Combustion instabilities and nanoparticles emission fluctuations in GDI spark ignition engine

The main challenge facing the concept of gasoline direct injection is the unfavourable physical conditions at which the premixed charge is prepared and burned. These conditions include the short time available for gasoline to be sprayed, evaporated, and homogeneously mixed with air. These conditions most probably affect the combustion process and the cycle-by-cycle variation and may be reflected in overall engine operation. The aim of this research is to analyze the combustion characteristics and cycle-by-cycle variation including engine-out nanoparticulates of a turbocharged, gasoline direct injected spark ignition (DISI) engine at a wide range of operating conditions. Gasoline DISI, turbo-intercooled, 1.6L, 4 cylinder engine has been used in the study. In-cylinder pressure has been measured using spark plug mounted piezoelectric transducer along with a PC based data acquisition. A single zone heat release model has been used to analyze the in-cylinder pressure data. The analysis of the combustion characteristics includes the flame development (0–10% burned mass fraction) and rapid burn (10–90% burned mass fraction) durations at different engine conditions. The cycle-by-cycle variations have been characterized by the coefficient of variations (COV) in the peak cylinder pressure, the indicated mean effective pressure (IMEP), burn durations, and particle number density. The combustion characteristics and cyclic variability of the DISI engine are compared with data from throttle body injected (TBI) engine and conclusions are developed.     

Effect of the fuel injection strategy on first-cycle firing and combustion characteristics during cold start in a TSDI gasoline engine

The first firing cycle is very important during cold-start for all types of spark ignition engines. In addition, the combustion characteristics of the first firing cycle affect combustion and emissions in the following cycles. However, the first-cycle fuel-air mixing, combustion and emissions generation within the cylinder of a two-stage direct-injection (TSDI) engine during cold start is not completely understood. Based on the total stoichiometric air-fuel ratio and local richer mixture startup strategy, the first-cycle firing and combustion characteristic at cold start were investigated in a two-stage direct injection (TSDI) gasoline engine. In addition, the effects of the first injection timing, second injection timing, 1st and 2nd fuel injection proportion and total excess air ratio on the in-cylinder pressure, heat release rate and accumulated heat release were analyzed on the basis of a cycle-by-cycle analysis. It is shown that a larger 2nd fuel injection amount and later 2nd injection timing are more beneficial to the firing of the first cycle in the case of a total excess air ratio of 1.0. The optimum 1st and 2nd injection timing fuel injection proportions are 120°CA ATDC during the intake stroke, 60°CA BTDC during the compression stroke and 1:1. In addition, the firing boundary is a 2nd injection timing later than 90°CA BTDC during the compression stroke in the case of the 1st injection timing from 60°CA to 180°CA ATDC during an intake stroke and involves a 1st and 2nd fuel injection proportion of 1:1 and an excess air ratio of 1.0. The study provides a detailed understanding of cold-start combustion characteristics and a guide for optimizing the reliable first-cycle firing at cold start.     

缸内直喷LNG发动机燃烧过程测量分析

将1台直列4缸汽油机改装为缸内直喷LNG发动机,用自行开发的发动机工作过程测量分析系统测量其缸内压力.分析了标定转速和最大扭矩转速下最高燃烧压力、压力升高率、缸内温度的变化,并计算分析了其放热规律.结果表明:与汽油机相比,改装后的天然气发动机燃烧较慢,后燃现象较严重;最大扭矩点的最大压力及最大压力升高率大于标定点;转速...     

甲醇发动机缸内EGR分层的研究

针对一台具有螺旋进气道的点火式甲醇发动机,采用进气道加装EGR管的方式实现了EGR和新鲜充量的分开引入。应用CFD仿真软件Fire模拟了不同EGR通入时间、不同燃烧室凹坑形状等对EGR分层的影响。结果显示,加装EGR管能够实现EGR的分层,EGR的通入时长和燃烧室凹坑形状都对EGR的分层产生影响。当燃烧室凹坑形状为浅圆柱型、新鲜充量的通入压力为100kPa、EGR通入压力为160kPa时,在300°BTDC(压缩上止点前)停止通入,能够形成火花塞周围EGR浓度低、越远离燃烧室顶部EGR浓度越高的EGR分层结构。同时,在保证EGR率和燃油消耗量相同条件下,通过改变点火提前角,分析分层EGR和均质EGR对甲醇发动机缸内燃烧的影响。分层EGR能有效地提高缸压峰值、缩短燃烧滞燃期、提前燃烧始点,有利于发动机缸内燃烧的改善。     

