Topological Development of Homogeneous-Charge and Stratified-Charge Flames in an Internal Combustion Engine.

Internal Combustion Engine;Engine Flame Topology;Homogeneous Charge Combustion;Stratified Charge Combustion;Optical Diagnostics;Flame Wrinkling;Mechanical Engineering;Engineering;Mechanical Engineering

Lillo, PeterReuss, David L ;

University of Michigan

关键词: Internal Combustion Engine;    Engine Flame Topology;    Homogeneous Charge Combustion;    Stratified Charge Combustion;    Optical Diagnostics;    Flame Wrinkling;    Mechanical Engineering;    Engineering;    Mechanical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/135897/plillo_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

No technology can currently replace fossil fuel powered internal combustion engines as the primary source of transportation power. For better or worse, the next generation of automobiles will continue to be powered by combustion. As such, it is in our best interest to learn how to burn fuel in the smartest manner.There are many advanced combustion strategies that promise efficiency improvements over conventional strategies, most of which have failed to make it onto the road due to technical deficiencies. Many of these strategies, such as spray-guided stratified-charge combustion, rely upon the precise partial mixing of fuel with oxidizer inside the combustion chamber. Advanced computational tools are being developed to aid such challenging designs. However, a lack of understanding of in-cylinder flame physics and computational power limitations continues to hinder the predictive abilities of engine models. In this work, engine flame topological development is studied.Flame wrinkled-ness is both one of the most important and poorly understood engine combustion phenomena. Generally, a flame may wrinkle for two reasons: (i) its own naturally instabilities and/or (ii) through interaction with turbulent flow. The relative contribution of these two causes towards flame wrinkled-ness in the engine environment was unclear so targeted experiments were performed to provide some clarity. The development of flame wrinkled-ness within an optically accessible engine was measured with a combination of planar laser induced fluorescence and stereo particle image velocimetry under homogeneous-charge and stratified-charge conditions. From this, equivalence ratio, charge velocities, and flame wrinkled-ness were quantified and analyzed. For the iso-octane/toluene mixtures studied the flame wrinkling was insensitive to thermo-diffusive flame front instabilities. The relative contribution of wrinkles of various spatial scales towards overall flame wrinkled-ness was also measured. Homogeneous-charge flames generally had lower wrinkling factors than stratified-charge flames. Overall, flame wrinkled-ness increased with flame size under both modes of engine operation. Large flames demonstrated an ability to maintain more large scale wrinkles than small flames, which contributed to their overall higher levels of wrinkled-ness. Based on the observations, suggestions are provided for those who are developing advanced homogeneous and stratified-charge engine models.