汽修专业毕业论文外文翻译.doc

本科毕业设计（论文）外文翻译浙江师范大学本科毕业设计(论文)外文翻译译文：废气再循环对压力波增压器平均价值建模的影响菲利克斯韦伯向瑞士联邦理工学院苏黎世提交的关于技术科学博士学位的论文摘要自然吸气式火花点火（汽油）发动机的三效催化尾气后处理系统本身已经在部分负荷条件下低效率运行，由于发动机扭矩是通过控制进气歧管压力容易导致火花点火发动机的泵气损失。试图改善这个缺点的方法是缩小发动机并回收增压发动机的功率。相比自然吸气式汽油机，小型增压汽油机工作在中等负荷和低负荷范围间的泵气损失更小，更为有效。压力波增压器可能是精简增压汽油机的一个代表。由于废气和新鲜空气在这里面直接接触，不良废气再循环可能通过增压器。突然的高压废气再循环，将会导致发动机扭矩崩溃。为了保证良好的操控性，废气再循环必须避免。因此，所提出的工作目标是建立模型，并排除排气压力波增压器内气体循环的影响。这项工作提出了一个具有小型气体增压阀的压力波增压汽油机的平均值系统模型。该系统模型能够预测如压力、温度、质量流量、发动机扭矩精度状态，并在排气稳态和瞬态工况时通过增压器进行废气再循环。这解释了为什么压力波增压器在净化时负荷会恶化。模型的推断表明，小型气阀门关闭过快会导致更难净化。整个系统最重要的部分是压力波增压器的模型。它可以计算基于线性一维气体动力学的简单压力波过程而不是压力波的快速动态过程。由四个物理模型参数验证识别。因此，压力波增压器的泄漏损失和混合区的长度不可测量，废气和新鲜空气才能被分辨出来。压力波增压验证模型显示大约5%的误差。揭露压力波增压汽油机系统的平均价值模型是一种模拟工具。该工具可用于系统分析和系统优化，并应用于模型控制器设计。简介1 增压汽油机1.1 精简和最小油耗增压现代火花点火（汽油）发动机都必须具有三效催化装置，以满足目前的排放标准。因此，必须进行化学计量空燃比操作。该发动机的扭矩只能通过改变进气歧管压力，即控制油门降低环境压力强度，耗损进气歧管压力强度。发动机在部分负荷条件下工作的负压差特点：PimPem0：节流发动机运转进气管和排气管之间的负面压力差造成发动机的吸气损失。这就是为什么自然吸气汽油机在部分负荷条件下低功率运行的原因。下面是几种改善这种情况的方法：1缸内直喷稀薄燃烧发动机2高速发动机3小型增压高速发动机4小型增压超速发动机概念1试图通过一个精简发动机的运行模式来减少燃料消耗这仍然是一个当前正在研究的课题，因此没有进一步讨论。与此相反，发动机概念2、3和4通过降低发动机排量来尽量避免泵气损失。相对普通汽油机，精简发动机更经常在节流不易损失的高负荷状态下运行，这导致了泵气损失可以忽略不计。发动机在接近最经济的工作点运行。通过缩小发动机来降低发动机动力回升的可能是：提高发动机转速上述环境压力加大进气歧管压力由于发动机在高速运行时引起的噪声，第一个概念对客车来说不是一个适当的选择。第二个概念是增加进气歧管压力至大于大气压来恢复损失的发动机动力。通过下面的途径可能实现：机械增压涡轮增压压力波增压器增压器在发动机曲轴机械能（机械增压器）或者是排气热能（涡轮增压气或者是压力波增压器）的作用下压缩新鲜空气。在增压状态下，发动机上的压力差变成零或者是正数。（如图1.1，举了一个涡轮增压汽油机的例子）：PimPem0：增压发动机运转图1.1:带有旁通阀的涡轮增压汽油机；a：外界大气；im：进气歧管；em：排气歧管；1：压缩机前；2：压缩机后；3：涡轮机前；4：涡轮机后增压发动机相对自然吸气发动机在低负荷和中负荷范围运转时的泵气损失更小，更加经济。因此，增压汽油机可减少燃料消耗。1.2 压力波增压汽油机的增压作用在节能项目中，小型汽油机都带有压力波增压器（PWS）。下面针对选择PWS作为增压装置的主要原因做简单的阐释：泄漏损失：预计小型汽油机的排气量是非常低的。涡轮机的几何尺寸太小会造成涡轮增压器在涡轮机上有较高的泄漏损失。因此，它的效率会降低。对于给定所需的增压压力P2，相对涡轮机无泄漏的原因，较低的涡轮机效率要求有较高的排气压力P3（见图1.1的压力命名）。这将增加发动机的泵气损失。相对涡轮增压器，对同样的小型发动机，压力波增压器比预期泄漏损失要小。因此，在增压状态下增压器的泵气损失可能忽略不计。负荷损失：通常，汽油机的排气流量在一个较宽的范围内变化。体积流量的不同，加上涡轮机前的实际压力、温度和涡轮转速，造成涡轮机的负荷损失。这些损失降低了涡轮机的效率，出于同样的原因，如上所述，导致油耗增加。质量流量特征：由于涡轮流量特性，压缩机的震喘线相对叶片边缘较厚，就小型涡轮增压汽油机来说，在低空气质量流量的最大升压力和发动机转速比压力波增压器还小。整个发动机转速范围内增压：增压器设备耦合到发动机的所有工作点和在整个发动机转速范围内的空气压缩。与此相反，当小型发动机使用机械增压时，发动机只在高速时被增压，因为发动机燃烧不会为了避免低速抖动的问题而降低压缩比。因此，在发动机低速运转时，机械增压器必须与发动机同步。为了保证良好的操控性，发动机扭矩在增压器同步或是不同步的时候不发生变化。由于扭矩恒定的问题尚未解决，机械增压是毫无疑问的。控制压缩比的增压器：从图中的压力波增压器分析，有一个通过排气热能控制增压过程的旁通阀。GPC执行机构不仅通过控制发动机进气歧管压力来避免抖动，而且也扩大了汽油机运行时不发生泵气损失的范围。原因是避开不需要排气质量流量热能那部分来降低增压装置前的压力。2 目前的研究动向如果汽油机装备了压力波增压器，不仅要控制增压来避免发动机抖动，而且还要避免外部的废气再循环（EGR）。如果气缸内的部分废气发生逆流超过一定水平，废气再循环会因为缺氧而导致发动机扭矩降低，超过这个着火水平会导致发动机扭矩完全崩溃。因此，为了保证压力波汽油机的动力操控性能，必须避免不良的废气再循环。3 目标研究的主要目标有以下几点：1压力波增压器被整合到一个发动机系统模型中作为一个子模型，将它与汽油机的平均值模型一起运行，模拟发展的稳态和瞬态。2该建模方法以物理为基础，以便推出模型。3压力波增压器模型的相对误差要小5%。4压力波增压器的模型仿真工具在短时间内的相对误差要小于10%。5仿真工具模拟实时过程以确保这里提出的模型可逐步用于以后的控制设计。4 方法为了模拟压力波增压器的整个系统，系统可以进入设备中存储质量和能量（接收器），然后在这些接收器中产生流量（广义的油门）。该模型的有关动态代表接收器能源和质量的存储。而“油门”描述了静态的代数关系。该压力波增压汽油机仿真工具的主要部分是模型的静态子模型。压力波增压器作为一个广义的“节流”，即模仿，压力波增压器模型输出的是质量和焓流。模型忽略建立一个快速动态的新型固定压力波图，因为系统动态造成歧管填充排空过程占据主导地位。基于一维线性气体动力学理论,压力波增压器模型计算出一个简化的压力波程序和相应的压力波图。压力波增压器模型进行了验证稳态测量。5 主要影响本文研究的主要影响：说明压力波增压过程包括基于物理平均值模型的稳态废气再循环方法。该模型计算输出值作为衡量压力波增压器压力和温度的一种渠道和增压器的实际转速。该计算是基于一维线性代数关系的气体动力学。由此产生的模型是压力波增压器的静态模型，其中显示的输出错误小于5%。据不完全推测，压力波增压器的泄漏损失不包括压气机轮，非计量混合区的长度和通过识别模型参数的废气气体比例。介绍并解释如何避免在负载时瞬态排放废气再循环。此外，这项研究明确指出了小型气体阀的工作原理，并解释了压力波动过程及其影响。开发一个用来进行系统分析的模拟工具，系统优化，以及模型的控制设计。6 结论压力波增压器由以下证明验证物理模型参数的：压缩效率反射效率扫气压力混合区的长度气体压降的绝对值取决于气阀门的关闭与否。气阀门关闭得越快，气体压力下降得越快：增加燃气阀门的关闭速度气体压力下降更慢消除不良影响此外，由该模型的推断表明，气体阀根据压力传感器测得气体体积轻微下降，在规定时间内进行关闭。只有一个不切实际的简短闭合时间，气体阀内的气体体积影响着它的动态压力。增加气体体积是在一个较小阀门中造成压降的原因，因此，要消除影响。今后采取的措施，制定模拟工具，可用于进一步的调查并进行优化，如改变歧管的体积，以不同的方式连接管，除了这些系统参数分析外，该工具主要可用于基于模型的控制设计。