车用汽油机点火正时的模糊控制仿真

为探索车用汽油机点火智能控制的有效方法,对ＣＳ４９２Ｑ汽油机进行台架实验,在得到汽油机性能与点火提前角关系的基础上,以汽油机曲轴转速变化量和转速相对于点火提前角增量的变化率为模糊输入量,点火提前角增量为模糊输出量,建立模糊控制器,对汽油机点火正时进行模糊控制仿真。结果表明,采用模糊控制技术调节汽油机的点火正时,对汽油机的各种工况都有较好的控制精度,对变工况过程有较好的适应性。     

Efficiency improvement for an unthrottled SI engine at part load

Variable valve timing (VVT) and cylinder deactivation (CDA) are promising methods in reducing fuel consumption and emission at part load in SI engines. An SI engine which uses electromagnetic valvetrain (EMV) will eliminate flow restriction from the throttle valve and produce higher indicated mean efficiency pressure (IMEP) due to the disabling of some of the working cylinders at part load. Therefore, pumping loss can be significantly reduced at part-load conditions. In addition, duration and timing of valve events are variably controlled at different operating conditions. This contributes to the improvement of engine efficiency. In this study, a dynamic model of an unthrottled SI engine has been developed to simulate the engine cycle. The model uses an EMV system that allows valvetrain control and cylinder deactivation techniques to be carried out in simulation flexibly. The simulated results find the optimal valve timing for different engine speeds. The optimal timing of intake valve closing depends on engine speed linearly, while the intake valve opening insignificantly influences engine performance. Additionally, this study also shows that cylinder deactivation modes can be successfully applied in improving engine efficiency at different engine loads. Different cylinder deactivation strategies have been applied for the full range of engine loads. It is concluded that the two-cylinder deactivation mode (50% CDA) considerably improves fuel consumption at low engine load. Meanwhile, one-cylinder deactivation (25% CDA) is an optimal fuel economy mode at medium engine load. With proper uses of VVT and CDA strategies, the efficiency of an SI engine can be increased more than 30% at low engine load and 11.7 % at medium engine load.     

Development of engine control using the in-cylinder pressure signal in a high speed direct injection diesel engine

Emission regulations are becoming more stringent and remain a principal issue for vehicle manufacturers. Many engine subsystems and control technologies have been introduced to meet the demands of these regulations. For diesel engines, combustion control is one of the most effective approaches for reducing not only engine exhaust emissions but also cylinder-by-cylinder variation. However, the high cost of pressure sensors and the complex engine head design for additional equipment present difficulties for manufacturers. In this paper, cylinder pressure-based engine control logic is introduced for a multi-cylinder high speed direct injection (HSDI) diesel engine. The time for 50% of the mass fraction to be burned (MFB50) and the IMEP are valuable for determining the combustion status. These two in-cylinder quantities are measured and applied to the engine control logic. Fuel injection timing is controlled to adjust the operating MFB50 to the target MFB50 using PID control logic, and the fuel injection quantity is controlled to adjust the measured IMEP to the desired IMEP. The control logic is demonstrated at steady state and during transient conditions and is applied to an NEDC mode test.     

Idle speed controller based on active disturbance rejection control in diesel engines

This study proposes a design for an idle speed controller to compensate for varying engine load and friction torque in passenger car diesel engines. An active disturbance rejection control (ADRC) framework, comprised of a disturbance compensator and a feedback controller, is applied to an idle speed controller to compensate for disturbances such as engine load and friction torque. In addition, a feedforward compensator is designed into the ADRC framework to improve disturbance rejection performance. The proposed controller is validated by engine and vehicle experiments and the experiment results are compared with a commercial controller.     

