点燃式发动机爆震测量及其强度分析

利用光纤传感器和压力传感器对发动机缸内爆震燃烧进行探测，在研究和测量临界爆震及轻度爆震时，探索其应用的可行性，利用信号变化率以及表征爆震强度的带通信号峰值幅值指标和信号幅值时域均方根指标，系统比较了光信号和压力信号在测量临界爆震方面的应用。试验研究表明，光信号在研究临界爆震及轻度爆震燃烧等方面具有更明显优势。     

12V190大功率燃气发动机爆震测量研究

在一台12V190大功率燃气发动机上利用非共振式机体振动测量方法对爆震测量系统进行了试验研究。试验表明:选择合适的爆震传感器,合理设计系统采样频率,利用Blackman-Harris_窗对快速傅里叶变换(FFT)算法进行加权处理,能够有效改善爆震测量效果,提高特征频率、参照频率、爆震强度等爆震辨识过程的效率和准确性。同时,以爆震测量为基础的实时控制系统,将爆震划分为轻度、中度、重度三段区域,针对性地采用不同的控制策略,也能够较好地满足大功率燃气发动机爆震保护与控制需求。     

基于HIP9011的燃气发动机的爆震检测的实现

为了提高燃气发动机的动力性和可靠性,在分析爆震产生原因的基础上,采用新型爆震处理芯片HIP9011设计了燃气发动机的爆震检测实验,采用TI公司的TMS320F2812控制专用DSP,完成了爆震信号的控制。     

煤层气发动机爆震的检测与控制

爆震现象的产生直接影响发动机的工作效率,本文论述了煤层气发动机工作过程中产生的爆震现象,阐述了爆震产生的机理、对爆震处理芯片的测试,以及使用爆震处理芯片对发动机爆震信号的检测方法。最后,提出了产生爆震时发动机点火提前角的实时闭环控制的策略。     

煤层气发动机爆震的检测与控制

爆震现象的产生直接影响发动机的工作效率,本文论述了煤层气发动机工作过程中产生的爆震现象,阐述了爆震产生的机理、对爆震处理芯片的测试,以及使用爆震处理芯片对发动机爆震信号的检测方法。最后,提出了产生爆震时发动机点火提前角的实时闭环控制的策略。     

基于缸内压力波检测的汽油机爆震控制系统

在一台单缸汽油机上对基于缸内压力波检测的爆震控制系统进行了实验研究。试验表明该系统能准确地检测到爆震信号,使发动机工作在轻微爆震状态,与通过机体振动频率检测的爆震控制系统相比,在不同的试验压缩比下,该控制系统均能较好地改善发动机的动力性能和经济性能。     

燃气发动机爆震及爆震控制

为了燃气发动机的高效稳定运行。从燃气发动机的爆震产生的主要原因出发,介绍了Waukesha最新一代的发动机系统管理模块(ESM),该模块根据发动机各气缸装设的爆震检测传感器信号,控制和调整各气缸的点火时间及发动机负载,避免爆震对发动机造成安全影响,可以实现Waukesha燃气发动机的安全稳定运行。     

V8汽油机爆震数字化监测及标定方法

针对V8汽油机爆震信号更新速度快、背景干扰强的特点，设计一种适合嵌入式控制系统应用的爆震数字化监测算法和标定方法．首先，根据爆震信号快速傅里叶变换(FFT)结果确定频率分布，设计含有3个带通滤波器的信号处理算法；其次，提出一种高实时性的爆震判断方法；然后，给出基于大量试验数据样本的爆震统计图标定方法，定义爆震统计图的统计学分布及各指标；最后，完成爆震判断阈值标定，并将缸压信号与电子控制单元(ECU)的计算结果对比．结果表明：爆震判断的正确检出率>95%，漏判率<5%，误判率<1%，满足工程应用．     

离子电流法爆震强度信号的评价分析

提供了一种无需使用传感器即可实现汽油发动机爆震测量的离子电流法。通过在火花塞电极两端加偏置电压的方法,在DA462－A型4缸汽油机的台架试验中,成功地检测出汽油机在不同爆震强度时的离子电汉信号,并根据离子电汉信号的特征选用了4种爆震强度评价指标,经分析计算表明各工况爆震强度的合理递进顺序,由此证明了火花塞离子电流爆震信号可以用于爆震强度的评价分析,作为汽油机爆震电控的反馈信号。     

