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Study on Ignition Mechanism of Non-Uniform Mixture

非均匀混合物点火机理研究

基本信息

批准号：
09450092
负责人：
IKEGAMI Makoto
金额：
$ 8.96万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09450092/
关键词：
Diesel Combustion Ignition Process Turbulent Mixing Ignition Delay Initial Combustion Stochastic Model Injection Rate 濃度不均一 2体衝突再分散モデル

项目摘要

To describe the ignition delay of diesel sprays, a stochastic model taking account of the endothermic process in the spray is proposed. In this model, generation of turbulence and turbulent mixing of fuel and air are taken into consideration. For the endothermic process, the rate of heat absorption due to vaporization and pyrolysis is assumed to be constant. Chemical reactions during the ignition delay period are expressed by a one-step global mechanism and ignition is assumed to occur when concentrations of active species exceed a threshold. It is shown that this model may reproduce the ignition delay of a diesel spray and pressure history in a rapid compression machine for a variety of conditions. Also, the ignition delay is dependent on spray formation at a high initial temperature, but on chemical reaction at a low initial temperature.Furthermore, this approach is applied to predict the initial combustion in diesel engines for various injection rates including pilot injection. In this model, heterogeneity of fuel concentration and temperature is expressed by probability density functions Due to the heat and mass exchange associated with the collision, the initial segregation tends to form a mixture of less heterogeneity as time goes on. Maximum rates of heat release correspond to the predicted results by varying delay mechanism. It is also shown that when injection pressure is high and nozzle diameter is small, pilot injection efficiently gives a smooth burning. When an appropriate constant of heat absorption is given as a function of injection pressure, nozzle diameter, ambient temperature and pressure, ignition delay periods are successfully predicted for a wide range of injection conditions. Based on the predicted results, a discussion is made about the effect of high-pressure injection on the ignition process.

为了描述柴油喷雾的点火延迟，提出了考虑喷雾吸热过程的随机模型。在该模型中，考虑了湍流的产生以及燃料和空气的湍流混合。对于吸热过程，假设由于汽化和热解而产生的吸热率是恒定的。点火延迟期间的化学反应由一步全局机制表示，并且假设当活性物质的浓度超过阈值时发生点火。结果表明，该模型可以在各种条件下重现快速压缩机中柴油喷雾的点火延迟和压力历史。此外，点火延迟取决于高初始温度下的喷雾形成，但取决于低初始温度下的化学反应。此外，该方法适用于预测柴油发动机中各种喷射率（包括引燃喷射）的初始燃烧。在该模型中，燃料浓度和温度的不均匀性由概率密度函数表示。由于与碰撞相关的热量和质量交换，随着时间的推移，初始分离倾向于形成不均匀性较小的混合物。最大放热率与不同延迟机制的预测结果相对应。研究还表明，当喷射压力较高且喷嘴直径较小时，引燃喷射可以有效地实现平稳燃烧。当给出适当的吸热常数作为喷射压力、喷嘴直径、环境温度和压力的函数时，可以成功地预测各种喷射条件下的点火延迟期。根据预测结果，讨论了高压喷射对点火过程的影响。