Efficient and accurate waveguide mode computation using BI‐RME and Lanczos methods

In this paper, a special purpose algorithm for solving large eigenvalue problems based on the Lanczos method is successfully applied to an engineering problem: the electromagnetic analysis and design of passive waveguide devices. For dealing with such complex problems, the boundary integral‐resonant mode expansion (BI‐RME) technique has been recently proposed. This technique solves integral equations (IEs) through the well‐known method of moments (MoM), thus leading to structured eigenvalue problems. These problems frequently become very large when solving complex arbitrary geometries with high accuracy. In such cases, the eigenvalue problem cannot be efficiently solved with standard methods by means of personal computers, essentially due to CPU time and memory allocation requirements. In this paper, we propose an alternative technique, based on the Lanczos method, for the fast and accurate solution of large BI‐RME generalized eigenvalue problems. The novel theoretical aspects of this approach, as well as the impacton the original BI‐RME formulation, are described. Comparative benchmarks are also successfully presented for the full‐wave analysis and design of real passive microwave devices. Copyright © 2005 John Wiley Sons, Ltd.     

Hydrogen dual-fuelling of compression ignition engines with emulsified biodiesel as pilot fuel

Dual-fuel compression ignition (CI) engine operation with hydrogen is a promising method of using hydrogen gas in CI engines via high-cetane pilot fuel ignition. However, hydrogen dual-fuel operation with neat pilot fuels typically produce: high NO_x emissions; and high combustion chamber pressure rise rates (leading to increased “Diesel knock” tendencies). While water-in-fuel emulsions have been used during normal CI engine operation to cool the charge and slow combustion rates in an effort to reduce NO_x emissions, these water-in-fuel emulsions have not been tested as pilot fuels during hydrogen dual-fuel combustion. In this work two water-in-biodiesel emulsions are tested as pilot fuels during hydrogen dual-fuel operation. Hydrogen dual-fuel operation generally produces at best comparable thermal efficiencies compared with normal CI engine operation, while the emulsified biodiesel pilot fuels generally increase thermal efficiencies when compared with the neat biodiesel pilot fuel during dual-fuel operation. There is also a clear reduction in NO_x emissions with emulsified pilot fuel use compared with the neat pilot fuel. The thermal efficiency increase is more apparent at higher engine speeds, while the NO_x reduction is more apparent at lower speeds. This is due to two conflicting effects (exclusive to emulsified pilot fuel) that occur in tandem. The first is the cooling effect of water vapourisation on the charge, while the second is the microexplosion phenomenon which enhances fuel-air mixing. The NO_x emission reduction is due to the emulsified pilot fuel lowering pressure rise rates compared with the neat pilot fuel, while the efficiency increase is due to a more homogeneous charge resulting from the violent microexplosion of the emulsified pilot fuel. Smoke, CO, HC and CO₂ emissions remain comparable to neat pilot fuel tests. Overall, emulsified pilot fuels can reduce NO_x emissions and increase thermal efficiencies, however not at the same instance and under different operating conditions. The general trends of reduced power output, reduced CO₂ and increased water vapour emission during hydrogen dual-fuel operation (with neat pilot fuels) are also maintained.     

Effect of pilot fuel quantity and type on performance and emissions of natural gas and hydrogen based combustion in a compression ignition engine

Natural gas and hydrogen have been extensively tested in dual fuel mode in a compression ignition engine. Many studies conclude that the emissions, especially those oxides of nitrogen (NO_x) are expected to form in the region around the pilot spray where high temperatures exist and the equivalence ratio is close to stoichiometric. The effect of changing the pilot fuel quantity has not been widely reported. This study investigates the effect of changing pilot fuel quantity, and type and the effect of this change on various combustion (ignition delay, in-cylinder pressure and rate of energy release) and emission (specific NO_x and hydrocarbons) parameters. Dual fueling of natural gas and hydrogen exhibit an increased ignition delay compared to the ignition delay exhibited by the pilot fuel at similar operating conditions. For dual fueling cases, the ignition delay is reduced as the quantity of pilot fuel is increased.     

