缸内直喷不同CH4/N2配比的混合燃料发动机掺氢燃烧负荷特性试验研究

在一台改装的单缸气体发动机上进行缸内直喷不同CH4/N2配比的混合燃料发动机掺氢燃烧负荷特性的试验,研究不同负荷下混合燃料中掺氢比和掺氮比对发动机动力性、排放性以及经济性的影响。研究结果表明,当混合气体燃料中氮气体积分数不同时,不同负荷区域,掺入氢气对缸内最大爆发压力影响不同。结果显示,掺氮25%燃料CO排放较掺氮15%的明显增大,且当不掺氢时,增长近30%,并且掺氢对减小HC排放有利,但氢气对不同氮气比燃料CO排放与NOx排放影响不同,对于掺氮15%燃料,掺氢10%后,CO排放升高,NOx排放降低,而对于掺氮25%燃料掺氢后CO排放降低,NOx排放升高。另外,随着负荷增大,有效燃气消耗率呈逐渐减小的趋势,而且掺氢有利于热效率的提高。     

基于PCCI燃烧模式下的工况扩展实现途径及参数耦合关系

压燃式发动机燃烧过程和排放直接受到燃烧室内燃油与空气的空间与时间分布状况影响,而油气混合的状况与燃油喷射参数息息相关。燃油喷射参数是燃烧边界条件的一部分,因此燃油喷射参数的优化是实现优化燃烧进程,降低NOx和Soot等排放不可缺少的手段之一。利用发动机燃油喷射参数实时控制系统试验研究了燃油喷射参数对压燃式发动机燃烧及排放的影响规律。同时结合燃料特性与燃油喷射参数藕合对压燃式发动机预混合压缩着火燃烧过程的影响,探索燃料特性与燃油喷射参数协同控制实现压燃式发动机高效清洁预混合压缩着火燃烧的潜力。     

点火角对小排量增压汽油机燃烧特性的影响研究

对465Q汽油机进行废气涡轮增压改造,研究点火角对增压后发动机燃烧特性的影响。随点火角的增大,缸内最高压力和压升率峰值都增大,其对应的曲轴转角提前,燃烧循环变动改善;每个工况下,都存在一个最佳的点火角,使发动机的功率最大,燃油消耗率最低。在最佳点火角附近,点火角每调整5°,动力性和经济性变动幅度在4%左右。     

点火式LPG发动机数值模拟与仿真分析

针对点火式LPG发动机进行了缸内燃烧过程的三维数值模拟,研究了LPG发动机在稀燃状态下的燃烧特性。使用FIRE软件,分析了点火提前角、压缩比以及燃烧室结构对LPG发动机燃烧过程中缸内、温度、累积放热量、已燃燃气质量分数以及NO质量分数等参数的影响,探索出对LPG发动机燃烧过程的影响规律,为LPG发动机设计以及性能试验研究提出方向性的建议。     

“双碳”目标下零碳燃料基础燃烧特性实验教学平台开发及应用研究

“双碳”目标背景下,为满足燃烧类相关课程实验教学环节的需求,基于氢气预燃室射流点火引燃氨气这一燃烧模式,设计了零碳燃料基础燃烧特性实验教学平台。平台由定容燃烧实验教学平台与光学发动机实验教学平台组成,通过对火焰传播图片与燃烧压力数据的分析实现对不同参数条件下预燃室射流引燃特性和主燃室着火特性的评价。实验教学实践表明,该实验教学平台完全满足零碳燃料基础燃烧特性研究的目标,取得了良好的教学效果。     

高替代率下CNG/柴油双燃料发动机燃烧特性研究

对高替代率下CNG/柴油双燃料电控发动机燃烧特性进行了研究,基于实测示功图分析气缸压力升高率、燃烧放热率及最大气缸压力循环变动随工况变化的规律。结果表明,高替代率下,转速和负荷是影响双燃料发动机燃烧的重要因素;转速不变时,随着负荷增加,双燃料发动机的压力升高率、最大气缸压力的平均值、最大放热率均增大,燃烧始点提前;负荷不变时,随着转速增加,双燃料发动机的燃烧放热率增大,燃烧始点相对滞后;高天然气替代率下CNG/柴油双燃料电控发动机的燃烧特性循环波动较小,燃烧过程较稳定。     

掺氨燃烧对重型发动机性能的影响

基于单点喷射的重型天然气发动机做掺氨燃烧性能特性实验对比,设计了液氨汽化测试与氨气与天然气按比例混合的管路系统,运用性能特性标定的方法控制及其计算空燃比。结果表明：掺氨30%混合后的气体压力0.6MPa、温度20℃,外特性下功率扭矩增加,扭矩区间区分明显,排温降低5℃到20℃;进氨燃料的压力0.7MPa、温度14℃是临界状态,否则液氨汽化失效;标定实际空燃比为14、燃料当量比为0.9到1.1和扭矩的万有特性图;降碳量的比重随着掺氨比例的增加而增加。     