Combustion and emission characteristics of a lean burn natural gas engine

Lean burn is an effective way to improve spark ignition engine fuel economy. In this paper, the combustion and emission characteristics of a lean burn natural gas fuelled spark ignition engine were investigated at various throttle positions, fuel injection timings, spark timings and air fuel ratios. The results show that ignition timings, the combustion duration, the coefficient of variation (COV) of the indicated mean effective pressure (IMEP) and engine-out emissions are dependent on the overall air fuel ratio, spark timings, throttle positions and fuel injection timings. With the increase of the air fuel ratio, the ignition delays and combustion duration increases. Fuel injection timings affect ignition timings, combustion duration, IMEP, and the COV of the IMEP. Late fuel injection timings can decrease the COV of the IMEP. Moreover, the change in the fuel injection timings reduces the engine-out CO, total hydrocarbon (THC) emissions. Lean burn can significantly reduce NOx emissions, but it results in high cyclic variations.     

稀燃增压CNG发动机起动及怠速控制试验研究

根据稀燃增压点燃电控调压式CNG发动机的特点,设计了起动及怠速控制策略,对目标怠速、节气门开度、废气旁通阀开度、燃气供给压差、点火提前角、点火能量、空燃比等参数进行控制。在6缸直列单一CNG发动机上进行了起动及怠速调速试验。试验结果表明:通过优化起动燃气供给量、初始节气门开度、起动点火提前角等参数,可以实现CNG发动机快速、可靠起动;通过标定怠速节气门调速和点火提前角调速控制参数,实现了怠速工况稳定运行。     

Investigation of engine restart stability after idle stop for a mild type HEV powertrain

Stringent regulations on exhaust emissions and fuel economy for vehicles have become major issues in the automotive industry. Hybrid electric vehicles (HEV) are one of the crucial alternative plans to current conventional vehicles, but they have drawbacks, which include increases in total hydrocarbon (THC) emission from the engine and deterioration of the combustion stability with frequent stopping and restarting of the engine. Intake port fuel film is evaporated up during the deceleration state due to the fuel-cut. The λ (relative A/F ratio) at engine restart is lean because part of injected fuel is used to form the fuel film in the intake port. This study revealed the behavior of a fuel film in engine stop with fuel-cut and in engine restart with a simulation model. To investigate the fuel film characteristics, a simulation model was applied and validated with a single-cylinder engine. The simulation result shows that λ of at least 1.2 is required for a stable engine restart. The minimum injection quantity of the first cycle for stable combustion is suggested to be at least 240% of the steady-state idle condition.     

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.     

Effects of altitude on combustion characteristic during cold start of heavy-duty diesel engine

Altitude has a significant effect on combustion of heavy-duty diesel engines, especially during cold start. An experimental study on a heavy-duty diesel engine operating at different altitudes was conducted. Tests were based on a direct injection (DI) turbocharged diesel engine with intake and exhaust pressure controlled by the plateau simulation test system to stimulate altitude conditions including 0 m, 1000 m, 2000 m, 3000 m and 4000 m. Results indicated that the compression and expansion resistance moment reduced and the speed increased during the cranking period. The peak pressure of several cycles was increased during the start-up period; however, the expansion pressure dropped more and the indicated mean effective pressure (IMEP) reduced as the altitude rose. While at an altitude of over 2000 m, the peak pressure fluctuated obviously during the start-up period. The higher the altitude was, the more the fluctuation amplitude and cycle number increased and combustion instability enhanced, which resulted the start-up period time increasing at high altitude. When the altitude rose, the cycle-to-cycle variation of the peak pressure and speed fluctuation increased during the idle, the ignition and CA50 were delayed and the combustion duration was shortened. The effect of altitude on combustion characteristics of the diesel engine was more significant during the start-up period than during its idle period.     

浅析电喷发动机怠速性能的检测

电喷发动机怠速性能的好坏对发动机的正常工作有着直接的影响。主要从最低稳定转速的检测项目和快怠速系统的检查内容说明了电喷发动机怠速系统正常运转的工作条件及检测手段,并以实例说明了典型怠速故障的诊断。     

H_∞鲁棒控制理论应用于CNG发动机怠速控制

针对CNG发动机的不确定性,将H∞鲁棒控制理论应用于CNG发动机的怠速控制,阐述了H∞加权混合灵敏度设计问题模型,建立了CNG发动机动力学模型,分析了发动机的不确定性.应用Matlab鲁棒控制工具箱,设计出基于H∞理论的CNG发动机的怠速控制器,并进行了仿真分析和试验.结果表明,H∞控制具有很好的鲁棒性,提高了CNG发动机怠速工况的稳定性.     

