Study of CNG／diesel dual fuel engine＇s emissions by means of RBF neural network

Great efforts have been made to resolve the serious environmental pollution and inevitable declining of energy resources. A review of Chinese fuel reserves and engine technology showed that compressed natural gas (CNG)/diesel dual fuel engine (DFE) was one of the best solutions for the above problems at present. In order to study and improve the emission performance of CNG/diesel DFE, an emission model for DFE based on radial basis function (RBF) neural network was developed which was a black-box input-output training data model not require priori knowledge. The RBF centers and the connected weights could be selected automatically according to the distribution of the training data in input-output space and the given approximating error. Studies showed that the predicted results accorded well with the experimental data over a large range of operating conditions from low load to high load. The developed emissions model based on the RBF neural network could be used to successfully predict and optimize the emissions performance of DFE. And the effect of the DFE main performance parameters, such as rotation speed, load, pilot quantity and injection timing, were also predicted by means of this model. In resum6, an emission prediction model for CNG/diesel DFE based on RBF neural network was built for analyzing the effect of the main performance parameters on the CO, NOx emissions of DFE. The predicted results agreed quite well with the traditional emissions model, which indicated that the model had certain application value, although it still has some limitations, because of its high dependence on the quantity of the experimental sample data.     

Experimental investigation on the cavity-based scramjet model

The present work focused on improving the engine performance with different fuel equivalence ratios and fuel injections. A scramjet model with strut/cavity integrated configurations was tested under Mach 5.8 flows, The results showed that the strut may sreve as an effective tool in a kerosene-fueled scramjet, The integration of strut/cavities also had great effect on stablizing the combustion in a wide range of fuel equivalence ratio. The one-sdimensional analysis method was used to analyze the main characteristics of the model. The two-stage fuel injection should have better performance in increasing the chemical reaction rate in the first cavity region.     

Integrated modeling of nitrogen oxides formation in diesel engines

To account for the effects of both chemistry and flow turbulence, the present study proposes an integrated NO sub-model that combines the extended Zel'dovich mechanism and engine CFD computations to simulate the NO histories in a diesel engine. NOx sub-model parameters and pollutant formation mechanisms can be more easily investigated by solving the NOx sub-model. The new NO formation model incorporating the effects of both chemical kinetics and turbulent mixing was applied to simulate a diesel engine with a quiescent combustion chamber, and one with a re-entrant combustion chamber; the premise of the model being the reaction rate is mainly determined by a kinetic timescale and a turbulent timescale. The results indicate that the predicted NO formulation from the new model agrees well with the measured data. As the utilization of fossil fuels continues to increase, the control of NOx emissions is a worldwide concern; and it is imperative to understand fully the NOx reaction processes in combustion systems. This technology has the potential to enhance the application of various combustion techniques used to reduce NOx emissions from practical combustion systems.     

Study of droplet size and velocity of fuel containing CO2 spray by means of PDA

Injection of fuel containing CO2 has potential to reduce NOx and soot emissions in a diesel engine. This paper presents an experimental study on the spray characteristics of fuel containing CO2 as measured by phase doppler anemometry (PDA). Experiments were performed under atmospheric conditions on diesel hole-type nozzles at constant injection pressure. Effects of CO2 concentration in diesel fuel on the spray pattern, droplet size and velocity were measured. Experimental results show that fuel atomization will improve greatly when the concentration of dissolved CO2 in the fuel exceeds the critical value. The axial and radial velocity of the fuel spray containing CO2 is larger than that of conventional diesel fuel spray near the nozzle exit due to flash boiling phenomena. Downstream of the spray, the radial velocity and droplet size of fuel containing CO2 is much more uniform and smaller than that of pure diesel spray. It is attributed to the greatly enhanced liquid-gas mixing resulting from flash separation of CO2 from the liquid. New insight into the atomization of the fuel containing CO2 was obtained and a possible mechanism to explain the phenomena was proposed. The method may be developed into a new technique for controlling diesel combustion and exhaust emis-sions.     

Influence factor of diesel soot formation in diesel engine combustion predicted by multistep soot model with highlight in soot surface activity

As more strict regulations on soot emission with increasing emphasis on the emitted soot particle size have been imposed, diesel engine partially premixed combustion had been proven to achieve ultra-low NOx and soot emissions with high thermal efficiency simulta- neously, by synergy control of mixing and chemical parameters. It calls for further study in the effect of com- bustion boundaries on soot formation. In this study, soot formation characteristic was investigated by CFD code coupled with reduced n-heptane model and improved multistep soot model. History of acetylene, which is taken as the main species of PAH formation and soot surface growth, plays more important roles on soot prediction. The revised parameter of fraction of active sites αCH was introduced as the indicator of soot surface activity in diesel soot formation. The effects of combustion boundaries on soot surface activity and soot surface growth were explored in this study. When the mixture was quite homogeneous, lowered combustion temperature was the main factor for reduced soot formation due to the lowered specific surface growth rate RCH, in spite of ec/4 increasing slightly due to the slowed decay rate of surface activity. As the inhomo- geneity of the mixture was increased, more unburned hydrocarbons were produced, promoting the formation of acetylene and soot surface activity. It was the dominated reason for higher soot surface growth rate, resulted wors- ened engine-out soot. In addition, residual of CO in later combustion phase impeded the re-oxidation of soot.     

