【作者】 姚栋伟；

【导师】 俞小莉； 吴锋；

【作者基本信息】 浙江大学 ， 动力机械及工程， 2010， 博士

【摘要】 随着全球汽车产量和保有量的逐年增加,能源短缺与环境污染问题日益加剧,而醇类燃料,尤其是掺醇汽油因其污染低、来源广,被认为是最具使用前景的代用燃料,因而受到了广泛关注。与普通汽油机类似,掺醇汽油机中,混合气空燃比仍旧是发动机管理系统核心控制内容之一,直接关系到整机动力性、经济性与排放水平。遗憾的是,由于进气系统充排气效应、燃油“湿壁”效应、空燃比控制回路时延等因素的存在,传统汽油机空燃比控制仍旧不够理想。此外,醇类组分加入引起的掺醇汽油理化特性,尤其是燃油蒸发特性的变化,又给掺醇汽油机空燃比控制带来了困难。本文围绕乙醇汽油空燃比控制主题,进行了一系列理论及试验研究,主要包括：乙醇汽油油膜蒸发特性研究：在深入分析与准确测定乙醇汽油相关基础物性基础上通过搭建Gilliland实物仿真试验平台,对不同掺混比例乙醇汽油液膜在空气流中的蒸发扩散特性及关键影响因素进行了研究,表明乙醇汽油液膜在进气管内空气流的蒸发扩散过程可用管内强制对流传质试验关联式描述。进气管空气动态特性建模：对进气管空气动态特性进行了深入分析,建立了进气管空气动态平均值模型,模型中通过引入转速修正项对节气门处空气质量流量进行了饱和非线性补偿。在此基础上,利用试验与仿真手段对进气管空气动态模型进行了参数辨识与模型验证。进气管燃油动态特性建模与分析：对进气管燃油动态及空燃比传输特性进行了深入分析,建立了燃油动态平均值模型。针对传统小偏差摄动法辨识油膜动态参数的不足,通过引入扩展卡尔曼滤波算法,构建了进气道燃油状态观测器,对典型掺混比例乙醇汽油油膜动态参数进行了离线高效估计。根据辨识结果分析了油膜动态参数随关键影响因素,尤其是掺混比例的变化规律,进而结合Gilliland试验结果,构建了油膜蒸发时间常数模型,在减少燃油动态模型辨识参数的同时,有效提高了模型精度。基于模型的空燃比控制策略研究：采用基于模型控制策略,给出了完整的乙醇汽油空燃比控制方案。为克服传统基于进气压力或流量传感器的进气流量测量方式不足,通过引入扩展卡尔曼滤波算法,建立了包含进气管空气动态模型的进气状态观测器,实现进气口空气流量的最优滤波估计。为消除进气道“湿壁”油膜对空燃比控制影响,基于已有进气管燃油动态模型设计了离散燃油动态补偿器,补偿器参数由油膜蒸发时间常数等相关模型预测给出。根据典型掺混比例乙醇汽油下喷油器燃油流量特性试验结果,给出了相应喷油器燃油修正策略。空燃比控制器实现及台架试验验证：针对吉利MR479Q汽油机设计开发了电控单元ECU及标定系统软硬件,其中ECU软件开发遵循AUTOSAR规范,标定系统主从机通信基于CCP协议。在典型掺混比例乙醇汽油下,对嵌有基于模型空燃比控制策略的电控单元ECU进行了台架试验验证。试验结果表明,所设计空燃比控制策略、算法对不同掺混比例乙醇汽油空燃比均具有较高的控制精度和效果,稳态工况控制偏差不超过化学计量空燃比的±2%,瞬态工况控制偏差稍大,但也基本维持在±4%以内,基本满足空燃比精确控制要求。本文通过理论及试验研究构建了准确完整的乙醇汽油机空燃比模型,并基于该模型设计了详细的空燃比控制策略和算法,较好地实现了乙醇汽油机空燃比的精确控制,为高掺混比例乙醇汽油发动机开发与性能预测奠定了理论基础。更多还原

