摘要
为研究车用涡轮增压柴油机加速工况的瞬态响应及氮氧化物（NO）排放特性，基于充．排法建立柴油机及其附件系统工作过程模型，初次考虑瞬发NO机理对瞬态工况下NO排放的影响，根据曲轴转矩平衡方程推导发动机瞬时角加速度与车辆状态参数的关系，在Matlab／Simulink环境下集成柴油机系统加速瞬态过程仿真模型。仿真和验证结果表明：柴油机稳态及加速瞬态工况仿真结果均与实际情况相符，模型设计合理准确；稳态工况下瞬发NO机理对总NO排放的贡献为5．26％～11．36％；瞬态工况下，涡轮迟滞时间约为0．14S，柴油机加速开始阶段油气混合不匀导致燃烧品质下降，热NO及瞬发NO生成均明显增加。研究结果可为发动机瞬态性能及NO排放的预测与分析提供参考。
Currently, the transient response and emission performance of turbocharged direct injection （DI） diesel engines under transient conditions become the research focus. To predict the performance and nitrogen oxides （NO） emission of vehicle turbocharged DI diesel engines during acceleration process, firstly, a zero-dimensional thermodynamic real time simulation model was developed to describe the working process in cylinder, which based on energy and mass conservation within the engine cycle and the filling and emptying method. The thermodynamic model takes all the engine subsystems into account, namely turbocharger, intercooler, fuel pump and speed governor. In order to simulate the accelerating operation more accurately, the two-vibe curve model was adopted to simulate the actual heat release rate and fuel burning speed. In addition, the incomplete combustion was taken into consideration. Furthermore, the convective heat transfer rate to the combustion chamber walls was simulated through the Woschni＇s heat-transfer coefficient with transient correction. Secondly, According to crankshaft torque balance based on the conservation of angular momentum principle, the instantaneous values for engine speed and angular acceleration were calculated. Specifically, the engine indicated torque that includes the contribution of gas and reciprocating inertia forces of all cylinders was calculated according to the instantaneous cylinder pressure and engine dynamics. The friction torque of diesel engine was assumed to be a function of the mean friction pressure, working volume of cylinder and instantaneous engine speed. Moreover, the load torque was determined via the torque balance of power-train system. Subsequently, both thermal and prompt NO mechanism were applied to predict NO emissions, and the extended-Zeldovich mechanism and overall reaction rate theory were adopted to simulate the net formation rate of NO. Finally, all above models were integrated and a simulation platform of the entire vehicle system was established based on the Matlab/Simulink. Using a step input signal as the step throttle （fuel pump rack position） change, and the model can be run to mimic vehicle real acceleration process under various （vehicle） speeds and gear. The model was validated through comparison of the simulation results with measured values. Fortunately, the simulation results are quite in line with the actual situation, and showed that the design of model was reasonable and accurate. Particularly, the prompt NO mechanism contribute about 5.26- 11.36 percent to the production of total NO under the steady-state operating conditions. During the early cycles of the acceleration transient conditions, the turbocharger lags behind about 0.14 seconds. Additionally, both thermal and prompt NO emissions increase considerably owing to the initially low air-fuel ratio. The results of this study can be greatly helpful to predict and analysis the transient performance and NO emission ofturbocharged diesel engines.
出处
《农业工程学报》
EI
CAS
CSCD
北大核心
2014年第3期63-69,共7页
Transactions of the Chinese Society of Agricultural Engineering
基金
国家科技支撑计划项目(2009BAG13A04)
关键词
柴油机
车辆
一氧化氮
排放控制
加速工况
瞬态特性
diesel engines
vehicles
nitric oxide
emission prediction
acceleration process
transient performance