大负荷下柴油-天然气双燃料发动机燃烧特性数值模拟

为提升柴油-天然气双燃料发动机在大负荷工况下的动力性、经济性和排放性等多种性能,利用某商用软件建立发动机三维气缸模型,探究了二次喷油策略下柴油的喷射时刻对发动机燃烧与排放的影响。研究表明,一定范围内较早的主、预喷时刻可以提高发动机的缸温、缸压、IMEP、燃烧效率等参数,使燃料燃烧更加充分,缸内温度分布更加均匀,并能实现较高的热效率和较低的排放。但是过早的主、预喷时刻会导致燃烧不充分,燃烧效率降低、发动机的性能减弱并产生大量废气等负面影响,由此可见,大负荷下适当提前引燃柴油的喷射时刻可优化燃烧,降低大负荷工况下的爆燃倾向,提高发动机的动力性和经济性,稳定燃烧过程。     

二冲程煤油发动机整机建模与初始点火提前角计算分析

针对二冲程汽油发动机改燃烧航空煤油后,初始点火提前角需重新标定的问题,利用GT-Power对以煤油为燃料的二冲程发动机进行整机建模。通过数值计算分析了转速、负荷、进气压力、进气温度和空燃比对点火提前角的影响,得出除转速和负荷外,进气温度对点火提前角的大小影响明显。针对不同的工况条件,充分考虑动力性而忽略经济性与排放性的前提下,通过计算获取了发动机初始点火提前角;通过仿真数据与实验结果对比验证了其一致性。     

基于欧Ⅲ标准的某型号汽油机稳态排放特性试验研究

编制了欧Ⅲ标准常温下“冷起动后排气排放试验”程序,在某型号汽油发动机的各种稳态工况下,测得不同点火提前角和空燃比条件下运行时尾气中的一氧化碳（CO）、碳氢化合物（HC）、氮氧化物（NOx）的排放特性。通过试验分析了各种运转参数对汽油机尾气排放特性的影响关系,为综合匹配各运转参数来达到降低车用汽油发动机尾气排放奠定了基础。     

A study on the characteristics of combustion variations of compression ignition engine

This paper describes the results of a study of the variation of combustion characteristics in a precombusion chamber type water-cooled diesel engine. Statiscal analysis on cycle-by-cycle variation of combustion characteristics such as rate of pressure rise, heat release rate, and mass burning rate from combustion pressure-crank angle data of one thousand cycles were made under several operating conditions. The influence of engine speed and coolant temperature upon maximum frequency of combustion characteristics are discussed also.     

Grinding Burn Detection Based on Cross Wavelet and Wavelet Coherence Analysis by Acoustic Emission Signal

Grinding burn monitoring is of great importance to guarantee the surface integrity of the workpiece. Existing methods monitor overall signal variation. However, the signals produced by metal burn are always weak. Therefore, the detection rate of grinding burn still needs to be improved. The paper presents a novel grinding burn detection method basing on acoustic emission(AE) signals. It is achieved by establishing the coherence relationship of pure metal burn and grinding burn signals. Firstly, laser and grinding experiments were carried out to produce pure metal burn signals and grinding burn signals. No-burn and burn surfaces were generated and AE signals were captured separately. Then, the cross wavelet transform(XWT) and wavelet coherence(WTC) were applied to reveal the coherence relationship of the pure metal burn signal and grinding burn signal. The methods can reduce unwanted AE sources and background noise. Novel parameters based on XWT and WTC are proposed to quantify the degree of coherence and monitor the grinding burn. The grinding burn signals were recognized successfully by the proposed indexes under same grinding condition.     

高温合金磨削烧伤表面的CCD图像特征研究

高温合金是航空工业中常用的难加工材料,磨削加工方式下极易发生烧伤。提出了采用CCD(charge coupled device,电荷耦合器件)图像特征评价烧伤程度新方法,运用数字图像处理技术,分析研究了不同烧伤程度的高温合金表面CCD图像在空域和频域的特征。研究结果表明,烧伤表面图像的色度方差具有明显特征,可以作为烧伤程度的评价指标。本研究为建立高温合金磨削烧伤程度的定量评价指标体系提供了新途径。     

Cycle-to-cycle variations under cylinder-pressure-based combustion analysis in spark ignition engines

Combustion analysis based on cylinder-pressure provides a mechanism through which a combustion researcher can understand the combustion process. The objective of this paper was to identify the most significant sources of cycle-to-cycle combustion variability in a spark ignition engine at idle. To analyse the cyclic variation in a test engine, the burn parameters are determined on a cycle-to-cycle basis through the analysis of the engine pressure data. The burn rate analysis program was used here and the burn parameters were used to determine the variations in the input parameter—i, e,, fuel, air, and residual mass. In this study, we investigated the relationship of indicated mean effective pressure (IMEP), coefficient of variation (COV) of IMEP, burn angles, and lowest normalized value (LNV) in a spark ignition engine in a view of cyclic variations.     