面向HIL应用的大功率柴油机半物理建模方法

为实现控制器硬件在环(Hardware-in-the-loop,HIL)测试,根据半物理建模方法,基于Matlab/Simulink建立了大功率高压共轨柴油机实时仿真模型。介绍了柴油机关键部件的建模原理,并进行了起动、怠速工况和测功机工况下的仿真试验,通过对比分析发现,仿真结果与试验数据误差小于6%,表明所建柴油机模型能够完成控制器控制功能的验证,可以应用于发动机控制策略的前期开发和控制器的HIL测试,模型具有较高的可靠性和通用性。     

Subjective absolute discomfort threshold due to idle vibration in passenger vehicles according to sitting posture

Idle vibration, occurring when a vehicle comes to a stop while the engine is on, is known to be a main cause of discomfort for passengers, and the customer effect has been recently growing. The frequency of idle vibration is determined by the engine type. To lower the vibration, various technologies have been applied to optimize the engine mount and vehicle body structure. In addition to the technological developments, research on human response with a consideration of idle vibration is needed to effectively reduce the level of discomfort experienced by passengers. Seats aimed at enhancing static comfort influence the sitting posture of passengers; sitting posture is a factor affecting human body characteristics that response to idle vibration. This study examined the absolute discomfort threshold of idle vibration according to the sitting postures of 13 taxi drivers. The four sitting postures of subjects on a rigid-body seat without a backrest were variables in the determination of absolute discomfort threshold of idle vibration. The absolute discomfort threshold curves obtained in this experiment were less sensitive to frequency changes than the frequency weighting function of ISO 2631-1.     

Combined effect of boost pressure and injection timing on the performance and combustion of CNG in a DI spark ignition engine

There is an increasing interest in supercharging spark ignition engines operating on CNG (compressed natural gas) mainly due to its superior knock resisting properties. However, there is a penalty in volumetric efficiency when directly injecting the gaseous fuel at early and partial injection timings. The present work reports the combined effects of a small boost pressure and injection timing on performance and combustion of CNG fueled DI (direct injection) engine. The experimental tests were carried out on a 4-stroke DI spark ignition engine with a compression ratio of 14. Early injection timing, when inlet valves are still open (at 300°BTDC), and partial injection timing, in which part of the injection occurs after the inlet valves are closed (at 180°BTDC), were varied at each operating speed with variation of the boost pressure from 2.5 to 10 kPa. A narrow angle injector (NAI) was used to increase the mixing rate at engine speeds between 2000 and 5000 rpm. Similar experiments were conducted on a naturally aspirated engine and the results were then compared with that of the boosting system to examine the combined effects of boost pressure and injection timing. It was observed that boost pressure above 7.5 kPa resulted in an improvement of performance and combustion of CNG DI engine at all operating speeds. This was manifested in the faster heat release rates and mass fraction burned that in turn improved combustion efficiency of the boosting system. An increased in cylinder pressure and temperature was also observed with boost pressure compared to naturally aspirated engine. Moreover, the combustion duration was reduced due to concentration of the heat release near to the top dead center as the result of the boost pressure. Supercharging was also found to reduce the penalty of volumetric efficiency at both the simulated port and partial injection timings.     

Torque-based optimal vehicle speed control

This paper describes an optimal vehicle speed controller that uses torque-based control concepts. The controller design was divided into two steps: first, for a given vehicle speed trajectory, the engine torque demand was determined; in the second stage, a torque controller was implemented to track this torque demand. The torque demand was determined by a primary component and a correction component. The primary component was determined by solving an off-line optimization problem, and the correction component was added to compensate for the error caused by the off-line optimization. A modelbased proportional-integral (PI) feedback torque controller was employed to realize the engine torque tracking. Simulation results generated by a benchmark simulator were given to demonstrate performance of the optimal vehicle speed controller and a conventional PI speed controller that was included for comparison.     