Cycle-simulation turbulence modelling of IC engines

Numerical simulations of IC engines are of high interest for automotive engineers worldwide. The simulation models should be as fast as possible, low-computational effort and predictive tool. The correct prediction of turbulence level inside the combustion chamber of spark ignition engines is the most important factor influencing to the engine working cycle. This paper presents a development of the k-ε turbulence model applied to the commercial cycle-simulation software with the high emphasis on the intake part. The validation was performed on two engine geometries with the variation of engine speed and load comparing the cycle-simulation results of the turbulent kinetic energy and in-cylinder temperature with 3-D CFD results. In order to apply the cycle-simulation turbulence model for the simulation of entire engine map, the parameterization model of turbulence constants was proposed. The parameterized turbulence model was optimized using NLPQL optimization algorithm where the single set of turbulence model parameters for each engine was found. A good agreement of the turbulent kinetic energy during the expansion was achieved when the turbulence affects the flame front propagation and combustion rate as well.     

侧向换气发动机分层和均质燃烧的试验研究

在1台侧向进气的单缸发动机上对分层和均质充气燃烧进行了试验研究。通过灵活的喷油和点火控制策略实现了缸内的分层充气和均质充气燃烧。在线分析了各种工况下分层和均质充气燃烧及排放状况。研究表明,随着过量空气系数的增加,分层燃烧的性能明显优于均质燃烧,并且在稀燃状态下,分层燃烧能获得比均质燃烧更好的燃烧稳定性。在所有研究工况下,分层燃烧都能够有效地降低NOx排放。     

Combustion phase detection algorithm for four-cylinder controlled autoignition engines using in-cylinder pressure information

For several decades, the primary goal of the automotive industry has been to reduce harmful emissions and improve fuel economy. Gasoline engines are clean and powerful propulsion systems, but have poorer fuel economy than that of diesel engines. However, due to the development of new technologies such as variable valve timing and lift and direct gasoline injection, controlled autoignition (CAI) combustion can be realized. CAI engines combine the advantages of cleaner emissions and lower fuel consumption than conventional spark-ignition gasoline engines. In this study, a cylinder-pressure-based combustion phase detection method for CAI combustion is proposed. This method utilizes a normalized difference pressure (NDP), which is defined as the normalized pressure difference between the firing and motoring in-cylinder pressures. The proposed method was developed and validated with steady-state experimental data from an inline 4 cylinder, 2 L gasoline direct injection (GDI) CAI engine. Because the calculations in the NDP method are faster and simpler than in the conventional combustion phase detection method in CAI engines, this method can be embedded in a real-time controller. Furthermore, the proposed method displayed good accuracy in detecting the combustion phase and thus stabilized CAI combustion. Finally, the detailed experimental results are presented.     

Effects of intake flow on the spray structure of a multi-hole injector in a DISI engine

The spray characteristics of a 6-hole injector were examined in a single cylinder optical direct injection spark ignition engine. The effects of injection timing, in-cylinder charge motion, fuel injection pressure, and coolant temperature were investigated using the 2-dimensional Mie scattering technique. It was confirmed that the in-cylinder charge motion played a major role in the fuel spray distribution during the induction stroke while injection timing had to be carefully considered at high injection pressures during the compression stroke to prevent spray impingement on the piston.     

电机驱动模式下汽油机快速起动首循环初探

针对起动—停止技术的应用,采用了1台高速电机拖动Jetta1.6 L发动机,进行热机起动试验。分析了不同喷油量和不同拖动转速对起动时首循环燃烧情况的影响。结果表明,在其他边界条件不变时,随着起动初期喷油量的提高,缸内燃烧会显著改善;随着拖动转速的提高,滞燃期有所增大,缸内最高燃烧压力有所下降。对于本发动机,最佳喷油脉宽为11 ms,最佳拖动转速为600 r/min。     

二甲醚发动机HCCI燃烧的试验和数值模拟研究

结合详细化学反应动力学机理,采用单区模型计算了二甲醚发动机均质充量压缩燃烧过程中缸内压力、缸内温度、重要中间产物浓度、NOx 浓度等的变化,并将计算结果与试验结果进行了比较。结果表明,二甲醚均质充量压缩燃烧具有两阶段着火特性,着火时间、NOx 排放和缸内压力变化趋势预测准确。     

轿车柴油机燃用生物柴油的循环变动特性

对轿车柴油机燃用柴油、柴油-生物柴油混合燃料及生物柴油的循环变动特性进行了研究,考察了生物柴油对轿车柴油机的平均指示压力、压力峰值、压力峰值相位、压力升高率峰值等缸内压力特征参数及燃烧始点、燃烧持续期等燃烧特征参数的循环变动特性的影响.结果表明:随着生物柴油混合比例的增加,该机的平均指示压力、压力峰值,压力升高率峰值、...     