原文：Mean Value Modeling of a Pressure Wave Supercharger Including Exhaust Gas Recirculation EffectsA dissertation submitted to the SWISS FEDERAL INSTITUTE OF TECHNOLOGY ZRICH for the degree of Doctor of Technical Sciences presented by Felix WeberAbstractNaturally aspirated spark ignition (SI) engines with three-way catalytic exhaust gas aftertreatment systems inherently have a poor efficiency at part-load conditions since engine torque then is controlled by changing intake manifold pressure which causes pumping losses for the spark ignition engine. One attempt at improving this drawback has been to downsize the engine and to recover the engine power by supercharging.The small supercharged SI engine operates more efficiently in the range between lower and middle loads compared to a naturally aspirated SI engine due to the smaller pumping losses.The pressure wave supercharger represents one possibility of supercharging a downsized SI engine. Since the exhaust gases and the fresh air are in direct contact in this charger,undesirable exhaust gas recirculation through the charger is possible. Sudden high exhaust gas recirculation causes a breakdown of the engine torque. In order to guarantee good driveability, exhaust gas recirculation must be avoided. Therefore, the target of the presented work is to investigate, to model, and to explain the effects of exhaust gas recirculation within a pressure wave supercharger.The work presents a mean value system model of an SI engine supercharged with a pressure wave supercharger with gas pocket valve. The system model is able to predict with good accuracy states such as pressures, temperatures, mass flows, engine torque, and exhaust gas recirculation through the charger in steady-state and transient operating conditions. It explains why the scavenging process of the pressure wave supercharger during a load step must deteriorate. Model extrapolation demonstrates that a faster closing velocity of the gas pocket valve causes a worse scavenging.The most important part of the overall system model is the model of the pressure wave supercharger. It calculates a simplified pressure wave process based on the relations of the linear one-dimensional gas dynamics neglecting the fast dynamics of the pressure wave process. It is validated by the identification of four physically motivated model parameters. As a result, the nonmeasurable leakage losses of the pressure wave supercharger, the nonmeasurable mixing zone length,and its profile between exhaust gases and fresh air can be determined. The validated model of the pressure wave supercharger shows an error on the order of 5%.The developed mean value system model of a pressure wave supercharged SI engine is a simulation tool. The tool may be used for system analysis, system optimization, and model based controller design in the future.Introduction1 Supercharging an SI Engine1.1 Downsizing and Supercharging for Minimal Fuel ConsumptionModern spark ignition (SI) engines are required to be equipped with a three-way catalyst in order to meet the current emission limits. Consequently, they have to be operated with stoichiometric air-to-fuel ratios. The engine torque thus may be controlled only by changing the intake manifold pressure, i.e., the throttle reduces the level of ambient pressure by energy dissipation to the level of intake manifold pressure. The engine then works at part-load conditions, which are characterized by a negative pressure difference over the engine:PimPem0: throttled engine operationThe negative pressure difference between intake and exhaust manifolds causes pumping losses for the engine. This is the main reason why naturally aspirated SI engines have a poor efficiency at part-load conditions. Among various approaches toward improving this situation several possibilities are found:1.lean burn engines with direct injection of gasoline2.high engine speed concept3.downsizing and supercharging for high engine speed only4.downsizing and supercharging over entire engine speed rangeThe concept 1 tries to reduce the fuel consumption by a lean engine operating mode which is still a subject of current research and therefore not further discussed here. In contrast, the engine concepts 2, 3, and 4 try to avoid the pumping losses of the engine by reducing the engine displacement. Compared to a regular SI engine, the downsized