Experimental studies on low pressure semi-direct fuel injection in a two stroke spark ignition engine

In this work a two-stroke scooter engine was modified to work with semi-direct injection of gasoline at a pressure of 8 bar from an injector in the cylinder barrel pointed toward the cylinder head. The influence of injection timing, injection pressure, spark plug location and air-fuel ratio, on performance, emissions and combustion characteristics has been investigated. In addition, a comparison has been made with manifold injection of gasoline on the same engine at a given speed and various outputs. A significant reduction in HC emissions and fuel consumption with no adverse effects on NOx emissions and combustion stability was observed. A small drop in power and increase in CO emission were observed disadvantages of the new injection system. Injection timing was found to be the most important factor and a balance between reduction in shortcircuited fuel by late injection, and time for mixture preparation by advancing the injection, was found to be essential.     

Application of a thermodynamic model with a complex chemistry to a cycle resolved knock prediction on a spark ignition optical engine

A combination of experimental and numerical methodologies is proposed for the investigation of knocking in spark ignition engines to aid in better understanding the physical and chemical processes that occur and to exploit the capabilities of a developed computational tool. The latter consists of a thermo-fluid dynamics model, which is part of an advanced 1-D fluid dynamics code for the simulation of the entire engine, and a complex chemistry model, which can be embedded into the thermo-fluid dynamics model using the same integration algorithm for the conservation equations and the reacting species. Their mutual interaction in the energy balance will be considered. The experimental activity was carried out in the combustion chamber of an optically accessible, single-cylinder P.F.I. engine equipped with a commercial head. The experimental data consisted of optical measurements correlated to the combustion and auto-ignition processes within the cylinder. The optical measurements were based on 2-D digital imaging, UV visible natural emission spectroscopy and the chemiluminescence of radical species (OH and HCO). The engine parameters, the pressure signals of the related data and optical acquisition are compared on an individual cycle basis in the simulation by running the engine at a constant speed and varying the spark advance from normal combustion to heavy knock conditions.     

汽油机怠速递阶模糊控制

介绍了怠速递阶模糊控制策略和发动机怠速状态的动态模型,针对怠速状态的内在不稳定性和怠速控制目标的多样性,提出了具体的控制方法,给出了实际应用结果。     

高压共轨柴油机燃烧与排放模型的研究

利用高速闪光摄影技术,对高压喷射喷雾体空间发展规律进行了试验分析,提出了一个计算高压喷射喷雾体发展的数学公式;在正确描述高压燃油喷雾的基础上,建立了一个能预测高压共轨柴油机性能和排放的准维燃烧模型,此模型改进了燃油喷射模型及碳烟的生成与氧化模型,考虑到燃烧区的区间传热和缸内工质的对流辐射传热,对一台高压共轨柴油机进行了仿真计算。计算与试验结果对比分析表明,改进后的燃烧与排放模型能较好地反映缸内各区的燃烧与排放情况。     

Vibration Control of a Passenger Vehicle Utilizing a Semi-Active ER Engine Mount

This paper presents vibration control of a passenger vehicle using an electronically controllable electro-rheological (ER) engine mount. A mixed-mode ER engine mount operating under the flow and shear modes is devised and manufactured. After establishing the dynamic model of the proposed ER engine mount, both field-dependent displacement transmissibility and dynamic stiffness of the ER engine mount are empirically evaluated. The ER engine mount is then incorporated with a full-vehicle model in order to investigate vibration control performance at the driver's seat position. The governing equation of motion of the full-vehicle model is formulated by considering engine excitation force, followed by designing a skyhook controller to attenuate unwanted vibration. The controller is implemented through a hardware-in-the-loop simulation (HILS), and control responses such as acceleration level at idle speed are evaluated in the frequency and time domains.