Integrated modeling of nitrogen oxides formation in diesel engines

To account for the effects of both chemistry and flow turbulence, the present study proposes an integrated NO sub-model that combines the extended Zel’dovich mechanism and engine CFD computations to simulate the NO histories in a diesel engine. NOx sub-model parameters and pollutant formation mechanisms can be more easily investigated by solving the NOx sub-model. The new NO formation model incorporating the effects of both chemical kinetics and turbulent mixing was applied to simulate a diesel engine with a quiescent combustion chamber, and one with a re-entrant combustion chamber; the premise of the model being the reaction rate is mainly determined by a kinetic timescale and a turbulent timescale. The results indicate that the predicted NO formulation from the new model agrees well with the measured data. As the utilization of fossil fuels continues to increase, the control of NOx emissions is a worldwide concern; and it is imperative to understand fully the NOx reaction processes in combustion systems. This technology has the potential to enhance the application of various combustion techniques used to reduce NOx emissions from practical combustion systems.     

Fuel design real-time to control HCCI combustion

In order to achieve lower emissions and extensive load in the homogeneous charge com- pression ignition (HCCI) engine system, a novel fuel design concept that high-octane number fuel and high-cetane number fuel are mixed real-time to con- trol HCCI combustion is proposed in this study. HCCI combustion fueled with iso-octane/n-heptane mix- tures controlled real-time on a single-cylinder HCCI combustion engine is studied. The test results show that the equivalence ratio of n-heptane in mixtures decides ignition and controls the combustion phase of HCCI combustion. The addition of iso-octane ex- tends knocking limit in equivalence ratio somewhat, but knocking occurrence mainly depends on the total concentration of mixture. Although operating range in equivalence ratio becomes narrow with the increas- ing proportion of iso-octane, the maximum load of HCCI combustion fueled with iso-octane/n-heptane mixtures controlled real-time is increased about 80% more than that of pure n-heptane. When iso-octane/ n-heptane mixtures are controlled in optimized method, it is proved that the load of HCCI combustion can be fully extended and emissions can be de- creased remarkably, while at the same time the higher indicated thermal efficiencies are obtained over the extensive operation range.     

Experimental study on interference effect of rarefaction wave on laminar propagating flame

In order to study the interference effect of rarefaction wave on the laminar flame propagating structure and pressure characteristics of methane-air mixture, a small scale combustion chamber has been built. The techniques of high speed Schlieren photograph, pressure measurement and so on, are used to study the influence of rarefaction wave on the laminar flame propagating through methane-air mixture. The results show that, after the rarefaction wave acts on the propagation laminar flame, the laminar combustion is fully transformed into turbulent combustion just during several milliseconds, which leads to a sharp increase in the burning surface area and the pressure rise rate.     

Moisture effect on the combustion of a single copper concentrate particle in a flash smelting furnace

A mathematical model has been presented to study the combustion of a single copper concentrate particle with high moisture content. By using the presented model, the effect of particle moisture content on particle temperature, sulfur oxidation, and combustion heat generation has been evaluated. The mineralogical composition of the commonly used concentrate at Khatoonabad flash smelting furnace has been used in this study. It was found that the particle moisture content is removed in the sub-second time range and thus the moisture has marginal impact on the variation of particle temperature and on the reaction rate when the gas temperature is assumed to be constant in the reaction shaft. When a concentrate with high moisture content is charged, the particle size enlargement due to the agglomeration of concentrate particles causes an abrupt fall in the particle reaction rate.     

Three-dimensional transient numerical simulation for intake process in the engine intake port-valve-cylinder system

This paper presents a KIVA-3 code based numerical model for three-dimensional transient intake flow in the intake port-valve-cylinder system of internal combustion engine using body-fitted technique, which can be used in numerical study on internal combustion engine with vertical and inclined valves, and has higher calculation precision. A numerical simulation (on the intake process of a two-valve engine with a semi-sphere combustion chamber and a radial intake port) is provided for analysis of the velocity field and pressure field of different plane at different crank angles. The results revealed the formation of the tumble motion, the evolution of flow field parameters and the variation of tumble ratios as important information for the design of engine in-take system.     

LPG-柴油双燃料发动机燃烧特性研究

提出了一种根据燃烧分析仪测录的示功图计算 LPG-柴油双燃料发动机燃烧放热规律的新模型 .简要介绍了该模型的计算原理和方法 .利用该模型分别计算了 LPG-柴油双燃料发动机的引燃柴油、LPG及总的燃烧放热率 ,分析了其燃烧过程及燃烧特性 ,并与试验结果进行了分析比较 ,从而为研究分析双燃料发动机的燃烧特性提供了一种便捷有效的方法     