大功率甲醇发动机爆震的仿真分析与研究

为了研究大功率甲醇发动机的爆震特性,文章采用GT-power软件建立甲醇发动机的仿真模型,通过台架试验数据对仿真模型进行标定并调试爆震模型,对发动机在低、中、高转速全负荷工况下的性能和爆震特性进行仿真分析。结果表明：随着压缩比或点火提前角的增大,发动机产生爆震的趋势明显增大、爆震强度增大、爆震开始时刻提前,其中点火提前角增大引起的爆震使发动机整体性能提高;轻微爆震时,发动机整体性能提高;严重爆震时,峰值缸压急剧升高,发动机整体性能恶化;不同转速下,爆震对发动机性能的影响程度不同,其中,在中转速工况下,严重爆震对发动机动力性及燃油经济性的影响较小。     

Effect of the turbulence intensity on knocking tendency in a SI engine with high compression ratio using biogas and blends with natural gas,propane and hydrogen

This research presents the test results carried out in a diesel engine converted to spark ignition (SI) using gaseous fuels, applying a geometry change of the pistons combustion chamber (GCPCC) to increase the turbulence intensity during the combustion process; with similar compression ratio (CR) of the original diesel engine; the increase in turbulence intensity was planned to rise turbulent flame speed of biogas, to compensate its low laminar flame speed. The research present the test to evaluate the effect of increase turbulence intensity on knocking tendency; using fuel blends of biogas with natural gas, propane and hydrogen; for each fuel blend the maximum output power was measured just into the knocking threshold before and after GCPCC; spark timing (ST) was adjusted for optimum generating efficiency at the knocking threshold. Turbulence intensity with GCPCC was estimated using Fluent 13, with 3D Combustion Fluid Dynamics (CFD) numerical simulations; 12 combustion chamber geometries were simulated in motoring conditions; the selected geometry had the greatest simulated turbulent kinetic energy (TKE) and Reynolds number (Re) during combustion. The increased turbulence intensity was measured indirectly through the periods of combustion duration to mass fraction burn 0–5%, 0–50% and 0–90%; for almost all the fuel blends the increased turbulence intensity of the engine, increased the knocking tendency requiring to reduce the maximum output power to keep engine operation just into the knocking threshold. Biogas was the only fuel without power derating by the conditions of higher pressure and higher turbulence during combustion by GCPCC and improve its generating efficiency. Peak pressure, heat release rate, mean effective pressure and exhaust temperature were lower after GCPCC. Tests results indicated that knocking tendency was increased because of the higher turbulent flame speed; fuel blends with high laminar flame speed and low methane number (MN) had higher knocking tendency and lower output power.     

Effect of equivalence ratio on knocking tendency in spark ignition engines fueled with fuel blends of biogas,natural gas,propane and hydrogen

This research evaluates the effect of the equivalence ratio on knocking tendency in two Spark Ignition (SI) engines fueled with gaseous fuels. A Lister Petter TR2 Diesel engine (TR2) converted to SI was used to evaluate the equivalence ratio effect when the engine was fueled with fuel blends of biogas, natural gas, propane, and hydrogen. A Cooperative Fuel Research (CFR) engine was used to study the effect of equivalence ratio on the Critical Compression Ratio (CCR) which is a metric to evaluate the knocking tendency of gaseous fuels. In both engines, the tests were conducted using the knocking threshold as the engine limit operation to quantify the effect of the equivalence ratio on knocking tendency. Experimental results in the CFR engine revealed that a lean mixture reduces the knocking tendency allowing to operate the CFR engine at higher CCR. In contrast, the effect of the equivalence ratio on the knocking tendency in the TR2 engine was different since leaner mixtures increased the engine knocking tendency. This tendency was caused by the increase in the % throttle which increased the mixture pressure at the end of the compression stroke. The high knocking tendency to lean mixtures forces to reduce the output power to find the knocking threshold for all fuel blends.     

Strategies to improve the performance of a spark ignition engine using fuel blends of biogas with natural gas,propane and hydrogen

