【作者】 唐娟；

【导师】 程勇；

【作者基本信息】 山东大学 ， 热能工程， 2010， 博士

【摘要】 内燃机燃烧过程决定了内燃机的动力性、经济性和排放性,对内燃机缸内燃烧状态进行检测,可及时发现缸内燃烧过程中存在的问题,使内燃机始终处于较为理想的运行工况,提高内燃机的使用性能和经济性能。内燃机燃烧状态检测方法有多种,如缸内压力法、瞬时转速法及振动信号法等。缸内压力法在试验研究中得到了广泛应用,但缸压传感器安装复杂,难以实现燃烧状态的不解体检测；瞬时转速法可实现燃烧状态的不解体检测,但在高转速低负荷工况下,发动机旋转不均匀度减小,瞬时转速波动的信噪比降低,同时,曲轴扭振的影响也导致瞬时转速信号无法有效反映缸内燃烧状态信息；振动信号法测量简便,且振动信号中包含丰富的缸内燃烧状态信息,是实现缸内燃烧过程不解体检测最有潜力的方法之一。因此,基于振动信号评价缸内燃烧状态的研究,具有重要的研究意义和实用价值。前期研究结果表明,燃烧时段振动信号具有分段特征,为更深入分析振动信号和缸内燃烧过程的关系,本课题采用模拟计算及试验研究相结合的方法,分析了缸内燃烧过程和不同形式振动信号的关系,讨论了利用缸盖表面振动信号描述缸内燃烧状态特征参数的方法,研究了非燃烧激励对燃烧激励振动响应信号的影响,并利用振动信号实现了缸内燃烧特征参数的提取。论文主要研究工作如下：1.燃烧激励及其振动响应信号关系的研究论文采用模拟计算的方法对燃烧激励及其振动响应信号的关系进行了分析。以195柴油机为对象,建立了195柴油机单质量受力模型及有限元分析模型,基于建立的模型分析了195柴油机的系统特性,结合燃烧激励频谱,对燃烧激励振动位移信号的特点进行了分析,对燃烧激励及其振动响应信号之间的关系进行了讨论。结果指出,燃烧激励振动位移存在明显的分段特征,缸内峰值压力前,振动位移和缸内压力为近似线性关系,振动位移可有效表征缸内压力的变化。峰值压力后,在惯性及弹性作用下,系统产生振动,振动位移取决于系统特性和激励频谱。振动速度和加速度分别是振动位移的一次和二次导数,因此,振动速度和加速度也具有分段特征,峰值压力前,振动速度和加速度也能较真实的表征压力升高率和压力二次导数的变化。据此,课题将研究重点放在峰值压力前振动信号的分析上,并利用峰值压力前的振动信号对缸内燃烧状态进行了估计。2.不同形式振动信号特征参数和缸内燃烧特征参数关系的研究峰值压力前,缸盖表面振动位移、振动速度和振动加速度分别与缸内压力、压力升高率和压力二次导数有相近的变化规律,因此,可利用峰值压力前的振动信号特征参数表征缸内燃烧状态特征参数。分析指出,刚性约束条件下,缸盖表面振动位移峰值、位移峰值出现时刻及平均位移分别和峰值压力、峰值压力出现时刻及平均指示压力存在对应关系；振动速度在压缩冲程中的折点、振动速度峰值后的第一个过零点、振动速度峰值出现时刻及振动速度峰值分别和燃烧始点、峰值压力出现时刻、最大压力升高率出现时刻及最大压力升高率相对应；最大振动加速度峰值前的第一个过零点和燃烧始点相对应,最大振动加速度峰值后的第一个过零点和最大压力升高率出现时刻相对应。3.非燃烧激励对燃烧激励振动响应信号输出结果影响的研究除燃烧激励外,活塞换向撞击、侧压力、曲轴主轴颈负荷及相邻缸气门开启、关闭激励等都可能激发缸盖表面振动,分析非燃烧激励振动响应信号的时频特点及其与燃烧激励振动响应信号之间的耦合关系,可为燃烧激励振动响应信号的提取提供理论依据。在195柴油机有限元模型上,模拟了活塞换向撞击、侧压力及曲轴主轴颈负荷等激励单独作用时的缸盖表面振动响应信号,对各激励振动响应信号的时频特点进行了分析。结果指出,在时域上,侧压力及曲轴主轴颈负荷激励振动响应信号的幅值比燃烧激励振动响应信号的幅值小两个数量级,两者不影响燃烧激励振动响应信号特征参数的提取；活塞换向撞击激励振动位移及振动速度分别比燃烧激励振动位移及振动速度小两个和一个数量级,对燃烧激励振动位移及振动速度信号输出结果也不产生影响,但活塞换向撞击激励振动加速度和燃烧激励振动加速度在同一数量级上,其影响不能忽略。在频域上,活塞换向撞击激励振动加速度主要分布在2000Hz以上的频带范围内,而燃烧激励振动加速度主要分布在2000Hz以下的频带范围内,其影响可通过频域方法去除。为分析相邻缸气门开启、关闭激励对燃烧激励振动响应信号输出结果的影响,建立了495柴油机有限元模型,分别模拟了燃烧激励单独作用时和燃烧激励与相邻缸气门开启、关闭激励共同作用时的缸盖表面振动响应信号。对比模拟分析结果表明,在时域上,燃烧激励较强时,实测振动响应信号的信噪比较高,相邻缸气门开启、关闭激励对燃烧激励振动响应信号的分析不产生影响；燃烧激励较弱时,实测信号的信噪比降低,气门开启、关闭激励振动响应信号对燃烧特征参数的提取将产生影响,但通过频域方法可滤除气门开启、关闭激励振动响应信号,提取仅与燃烧激励相关的振动响应信号。4.支架约束作用对燃烧激励振动响应输出结果影响的研究除内燃机内部激励作用外,发动机支架的约束作用也会影响燃烧激励振动响应输出结果,为分析其影响,在195柴油机有限元模型上模拟了不同约束条件下的缸盖表面振动响应信号。结果指出,缸盖表面振动响应是约束作用引起的系统自由振动和燃烧激励受迫振动的叠加。时域上,支架约束作用对缸盖表面振动位移信号输出结果的影响很大,某些工况下,燃烧激励振动位移完全被系统自由振动位移淹没,导致振动位移信号不能有效应用于缸内燃烧状态的识别。相对振动位移信号,自由振动对燃烧激励振动速度信号输出结果的影响减弱,对燃烧激励振动加速度信号输出结果的影响几乎可以忽略,实测振动速度和加速度都可反映出缸内燃烧状态的相关信息。在频域上,自由振动信号的频率远低于燃烧激励振动速度信号的频率,自由振动对燃烧激励振动速度信号输出结果的影响可采用适当的频域方法予以剔除。5.基于振动速度信号识别缸内燃烧特征参数的研究在195、495、C6190ZLC及CP12V190ZL柴油机上进行的试验研究结果表明,实测燃烧激励振动速度信号中混杂有支架约束引起的系统自由振动的干扰,系统自由振荡主要集中在250Hz以内的低频频带上,该振动信号可通过适当的时域或频域方法去除。利用处理后的振动速度信号对燃烧特征参数进行了识别,结果表明,基于振动速度可识别燃烧始点、峰值压力出现时刻及最大压力升高率出现时刻,但受系统特性影响,振动速度识别的燃烧特征点出现时刻和压力升高率识别的燃烧特征点出现时刻之间存在一定偏差,对同一发动机来说,该偏差可视为系统偏差。此外,利用振动速度峰值的大小可对最大压力升高率随负荷的变化趋势进行定性分析。6.基于振动加速度信号提取缸内燃烧特征参数的研究分析了195、495、C6190ZLC及CP12V190ZL柴油机缸盖表面振动加速度信号的时频特点及影响因素。指出支架约束作用引起的自由振动加速度信号较弱,与燃烧激励振动加速度信号相比,其影响可以忽略。相邻缸气门开启、关闭激励及活塞换向撞击激励振动加速度信号主要集中在2000Hz以上的频带内,燃烧激励振动加速度信号则主要集中2000Hz以下的谐波分量,且随负荷的增大,2000Hz以下的谐波分量所占比例明显增大。分析结果表明,2000Hz以下的振动加速度信号含有足够的信息用于燃烧始点及最大压力升高率出现时刻的识别。7.振动信号在HCCI发动机着火时刻识别中的应用HCCI发动机着火时刻是HCCI燃烧控制的重要反馈参数,基于论文的研究结果,引入振动速度及振动加速度信号对HCCI发动机着火时刻进行了识别。实测结果指出,HCCI发动机缸盖表面振动信号也是燃烧激励响应信号及系统自由振动信号的叠加,利用滤波后的振动速度或加速度信号,可实现HCCI发动机着火时刻的识别。更多还原

