The effect of chemical structure of dimethyl ether (DME) on NOx formation in nonpremixed counterflow flames

To clarify the effect of chemical structure of Dimethyl ether(DME) on NOx formation in nonpremixed counterflow flame, DME flame was investigated numerically to compare the flame structures and NOx emissions with C₂H₆ and Mixed-fuel. Numerically, the governing equations were solved using the Oppdif code coupled with CHEMKIN package, and DME flames were calculated by Kaiser’s mechanism, while the C₂H₆ flames and Mixed-fuel flames were calculated by the C₃ mechanism. These mechanisms were combined with the modified Miller-Bowman mechanism for the analysis of NOx. Numerical results of nonpremixed counterflow flames show that the EI_NO of DME nonpremixed flame is low as much as 50 % of the C₂H₆ nonpremixed flame. The cause of EI_NO reduction is attributed mainly to the characteristics of partial premixed flame due to the existence of oxygen atom in DME and partly to the O-C bond in DME, instead of C-C bond in hydrocarbon fuels. This paper was presented at the 7th JSME-KSME Thermal and Fluids Engineering Conference, Sapporo, Japan, October 2008. Chang-Eon Lee received his B.S. and M.S. degrees in Mechanical Engineering from Inha University, Korea, in 1983 and 1985, respectively. Then he received his Ph.D. degree from Toyohashi National University of Technology, Japan in 1992. Dr. Lee is currently a Professor at the School of Mechanical Engineering at Inha University in Incheon, Korea. He serves as an Editor of the Journal of the Korean society of combustion and serves as an associate Editor of Transactions of the Korean society of mechanical engineers. Dr. Lee’s research interests include fluid mechanics, combustion and environmental pollution, and total energy.     

液化石油气中二甲醚含量检测方法研究

通过对液化石油气和二甲醚的物理、化学特性分析研究,建立恒温水浴气化取样手段,保证样品不失真。经过反复实验,建立了毛细管色谱柱气相色谱法测定液化石油气中二甲醚含量的分析方法。结果表明,该方法具有良好的准确度和精密度。     

An investigation of the effects of spray angle and injection strategy on dimethyl ether (DME) combustion and exhaust emission characteristics in a common-rail diesel engine

An experimental investigation was performed on the effects of spray angle and injection strategies (single and multiple) on the combustion characteristics, concentrations of exhaust emissions, and the particle size distribution in a direct-injection (DI) compression ignition engine fueled with dimethyl ether (DME) fuel. In this study, two types of narrow spray angle injectors (θ_spray = 70° and 60°) were examined and its results were compared with the results of conventional spray angle (θ_spray = 156°). In addition, to investigate the optimal operating conditions, early single-injection and multiple-injection strategies were employed to reduce cylinder wall-wetting of the injected fuels and to promote the ignition of premixed charge. The engine test was performed at 1400 rpm, and the injection timings were varied from TDC to BTDC 40° of the crank angle.The experimental results showed that the combustion pressure from single combustion for narrow-angle injectors (θ_spray = 70° and 60°) is increased, as compared to the results of the wide-angle injector (θ_spray = 156°) with advanced injection timing of BTDC 35°. In addition, two peaks of the rate of heat release (ROHR) are generated by the combustion of air-fuel premixed mixtures. DME combustion for all test injectors indicated low levels of soot emissions at all injection timings. The NO_x emissions for narrow-angle injectors simultaneously increased in proportion to the advance in injection timing up to BTDC 25°, whereas BTDC 20° for the wide-angle injector. For multiple injections, the combustion pressure and ROHR of the first injection with narrow-angle injectors are combusted more actively, and the ignition delay of the second injected fuel is shorter than with the wide-angle injector. However, the second combustion pressure and ROHR were lower than during the first injection, and combustion durations are prolonged, as compared to the wide-angle injector. With advanced timing of the first injection, narrow-angle injectors with multiple injections could achieve low NO_x levels and soot levels similar to single-injection cases.     