This work presents the strategies applied to improve the performance of a spark ignition (SI) biogas engine. A diesel engine with a high compression ratio (CR) was converted to SI to be fueled with gaseous fuels. Biogas was used as the main fuel to increase knocking resistance of the blends. Biogas was blended with natural gas, propane, and hydrogen to improve fuel combustion properties. The spark timing (ST) was adjusted for optimum generating efficiencies close to the knocking threshold. The engine was operated on each blend at the maximum output power under stable combustion conditions. The maximum output power was measured at partial throttle limited by engine knocking threshold. The use of biogas in the engine resulted in a power derating of 6.25% compared with the original diesel engine (8 kW @ 1800 rpm). 50% biogas + 50% natural gas was the blend with the highest output power (8.66 kW @1800 rpm) and the highest generating efficiency (29.8%); this blend indeed got better results than the blends enriched with propane and hydrogen. Tests conditions were selected to achieve an average knocking peak pressure between 0.3 and 0.5 bar and COV of IMEP lower than 4% using 200 consecutive cycles as reference. With the blends of biogas, propane, and hydrogen, the output power obtained was just over 8 kW whereas the blends of biogas, natural gas, and hydrogen the output power were close to 8.6 kW. Moreover, a new approach to evaluate the maximum output power in gas engines is proposed, which does not depend on the engine % throttle but on the limit defined by the knocking threshold and cyclic variations.     

Influence of temperature inhomogeneities on knocking combustion

The use of a rapid compression and expansion machine (RCEM) provides the possibility of investigating the fundamental kinetic behavior of combustion. The aim of this work is the investigation of the influence of temperature inhomogeneities on the reaction kinetics of knocking combustion under well-known conditions without having random fluctuations. In the RCEM a clearly defined temperature distribution was generated that covers a large area and facilitates the investigation of the influence of a temperature gradient on knocking combustion. The paper deals with the analysis and characterization of the different phases of low-temperature kinetics during knocking as well as nonknocking combustion. Combustion was controlled by ignition timing, variation of the spark plug position, compression ratio, and temperature distribution. The results show the formation of a fast-propagating flame due to local and sequentially progressing autoignitions, which initiate a detonation as a consequence of pressure waves, which progress into an already reacting gas mixture enriched with intermediate species and radicals.     

Improving the performance of dual fuel engines running on natural gas/LPG by using pilot fuel derived from jojoba seeds

The use of jojoba methyl ester as a pilot fuel was investigated for almost the first time as a way to improve the performance of dual fuel engine running on natural gas or liquefied petroleum gas (LPG) at part load. The dual fuel engine used was Ricardo E6 variable compression diesel engine and it used either compressed natural gas (CNG) or LPG as the main fuel and jojoba methyl ester as a pilot fuel. Diesel fuel was used as a reference fuel for the dual fuel engine results. During the experimental tests, the following have been measured: engine efficiency in terms of specific fuel consumption, brake power output, combustion noise in terms of maximum pressure rise rate and maximum pressure, exhaust emissions in terms of carbon monoxide and hydrocarbons, knocking limits in terms of maximum torque at onset of knocking, and cyclic variability data of 100 engine cycles in terms of maximum pressure and its pressure rise rate average and standard deviation. The tests examined the following engine parameters: gaseous fuel type, engine speed and load, pilot fuel injection timing, pilot fuel mass and compression ratio. Results showed that using the jojoba fuel with its improved properties has improved the dual fuel engine performance, reduced the combustion noise, extended knocking limits and reduced the cyclic variability of the combustion.     

Experimental investigation on effects of knocking on backfire and its control in a hydrogen fueled spark ignition engine

The experimental study was carried out on a multi-cylinder spark ignition engine fueled with hydrogen for analyzing the effect of knocking on backfire and its control by varying operating parameters. The experimental tests were conducted with constant speed at varied equivalence ratio. The equivalence ratio of 0.82 was identified as backfire occurring equivalence ratio (BOER). The backfire was identified by high pitched sound and rise in in-cylinder pressure during suction stroke. In order to analyze backfire at equivalence ratio of 0.82, the combustion analysis was carried out on cyclic basis. Based on the severity of in-cylinder pressure during suction stroke, the backfire can be divided into two categories namely low intensity backfire (LIB) and high intensity backfire (HIB). From this study, it is observed that there is frequent LIB in hydrogen fueled spark ignition engine during suction stroke, which promotes instable combustion and thus knocking at the end of compression stroke. This knocking creates high temperature sources in the combustion chamber and thus causes HIB to occur in the subsequent cycle. A notable salient point emerged from this study is that combustion with knocking can be linked with backfire as probability of backfire occurrence decreases with reduction in chances of knocking. Retarding spark timing and delaying injection timing of hydrogen were found to reduce the chances of backfire occurrence. The backfire limiting spark timing (BLST) and backfire limiting injection timing (BLIT) were found as 12 ⁰bTDC and 40 ⁰aTDC respectively.     