天然气发动机稀燃工况燃烧循环变动特性研究

对一台点燃式多点电喷天然气发动机在稀燃工况下进行试验,获得了各工况下的连续循环缸内压力数据,并计算了每循环与压力相关的燃烧循环变动特征参数及循环变动系数,进而研究了稀燃工况下天然气发动机的燃烧循环变动特性。结果表明,在稀燃条件下,每循环缸内峰值压力与平均指示压力有稳定的线性相关关系,每循环缸内峰值压力出现时刻与峰值压力和平均指示压力的线性相关关系随当量比的减小,均出现了由负相关到正相关的转变,并且混合气当量比越小,天然气发动机的燃烧循环变动越明显,在当量比为0.60~0.65时,平均指示压力变动系数有加速增长的趋势。     

HCCI combustion characteristics during operation on DME and methane fuels

The Homogeneous Charge Compression Ignition (HCCI) engine has attracted much interest because it can simultaneously achieve high efficiency and low emissions. However, the ignition timing is difficult to control because this engine has no physical ignition mechanism. In addition, combustion proceeds very rapidly because the premixed mixture ignites simultaneously at multiple locations in the cylinder, making it difficult to increase the operating load. In this study, an HCCI engine was operated using blended test fuels comprised of dimethyl ether (DME) and methane, each of which have different ignition characteristics. The effects of mixing ratios and absolute quantities of the two types of fuel on the ignition timing and rapidity of combustion were investigated. Cool flame reaction behavior, which significantly influences the ignition, was also analyzed in detail on the basis of in-cylinder spectroscopic measurements. The experimental results revealed that within the range of the experimental conditions used in this study, the quantity of DME supplied substantially influenced the ignition timing, whereas there was little observed effect from the quantity of methane supplied. Spectroscopic measurements of the behavior of a substance corresponding to HCHO also indicated that the quantity of DME supplied significantly influenced the cool flame behavior. However, the rapidity of combustion could not be controlled even by varying the mixing ratios of DME and methane. It was made clear that changes in the ignition timing substantially influence the rapidity of combustion.     

点火位置对汽油转子发动机燃烧过程的影响

以点燃式汽油转子发动机为研究对象,建立了相应的湍流和燃烧模型,实现了发动机工作过程的三维动态模拟,并利用试验结果进行对比验证。在此模型基础上,模拟计算和分析了4种不同点火位置对缸内压力、温度、火焰传播及NO_x生成的影响。结果表明:点火位置选择在燃烧室中轴线上,与转子凹坑中心位置重合,能优化燃烧,获取较大的功率;在燃烧室后部点火时,燃烧初期火焰传播速度快,压力升高率大,但是受限于燃烧室后部燃料少,压力峰值不高,且NO_x的生成量偏高;在燃烧室前部点火时,在补燃期阶段燃烧速度最快,但是点燃后压力升高阶段的燃烧效率一般;点火位置位于燃烧中轴线两侧错位排布时,燃烧效率低下导致压力峰值最低,同时NO_x的生成量稍高;一定工况下,双点火位置的坐标分别为(10 mm,-56 mm,-37.2 mm)和(-10 mm,-56 mm,-37.2mm)时,该发动机能获得最大的功率且NO_x生成量较少。     

排气道EGR策略对CAI燃烧过程影响的模拟研究

通过一维流体动力学软件GT-Power与化学动力学软件CHEMKIN联合模拟发动机循环,建立乙醇燃料排气道EGR模型,研究了发动机CAI燃烧的控制因素。分析了排气道EGR策略中的排气门晚关、进气门晚开和进气门开启时刻与排气门关闭时刻同时变化3种配气定时方案对EGR率的影响。由模拟计算可知排气道EGR策略对发动机缸内的换气过程、燃烧过程有强烈的影响。模拟结果表明:随着排气门逐渐晚关,EGR率增大,进气门关闭时刻缸内温度升高;进气门晚开策略中,EGR率受进气回流的影响较大;排气门晚关、进气门晚开同时变化策略扩大了CAI燃烧的EGR率范围;适当的EGR率有利于CAI燃烧的实现,EGR率过低或过高将导致失火和爆震,在不同的转速下EGR率的分布也不相同。     

