel conversion and ethylene production under a variety of reforming conditions, ranging from steam reforming to catalytic partial oxidation. Assuming that the reactants are perfectly mixed at 800 K, the predictions suggest that a mixture must reach the catalyst in less than 0.1 s to avoid formation of potentially troublesome quantities of ethylene. Additional calculations using a simple model to account for improper mixing demonstrate the need for the components to be transported to the catalyst on a much shorter time scale, since both the relatively lean and relatively rich regions react faster and rapidly form ethylene.