湍流射流点火甲醇发动机燃烧特性及预燃室喷射策略研究北大核心CSCD

基于一台四冲程单缸发动机开展湍流射流点火甲醇发动机的性能表现和燃烧特性研究。结果表明,湍流射流点火(turbulent jet ignition,TJI)燃烧模式放热率(heat release rate,HRR)曲线呈现“双峰”现象,放热率峰值明显高于火花塞点火(spark ignition,SI)模式,且具有更短的燃烧持续期。过量空气系数λ=1.0时,预燃室内不喷射甲醇的被动式TJI模式的平均指示压力略低于SI模式,指示燃油消耗率略高于SI模式。对于主动式TJI燃烧模式,λ=1.5,预燃室甲醇喷射时刻为压缩上止点前180°曲轴转角,喷射脉宽保持在350μs~600μs之间时,TJI甲醇发动机燃烧稳定性较好,同时动力性与经济性均有所提升。     

预燃室湍流射流点火甲醇发动机稀薄燃烧和排放特性试验研究

基于一台四冲程单缸发动机开展预燃室湍流射流点火(turbulent jet ignition,TJI)甲醇发动机燃烧特性、性能表现和排放特性的试验研究。结果表明,TJI燃烧模式燃烧速率较快,放热率(heat release rate,HRR)峰值明显较高,且具有更短的滞燃期和燃烧持续期。随着过量空气系数变大,缸内压力和放热率峰值变小,TJI和火花塞点火(spark ignition,SI)燃烧模式滞燃期和燃烧持续期均变长。此外,TJI燃烧模式可有效提升甲醇发动机的稀薄燃烧稳定性,可将稀燃极限拓展至过量空气系数2.0。TJI燃烧模式下平均指示压力略低于SI模式;然而对于过量空气系数大于1.1的稀燃工况,TJI燃烧模式指示燃油消耗率更低,在过量空气系数1.3时低于570 g/(k W·h),说明其具有更好的燃油经济性。TJI燃烧模式下氮氧化物排放量明显低于SI燃烧模式,过量空气系数1.1时降低约37.2%,并且在过量空气系数大于1.3的极稀燃工况具有相对较低的甲醛CH₂O和碳氢化合物排放。     

电喷LPG发动机快速燃烧过程的应用研究

介绍了应用于高速单燃料LPG电喷发动机的高能双火花塞快速燃烧系统的组成及其在发动机稳态运行工况的稀燃研究。开发了发动机多通道瞬态燃烧分析系统用于LPG快速燃烧过程的研究,快速燃烧系统的同步、异步点火通过ECU及其控制策略的控制实现。试验结果表明：LPG混合气的火焰传播速度得到提高,LPG的燃烧稀限由过量空气系数1．25—1．4拓展为1．4—1．5;结合燃烧室和火花塞位置的优化,火焰传播距离被缩短以实现LPG稀混合气的快速燃烧。     

主动预燃室式直喷汽油机稀薄燃烧性能研究

为明晰不同点火方式对汽油机稀薄燃烧特性的影响规律,在一款排量为0.5L的研究型单缸机上试验研究了传统火花塞和主动预燃室两种不同点火方式下发动机燃烧及排放特性,探索主动预燃室拓展稀薄燃烧极限的多种影响因素。研究结果表明,稀薄燃烧可有效降低油耗,提高发动机热效率。传统点火线圈的稀燃极限处于过量空气系数1.5附近,最高指示热效率为45.0%,而采用主动预燃室系统后,稀燃极限可进一步拓展,过量空气系数可达2.0,指示热效率提升至46.5%,氮氧化物排放比采用传统火花塞点火技术时降低约88%;主动预燃室匹配高压缩比14.80的燃烧系统,可进一步拓展稀燃极限至过量空气系数2.1,指示热效率可达48.0%,氮氧化物排放继续降低,在过量空气系数采用2.1时NOx排放最低可达58×10-6。     

低压缸内直喷CNG发动机燃烧特性的影响因素

自主研发了低压缸内直喷压缩天燃气(CNG)发动机,研究了过量空气系数、喷气时刻、点火能量、点火时刻等 对发动机燃烧特性的影响.结果表明,喷气时刻对低压缸内直喷CNG发动机的燃烧性能有很大影响,对于给定的工况,发动机存在一个最佳喷气提前角;提高点火能量有助于改善CNG发动机的燃烧过程,增大点火提前角,可以在一定程度上弥补由于天然气燃料火焰传播速度慢所导致的热效率下降,从而改善发动机缸内的燃烧过程,使其功率增加,燃气消耗率降低.     