End-gas autoignition and knocking combustion of ammonia/hydrogen/air mixtures in a confined reactor

End-gas autoignition and detonation development in ammonia/hydrogen/air mixtures in a confined reactor is studied through detailed numerical simulations, to understand the knocking characteristics under IC engine relevant conditions. One-dimensional planar confined chamber filled with ammonia/hydrogen/air mixtures is considered. Various initial end-gas temperature and hydrogen concentration in the binary fuels are considered. Homogeneous ignition of stochiometric ammonia/hydrogen/air mixtures is firstly calculated. It is found that H₂ addition significantly promotes autoignition, even if the amount of addition is small. For ammonia/air mixtures and ammonia/hydrogen/air mixtures with low hydrogen mole ratios, it is found from chemical explosive mode analysis results that NH₂ and H₂NO are most important nitrogen-containing species, and R49 (NH₂+NO<=>N₂+H₂O) is a crucial reaction during thermal runaway process. When the hydrogen mole ratio is high, the nitrogen-containing species and reactions on chemical explosive mode becomes less important. Moreover, a series of one-dimensional simulations are carried out. Three end-gas autoignition and combustion modes are observed, which includes forcibly ignited flame propagation, autoignition (no detonation), and developing detonation. These modes are identified within wide ranges of hydrogen contents and initial end-gas temperatures. Furthermore, chemical kinetics at the reaction front and autoignition initiation locations are also studied with chemical explosive mode analysis. Finally, different thermochemical conditions on knocking intensity and timing are investigated. It is found that a higher initial temperature or a higher H₂ content does not always lead to a higher knocking intensity, and the knocking timing decreases with the reactivity of end-gas.     

基于时频分布的发动机异响特征分析及故障诊断研究

针对发动机异响故障振动信号的时变非平稳特性 ,引入一种重分配方法 ,得到干扰项少而分辨率高的重分配平滑伪魏格纳维尔分布 (RSPWVD) ,对发动机活塞敲缸响、活塞销响、曲轴轴承响、连杆轴承响、气门响和挺杆响等常见异响故障特征信号进行了比较分析 ,并提出了一种基于 RSPWVD的发动机多异响故障诊断策略。试验结果表明 ,采用 RSPWVD可以有效地提取异响故障特征信息 ,利用基于RSPWVD的诊断策略可以准确识别不同的发动机异响故障。     

Use of hydrogen in dual-fuel diesel engines

Hydrogen is a promising future energy carrier due to its potential for production from renewable resources. It can be used in existing compression ignition diesel engines in a dual-fuel mode with little modification. Hydrogen's unique physiochemical properties, such as higher calorific value, flame speed, and diffusivity in air, can effectively improve the performance and combustion characteristics of diesel engines. As a carbon-free fuel, hydrogen can also mitigate harmful emissions from diesel engines, including carbon monoxide, unburned hydrocarbons, particulate matter, soot, and smoke. However, hydrogen-fueled diesel engines suffer from knocking combustion and higher nitrogen oxide emissions. This paper comprehensively reviews the effects of hydrogen or hydrogen-containing gaseous fuels (i.e., syngas and hydroxy gas) on the behavior of dual-fuel diesel engines. The opportunities and limitations of using hydrogen in diesel engines are discussed thoroughly. It is not possible for hydrogen to improve all the performance indicators and exhaust emissions of diesel engines simultaneously. However, reformulating pilot fuel by additives, blending hydrogen with other gaseous fuels, adjusting engine parameters, optimizing operating conditions, modifying engine structure, using hydroxy gas, and employing exhaust gas catalysts could pave the way for realizing safe, efficient, and economical hydrogen-fueled diesel engines. Future work should focus on preventing knocking combustion and nitrogen oxide emissions in hydrogen-fueled diesel engines by adjusting the hydrogen inclusion rate in real time.     

活塞结构刚度对动力学性能影响的研究

用矩阵来描述活塞的径向刚度,并在试验台架上对不同位置加载,测得规定点处的变形量,从而确定活塞整体刚度的分布情况。利用建立的动力学模型分析活塞刚度变化对二阶运动、敲击动能及摩擦功损失等的影响,为确保活塞温度场、热变形及缸套安装变形等边界条件的准确性,使用硬度塞测温试验、缸孔轮廓仪等得到的实测数据对模拟过程进行标定和验证。计算结果表明:活塞动力学分析要同时考虑缸套和活塞刚度的影响,否则计算得到的活塞摆角偏小,摩擦损失偏大,而敲击动能则随着曲轴转角的不同而与实际情况产生周期性偏差,有些偏差值甚至会达到70%;改变活塞结构会改变活塞的刚度,通常当裙部刚度增大后,活塞在每个换向时刻的最大摆角会减小,同时在每个敲击时刻的敲击能量峰值也会减小。