二甲基醚（DME）燃烧特性研究

作者在定容燃烧弹上用火焰直接成像法研究二甲基醚 (DME)燃烧过程 ,研究了 DME的滞燃期和火焰传播特性以及不同环境温度和压力对燃烧过程的影响。研究结果表明 ,DME的滞燃期比柴油短 ,燃烧室内的温度和压力升高时 ,滞燃期缩短 ;DME的着火位置靠近喷嘴一侧 ,柴油与 DME的体积相同时 ,DME的燃烧持续期比柴油短 ;DME的燃烧火焰亮度比柴油小 ,表明 DME的燃烧温度比柴油低。燃烧后期 ,燃用 DME时 ,喷嘴有明显的泄漏现象。此外 ,作者在单缸直喷式柴油机上进行了燃用 DME的燃烧特性试验研究 ,研究结果表明 ,DME的预混合燃烧放热率比柴油低 ,缸内最大爆发压力和最大压力升高率比柴油低。由于喷油持续期延长 ,DME的燃烧持续期比柴油长 ,在上止点后 80° CA出现一个较大的放热峰值。     

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。     

废气再循环对二甲醚/甲醇均质压燃燃烧过程影响的试验研究

在单缸柴油机上进行了冷却废气再循环(EGR)对二甲醚(DME)/甲醇均质压燃(HCCI)燃烧过程影响的试验研究。结果表明,EGR对拓宽二甲醚/甲醇HCCI发动机的最大负荷作用不大;随着EGR率增大,主燃烧开始时刻和放热峰值明显后移,主燃烧持续期延长,放热峰值降低。EGR率为25%时的最大爆发压力比没有EGR时降低了近1.3 MPa,最大爆发压力出现的位置推迟了7°CA;EGR率增大,二甲醚/甲醇HCCI发动机的指示热效率升高。对应给定的EGR率,存在一个热效率较高的DME比例区间;HC和CO排放随EGR率的增大而增加,随DME比例的增加而降低,NOx排放接近于零。控制EGR率和DME比例是控制二甲醚/甲醇HCCI发动机燃烧过程、性能和排放的关键。     

二甲醚发动机湍流燃烧模型的研究

根据二甲醚发动机燃烧过程的特点，提出一种湍流燃烧模型。该模型在传统化学动力学模型的基础上，增加了拟序火焰片湍流燃烧模型以考虑湍流对燃烧的促进作用。数值模拟表明，二甲醚在发动机中油束贯穿度比柴油短；油孔附近的油束上边缘处具有合适的燃料浓度和较高温度，最先发生自燃；在扩散燃烧时燃料与空气混合速度慢，燃烧速度慢，持续时间长。计算结果与试验观察基本相符。     

柴油机燃用二甲醚的燃烧特性

对直喷式柴油机燃用二甲醚的燃烧特性进行了研究,测量了示功图和油器针阀升程,计算了燃烧特性并与燃用柴油进行对比。结果表明,与柴油相比,发动机燃用二甲醚时的喷油延迟期延长,滞燃期缩短,最高爆发压力和最大压力升高率均低于柴油机。研究表明发动机燃用二甲醚具有良好燃烧特性。     

二甲基醚均质压燃化学动力学简化模型的研究

由于详细的化学动力学模型与多维流动动力学模型耦合的高度复杂性,很难将其应用于模拟实际发动机的工作过程。在详细反应动力学研究基础上,通过对二甲基醚(DME)均质压燃燃烧反应途径和敏感性分析,建立了均质压燃二甲基醚的简化动力学模型。此模型在Curran et al模型基础上构建,包括26种产物和28个基元反应。结果表明,提出的二甲基醚简化动力学模型与详细动力学模型计算结果相当吻合,简化模型在对着火时刻、缸内温度和压力计算结果与详细模型基本一致,简化机理对变初始温度和混合气浓度也有较好的预测能力,可应用于模拟二甲基醚HCCI的燃烧过程。     