多火花塞点火实现快速燃烧的试验研究

使用快速压缩-膨胀机改装的多火花塞点火试验台架,研究了火花塞数目对指示功大小、最高燃烧压力和最大压升率、燃料放热速率及爆震特性的影响。得到结果如下:液压源压力及混合气浓度相同,点火相位从上止点前5~35mm逐渐增大时,指示功先增大后减少,即存在最佳点火相位;随着火花数目的增加,最佳点火时刻后移;多火花塞点火的放热速率、最高燃烧压力和压升率、指示功均比单火花塞点火有明显提升,提升幅度和火花塞数目并不成线性关系;在混合气稀薄时,多火花塞点火对燃烧速率及指示功的提升作用更加明显;随着液压源压力的增大,相同点火相位时,多火花塞比单火花塞点火爆震倾向更加严重。     

高压缩比下扫气式预燃室湍流射流点火对废气再循环稀释汽油机性能影响研究北大核心CSCD

基于一台可调压缩比(compression ratio,CR)的单缸发动机和自主设计的湍流射流点火(turbulent jet ignition,TJI)系统,开展高压缩比下扫气式预燃室湍流射流点火对废气再循环(exhaust gas recirculation,EGR)稀释汽油机性能影响的研究。研究发现在高EGR率时,扫气式TJI的点火方式燃烧稳定性最高,可以在EGR率超过30%时实现稳定燃烧。提升压缩比对提升TJI在高EGR率下的燃烧稳定性有积极作用,然而对提升高EGR率下火花塞点火(spark ignition,SI)的稳定性作用不大。对于TJI,在低EGR率时提升压缩比会造成发动机强烈爆震,过于推迟点火造成燃烧定容度下降,燃油消耗率上升。在高EGR率时,发动机爆震受到抑制,可以提前点火优化燃烧相位,降低燃油消耗率,在压缩比15时最低燃油消耗率相比压缩比11时降低2.2%。高EGR率时,提升压缩比有利于提升燃烧速率,降低滞燃期和燃烧持续期,提升发动机燃烧稳定性。在EGR率为30%而压缩比为15时,逐渐提前点火时刻会加大末端混合气自燃倾向,放热率出现两阶段高峰。     

稀燃条件下主动预燃室式直喷汽油机燃烧和排放特性研究

为明晰不同点火方式对汽油机稀薄燃烧特性的影响规律,在一款排量为0.5 L的研究型单缸机上试验研究了传统火花塞和主动预燃室两种不同点火方式下发动机燃烧及排放特性,探索主动预燃室拓展稀薄燃烧极限的多种影响因素.研究结果表明,稀薄燃烧可有效降低油耗,提高发动机热效率.传统点火线圈的稀燃极限处于过量空气系数1.5附近,最高指示...     

直喷二甲醚对稀汽油混合气燃烧过程影响的研究

在一台四冲程单缸汽油机上,通过缸内直喷二甲醚(DME)实现了空气稀释汽油混合气的稳定燃烧。研究结果表明:在1 500r/min下,固定循环燃油热值时,直喷DME可以降低汽油机稀燃下的循环变动,加速初期火焰发展速度,缩短燃烧持续期,提高汽油稀燃稳定燃烧的过量空气系数上限。稀燃和直喷DME相结合可以改善发动机在稀燃下的燃油经济性。与理论空燃比混合气相比,稀燃能使指示燃油消耗率最多降低11.7%。改变点火时刻和直喷DME比例能实现不同过量空气系数下的最佳燃烧相位。随着过量空气系数的增加,最佳放热中心相位提前。     