【Abstract】 Combustion process of internal combustion engines is the most critical factor that influences the dynamic, economic and emission performances of the engines. Combustion process monitor can detect combustion faults in the early stage to make sure the engines operate around design conditions. There are several combustion monitor methods, such as methods based on in-cylinder pressure, instantaneous speed and vibration signals. In-cylinder pressure is one of the most efficient signals to estimate the combustion states. Unfortunately, the piezoelectric pressure transducers are not convenient for install and not feasible for all situations, especially for non-intrusion application. Instantaneous speed signal is more available for on-line applications. However, when the engine operates at high speed and small load situations, the rotating unevenness and the signal-to-noise ratio becomes lower, also the influence of the torsional vibration becomes larger. This limits the application of the instantaneous speed. Compared to the in-cylinder pressure and the instantaneous speed, vibration signal is one of the most potential methods to realize non-intrusion combustion process estimation. Combustion process estimation using vibration signals has great significant for the future non-intrusion application.Earlier research shows that the vibration responses that excited by combustion can be divided into several segmentations. In order to study the relationship between the combustion and the vibration responses, simulation and experimental methods are applied in this paper. Also the methods of how using different vibration signals to monitor the combustion process is talked about, the influence of non-combustion excitations on combustion vibration responses is studied. The main works of this paper are described in the following sections.1. Relationship between combustion process and vibration signalsIn order to analyze the relationship between vibration signals and combustion process, a single-mass force model and a finite element model are constructed according to the 195 diesel engine structure. The amplitude-frequency and phase-frequency characteristics are obtained using these models. Combined with the spectral analysis of the in-cylinder pressure, the characteristics of the vibration displacements are analyzed. Results show that the vibration responses can be divided into two segments. Before the location of the peak pressure, the vibration displacement is approximately linearly related to the in-cylinder pressure; after the location of the peak pressure, the system becomes to vibrate, the vibration displacement is determined by the system amplitude-frequency characteristics, phase-frequency characteristics and the spectrum of the cylinder pressure. For vibration velocity and acceleration are separately the derivative and the second derivative of the vibration displacement, the vibration velocity and acceleration can efficiently describe the trends of the rate of pressure rise and the second derivative of the cylinder pressure before the location of the peak pressure. According to this segment feature, the research work is focused on the vibration analysis before the location of the peak pressure.2 Relationship between combustion characteristic parameters and vibration parametersBefore the location of the peak pressure, there are similar tendencies between the cylinder pressure and the vibration displacement, the rate of pressure rise and the vibration velocity, the second derivative of the pressure and the vibration acceleration. Based on this relationship, the combustion characteristic parameters can be identified by the vibration responses. Results indicate that when supposing the engine supporting system to be a rigid body, the location of the vibration displacement, the displacement peak value and the mean displacement are separately related to the location of the peak pressure, the value of the peak pressure and the indicate mean efficient