【Abstract】 As global automobile production and population increase every year, energy shortage and environmental pollution are growing in tensity. Alcohol fuels, especially alcohol-gasoline blends, were considered as the most promising alternative fuels, and have aroused extensive attentions for their low emission level and wide resources. Like ordinary gasoline engines, air-fuel ratio control is still one of the most important parts in engine management systems under different alcohol-gasoline blends, and it directly affects the whole engine power, economy and emission levels. Unfortunately, as existence of intake air-pump effect, fuel wall-wetting effect and air-fuel ratio control loop delay, traditional air-fuel ratio control is still very poor. In addition, special physicochemical properties of alcohol-gasoline blends, especially the evaporation characteristics, make the air-fuel ratio control design of alcohol-gasoline blend engines even more difficult.This thesis focused on the subject of air-fuel ratio control with ordinary gasoline engines burning ethanol-gasoline blends, and carried out a series of theoretical and experimental researches, including:Research on fuel film evaporation characteristics of ethanol-gasoline blends:Basic physical properties of ethanol-gasoline blends were analyzed and accurately determined at first. Then the Gilliland experimental platform was set up, fuel film evaporation and diffusion characteristics of different ethanol-gasoline blends in air streams were studied, and critical influencing factors were discussed as well. Results showed that the evaporation and diffusion process of ethanol-gasoline blends into intake air streams can be also described by the traditional correlation of forced convective mass transfer inside pipes.Modeling of intake manifold air dynamic characteristics:An intake air dynamic mean value model was built. In this model, a speed correction term was introduced to compensate the saturated nonlinear characteristic of throttle air mass flow in large throttle opening areas. Both model parameters identification and model validation were carried out by means of experimental and simulation methods.Modeling and analyzing of intake manifold fuel dynamic characteristics:An intake fuel dynamic mean value model was built. Unlike traditional methods of fuel film dynamic parameters identification, Extended Kalman Filter algorithm was introduced to construct an offline intake port fuel dynamic observer which could estimate fuel film dynamic parameters efficiently. According to the identification results, critical influencing factors of fuel film dynamic parameters, especially mixing ratio of ethanol-gasoline blends, were discussed. A fuel film evaporation time constant model based on Gilliland test results was then built to reduce calibration parameters and improve model accuracy simultaneously.Strategy research on model-based air-fuel ratio control:A complete model-based air-fuel ratio control solution under different ethanol-gasoline blends was presented. Unlike traditional detecting method of intake air mass flow, Extended Kalman Filter algorithm was introduced to construct a model-based intake air state observer which could estimate intake port air mass flow precisely. To eliminate intake fuel wall-wetting effect, a discrete model-based fuel dynamic compensator was also designed and verified, and its control parameters were always from prediction of fuel film evaporation time constant model. In addition, fuel injector correction strategy under different ethanol-gasoline blends and battery voltages was also designed, according to the results of fuel injector flow characteristic test.Designing and verification of air-fuel ration controller:According to the features of MR479Q gasoline engine, an electrical control unit and its corresponding calibration system were developed. ECU software followed AUTOSAR specifications, while calibration system communications based on CCP. Verification tests of ECU embedded model-based air-fuel ratio control strategy were carried out under several different ethanol-gasoline blends. Test results show that under varies of ethanol-gasoline blends good control effectiveness could be always achieved by the model-based air-fuel ratio control strategy and algorithm, the control error is less than 2% under steady conditions, while not exceed 4% under transient conditions.The thesis built an accurate air-fuel ratio model of ethanol-gasoline blend engines, designed model-based air-fuel ratio control strategy and algorithm, and achieved perfect air-fuel ratio control effect under varies of ethanol-gasoline blends, made good foundations for the further research on development and performance prediction of ethanol-gasoline blend engines.更多还原