Study on coolant-induced hydrodynamic pressure in contact zone while deep grinding with CBN wheels

The use of coolant has been considered an effective way to avoid workpiece burn in the grinding process. Hydrodynamic pressure induced by coolant in the contact zone is always measured to characterize the coolant condition in the contact zone. In this study, grinding experiments with a cubic boron nitride wheel were first performed to determine the evolution of hydrodynamic pressure during the grinding process. The experimental results showed that when burn happened, hydrodynamic pressure was at a low level and decreased gradually while the temperature and power signals fluctuated sharply. A theoretical calculation model and a 3D air–liquid two-phase numerical simulation model were subsequently constructed to predict the hydrodynamic pressure. Both theoretical calculation and numerical simulation results showed that the hydrodynamic pressure in such a case is in inverse proportion to the gap distance between the wheel and the workpiece. The theoretical calculation results are higher than the numerical simulation results. Furthermore, the experimental results correspond to the results of the 3D air–liquid two-phase simulation, which confirms the validity of this simulation. This article presents an accurate approach to predict hydrodynamic pressure, which provides an effective analytical method of studying and avoiding workpiece burn.     

Laser dispersion and ignition of metal fuel particles

The development of a laser-shock technique for dispersing Al metal fuel particles at velocities approaching those expected in a detonating explosive is discussed. The technique is described in detail by quantifying how air drag affects the temporal variation of the velocity of the dispersed particle plume. The effect of particle size is incorporated by examining various poly-dispersed commercial Al powders at different dispersion velocities (390-630 m/s). The technique is finally tested within a preliminary study of particle ignition delay and burn time, where the effect of velocity is highlighted for different particle sizes. It was found that plume velocity exhibits a modified exponential temporal profile, where smaller particles are more susceptible to air drag than larger ones. Moreover, larger particles exhibit longer ignition delays and burn times than smaller ones. The velocity of a particle was found to significantly affect its ignition delay, burn time, and combustion temperature, especially for particles in the diffusion-controlled regime. Shorter ignition delays and burn times and lower temperatures were observed at higher particle velocities. The utility of this technique as a combustion screening test for future, novel fuels is discussed.     

Experimental study of burn classification and prediction using indirect method in surface grinding of AISI 1045 steel

Grinding burn is a discoloration phenomenon according to the thickness of oxide layer on the ground surface. This study tries to establish an automatic grinding burn detection system with robust burn features that are caused by burn and not by the design parameters. To address this issue, a method based on acoustic emission sensor, accelerator, electric current transducers, and voltage transducers was proposed in an attempt to extract burn signatures. A trial-and-error experimental procedure was presented to find out burn threshold. Vitrified aluminum oxide grinding wheel and AISI 1045 steel workpiece were used in the grinding test, as they were the most commonly used wheel–workpiece combinations in conventional grinding process. With the help of fast Fourier transform and discrete wavelet transform, the spectral centroid of AE signal, the maximum value of power signal, and the RMS of the AE wavelet decomposition transform from wavelet decomposition levels d1 to d5 were extracted as burn features. The spectral centroid of AE signal was believed not to be affected by grinding parameters. A classification and prediction system based on support vector machine was established in order to identify grinding burn automatically. Results indicate that the classification system performs quite well on grinding burn classification and prediction.     

高速深磨磨削表面烧伤的实验研究

高速深磨磨削表面烧伤研究是高速深磨的非常重要的内容。文章通过测量40Cr钢高速深磨磨削试件表面烧伤层的深度,观察磨削表面质量,分析了高速深磨各种工艺参数对磨削烧伤层厚度的影响规律,研究了避免磨削烧伤和磨削裂纹的高速深磨磨削参数优化准则。     

保载时间对P92钢蠕变-疲劳交互行为的影响

为研究保载时间对蠕变-疲劳寿命和应力-应变响应的影响规律,对P92钢在650℃下进行了应变幅为±0.5％,保载时间为36,600,3600 s的蠕变-疲劳试验,采用Chaboche塑性本构模型和应变强化蠕变模型进行有限元模拟,并对P92钢断裂试样进行透射电镜检测.试验结果表明:保载时间增长导致拉压屈服极限降低,最大拉应...     

形状记忆合金的动态加热控制方法研究

由于环境温度、热对流和热辐射条件以及输入的加热电流强度的不同，致使嵌在复合材料中的形状记忆合金的温度难以确定。为了在最短时间促成形状记忆合金的相变并防止因过热而烧毁复合材料或形状记忆合金驱动元件，提出了一种基于电阻变化率反馈的动态自传感加热方法，它可以实时监测相变的起始点和结束点，有效地防止过热。试验结果与理论分析吻合良好。