Combustion and emission characteristics of a hydrogen-diesel dual-fuel engine

Hydrogen generated from renewable sources is an eco-friendly fuel that can be used in automotive industry or for energy generation purposes. Hydrogen is a high-energy content gas and its carbonless chemical structure can provide significant benefits of high thermal efficiency and near zero or very low carbon emissions when combusted with other fuels.In this study, the implementation of hydrogen fuel was tested at low and medium operating loads in a heavy-duty hydrogen-diesel dual-fuel engine. The paper provides a detailed experimental analysis of the effects of hydrogen energy share ratio and various combustion strategies such as exhaust gas recirculation, diesel injection pressure and diesel injection patterns.At low load conditions, engine operation with an H₂ energy share ratio of up to 98% was achieved without any engine operation implications. This condition provided a simultaneous reduction of carbon and NOx emission of over 90% while soot emissions were dropped by 85% compared to the conventional diesel-only operation. At medium load, the increased NOx emission due to the high energy content of hydrogen fuel was found to be the primary challenge.     

Performance and emission characteristics of QHCCI dimethyl ether engine

Experimental investigation into the effects of different pilot amounts of dimethyl ether (DME) on the performance and emission of a single-cylinder directinjection DME engine is conducted. The results show that a DME engine can operate at a wider range of speeds and loads at quasi-homogenous charge compression ignition (QHCCI) mode. The brake thermal efficiency increases while the exhaust temperature decreases. NO _x emission decreases by about 30%–50% although there is a slight increase in HC and CO emissions. NO _x , HC and CO emissions increase with an increase in the amount of DME pilot. QHCCI is a good way to increase thermal efficiency and decrease NO _x emission. __________ Translated from Chinese Internal Combustion Engine Engineering, 2007, 28(3): 67–70 [译自: 内燃机工程]     

二甲基醚（ＤＭＥ）喷雾一般牧场生的试验研究

介绍了在高压环境下对二甲基醚（ＤＭＥ）喷雾一般特性的试验研究结果,并与柴油的喷雾特性进行了比较。试验研究是在定容燃烧弹上进行的,用阴影法通过高速数字摄影机拍摄了二甲基醚和柴油的喷雾发展过程,应用计算机图像处理进行喷雾过程图像再现。研究结果表明：ＤＭＥ的喷雾贯穿蹁距离比柴油小,喷雾锥角比柴油大;在喷雾自由发展过程中,ＤＭＥ的蒸发速度比柴油快;环境密度对ＤＭＥ喷雾特性的影响与柴油相似,即密度增大,锥角增大,贯穿距离减小。在燃烧室壁面附近,柴油的喷雾锥角迅速增大,而ＤＭＥ喷雾锥角几乎没有明显的变化。     

二甲醚发动机燃油喷射过程的数值模拟及其试验研究

针对采用普通油泵—油管—油嘴燃油系统的二甲醚发动机,建立了燃油喷射过程的数学模型,通过对不同工况下燃用DME和柴油的燃油喷射过程的数值模拟与计算结果的试验验证,揭示了二甲醚发动机燃油喷射过程的物理本质及其特性参数的变化规律。研究表明,由于DME具有较高的可压缩性,致使其泵端与嘴端压力上升及下降都较柴油缓慢,压力上升始点延迟,实际喷油始点滞后,嘴端油管压力峰值较低,高压油管中的残余压力较高,较易出现二次喷射现象。     

Combustion and emission characteristics of a turbo-charged common rail diesel engine fuelled with diesel-biodiesel-DEE blends