生物制气-柴油双燃料发动机的燃烧噪声

燃烧噪声对发动机的噪声有重要影响，从时域和频域两个方面对生物制气-柴油双燃料发动机的燃烧噪声进行了综合评价，计算出燃烧总声压级，与纯柴油发动机的相关数据进行了比较，分析了不同的供油提前角、负荷和转速对燃烧噪声的影响．结果表明：燃烧噪声随负荷及转速变大而变大；在相同负荷下供油提前角变大其燃烧噪声变大，燃用生物制气双燃料发动机比燃用纯柴油的燃烧噪声低约A声压级3dB．     

二甲基醚发动机工作过程的数值模拟研究

以二甲基醚着火反应机理和热力学燃烧模型为基础,建立了二甲基醚着火数据库及发动机工作过程的数学模型,藉此进行了发动机的循环模拟计算．计算结果与验证实验结果对比表明,Wiebe模型、Watson模型和Whitehouse-Way模型均可应用于二甲基醚发动机工作过程的模拟计算．应用化学反应动力学模型对DME发动机着火过程模拟计算结果所建立的着火数据库表明,滞燃期是缸内温度、压力和燃空当量比的函数,在一定的燃空当量比范围内,着火滞燃期随燃空当量比增大而变小．而采取将着火数据库与Watson燃烧子模型相耦合的模拟计算能够与实验结果相吻合。     

用改进的多区模型计算柴油机中的燃烧和排放

在广安博之直喷式柴油机多区燃烧模型的基础上,改进了燃油雾滴的运动和蒸发模型,以及碳烟的生成与氧化模型,增加了缸内挤流和涡流模型、油滴碰壁和反弹模型,计算结果表明,改进后的油束运动模型比原模型更加合理,较好地解决了空气卷吸问题,在不同转速和负菏工况下均能获得令人满意的精度,能够反映缸内与各区内的燃烧与排放物生成情况,用改进的多区模型可以较好地研究直喷式柴油机的工作过程及其排放。     

大功率车用柴油机燃用航空煤油的燃烧仿真研究

建立了大功率车用柴油机燃用柴油和航空煤油的缸内燃烧模型。该模型利用喷雾试验结果对KH-RT破碎子模型进行了标定,同时耦合了燃油的化学反应动力学机理,具有较高的仿真精度。计算结果表明:相比柴油,柴油机燃用航空煤油喷雾破碎过程中雾化质量提高;燃烧过程中缸内滞燃期缩短,放热率峰值下降,缸内机械负荷及热负荷均得到缓解;柴油机燃用航空煤油在标定工况点相比燃用柴油功率下降5.8%,油耗率相当。     

生物制气-柴油发动机放热规律的影响因素

采用气化炉热解气化各种农林废弃的生物质,产生可燃生物制气,作为以柴油引燃的双燃料发动机的主要燃料．双燃料发动机由一单缸、四冲程、水冷、直喷式柴油机改装而成,生物制气通过发动机进气管,在进气过程中被吸入气缸．实测生物制气-柴油双燃料发动机气缸压力,根据气缸压力计算放热规律并分析转速、负荷及供油提前角对它的影响．负荷增大时,双燃料发动机燃烧始点提前,最大燃烧放热率增高,最高燃烧温度升高,后燃加重;转速增大时,燃烧推迟;供油提前角增大时,最大放热率降低,对应相位提前,后燃减少．     

基于可变压缩比技术大功率低热值气体燃料发动机性能优化

为充分利用低热值气体燃料以缓解能源危机带来的压力,改善大功率低热值气体燃料发动机的燃烧过程和热效率,建立了大功率低热值气体燃料发动机的热力学循环仿真模型。研究了可变压缩比对发动机各负荷下性能和燃烧过程的影响规律,并对各工况下的压缩比进行数值优化。结果表明:大功率低热值气体燃料发动机应用可变压缩比技术,可以使发动机适应不同成分和理化性质的低热值燃料。部分负荷工况下,可以使发动机压缩比大幅提高,提高部分负荷下混合气压缩效果,改善了发动机的燃烧过程。应用可变压缩比技术,在中等负荷工况下热效率改善效果在4%~8%左右,小负荷较高转速下,热效率改善效果接近10%。可变压缩比改善了大功率低热值气体燃料发动机的热效率,为充分利用低热值气体燃料奠定了理论基础。     

基于准维多区模型的DME发动机燃烧数值模拟

提出了一种基于准维多区模型的直喷式二甲醚发动机燃烧过程的数值模拟方法,其中喷雾模拟考虑了燃油分布、液滴蒸发和空气卷吸对喷雾混合的影响。自燃着火过程的模拟以二甲醚着火反应机理为基础,建立了计及温度、压力和燃空当量比因索的着火滞燃期数据库,通过将该数据库与准维多区喷雾混合模型相耦合,对二甲醚发动机的性能和一氧化氮排放进行了预测分析．实验结果表明,模拟计算结果与实测数据符合较好．     

DME发动机着火与燃烧过程的数值模拟研究

从含氧清洁燃料二甲醚（DME）低温着火的化学反应机理入手，开展了DME自燃着火过程的数值模拟研究，进而建立了不同温度、压力和燃空当量比条件下DME着火滞燃期的数据库，通过将该数据库与发动机工作过程的模拟模型相耦合，对DME发动机的运转性能进行了变参数预测分析，预测结果与实验结果符合较好。