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Near-Wall Flame and Flow Measurements in an Optically Accessible SI Engine
Flow, Turbulence and Combustion ( IF 2.4 ) Pub Date : 2020-05-14 , DOI: 10.1007/s10494-020-00147-9
Marius Schmidt , Carl-Philipp Ding , Brian Peterson , Andreas Dreizler , Benjamin Böhm

Near-wall processes in internal combustion engines strongly affect heat transfer and pollutant emissions. With continuously improving capabilities to model near-wall processes, the demand for corresponding measurements increases. To obtain an in-depth understanding of the near-wall processes within spark-ignition engines, flame distributions and flow fields were measured simultaneously near the piston surface of an optically accessible engine operating with homogeneous, stoichiometric isooctane–air mixtures. The engine was operated at two engine speeds (800 rpm and 1500 rpm) and two different intake pressures (0.95 bar and 0.4 bar). Flame distributions were obtained at high spatial resolution using high-speed planar laser induced fluorescence of sulfur dioxide ( $$\hbox {SO}_{{2}}$$ SO 2 ). Particle tracking velocimetry was utilized to measure the flow field above the piston at high spatial resolution, which enabled the determination of hydrodynamic boundary layer profiles. Flame contours were extracted and statistical distributions of the burnt gas area determined. The burnt gas distributions were compared with the simultaneously recorded high-speed flow field measurements in the unburnt gas. A direct comparison with motored engine operation showed comparable boundary layer profiles until the flame approaches the wall. Flow acceleration due to flame expansion rapidly increases velocity gradients and the boundary layer development becomes highly transient. The interaction of flame and flow depends on the operating conditions, which results in a different evolution of burnt gas positions within the field-of-view. This has additional implications on the development of the velocity boundary layer. Depending on the operating conditions, the flame strongly affects the velocity boundary layer profiles resulting in boundary layer thicknesses (defined by 50% maximum velocity) in the order of $$80{-}180\, \upmu \hbox {m}$$ 80 - 180 μ m .

中文翻译:

光学可访问 SI 引擎中的近壁火焰和流量测量

内燃机中的近壁过程强烈影响热传递和污染物排放。随着近壁过程建模能力的不断提高,对相应测量的需求也在增加。为了深入了解火花点火发动机内的近壁过程,在以均匀、化学计量的异辛烷-空气混合物运行的光学可接近发动机的活塞表面附近同时测量火焰分布和流场。发动机以两种发动机速度(800 rpm 和 1500 rpm)和两种不同的进气压力(0.95 bar 和 0.4 bar)运行。使用高速平面激光诱导二氧化硫荧光($$\hbox {SO}_{{2}}$$ SO 2 )以高空间分辨率获得火焰分布。粒子跟踪测速技术用于以高空间分辨率测量活塞上方的流场,从而能够确定流体动力边界层剖面。提取火焰轮廓并确定燃烧气体区域的统计分布。将燃烧后的气体分布与同时记录的未燃烧气体中的高速流场测量值进行比较。与机动发动机操作的直接比较显示,在火焰接近壁之前,边界层轮廓具有可比性。由于火焰膨胀引起的流动加速迅速增加了速度梯度,并且边界层的发展变得高度瞬态。火焰和流动的相互作用取决于操作条件,这会导致视场内燃烧气体位置的不同演变。这对速度边界层的发展有额外的影响。根据操作条件,火焰强烈影响速度边界层剖面,导致边界层厚度(由 50% 最大速度定义)的数量级为 $$80{-}180\, \upmu \hbox {m}$$ 80 - 180微米。
更新日期:2020-05-14
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