pressure. The turning point of the vibration velocity in compression stroke, the first zero-crossing point after the location of the peak velocity, the location of the peak velocity and the value of the peak velocity are highly corresponding to the combustion timing, the location of peak pressure, the location of the maximum rate of pressure rise and the value of maximum rate of pressure rise. The first zero-crossing point before the location of the peak vibration acceleration can identify the combustion timing and first zero-crossing point after the location of the peak vibration acceleration can identify the combustion timing and the location of the maximum rate of pressure rise.3 Influence of non-combustion excitations on vibration responses excited by combustionExcluding combustion, there are several non-combustion excitations include piston slap, piston side pressure, crack shaft main journal load and valves opening and crash of adjacent cylinders. The influence of these non-combustion excitations on vibration responses excited by combustion is necessary to study for combustion vibration extracting.The vibration responses of the piston slap, piston side pressure and crack shaft main journal load are simulated on the 195 FEM model. The time-frequency characteristics of the vibrations excited by these non-combustion forces are compared to the vibrations excited by combustion. Results show the vibration responses’amplitudes excited by the side pressure and the crack shaft main journal load are two orders smaller than the vibration amplitude excited by combustion. The side pressure and crack shaft main journal load will not affect the combustion vibration response. The vibration displacement and velocity excited by the piston slap is separately two orders and one order smaller than the vibration displacement and velocity induced by combustion. However the vibration acceleration excited by piston slap can’t be ignored. In frequency domain, the vibration acceleration excited by piston slap is mainly distributed on the frequency band upper 2000Hz and the vibration acceleration excited by combustion is mainly distributed on the frequency band below 2000Hz. The influence of the piston slap can be removed by digital filters.For multi-cylinder engines, the influence of valves opening and crash of adjacent cylinders on combustion vibration responses is also need to analysis. Study is based on the 495 FEM model. The vibration responses excited only by combustion and the vibration responses excited by combustion and valves opening and crash of adjacent cylinders are conducted on the model. The influence of the valves opening and crash of adjacent cylinders on combustion vibration responses are analyzed based on these two simulation results. Results show that in time domain, when combustion is intensive, the signal-to-noise ratio is high and the influence of the valves opening and crash on combustion vibrations can be ignored. However when combustion is poor, the signal-to-noise ratio is low. The valves opening and crash will affect the combustion parameters extraction. But the influence of valves opening and crash can be removed by digital filters.4 Influence of supporting system constraints on vibration responses excited by combustionThe restraints of the supporting system may also influence the vibration responses excited by combustion. To analyze the influence of the restraints of the supporting system, simulation is conducted on the 195 FEM model under different supporting system stiffness. Results show that the vibration of cylinder head is a combination of the