A limited LCA comparing large- and small-scale production of rape methyl ester (RME) under Swedish conditions

Production of rape methyl ester (RME) can be carried out with different systems solutions, in which the choice of system is usually related to the scale of the production. The purpose of this study was to analyse whether the use of a small-scale RME production system reduced the environmental load in comparison to a medium- and a large-scale system. To fulfil this purpose, a limited LCA, including air-emissions and energy requirements, was carried out for the three plant sizes. For small plants and physical allocation, the global warming potential was 40.3 g CO₂-eq/MJ_fuel, the acidification potential 236 mg SO₂-eq/MJ_fuel, the eutrophication potential 39.1 mg PO₄³⁻-eq/MJ_fuel, the photochemical oxidant creation potential 3.29 mg C₂H₄-eq/MJ_fuel and the energy requirement 295 kJ/MJ_fuel. It was shown that the differences in environmental impact and energy requirement between small-, medium- and large-scale systems were small or even negligible. The higher oil extraction efficiency and the more efficient use of machinery and buildings in the large-scale system were, to a certain degree, outweighed by the longer transport distances. The dominating production step was the cultivation, in which production of fertilisers, soil emissions and tractive power made major contributions to the environmental load. The results were, however, largely dependent on the method used for allocation of the environmental burden between the RME and the by-products meal and glycerine. This indicates that when different biofuels or production strategies are to be compared, it is important that the results are calculated with the same allocation strategies and system limitations.     

A novel CAD tool for the wideband modeling of 3D waveguide components

This paper describes a fast and flexible CAD tool for the wideband modeling of arbitrarily shaped three‐dimensional waveguide components. The algorithm is based on the evaluation of the poles and the residues of the Y‐parameters by the “boundary integral‐resonant mode expansion” (BI‐RME) method. Some examples demonstrate the efficiency and flexibility of the method. © 2000 John Wiley & Sons, Inc. Int J RF and Microwave CAE 10: 183–189, 2000.     

增压柴油机燃用不同掺比菜籽油甲酯的燃烧和排放的试验研究

在D6114ZLQB车用增压柴油机上比较研究了不同比例的菜籽油甲酯和0号柴油的混合燃料对发动机燃烧过程、燃油经济性和排放特性的影响。试验结果表明：燃用体积比低于15%的菜籽油甲酯,发动机的缸内燃烧过程和纯柴油基本一致;增压柴油机燃用菜籽油甲酯和柴油的混合燃料可以有效降低碳烟、HC和CO的排放;NOx排放略有上升;15%以内的菜籽油甲酯对柴油机燃料经济性影响很小。研究认为：增压柴油机相对自然吸气式柴油机具有更好的生物柴油燃料适应性;在不改变发动机参数的条件下,低比例的菜籽油甲酯具有良好的推广应用前景。     

Experimental analysis of alternative fuel impact on a new “torque-controlled” light-duty diesel engine for passenger cars

The present paper describes the results of an experimental study performed burning alternative fuels, different per quality and feedstock, in a modern diesel engine compliance the Euro 5 emission standards. Three alternative fuels were tested on the engine and compared with a reference fossil fuel in terms of combustion characteristics, fuel consumption, noise and emissions. The alternative fuels were two biodiesels (RME and SME) and a Fischer-Tropsh (GTL), while the reference fuel was an EU certification diesel fuel. The engine employed in the study was a light-duty diesel engine developed for passenger car and light truck application, and equipped with the new generation ECU able to drive the engine under “torque-controlled” mode by means of instrumented glow-plugs with pressure sensor. The experiments were carried out in a fully instrumented test bench fuelling the engine with the various fuels. The tests were done in a wide range of engine operation points for the complete characterization of the biodiesels performance in the NEDC cycle. Moreover, the trade-off NO_x-PM by EGR sweep in the three most critical test points for the engine emission performance was carried out for all fuels. The test methodology was selected carefully in order to evaluate the interaction between the fuel quality and the engine management strategy. The results put in evidence a strong interaction between the alternative fuel quality and the engine control mode highlighting the great benefits reachable by exploiting simultaneously the alternative fuel quality and the flexibility of the new engine management strategies.     

