功率超声对燃烧工质活性与反应路径的调控特性

Regulation of combustion working medium activity and reaction path by power ultrasound

提出一种将功率声源物理嵌入汽油机燃烧室的多场耦合燃烧数值模拟方法,利用功率超声馈入策略研究了缸内极端环境下工质活性与燃烧反应路径精细化调控特性。基于台架试验数据校正原机三维数值模型,通过在燃烧室嵌入功率声源面特征,构建出声场与燃烧场耦合的多场数值模型,并利用动网格实现将频率20 kHz振幅30μm功率超声馈入汽油机缸内工作循环。通过对比分析4种超声馈入方案和无超声馈入方案的缸内燃烧数据,得出在压缩和点火燃烧阶段超声馈入燃烧室的S2方案对工质湍动能影响最为显著,其缸压峰值相比原机提升0.1 MPa,且各方案缸压曲线在0°CA TDC(top dead center,TDC)~30°CA ATDC(after top dead center,ATDC)出现明显分离。研究表明,合理利用功率超声馈入燃烧场能促进燃料氧化与燃烧进程,并加速OH自由基生成速率。在汽油机缸内瞬变极端燃烧环境下,低于10 ms的功率超声馈入已能对燃料活性及反应路径产生显著量化调控作用。

A numerical simulation method for multi-field coupling combustion is proposed,in which power sound is fed into the chamber of a gasoline engine.The fine-grained control of working medium activity and combustion reaction path under extreme in-cylinder conditions is studied by using different ultrasonic-fed strategies.Based on the bench test data,a three-dimensional model of the original engine is calibrated.A multi-field coupling model of the sound field and the combustion field is established by embedding the characteristics of sound source surface in the chamber.The ultrasonic with 20 kHz frequency and 30μm amplitude is fed into the chamber using the dynamic grid.By analyzing the in-cylinder combustion data of four ultrasonic-fed schemes and an ultrasonic-free scheme,it is concluded that the S2 scheme has the most significant influences on turbulent kinetic energy of the working medium during compression and ignition.Its peak cylinder pressure is 0.1 MPa higher than an engine operation without any schemes.The cylinder pressure curves in each scheme are obviously separated within the range of 0°CA TDC(top dead center)~30°CA ATDC(after top dead center).The results show that a good use of an ultrasonic-fed field can promote fuel oxidation and combustion process,and accelerate the formation of the OH radicals.In an extreme transient combustion environment for a chamber of a gasoline engine,an ultrasonic-fed of less than 10 ms can have a significantly quantitative control effect on fuel activity and reaction path.