液化石油气与汽油燃烧特性的对比试验研究

在点燃式发动机上分别燃用液化石油气和汽油,通过采集示功图并进行放热规律计算,对两种燃料在相似工况、相同过量空气系数下的燃烧特性进行对比分析。结果表明,在不改变样机结构和点火提前角的情况下,燃用液化石油气造成样机最大输出功率下降了7.64%。标定工况下,过量空气系数的变化对样机燃用汽油时的功率影响较大。两种燃料标定工况下的比热耗均随过量空气系数的增大而降低,但液化石油气降低的幅度较小。相似工况、相同过量空气系数下,相对于汽油,液化石油气的滞燃期短,燃烧持续期短,燃烧速度快。     

Effects of ignition advance on a dual sequential ignition engine at lean mixture for hydrogen enriched butane usage

In this study, the effects of ignition advance on dual sequential ignition engine characteristics and exhaust gas emissions for hydrogen enriched butane usage and lean mixture were investigated numerically and experimentally. The main purpose of this study is to reveal the effects of h-butane application in a commercial spark ignition gasoline engine. One cylinder of the commercially dual sequential spark ignition engine was modeled in the Star-CD software, taking into account all the components of the combustion chamber (intake-exhaust manifold connections, intake-exhaust valves, cylinder, cylinder head, piston, spark plugs). Angelberger wall approximation, k-ε RNG turbulence model and G-equation combustion model were used for analysis. In the dual sequential spark ignition, the difference between the spark plugs was defined as 5° CAD. At the numerical analysis; 10.8:1 compression ratio, 1.3 air-fuel ratio, 2800 rpm engine speed, 0.0010 m the flame radius and 0.0001 m the flame thickness were kept constant. The hydrogen-butane mixture was defined as 4%–96% by mass. In the analysis, the optimal ignition advance was determined by the working conditions. In addition, the effects of changes in ignition advance were examined in detail at lean mixture. For engine operating conditions under investigation, it has been determined that the 50° CAD ignition advance from the top dead center is the optimal ignition advance in terms of engine performance and emission balance. It has also been found that the NO_x formation rises up as the ignition advance increases. The BTE values were approximately 12.01% higher than butane experimental results. The experimental BTE values for h-butane were overall 3.01% lower than h-butane numerical results.     

不同过量空气系数下射流点火发动机燃烧、排放和爆震特性的试验研究

基于单缸试验机研究了过量空气系数对射流点火发动机性能的影响.通过分析发动机性能曲线、缸内燃烧情况及爆震特性探究射流点火最佳运行区间,并与火花点火燃烧方式进行对比.结果表明,射流点火可以有效提升瞬时放热率并拓展发动机稀燃极限,缩短缸内混合气滞燃期与燃烧持续期,同时燃油经济性有一定提升.在稀燃条件下氮氧化物排放极低.爆震方...     

发动机单双火花塞点火性能对比研究

在一台传统的四冲程摩托车发动机上进行了单火花塞和双火花塞点火性能的试验研究,通过对两种点火情况下压力传感器采集的气缸燃烧压力信号的比较分析。结果表明,采用双火花塞点火不但有利于发动机动力性能的提高,而且使发动机的循环变动率大大降低,明显改善了发动机的性能。     

Numerical simulation of the mixture distribution and its influence on the performance of a hydrogen direct injection engine under an ultra-lean mixture condition

In this study, a three-dimensional numerical model of a hydrogen direct-injection engine was established, and the combustion model was verified by experimental data. The influence of the injection timing and nozzle diameter on ultra-lean combustion was evaluated. The results suggest that, with the delay in the injection timing, the mixture concentration near the spark plug and combustion speed gradually increase. The maximum thermal efficiency increased from 47.44% to 49.87%. The combustion duration and ignition lag are shortened from 19.15°CA to 11.15°CA to 16.13°CA and 5.92°CA, respectively. As the nozzle diameter increased, the injection duration was shortened, and the mixture distribution area became more concentrated. Furthermore, under ultra-lean combustion, the combustion rate is more sensitive to the distribution of the mixture. Appropriately increasing the equivalence ratio near the spark plug can significantly shorten the ignition lag and combustion duration and obtain a higher thermal efficiency.     