engine more often operates at high loads where the throttling losses hardly occur. This leads to negligible pumping losses. The engine then operates near its most economical operating point. The engine power lost by downsizing may be recovered by:Increasing the engine speed.Increasing the intake manifold pressure above ambient pressure.The first concept is not a suitable choice for passenger cars due to the noise caused by an engine operating at high engine speeds. The second concept recovers the missing engine power by increasing the intake manifold pressure above ambient pressure. This may be realized by the adding a:mechanical chargerturbochargerpressure wave superchargerA charger compresses the fresh air either with the help of mechanical energy from the crankshaft of the engine (mechanical charger) or with the help of the exhaust gas enthalpy from the engine (turbocharger or pressure wave supercharger). In supercharged engine mode, the pressure difference over the engine becomes zero or even positive (see Fig.1.1, showing a turbocharged SI engine as an example):PimPem0:supercharged engine operationFigure 1.1: SI engine supercharged with a turbocharger with a bypass valve; a: ambient; im: intake manifold; em: exhaust manifold; 1: before compressor; 2: after compressor; 3: before turbine; 4: after turbineThe downsized supercharged engine operates more economically in the range between lower and medium loads compared to a naturally aspirated engine due to smaller pumping losses in this load range. Therefore, supercharging an SI engine may reduce the fuel consumption.1.2 Supercharging an SI Engine with a Pressure Wave SuperchargerIn the SAVE project, a downsized small SI engine is supercharged with a pressure wave supercharger (PWS). The main reasons for choosing a PWS as the charging device in that project are briefly explained in the following:Leakage losses: The expected exhaust gas volume flow of a small SI engine is very low. A turbocharger would have relatively high leakage losses over the turbine as a result of the very small turbine geometry. Therefore, its efficiency decreases. For a given desired boost pressure p2, the lower turbine efficiency requires a higher exhaust gas pressure p3 compared to the case without leakage losses over the turbine (for the nomenclature of the pressures see Fig.1.1). This causes increased pumping losses for the engine. In contrast to a turbocharger, the expected leakage losses of a PWS for the same small engine are lower. Thus, pumping losses in supercharged mode are negligible.Incidence losses:Typically, in an SI engine the exhaust gas volume flow varies over a wide range. The varying volume flow, together with the actual pressure and temperature before turbine and the turbine rotational speed, cause incidence losses for the turbine. These losses lower the turbine efficiency and, for the same reasons as explained above, lead to an increased fuel consumption.Mass flow characteristic: Due to the turbine flow characteristic, the surge line of the compressor, and the relatively thicker boundary layer at the blades in the case of a turbocharger for small SI engines, the maximum boost pressure at low air mass flows and therefore at low engine speeds is smaller than for a PWS . Since good driveability is characterized by high engine torque at low engine speeds, a PWS may be the preferable charger for small SI engines.Supercharging over entire engine speed range:The charging device is coupled to the engine for all engine operating points and compresses the air over the entire engine speed range. In contrast, when a downsized engine is supercharged with a mechanical charger,the engine is supercharged only at higher engine speeds since the inner compression ratio of the combustion engine does not need to be reduced in order to avoid the problem of knocking at low engine speeds. Therefore, at low engine speeds the mechanical charger