Effects of dimethyl-ether (DME) spray behavior in the cylinder on the combustion and exhaust emissions characteristics of a high speed diesel engine

The purpose of this study was to analyze the exhaust emissions of DME fuel through experimental and numerical analyses of in-cylinder spray behavior. To investigate this behavior, spray characteristics such as the spray tip penetration, spray cone angle, and spray targeting point were studied in a re-entrant cylinder shape under real combustion chamber conditions. The combustion performance and exhaust emissions of the DME-fueled diesel engine were calculated using KIVA-3V. The numerical results were validated with experimental results from a DME direct injection compression ignition engine with a single cylinder.The combustion pressure and IMEP have their peak values at an injection timing of around BTDC 30°, and the peak combustion temperature, exhaust emissions (soot, NO_x), and ISFC had a lower value. The HC and CO emissions from DME fuel showed lower values and distributions in the range from BTDC 25° to BTDC 10° at which a major part of the injected DME spray was distributed into the piston bowl area. When the injection timing advanced to before BTDC 30°, the HC and CO emissions showed a rapid increase. When the equivalence ratio increased, the combustion pressure and peak combustion temperature decreased, and the peak IMEP was retarded from BTDC 25° to BTDC 20°. In addition, NO_x emissions were largely decreased by the low combustion temperature, but the soot emissions increased slightly.     

二甲醚与液化石油气的合作性竞争

分析了二甲醚(DME)替代液化石油气(LPG)的可行性,DME替代LPG的现状、MDE产业发展面临的问题、DME与LPG进行合作的可行性。提出双方应开展合作性竞争,取长补短,规范市场,分担社会责任,实现市场双赢。     

高原地区二甲醚燃烧器的选型研究

二甲醚作为清洁能源,不仅可以解决我国"缺油、少气"的能源现状,而且可以减少对环境的污染。二甲醚燃烧器是将二甲醚与空气中的氧气充分混合燃烧后转变为热能的装置。主要研究二甲醚燃烧器在高原地区使用时修正系数的计算过程,以及二甲醚燃烧器在高原地区的选型方法。为二甲醚燃烧器在高原地区的应用提供了理论基础。     

Effect of the P/Al ratio on the performance of modified HZSM-5 for methanol dehydration reaction

The precipitation method was used to modify HZSM-5 by coating it with aluminophosphate at P/Al molar ratios of 0.3, 0.8, 1.2 and 1.5. These catalysts were characterized by XRD, NH₃-TPD, BET, FT-IR, ICP-TEOS and SEM and evaluated as catalysts for the methanol dehydration reaction. The ZALPO0.8 catalyst achieved 86% conversion which was the highest conversion till 315 °C. It was found that primary benefits of AlPO modification were that it tended to retard the activity of the highly active acid sites which promote dimethyl ether decomposition and led to decrease in the apparent activation energy.     

废气再循环对二甲基醚均质压燃燃烧过程影响的试验研究

在一台单缸发动机上进行了废气再循环(EGR)对二甲基醚(DME)均质压燃(HCCI)燃烧过程影响的试验研究。结果表明，EGR比例小于20％对运行最大负荷工况范围影响不大；采用高比例EGR可以拓宽DME均质压燃运行工况范围，随着EGR率增大，HCCI运行的最大负荷工况增大，着火燃烧时刻推迟，燃烧放热率降低，缸内最大爆发压力降低，发动机热效率增大；EGR率小于75％，HC排放略有降低或相当，EGR率为75％时，HC排放显著增加；EGR率大于25％，随着EGR率增加，CO排放增大，小负荷工况尤其明显，在中高负荷工况，EGR率对CO排放影响较小。     

直喷式柴油机燃用二甲基醚(DME)试验研究

介绍了在1100单缸直喷式柴油机上燃用DME的发动机试验研究结果。研究表明：通过增加循环供油量可使柴油机燃用DME后恢复到原机略低，同时缸内最大爆发压力降低，发动机碳烟排放为零，HC和CO排放比原机略高，NOx排放比原柴油机降低约50%以上，供油提前角减少，缺内最大爆发压力降低，NOx排放可进一步大幅度降低，但HC排放略有升高；加大喷孔直径，缸内爆发压力升高，NOx排放升高，HC和CO排放在中低负荷相差不大，但在大负荷工况有所升高。     

内燃机代用燃料(二)

较为详细地介绍了内燃机代用燃料-天然气和液化石油气，氢气，醇类燃料，生物类燃料，二甲醚（DME）和碳酸二甲脂（DMC）的物理特性，排放特点，优缺点及使用时应解决的问题。