Evaluation and Control of Cyclic Variation in Spark Ignited Engines by a Thermodynic Model

An evaluation method of engine cyclic variation is proposed based on fuzzy mathematics concept. The degree of engine cyclic variation is divided into 4 levels: stable, slight variation, moderate variation and serious variation based on the statistic standard deviation of residual gas temperatures within the specified simulation cycles and the function of cyclic variation is also inducted for the cyclic variation control. Because the degree of engine cyclic variation can be estimated qualitatively, the effective control means can be applied to appease the undesired cyclic variation. Simulation result shows that for a very serious cyclic variation through the proper adjustment of the spark angle and the cyclic variation will disappear.     

关于发动机循环变动Kantor模型的讨论

为了对Kantor模型进行改进,提出了一个修正的Kantor模型.研究表明,在Kantor模型中忽略的定容放热过程和可变残余废气质量分数可以在很大程度上减小循环变动,然而在Kantor模型中未考虑的来自上一个循环的未燃燃油则明显使下一个循环的循环变动加剧,三者相互作用导致循环变动减弱甚至消失,在合理的参数范围内,没有循环变动出现,只有选取不合理的模型参数,循环变动方出现.即使是Kantor模型,循环变动也只出现在相当极端的模型参数的情况下.     

Numerical Simulation of a Spark Ignited Two-Stroke Free-Piston Engine Generator

A numerical program is built to simulate the performance of a spark ignited two-stroke free-piston engine coupled with a linear generator. The computational model combines a series of dynamic and thermodynamic equations that are solved simultaneously to predict the performances of the engines. The dynamic analysis performed consists of an evaluation of the frictional force and load force introduced by the generator. The thermodynamic analysis used a single zone model to describe the engine’s working cycle which includes intake, scavenging, compression, combustion and expansion, and to evaluate the effect of heat transfer based on the first law of thermodynamics and the ideal gas state equation. Because there is no crankshaft, a time based Wiebe equation was used to express the fraction of fuel burned in the combustion. The calculated results were validated by using the experimental data from another research group. The results indicate that the free-piston generator has some advantages over conventional engines.     

火花点火发动机运行参数对其循环变动的影响——建模和仿真

基于循环间变动的排气温度建立了一个发动机循环变动模型. 在这个模型中,第n个循环的排气温度作为模型的输入,通过定压进气过程、绝热压缩过程、定容燃烧过程、绝热膨胀过程、定容放热过程和定压排气过程来近似汽缸内的热力学过程,最后得出第n+1个循环的排气温度. 由于把发动机运行参数,如转速、点火角、计量比、进气压力和进气温度等加入该模型,可定量地估计这些参数对发动机循环变动的影响. 因为循环间排气温度的波动反映了循环变动程度,对排气温度影响最敏感的参数最可能被用于循环变动控制. 模型仿真结果表明,对于接近化学计量比的混合气,循环变动不明显,对于稀薄混合气,在部分负荷和较大点火角的情况下,循环变动以混沌或分岔的形式出现.     

Combustion Characteristics of a Single Cylinder Spark Ignition Engine Fueled with Coal Mine Methane

An experimental investigation was conducted on combustion characteristics of a single cylinder spark ignition engine fueled with coal-mine methane (CMM). The CMM was simulated by the compressed nature gas (CNG)/nitrogen blend fuels. The cylinder pressure was measured. The maximum heat release ratio, the flame development duration and the main combustion duration were analyzed with the nitrogen volume fraction in the blends changing from 0% to 35%. The results indicate that the maximum cylinder pressure, the maximum rate of pressure, the flame development duration and the main combustion duration increase and the maximum rate of heat release decreases with increasing nitrogen fraction. When the level of nitrogen volume fraction in coal-mine methane is lower than 20%, the combustion process of engine is stable. But with the level of nitrogen volume fraction over 30%, the cycle to cycle combustion variation is large, especially under low load condition.     

汽油机最高爆发压力循环变动的分布规律

基于315个试验点,样本容量为4 000的最高爆发压力pz试验数据,分别用正态分布、对数正态分布、威布尔分布、伽玛分布和贝塔分布对样本数据进行了拟合,并用分布拟合优度进行了检验.检验结果表明:在未发生爆震试验点,最高爆发压力循环变动服从3个参数的威布尔分布(置信度α=0.05).     

