内燃机燃烧压力振荡对燃烧过程影响的模拟研究

结合可视化发动机、高速摄影和激光剪切干涉测量设备拍摄的燃烧过程照片和获得的燃烧二维温度场,建立了燃烧室空腔模型,并将空腔声学模型划分为未燃区和已燃区,通过空腔声模态和瞬态响应研究,获得了燃烧室空腔在多点激励下的声场变化情况,结果表明,燃烧室空腔在多点激励下在未燃区产生局部压力集中现象,燃烧压力振荡可能是引起燃烧过程未燃区出现局部自燃现象的根本原因。     

内燃机燃烧技术综述

分析了传统内燃机的燃烧技术特点;对围绕节能、环保两大主题而发展的内燃机新技术做了概述,并着重分析了内燃机的新燃烧技术,该新燃烧技术试图吸收现有压燃式以及点燃式发动机的各自优点,使内燃机的燃油经济性以及排放性能得到进一步改善;对新燃烧技术的发展前景进行了展望。     

燃烧室形状对燃烧过程的影响研究

针对燃烧室形状对燃烧过程的影响进行了研究,得到了喉口直径对喷雾贯穿距离、索特平均直径(SMD)、湍动能、涡流强度、缸内压力、放热规律以及NO-SOOT的影响规律,并通过三维对比分析了燃烧反应率场、温度场、浓度场以及速度场的变化趋势.分析表明:在本次研究中燃烧室喉口直径的合理范围是100～120 mm.     

柴油机预混合燃烧滞燃期的试验

滞燃期是柴油机预混合燃烧当中一个极为重要的参数.在电控共轨柴油机上进行了EGR率、喷油始点、喷油压力、负荷、转速和进气温度等单一参数对预混合燃烧滞燃期的试验研究.结果表明,名义过量空气系数能够帮助解释各试验参数对柴油机预混合燃烧滞燃期的影响.混合气的温度、压力和混合气中O2浓度影响柴油机预混合燃烧的滞燃期.提高进气温度...     

Mild Combustion

The Mild Combustion is characterized by both an elevated temperature of reactants and low temperature increase in the combustion process. These features are the results of several technological demands coming from different application fields. This review paper aims to collect information which could be useful in understanding the fundamentals and applications of Mild Combustion. The information in this field are still sparse, because of the recent identification of the process, so that many speculative considerations have been presented in order to make the whole framework more consistent and rich with potential new applications.A rigorous definition of Mild Combustion is preliminarily given in order to fix the input variables of the process. Under these constraints the influence of the physical, thermodynamic and chemical variables on the most relevant outlet parameters are analyzed.The physical aspects taken into account are atomization, evaporation, mixing and radiative heat transfer. In particular, the evolution of the mixing layer for high temperature diluted oxidant is analyzed. It is shown that mass fluxes through the stoichiometric isosurfaces are lower than those in not diluted conditions and that the annihilation of these isosurfaces is enhanced in the Mild Combustion conditions. Both effects infer low rates of heat release according to the experimental results reported in the literature.The thermodynamic aspects are dealt through the comparative analysis of the minimum, maximum and equilibrium temperature profiles versus the mixture fraction in the whole allowable range for the diluted and not-diluted cases.The chemical aspects have been analyzed in relation to the chemical kinetics rates for different oxidative routes and the temporal evolution of the self-ignition process. The molecular oxygen addition, the hydroperoxide dissociation and atomic hydrogen oxidation are evaluated in wide pressure and temperature ranges. In such a way self-ignition regimes which rely on different preferential chemical kinetics routes are identified and comparison between diluted/not diluted conditions are performed for a fixed evolution time. In this case it is shown that Mild Combustion conditions extend the pressure–temperature range, in which the oxidation is depressed, at relatively low pressure, whereas the ‘ceiling temperature’ is shifted to lower temperature for Mild Combustion condition at higher pressure.The second part of the review shows the potentialities of the diluted high temperature air combustion in applications related both to efficiency and pollution of thermal generation as well as to abatement of the pollutants along the flue gas stream of a primary combustion system.Some selected examples in these fields as land-base gas-turbines, boiler combustion chamber and domestic heating systems are presented. In these, the emphasis, is put preliminarily on aspects related more to efficiency than to pollution reduction, even though this target is implicitly taken into consideration. Then environmental benefits are dealt in relation to the major and minor species, either organic or inorganic, which can be produced in gas/liquid combustion. They include carbonaceous material, unburned hydrocarbons, nitrogen oxides and sulphur oxides.Finally, a classification of the possible processes relevant along the whole fuel transformation in Mild Combustion is given. In particular ‘clean’, ‘cleaning’, ‘clearing’ combustion processes are identified as a convenient categorization in relation to the incorporation of pre-combustion or post-combustion units in the main combustion systems.     

BUMP燃烧室的稀扩散燃烧机理

开发了BUMP燃烧室并进行了对比实验,发现BUMP燃烧室中可以形成稀的扩散燃烧氛围,使NOx和碳烟排放同时降低．喷射定时3°CA ATDC时,烟度排放降低了约70％,NOx排放与对比燃烧室相当．CFD模拟研究表明,不同的喷射定时下,燃油到达燃烧室壁面时的混合和燃烧状态不同,只有油束在滞燃期内到达燃烧室壁面,由限流沿(BUMP环)扰动形成的二次空间射流才能充分形成,稀扩散燃烧才能明显发生．     

采用快速混合燃烧过程降低爆压和工作粗暴度的研究

介绍了快速混合燃烧过程采用较小柱塞直径、较大行程的НТД４０ 喷油泵,提高进气涡流转速和排气道流通系数,配合喷油提前角及进气压力参数的合理匹配,初步实现了高热效率、低爆压和低粗暴度的性能指标。通过 Ａ Ｖ Ｌ６５７ 数字采集分析系统的测量,分析了改进后的燃烧系统。喷油提前角和进气压力的合理匹配降低了爆压;较小柱塞喷油泵的采用,减小了速燃期的放热速度,从而获得较小的工作粗暴度;提高涡流转速保证了快速混合燃烧过程的实现,从而获得高的热效率。     

内燃机燃料研究的新进展

2004年后对NOx排放的要求更加严格,采用以下两种措施有望达到法规要求.一种是使用NOx后处理器,另一种是改变柴油机扩散燃烧过程.本文介绍了柴油机燃烧过程研究的新近展情况,包括均匀充量压缩燃烧(HCCI)、可控自燃(CAI)、预混合稀气燃烧(PREDIC)和调谐动力(MK)等燃烧模式.     

内燃机缸内压力与燃烧噪声

利用小波包分析提取缸内压力和测量噪声的时频信息，结合频谱分析技术，对缸内压力和测量噪声特性进行了研究．结合缸内压力和测量噪声的传递函数及相干分析，讨论了测量噪声各频带活塞拍击噪声和燃烧噪声的情况，并对缸内压力和燃烧噪声各频带所占能量进行了计算和研究．结果表明，通过缸内压力和噪声的时频及频谱分析，能获取更加详细的燃烧噪声和活塞拍击噪声信息，为燃烧噪声的分离以及机理研究提供了技术支撑．