The combustion and emission characteristics of a turbo-charged, common rail diesel engine fuelled with diesel-biodiesel-DEE blends were investigated. The study reports that the brake-specific fuel consumption of diesel-biodiesel-DEE blends increases with increase of oxygenated fuel fractions in the blends. Brake thermal efficiency shows little variation when operating on different diesel-biodiesel-DEE blends. At a low load, the NO_x emission of the diesel-biodiesel-DEE blends exhibits little variation in comparison with the biodiesel fraction. The NO_x emission slightly increases with increase in the biodiesel fraction in diesel-biodiesel-DEE blends at medium load. However, the NO_x emission increases remarkably with increase of the biodiesel fraction at high load. Particle mass concentration decreases significantly with increase of the oxygenated-fuels fraction at all engine speeds and loads; particle number concentration decreases remarkably with increase of the oxygenated-fuels fraction. HC and CO emissions decrease with increasing oxygenated-fuels fraction in these blends.     

基于不同燃烧模型的二甲基醚发动机工作过程模拟研究

利用韦伯(Wiebe)模型、Watson模型、Whitehouse-Way模型以及化学动力学着火模型模拟计算了DME发动机的燃烧放热率，并将模拟计算结果与试验结果进行了对比。在对喷油正时、燃烧始角、循环供油量以及燃料热值等计算初始参数进行适当调整的基础上，上述模型的模拟计算结果与DME发动机实测数据基本吻合，说明上述各模型不仅适用于柴油发动机的性能预测分析，亦适用于DME发动机运行参数的预测。     

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。     

二甲醚和柴油喷雾特性的数值模拟分析

在定容室内对二甲醚和柴油的喷雾特性进行了数值模拟，研究了计算网格、破碎模型和环境条件对喷雾特性的影响，比较了二甲醚和柴油的喷雾特性，并与实验值进行了比较。研究结果表明：二甲醚的喷雾贯穿距和索特平均半径(SMR)比柴油小，受蒸发的影响比柴油大。     

Combustion and emissions performance of a DME-enriched spark-ignited methanol engine at idle condition

Dimethyl ether (DME) and methanol are thought to be one of the most promising alternative fuels for IC engines. Meanwhile, previous investigations also have pointed out the good prospects for adopting DME and methanol in IC engines. The experiments in this paper were carried out at idle condition to investigate the effect of applying the methanol/DME blended fuel in a SI engine. The engine was modified to be fueled with the mixture of methanol and DME which were injected into the engine intake ports simultaneously. Various DME fractions were selected to investigate the effect of DME addition on engine performance. The experimental results showed that indicated thermal efficiency was increased by 25% and coefficient of cyclic variation in engine speed was decreased by 29.2% at the DME energy fraction of 85.2% in the total fuel. In addition, both flame development and propagation durations were shortened with the increase of DME enrichment level at idle condition. Meanwhile, the largest drop of HC emissions was nearly 50% compared with the original methanol engine at stoichiometric condition. However, CO and NO_x emissions increase with the addition of DME.     

A study of spray strategies on improvement of engine performance and emissions reduction characteristics in a DME fueled diesel engine

This paper investigated the impact of injection angle and advance injection timing on combustion, emission, and performance characteristics in a dimethyl ether (DME) fueled compression ignition engine through experimentation on spray behaviors and the use of numerical methods. To achieve this aim, a visualization system and two injectors with different injection angles were used to analyze spray characteristics. The combustion, emission, and performance characteristics were analyzed by numerical methods using a detailed chemical kinetic DME oxidation model. Each of five injection angles and timings were selected to examine the effect of injection angle and timing. It was revealed that the injected spray with narrow injection angles was impinged on the bottom wall after the SOI of BTDC 60°, and most of the fuel spray and evaporation with the wide injection angles had a distribution at the crevice region when the injection timing was advanced. In addition, NO_x emissions at the SOI of BTDC 20° and TDC had higher values, and the soot emission quantities were extremely small. The narrow injection angles had good performance at the advanced injection timing, and the injection timing over a range of BTDC 40-20° showed superiority in performance characteristics.     

