【作者】 周红秀；

【导师】 姚春德；

【作者基本信息】 天津大学 ， 动力机械及工程， 2007， 博士

【摘要】 由于柴油机具有的高燃油经济性,车用柴油机的数量越来越多。但是柴油车在起动和加速易于冒烟的现象,正随着公交汽车迅速向柴油化过渡而在城市里日渐突出。柴油机碳烟形成的根本原因是在加速或加载过程中,进入气缸中的空气量跟不上加油量的变化速率,使瞬态过量空气系数以及混合气形成质量下降,进而导致燃烧质量下降,柴油机排放烟度恶化。所以改善加速烟度必须首先缓解加速初期的供油量和供气量的矛盾。为解决柴油机在加速时带来的加速冒烟问题,提出了采用电动压气机在柴油机加速时进行补气的技术路线,并设计一套在柴油机加速工况下能够快速响应的智能补气系统,包括发动机进气气路的快速切换系统,自动识别发动机工况的识别系统,以及补气的执行装置——电动压气机。通过对柴油机在加速时进行快速补气,来降低柴油机的排放烟度。为了研究电动压气机对于柴油机加速补气减少碳烟排放这一方法的可行性,将初步研制的电动压气机样机应用到试验台架中去。在发动机试验台架装置研究中,改造了发动机进气布置,并开发了补气系统的控制单元。控制单元通过发动机工况识别系统来检测到油门传感器输送的油门踏板变化速率信号,控制电动压气机快速实施补气,并同时控制进气气路在补气时和补气结束后能够按照需求自动快速的切换。同时基于普通电涡流测功机,设计了柴油机瞬态工况的控制以及重要参数的数据采集系统。利用开发的加速补气系统以及发动机瞬态工况的控制及数据采集系统,研究了电动压气机快速补气对于柴油机的加速过程中的烟度排放的影响。研究表明,无论是恒扭矩加速试验还是从恒转速加载试验,电动压气机对柴油机加速补气都能明显降低柴油机的烟度,而且在大扭矩加速和低转速加载工况下其动力性也有所提高。所以这表明利用电动压气机对柴油机加速补气的方案是可行的。在试验中所应用的加速补气用的电动压气机系J80废气涡轮增压器改制而成,该增压器的在正常工作时最高转速超过100,000 r/min。由于电动机最高转速的限制,尽管试验中工作在其低效率的区域内,但是其补气后降低烟度排放的效果还是非常显著的。研究表明,欲提高进气压力和补气量,瞬态过量空气系数应超过2.0,会更有效的达到降低烟度并提高瞬态动力性的目标。为了进一步优化电动压气机以提高瞬态响应的能力,利用热线风速仪和fluent流体动力学软件从实验方法和计算方法两方面对研制的电动压气机流量特性以及瞬态响应特性进行了研究。研究结果发现现用电动压气机的出口速度分布不均匀,这对于压气机的效率是不利的,从压气机内部流场数值分析可知造成压气机的出口速度不均是由于涡壳结构设计不当造成,通过优化涡壳结构可以改善出口速度分布。另外,测量结果显示,在电动压气机的工作范围内,流量随着转速的增加基本呈线性增加。提高电动压气机的转速不仅可以提高电动压气机能够提供的补气量,还可以提高其瞬态响应特性。通过研究得知,由于电动压气机的响应时间是由变频器设定时间以及设定转速所决定,所以提高变频器启动时间也是加快电动压气机流量的重要方面。更多还原

【Abstract】 The diesel engine for vehicle is increasing because of its high fuel economy, but most vehicles with diesel engine frequently produce black smoke when starting up and accelerating on the road. With dieselization of automobiles which make the number of diesel engines increase, this problem becomes serious in cities.The essential reason producing smoke is that the air-fuel ratio declines at the transient process during the sharp acceleration and load changing operations, i.e. the mass rate of the air flow into the engine don’t match with the variation of fuel flow rate, which makes the quality of mixture poor and combustion insufficient. Consequently, to ameliorate the smoke emission in acceleration, the transient excess air coefficient must be boosted up during period of acceleration.To solve this problem, the method was presented to inject air into engine in acceleration with an electric supercharger. In this desertation the air injection system in fast response was designed, which consisted of the air intake shifting system of engine, and the automatic recognization system for engine operation, and the air injection unit—the electric supercharger (ES).To illustrate this method feasibility to reduction the smoke emission, the air injection system developed was applied to the naturally aspirated engine experimental station. A test bench was set up for verification of the system feasible. The air intake duct was modified, and an electrically controlled unit (ECU) for the air injection system was developed. The ECU controlled the ES and the air intake switch system through detecting change rate of the accelerator pedal position with a sensor at same time. An eddy current dynamometer was modified to meet the demand of the control system of transient operation conditions and data aquasition system.By the air injection system and the control of transient operation conditions as well as data aquasition system, the tests were conducted to study the influence on smoke emission in engine acceleration with electric supercharger injecting air. Testingl results showed that ES injecting air into engine at the acceleration or load increasing operation conditions could remarkably reduce the smoke emission, and improve the transient performance at the high load and low speed conditions. Consequently, using electric supercharger to inject air to reduce the smoke emission was feasible. Although the ES used was rebuilt from the type of J80 turbocharger of which rating speed usually is at or over the speed 100,000 r/min, it ran at the low efficiency region, however,the effects of air injection on the engine to reduce smoke emission were prominent. Testing results also showed that if the transient excess air coefficient was boosted up to 2.0 by enhancing the pressure and flux of the air intake, the higher aim to reduce the smoke and improve the transient power of engine in acceleration could be achieved.For the sake of further optimizing ES and improving the transient response performance, ES’s flux and transient response characteristics were studied in experiment and numerical simulation methods respectively by the hot-wire anemometry system and computational fluid dynamic software of fluent. The research results showed that the distribution of outlet’s velocity was not symmetrical, which was disadvantageous to the compressor’s efficiency. According to the numerical analysis, the symmetrical distribution of outlet’s velocity was caused by the inappropriate structure design of the house, and could be improved by optimizing the structure of the house. In addition, the measurement result showed that the flux was basically linear increased along with speed in the work range of ES. Upgrading the speed of ES could not only increase air injection to engine, but enhance its transient response characteristics. Research indicated that the respond time of ES was depended on the initialization set of start time and speed of the transducer, so it was important to improve the flux response of ES by advancing the start time of transducer.更多还原