气缸壁涂加催化剂对均质压燃发动机燃烧特性的影响

通过修改CHEMKIN软件包中的SENKIN模块,对气缸壁涂有催化剂的HCCI燃烧过程进行了数值计算。对比分析了缸内催化燃烧对HCCI发动机的着火时刻及NOx排放的影响;讨论了当气缸壁涂有催化剂时进气温度、进气压力、压缩比、过量空气系数及催化剂种类等多种工况参数对HCCI燃烧特性的影响。     

车用增压直喷汽油机燃烧噪声试验研究

利用倒拖法对某车用涡轮增压缸内直喷汽油机空载加速和半载加速工况进行了燃烧噪声试验研究。联合发动机缸内燃气压力测试结果,通过分析气体动力载荷对其燃烧噪声的影响,进一步探讨燃烧噪声产生的根本原因。试验结果表明,在中低转速时,燃烧噪声随着发动机负荷的增加而增加,同时燃烧噪声对整机总声功率的贡献值也在随之增加。在较高转速时,燃烧噪声对整机总声功率的贡献值随着发动机负荷的增加变化不显著。就半载加速和空载加速工况时燃烧噪声的平均贡献值来看,空载加速时燃烧噪声对整机噪声的平均贡献值为22.2%,明显小于半载加速时的43.6%。随着发动机转速的提高,最大气缸压力及最大压力升高率总体变化趋势和燃烧噪声变化趋势一致,同时加速时最大气缸压力变化对燃烧噪声的影响更明显。     

火花塞对汽油机缸内湍流的影响

针对4种不同火花塞,利用三维模拟软件建立了缸内直喷汽油机的仿真计算模型,在2 000r/min冷态情况下,对缸内湍流进行了计算,得到发动机在进气冲程、压缩冲程、点火时刻气缸内及火花塞附近的流场,评价了缸内速度场、湍动能参数。结果表明:在进气初期,火花塞对周围湍动能和缸内速度场影响最大,决定了缸内初期涡团的形成以及此后缸内湍流的发展变化;随着进气门的关闭和气缸容积的增大,火花塞对缸内湍流的影响越来越小;直至活塞靠近上止点,火花塞对局部流场的影响再一次显现。采用恰当的火花塞结构,使点火位置气流处于低速且具有足够湍流强度,对点火的稳定性和火焰的传播具有深远的影响。     

Flamelet combustion model for stratified EGR distribution in a diesel engine

Numerous research has been devoted to finding a method to simultaneously reduce NOx and soot emissions from diesel engines. In-cylinder EGR stratification is a technique that simultaneously reduces NOx and soot using a nonuniform EGR distribution in the combustion chamber. To study the potential of in-cylinder EGR stratification, a new combustion model is required that considers the non-uniform EGR distribution and the chemical kinetics. In this study, a new combustion model, the Flamelet for Stratified EGR (FSE) model, was developed to consider the non-uniform in-cylinder gas distribution based on chemical kinetics. The concept of the FSE model is based on using multiple flamelets with the multizone concept. To describe the non-uniform gas distribution, the combustion chamber is divided into several zones by oxygen concentration at the start of injection. Then, the flamelet equations are solved at the boundary of each zone. The final species mass fraction of each cell is calculated using linear interpolation between two results from the boundaries. In this paper, the FSE model was validated under in-cylinder EGR stratification conditions, and then, the potential of in-cylinder EGR stratification was studied by using the FSE model. The effect of in-cylinder EGR stratification was verified under various injection timing, engine speed, and road conditions with optimized engine geometries. The results shows simultaneous NOx and soot reductions under the stratified EGR condition.     

基于仿真的缸内直喷汽油机燃烧系统的开发与改进

以某款采用均质混合气燃烧模式的缸内直喷汽油机燃烧系统的开发为例,介绍了CFD技术在喷雾模拟中的应用.首先对喷油器的喷雾模型进行试验标定,然后将标定好的模型应用到缸内瞬态流动和喷雾仿真中.对最大转矩点(1 800r/min)和额定功率点(5 500r/min)两种工况下的缸内流场、混合气形成过程和点火时刻的浓度分布进行详...