电火花成型机数控系统抗干扰技术的研究与分析

为了增强电火花成型机数控系统的抗干扰能力，确保系统稳定可靠运行，立足于抗干扰3要素，在全面分析系统中高压电源电路、稳压电源电路干扰成因的基础上，重点提出了在该系统中的多种干扰抑制方案，并在实践中加以验证，取得明显效果。对电火花成型机数控系统的抗干扰理论研究和工业应用均有较强的指导意义。     

建筑用钢循环塑性本构模型

本文简述建筑用钢循环塑性本构响应特性及现有建筑用钢循环塑性本构模型的发展及应用。     

汽车ABS制动压力抖动仿真与控制

建立复杂的非线性ABS系统与四分之一车数学模型,对不同参数下ABS的性能进行仿真,发现在传统控制方式下,ABS的制动压力抖动与滑移率波动存在一定的矛盾性。提出利用PWM方式控制高速电磁阀的开关,实现制动液流量的连续控制方法,有效地防止了汽车制动主缸压力抖动与滑移率的波动,提高了制动舒适性与安全性。     

基于模型汽油发动机的空燃比控制器仿真研究

建立了合理的四缸四冲程汽油发动机数学模型,对模型发动机进行仿真标定实验,获得其喷油MAP图.根据发动机运行特点及控制要求,在均值模型的基础上,建立了稳态部分负荷、瞬态、怠速3种主要运行工况下的控制器模型,并给出了以上模型在Matlab/Simulink环境下的结构框图和综合仿真过程.仿真结果表明:控制器能够判断不同工况,并自动切换到相应的控制模块,使空燃比达到预期要求,具有良好的控制性能、控制策略与控制算法可行.     

A/F闭环控制区域基本点火提前角优化研究

讨论了A／F闭环控制区域的特点，提出了初选点火提前角集合的概念。根据发动机台架试验结果，分析了电控汽油机工况对初选点火提前角集的影响，点火提前角对电控汽油机主要性能影响，介绍了基本点火提前角优化的一般原则。     

双线圈点火系统特性仿真与试验研究

为了降低稀燃CNG发动机燃烧循环变动,设计了一种双线圈点火系统。利用Multisim软件仿真研究了新点火系统次级电压的变化规律,并在发动机台架上研究了此点火系统对CNG发动机燃烧稳定性的影响。次级电压的仿真结果表明,在不同放电间隔的条件下,新点火系统分别能够有效提高次级电压,增加火花持续期并能实现多次放电。台架试验表明,在合适的放电模式下新点火系统能够降低发动机的循环变动系数,提高稀燃CNG发动机燃烧稳定性。     

柴油机喷油泵功能可靠性比较评估

目的对柴油机喷油泵功能可靠性进行比较评估，解决提高柴油机喷油泵可靠性问题．方法根据柴油机现场故障数据建立了柴油机燃料系喷油泵、喷油器、滤清器、输油泵和高压管道以及冷却系离心泵和润滑系齿轮泵的故障流参数模型，求出了喷油泵等单元的功能可靠性综合指标R^（t）．利用功能可靠性综合指标，对喷油泵等单元功能可靠性进行了比较评估，并对喷油泵故障模式作了分析．结果喷油泵功能可靠性综合指标值最小，表明喷油泵功能可靠性水平最低，是柴油机最薄弱环节．喷油泵等单元之间功能可靠性综合指标最大差异量较大，表明喷油泵等单元功能可靠性综合指标值分散性较大．结论喷油泵主要故障模式是泵体裂纹（断裂）及柱塞偶件和出油阀腐蚀、磨损．喷油泵最薄弱件是柱塞偶件．本研究可为柴油机设计及确定柴油机最佳维修周期和备件数量提供参考．     

循环滞回能的瞬态响应及数学模型

分析了低循环疲劳循环滞回能的循环相关性特点，给出了循环滞回能瞬态响应的数学模型．与已有的模型比较，本文给出的模型能准确地描述循环滞回能的循环相关事实，并且与试验结果符合较好．另外，在本模型的基础上还给出了总失效吸收能的计算式     

Fabrication of MoSi2-SiC Composites by a Spark Plasma Sintering Method

MolybdenUmdisilicidepeoSi,)hashighmeltingpoint(2293K),relativelylowdensity(6.249/cm3),abrittle-to-ductiletemper~atabout1173K[l]andoutstandingoxidationresistance[2M].Forthisreason,thedisilicidematrixcompositesarebeingconsideredasoneofthemoStPromisingc...     