Experimental study of stratified lean burn characteristics on a dual injection gasoline engine

Due to increasingly stringent fuel consumption and emission regulation, improving thermal efficiency and reducing particulate matter emissions are two main issues for next generation gasoline engine. Lean burn mode could greatly reduce pumping loss and decrease the fuel consumption of gasoline engines, although the burning rate is decreased by higher diluted intake air. In this study, dual injection stratified combustion mode is used to accelerate the burning rate of lean burn by increasing the fuel concentration near the spark plug. The effects of engine control parameters such as the excess air coefficient (Lambda), direct injection (DI) ratio, spark interval with DI, and DI timing on combustion, fuel consumption, gaseous emissions, and particulate emissions of a dual injection gasoline engine are studied. It is shown that the lean burn limit can be extended to Lambda= 1.8 with a low compression ratio of 10, while the fuel consumption can be obviously improved at Lambda= 1.4. There exists a spark window for dual injection stratified lean burn mode, in which the spark timing has a weak effect on combustion. With optimization of the control parameters, the brake specific fuel consumption (BSFC) decreases 9.05% more than that of original stoichiometric combustion with DI as 2 bar brake mean effective pressure (BMEP) at a 2000 r/min engine speed. The NO_x emissions before three-way catalyst (TWC) are 71.31% lower than that of the original engine while the particle number (PN) is 81.45% lower than the original engine. The dual injection stratified lean burn has a wide range of applications which can effectively reduce fuel consumption and particulate emissions. The BSFC reduction rate is higher than 5% and the PN reduction rate is more than 50% with the speed lower than 2400 r/min and the load lower than 5 bar.     

Characterization of HCNG combustion and emission characteristics in a constant volume chamber with a single and a dual spark plug configuration

In an effort to reduce the dependency on crude oil based fuels and to decrease pollutant emissions, hydrogen-CNG (HCNG) attracted a considerable attention with its low HC/CO₂ emission and fast burn rate. In this study, a constant volume chamber with a single spark plug and a dual spark plug configuration was designed to obtain fundamental combustion characteristics of HCNG and to evaluate possible advantages of the dual spark plug over the single spark plug ignition setup. Various mixtures of hydrogen and CNG were systematically experimented to evaluate effects of hydrogen fraction to lean burn limit, combustion pressure, rate of heat release and emission characteristics for both configurations. With the current experimental results, it was clearly demonstrated that an appropriate mixture of HCNG along with a suitable spark plug configuration, could become a promising candidate to replace the crude oil based IC engine fuels to alleviate the dependency on the depleting petroleum resource and to meet the stricter emission regulation.     

采用离子电流分析法实现发动机爆震信号的正确检测

本描述了了种直接利用火花塞电极作为传感器检测发动机爆震的方法。作在章中详细分析及讨论了离子电流的产生机理及影响其测量的因素，并利用这一方法在发动机做了大量的试验研究，获得了宝贵的第一手资料。为了获得正确的信号检测，作在火花塞电极上加一定的直汉电压、使其能灵敏的感受燃气密度的变化。     

Effect of different excess air ratio values and spark advance timing on combustion and emission characteristics of hydrogen-fueled spark ignition engine

This study investigated the effect of varying the spark advance timing and excess air ratio (air excessive ratio; λ) on the combustion and emission of nitrogen oxide (NOx) in a hydrogen-fueled spark ignition engine under part load conditions. The engine test speed was fixed at 2,000 rpm and the torque condition was 60 Nm. Excess air ratio was varied from the stoichiometric (λ = 1) to the lean mixture condition (λ = 2.2) by throttling. The spark advance timing was controlled to determine the maximum brake torque timing (MBT) for each excess air ratio value. Subsequent to the determination of the spark advance timing for MBT, the spark timing was varied from MBT timing to top dead center. Based on the results, it is concluded that the leanest mixture condition (λ = 2.2) with MBT spark timing exhibited the highest brake thermal efficiency of 34.17% and the NOx emissions were as low as 14 ppm.