用于TD—LTE系统的一种上行调度新算法

针对目前TD—LTE系统上行调度过程中存在的系统吞吐量低、业务QoS（服务质量）得不到保障、物理资源分配不合理等问题,对传统上行调度算法进行了改进研究。首先,在传统PF算法（比例公平算法）基础上加入对业务优先级的考虑;其次,在资源分配过程中结合用户的实际信道质量引入RME算法（极大值扩张算法）。实验结果表明,所提出的上行调度算法,能够有效提高系统吞吐量,改善数据业务传输性能,并能解决上行调度资源分配连续性限制的问题,有助于提升TD—LTE系统整体性能。     

Biodiesel,emulsified biodiesel and dimethyl ether as pilot fuels for natural gas fuelled engines

Dual-fuelling in compression–ignition (CI) engines is a mode of combustion where a small pilot injection of high-cetane fuel (i.e. diesel) ignites a premixed high-octane fuel (i.e. methane) and air mixture. This allows conventional CI engines to lower their emissions of smoke and nitrogen oxides (NO_x)$({\text{NO}}_x)$ while maintaining their high thermal efficiencies. However, poor ignitability of the main fuel–air charge results in increased emissions of unburnt hydrocarbons (HC) and carbon monoxide (CO). Conventional pilot fuels such as diesel and biodiesel (methyl esters transesterified from raw plant oil) have been researched extensively in prior work, showing that in terms of performance and emissions they perform fairly similarly. This is because the physical, chemical and combustion properties of various methyl esters are comparable to those of conventional diesel. In order to reduce these emissions of HC and CO, alternative pilot fuels need to be considered. As fuels employed during normal CI engine operation, both dimethyl ether (DME, a gaseous CI engine fuel) and water-in-fuel emulsions (conventional biodiesel mixed with varying concentrations of water) have shown that they reduce smoke and _NOx${\mathrm{NO}}_x$ emissions significantly, while improving combustion quality. In this work, the performance of DME and water-in-biodiesel emulsions as pilot fuels was assessed. It was seen that the water-in-biodiesel emulsions did not perform as well as expected, as increased HC and CO emissions coupled with a mild change in _NOx${\mathrm{NO}}_x$ levels was encountered (compared to conventional pilot fuel, in this case neat biodiesel). The emulsions performed very poorly as pilot fuels below a certain BMEP threshold. DME, while producing higher levels of HC and CO than neat biodiesel, managed to reduce _NOx${\mathrm{NO}}_x$ significantly compared to neat biodiesel. Emissions of HC and CO, while higher than neat biodiesel, were not as high as levels seen with the emulsions. Thermal efficiency levels were generally maintained with the liquid pilot fuels, with the DME pilot producing comparatively lower levels.     

First and second generation biodiesels spray characterization in a diesel engine

Potential improvement on exhaust emissions, biodegradability and the possibility to reduce dependence on fossil fuel resources has led to an increasing interest on the use of biofuels for transport application. In this work, the analysis of the spray behaviour of first and second generation biodiesel in a Euro 5, common rail transparent diesel engine has been performed. GTL, SME and RME fuels have been used in blends at 100% and 50% in volume; while reference fuel consisted of commercial diesel. Two engine operating conditions of the NEDC have been selected: 1500 rpm at 2 bar of brake mean effective pressure (BMEP) and 2000 rpm at 5 bar BMEP. The injection process has been accurately studied, and the influence of the combustion process on the spray behaviour has been taken into account. Typical jets parameters such as penetration and cone angles have been detected and a comparison with theoretical models of Hiroyasu and Siebers has been performed. A new correlation for the forecasting of the jet penetration has been obtained starting from Hiroyasu equations. An image-based method has been applied for the identification of the phenomena that control the spray behaviour during its evolution in the combustion chamber.First generation biodiesels, pure and blends, show longer penetration with respect to the reference fuel at both the engine speed analysed. Moreover, they penetrate for a longer time in the combustion chamber, because of the longer energizing time set, so impingement phenomena can be observed. On the other hand, the second generation biodiesels penetrate less than reference one, due to its lower density, but also because the combustion of the pilot injection causes an increase of pressure that obstructs the penetration in the combustion chamber. Finally, a good agreement between the breakup times computed by means of the Hiroyasu and Siebers correlations and the ones from the experimental data has been found.