must be uncoupled from the engine. In order to guarantee good driveability, the engine torque may not change during the uncoupling and coupling of the charger. As this torque constancy still is an unsolved problem, a mechanical charger was out of question.Controlling compression ratio of the charger: The PWS analyzed in this project has a bypass valve-the gas pocket valve (GPV)-which allows to control the exhaust gas enthalpy available for the charging process. The actuator GPV not only avoids engine knocking by controlling intake manifold pressure, but it also widens the range in which the SI engine operates without pumping losses.The reason is that bypassing that part of the exhaust gas mass flow whose enthalpy is not needed for the compression process lowers the pressure before the charging device.2 Motivation for the Research PresentedIf an SI engine is supercharged with a PWS, not only boost pressure has to be controlled in order to avoid engine knocking, but also external exhaust gas recirculation (EGR). If the fraction of the re-circulated exhaust gases within the cylinder is lower than a certain level the recirculated exhaust gases lower the engine torque as a result of a lack of oxygen, above that level misfiring may lead to a complete breakdown of the engine torque. Therefore, in order to guarantee good driveability of a car powered by a pressure wave supercharged SI engine, undesirable EGR must be avoided.3 GoalsThe main objectives of the research described here are the following:1.The development of a mean value model of a PWS which can be integrated as a submodel into an engine system model in order to simulate the steady-state and the transient operating behavior of a PWS together with an SI engine.2.The modeling approach has to be physically based in order to allow model extrapolation.3.The relative error of the PWS Model has to be smaller than 5%.4.The relative error of the simulation tool PWS Engine Model during transient has to be smaller than 10%.5.The simulation tool has to simulate the processes in real time in order to ensure that the model proposed here can be used-in a future step-for controller design.4 ApproachIn order to model the entire systemPWS SI engine, the system is substructured into devices which can store mass and energy (receivers) and devices which produce the flows between these receivers (generalized throttles). The relevant dynamics of the model are represented by the energy and mass storage of thereceivers, whereas the throttles are described by static algebraic relations.The main part of the simulation tool PWS Engine Model is the static submodel PWS Model. The PWS is modeled as a generalized throttle, i.e., the outputs of the PWS Model are mass and enthalpy flows. The model neglects the fast dynamics of building a new stationary pressure wave diagram since the dynamics of the system caused by the filling-emptying process of the tubes are predominate. The PWS Model calculates a simplified pressure wave process and the corresponding pressure wave diagram, based on the theory of the one-dimensional,linear gas dynamics. The PWS Model is validated by steady-state measurements.5 Main ContributionsThe main contributions of this research are:Description of the pressure wave process of a pressure wave supercharger including steady-state exhaust gas recirculation by a physically based mean value model approach. The model calculates the outputs as a function of the measured states as pressures and temperatures in the channels of the PWS and of the actual PWS rotational speed. The calculation is based on the algebraic relations of the one-dimensional linear gas dynamics. The resulting model is the static model PWS Model whose outputs show an error which is smaller than 5%. Derivation of the non-measurable, PWS typical leakage losses out of the cell wheel, the non-measurable mixing zone length, and its exhaust gas fraction profile