應用顯微攝影與碎形分析技術建立柴油引擎排放微粒型態特徵研究

The Morphology and Fractal analysis of diesel soot particles

賴燕秋(Yen-Chiu Lai)

指導教授 ： 李慧梅

國立臺灣大學/工學院/環境工程學研究所/碩士(2004年)

https://doi.org/10.6342/NTU.2004.00418

摘要

本研究以柴油動力計模擬柴油引擎的運作，對於其排放的柴油微粒和聚集體，藉著電子顯微鏡顯微攝影技術建立起其圖譜資料庫，並藉碎形模式的使用，直接對聚集體之表面聚集結構紋理進行分析，計算出其二維的獨特碎形參數，經由影像資料庫以及獨特碎形參數的計
算，便能提供鑑定微粒之直接而有力的證據。

動力計在不同的操作條件下，控制引擎轉速分別處於2900 rpm、1740 rpm和1160 rpm，從SEM的微影圖片顯示動力計排放的柴油黑煙微粒型態非常的相似，柴油黑煙微粒形狀為圓球狀，粒徑介於10~100 nm之間；而其形成的聚集體，由陶多多的柴油黑煙主要微
粒所組成，這些聚集體的型態以鍊狀的聚集體或塊狀的結塊體存在。
碎形模式特性試探的實驗中，改變影像的明暗度，不會影響影像的碎形特性；不同SEM倍率之影像，當碎形模式選取框架為依等比例選取時，兩張影像的碎形參數最為接近；若使用影像處理軟體將影像放大縮小，結果顯示放大之影像發生失真，碎形參數改變；縮小之影
像，卻不改變其碎形特性。

在碎形模式的分析研究中，我們挑選出柴油微粒聚集體之SEM 10萬倍之影像進行碎形模式分析，模式框架的選取為65x65~80x80像素，經統計計算，結果顯示，當動力計在不同操作條件下，柴油黑煙微粒的碎形參數非常接近，並且得到柴油黑煙微粒聚集體的獨特碎形
參數，碎形參數值介於0.194~0.374，而平均碎形維度為1.716。

在比對研究中，我們利用MOUDI採樣器將台北市基隆路、台中縣中棲路與南投縣原始森林區的懸浮微粒進行採樣，挑選出粒徑介於10~100 nm的微粒SEM微影圖，與柴油黑煙微粒進行型態與碎形參數的比對，結果顯示，這些微粒在型態上和碎形參數皆與柴油黑煙微粒相當的吻合，其來源可能來自於柴油車的排放。

關鍵字

碎形維度 ； 顯微影像 ； 黑煙 ； 柴油 ； 聚集體

並列摘要

We use a dynamometer to simulate a diesel engine in order to produce diesel soot particles. Size, morphology, hurst coefficient and fractal dimension of the diesel soot aggregates generated from dynamometer were investigated with scanning electron microscopy (SEM) and fractal model analysis.

The size distribution of primary particles derived from SEM is about 10∼100 nm at engine speed 2900, 1740 and 1160 rpm. The shape of the primary particles is spherical. A lot of aggregates are also observed in the SEM micrographs. These aggregates are formed by condensation or aggregation of primary particles. The SEM images show that the aggregates are irregular in shape.

The characteristics of fractal model were studied in this research. The fractal properties of images were the same when the brightness of them was changed. The hurst coefficients of two SEM images become more closer when the chosen grids of two images are getting more proportional to their image scales. Additionally, the scales of SEM images were adjusted with software. The fractal property of images didn’t change as the images were magnified, but the fractal property changed as the images were minified.
Fractal properties of diesel soot aggregates were determined from SEM images by fractal model. The hurst coefficient of diesel soot aggregates is about 0.194∼0.374 at different engine speed and the mean fractal dimension is 1.716. It indicates that the fractal dimension is independent of the operation conditions of diesel engine.

The particles sampled from two roadsides and one forest were also investigated by SEM and fractal model. The results show that the particles at 10∼100 nm agree well with diesel soot in morphology and fractal dimension. Therefore, it indicates that these particles are possible to be generated from diesel vehicles.

並列關鍵字

morphology ； diesel ； fractal dimension ； soot ； aggregate

參考文獻

1.Amann, C. A. and Siegla, D. C., ” Diesel particulates-what they are and why,” Aerosol Sci. Technol., 1, 73-101 (1982)

2.Burtscher, H., ”Measurement and characteristics of combustion aerosols with special consideration of photoelectric charging and charging by flame ions,” J. Aerosol Science, 23, 549-595 (1992)

3.Brasil, A. M., Farias, T. L. and Carvalho, M. G., “A recipe for image characterization of fractal-like aggregates, “J. Aerosol Science, 30, 1379-1389 (1999)

4.California Environment Protection Agency, Air Resources Board, Risk Reduction Plan to Reduce Particulate Matter Emissions from Diesel Fueled Engines and Vehicles (2000)

5.Carpenter, K. and Johnson, J. H., ”Analysis of Physical Characteristics of Diesel Particulate Matter Using Transmission Electron Microscope Techniques,” Off-Highway Vehicle Meeting and Exposition, 10, 13 (1979)