Flame front analysis of ethanol, butanol, iso-octane and gasoline in a spark-ignition engine using laser tomography and integral length scale measurements
Flame front analysis of ethanol, butanol, iso-octane and gasoline in a spark-ignition engine using laser tomography and integral length scale measurements
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DOI：
10.1016/j.combustflame.2015.09.008
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发表时间：
2015-12
影响因子：
4.4
通讯作者：
P. Aleiferis;M. Behringer
中科院分区：
文献类型：
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作者：
P. Aleiferis;M. Behringer
直喷式火花点火发动机因其喷射策略的灵活性和更高的效率而变得流行；然而，高压缸内喷射过程可以通过动量交换改变气流场，对不同性质的燃料产生不同的影响。本文介绍了直喷式火花点火发动机中乙醇、丁醇、异辛烷和汽油化学计量燃烧的光学研究结果，该发动机以 1500 RPM 运行，进气压力为 0.5 bar，并采用早期进气冲程燃油喷射来制备均匀混合物。该分析最初涉及使用和不使用燃料时点火正时流场的粒子图像测速测量，以进行比较。火焰化学发光成像用于表征整体火焰行为，双脉冲激光片火焰断层扫描通过米氏散射来量化火焰锋面的局部拓扑。通过燃油喷射进行的流量测量显示，仅在翻滚面上的整体长度尺度与空气的整体长度尺度相同，但在水平面上的尺度更大，达到 9 毫米。两个测量平面的平均长度尺度在 4 至 6 毫米之间，其中乙醇最大，丁醇最小。在无量纲形式下，整体长度尺度可达间隙高度的20%和缸径的5%~12%。火焰断层扫描显示，在半径 8 至 12 毫米之间，乙醇燃烧最快，其次是丁醇、异辛烷和汽油。相关的湍流燃烧速度比层流燃烧速度大 4.6-6.5 倍，比火焰化学发光成像获得的速度低约 13-20%。断层扫描平面上的火焰圆度为 10-15%，乙醇的值最大，其次是丁醇、汽油和异辛烷；化学发光成像显示较大的圆度（18-25%），尽管燃料之间的顺序相同。瞬时火焰轮廓相对于按等效半径过滤的位移的标准偏差可作为火焰刷厚度的度量，并且与等效火焰半径密切相关；当按半径归一化时，所有燃料的误差均为 4-6%。瞬时火焰轮廓和过滤火焰轮廓之间的交叉点数量与火焰半径呈强烈负相关，与燃料类型无关。交叉点频率为 0.5–1.6 mm−1。火焰刷厚度约为整体长度尺度的1/10。积分长度尺度与火焰刷厚度呈正相关，与交叉频率呈负相关。
Direct-injection spark-ignition engines have become popular due to their flexibility in injection strategies and higher efficiency; however, the high-pressure in-cylinder injection process can alter the airflow field by momentum exchange, with different effects for fuels of diverse properties. The current paper presents results from optical studies of stoichiometric combustion of ethanol, butanol,iso-octane and gasoline in a direct-injection spark-ignition engine run at 1500 RPM with 0.5 bar intake plenum pressure and early intake stroke fuel injection for homogeneous mixture preparation. The analysis initially involved particle image velocimetry measurements of the flow field at ignition timing with and without fuelling for comparison. Flame chemiluminescence imaging was used to characterise the global flame behaviour and double-pulsed Laser-sheet flame tomography by Mie scattering to quantify the local topology of the flame front. The flow measurements with fuel injection showed integral length scales of the same order to those of air only on the tumble plane, but larger regions with scales up to 9 mm on the horizontal plane. Averaged length scales over both measurement planes were between 4 and 6 mm, with ethanol exhibiting the largest and butanol the smallest. In non-dimensional form, the integral length scales were up to 20% of the clearance height and 5–12% of the cylinder bore. Flame tomography showed that at radii between 8 and 12 mm, ethanol was burning the fastest, followed by butanol,iso-octane and gasoline. The associated turbulent burning velocities were 4.6–6.5 times greater than the laminar burning velocities and about 13–20% lower than those obtained by flame chemiluminescence imaging. Flame roundness was 10–15% on the tomography plane, with largest values for ethanol, followed by butanol, gasoline andiso-octane; chemiluminescence imaging showed larger roundness (18–25%), albeit with the same order amongst fuels. The standard deviation of the displacement of the instantaneous flame contour from one filtered by its equivalent radius was obtained as a measure of flame brush thickness and correlated strongly with the equivalent flame radius; when normalised by the radius, it was 4–6% for all fuels. The number of crossing points between instantaneous and filtered flame contour showed a strong negative correlation with flame radius, independent of fuel type. The crossing point frequency was 0.5–1.6 mm−1. The flame brush thickness was about 1/10th of the integral length scale. A positive correlation was found between integral length scale and flame brush thickness and a negative correlation with crossing frequency.