vibration excited by combustion and the free vibration induced by the restraint forces. The restraints of the supporting system have great effects on combustion vibration displacement. In some operating conditions, the combustion vibration displacement may be submerged by the displacement induced by the restrain forces. That mean the measured vibration displacement can’t be effectively used to monitor combustion states. Compared to the vibration displacement, the influence of the restrain forces on vibration velocity is much smaller, and the vibration velocity can reflect the combustion information effectively. The free vibration can be removed by proper time domain or frequency domain methods. The influence of the constraints on the combustion vibration acceleration can be ignored and the vibration acceleration can reflect the combustion information efficiently.5 Combustion parameters extracting based on vibration velocityExperiments are conducted on the 195,495, C6190ZLC and CP12V190ZL diesel engines. Results indicate that the vibration velocity is a combination of the free vibration velocities induced by constraints and the vibration induced by combustion. The free vibration velocities are mainly concentred on the frequency band below 250Hz and its influence can be removed by proper time domain and frequency domain methods. The vibration velocity after treatment is used to identify the combustion parameters. Results show that the combustion timing, the location of the rate of pressure rise and the location of the peak pressure can be fixed effectively by the velocity. But there is a phase shift between the parameters fixed by velocity and by the rate of pressure rise due to the phase-frequency characteristics of the system. The phase shift can be seen as system deviation for a special engine. Also the tendency of the maximum value of the rate of pressure rise can be expressed by the maximum value of vibration velocity.6 Combustion parameters extracting based on vibration accelerationTime-frequency characteristics and the influence factors of vibration accelerations measured on different diesel engines are analyzed under different conditions. Results show that the influence of the supporting system constrains can be ignored. The vibration accelerations excited by the piston slap and the valves opening and crash are mainly concentrated on the frequency band upper 2000Hz, while the acceleration excited by combustion is mainly concentrated below 2000Hz. And the energy of the vibration under 2000Hz is increased obviously with the rise of the combustion load. The vibration acceleration excited by combustion can be extracted by a low-pass filter with a 2000Hz limiting frequency.7 Application of vibration signals in HCCI engineCombustion timing is one of the most important feedback parameters for HCCI combustion control. Base on the results of the prior chapters, the vibration signals are used to determining the combustion timings of the HCCI engine. Experimental results show that the vibration velocity excited by the combustion of the cylinder head is also influenced by the constraints of the supporting system. However the influence of the constraints can be removed by least square fitting method or by high pass filter. In addition the vibration signals also disturbed by environmental noises. Analysis indicates that the noises signals are mainly distributed on the band exceeded 2000Hz, and the noise signal can be removed by a low-pass filter. The vibration velocity and acceleration can be effectively used for combustion timings’identification in the HCCI engine.更多还原