Hydrogen effects on the diesel engine performance and emissions

In this research, effects of hydrogen addition on a diesel engine were investigated in terms of engine performance and emissions for four cylinders, water cooled diesel engine. Hydrogen was added through the intake port of the diesel engine. Hydrogen effects on the diesel engine were investigated with different amount (0.20, 0.40, 0.60 and 0.80 lpm) at different engine load (20%, 40%, 60%, 80% and 100% load) and the constant speed, 1800 rpm. When hydrogen amount is increased for all engine loads, it is observed an increase in brake specific fuel consumption and brake thermal efficiency due to mixture formation and higher flame speed of hydrogen gas according to the results. For the 0.80 lpm hydrogen addition, exhaust temperature and NOx increased at higher loads. CO, UHC and SOOT emissions significantly decreased for hydrogen gas as additional fuel at all loads. In this study, higher decrease on SOOT emissions (up to 0.80lpm) was obtained. In addition, for 0.80 lpm hydrogen addition, the dramatic increase in NOx emissions was observed.     

Effect of ethanol–gasoline blends on engine performance and exhaust emissions in different compression ratios

Renewable energy sources for the gasoline engines alcohols gain importance recently. These renewable energy sources have attracted the attention of researchers as alternative fuel due to their high octane number. In addition, these are also clean energy sources and can be obtained from the biomass alcohols with low carbon like ethanol. In this study, the effect of compression ratio on engine performance and exhaust emissions was examined at stoichiometric air/fuel ratio, full load and minimum advanced timing for the best torque MBT in a single cylinder, four stroke, with variable compression ratio and spark ignition engine.     

Research of performance and emission indicators of the compression-ignition engine powered by hydrogen - Diesel mixtures

The purpose of this study is to use the hydrogen – diesel mixture in Audi/VW 1.9 TDI turbocharged CI engine equipped with dynamometer and examine the performance and emission indicators by comparing it with sole diesel mode. The recent diesel emission scandals because of manufacturers cheating the laboratory tests, have initiated the discussions about the sustainable and environmentally friendly diesel engines. The CI engine without major engine modifications was set to operate at two speeds of 1900 rpm and 2500 rpm. At each of speed, the experiment was conducted at three BMEP: 0.4 MPa, 0.6 MPa, and 0.8 MPa. The test engine was operated using diesel fuel with amounts of 10 l/min, 20 l/min, and 30 l/min of hydrogen gas, supplied with air into intake manifold before the turbocharger. Relatively low hydrogen fraction (max. 15.74%) has effect on diesel combustion process and performance indicators at the all range of BMEP. The in-cylinder peak pressure at both speeds of 1900 rpm and 2500 rpm was lower than that with pure diesel fuel, as the small amount of hydrogen shortens the CI engine ignition delay period and decreases the rate of pressure rise. The decrease of BTE noticed, and increase of BSFC was registered with low hydrogen fraction (hydrogen amounts of 10 l/min, 20 l/min). However, with increase of hydrogen amount to 30 l/min, the BTE increased and BSFC decreased to the level, which was lower than that at the pure diesel test. The supply of hydrogen positively effects on engine emissions: the smokiness, NO_x, CO₂, CO decreased, the only hydrocarbon increased. The effect of hydrogen fraction on the combustion and emission characteristics of the diesel - hydrogen mixture was validated by AVL (Anstalt für Verbrennungskraftmaschinen List) BOOST and analysed with presentations of the main limitations and perspectives.     

二甲醚发动机与汽车研究

在车用能源供应短缺与大气环境保护的双重压力下,人们一直在寻求内燃机新型清洁代用燃料。本文结合上海交通大学10年来对二甲醚发动机与汽车的应用基础研究,系统介绍了二甲醚发动机燃料喷射、燃烧、性能、排放特性和二甲醚城市客车的动力性、经济性、排放和噪声情况。研究表明二甲醚发动机能实现高效、清洁燃烧,对缓解我国石油供需矛盾和保护城市大气环境具有重要意义。