Study on a Closed-Loop Air-Fuel Control System of Gasoline Engines by Simulation

In order to study the factors that influence the air-fuel ratio(A/F), the amplitude and frequency of A/F fluctuation, to reform the control strategy, and to improve the efficiency of three-way catalyst(TWC), a model of closed-loop control system including the engine, air-fuel mixing and transportation, oxygen sensor and controller, etc., is developed. Various factors that influence the A/F control are studied by simulation.The simulation results show that the reference voltage of oxygen sensor will influence the mean value of A/F ratio, the controller parameters will influence the amplitude of A/F fluctuation, and the operating conditions of the engine determine the frequency of A/F fluctuations, the amplitude of A/F fluctuation can be reduced to within demanded values by logical selection of the signal acquisition method and controller parameters. Higher A/F fluctuation frequency under high speed and load can be reduced through software delay in the controller.The A/F closed-loop control system based on the simulation results, accompanied with a rare-earth element TWC, gives a better efficiency of conversion against harmful emissions.     

新型天然气汽车尾气净化催化剂载体的制备研究

文章对天然气汽车尾气净化催化剂的关键性材料--耐高温高比表面载体材料的制备及性能进行了深入的研究。结果证明,新型载体YSZ—Al2O3材料具有高比表面和耐高温性能,YSZ～Al2O3的添加对全Pd三效催化剂的耐高温性能改善明显。     

超化井田煤厚变化的构造控制因素研究

构造作用是控制井田范围内煤层厚度变化的主要地质因素．超化井田二１煤层厚度变化规律研究表明,中生代以来三期挤压应力场作用导致煤层厚度展布的分带性和方向性;重力作用下的长期流变促使煤层展布具有南厚北薄的总体趋势;小型不协调褶皱和断裂构造,是造成煤厚局部变化的根本原因．     

Synthesis and Sintering of Mg2Si Thermoelectric Generator by Spark Plasma Sintering

Raw Mg,Si powder were used to fabricate Mg2Si bulk thermoelectric generator by spark plasma sintering (SPS).The optimum parameters to synthesize pure Mg2Si powder were found to be 823 K,0 MPa,10 min with excessive content of 10wt% Mg from the stoichiometric Mg2Si.Mg2Si bulk was synthesized and densified simultaneously at low temperature (823 K) and high pressure (higher than 100 MPa) from the raw powder,but Mg,Si could not react completely,and the sample was not very dense with some microcracks on the surface.Then,Mg,Si powder reacted at 823 K,0 MPa,10 min in SPS chamber to form Mg2Si green compact,again sintered by SPS at 1023 K,20 MPa,5 min.The fabricated sample only contained MgESi phase with fully relative density.     

Analysis of Discharge Spark Energy in Buck Converter of a Continuous Mode of Inductive Current

The basic idea of intrinsically safe circuit and the discharge spark in the Buck converter in the explosive atmospheres were introduced. The Buck converter is the main topological structure of the switch type of intrinsically safe circuit, which has two working modes： continuous inductive current （CCM -- continuous conduction mode） and discrete inductance current （DCM -- discontinuous conduction mode）. The operating state of the continuous inductive current mode is analyzed in detail and the energy of discharge spark in various operating modes is discussed. The total energy will decrease with the increase of switch frequency, in a switching cycle; the discharge spark energy has a maximum and a minimum value. Therefore, the Buck converter has smaller discharge spark energy than the linear power circuit and the switch type of intrinsically safe circuit can enhance the output power and the conversion efficiency of the intrinsically safe power.