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The Analysis and Measurement of the White Smoke Opacity at Single Cylinder 2-Stroke Engine
Tsai, Sheu Chin
White smoke is the most obvious part of the exhaust emitted from Two-Stroke engines. The method for smoke testing currently used in Taiwan is the rapid acceleration test under no load. The current situation of white smoke emission was studied in this paper. It was found that the white smoke is gamma distributed. Four ways to treat the original smoke data were carried out and the results showed that the averaged peak values and the maximum integral values are the most suitable ways to define the white smoke level of motorcycles.
The components of white smoke are different at hot test and cold test. At cold test the white smoke is mainly composed of carbon and unburned oil however, while at hot test only the unburned oil is the major component. Lubrication oil is the source of white smoke. Increasing the oil/fuel ratio would cause the smoke opacity to arise slowly due to the absorption effect of muffler. In order to explain this phenomenon successive chambers model was established. Experiment results have good correspondence with the model. At the start and the end smoke opacity arise slowly but rapidly in the middle. On the bench test we find that the engine temperature has significant affect on the smoke opacity. At hot test with an used muffler, the opacity is always low except at high engine speed and exhaust temperature.
The white smoke photography using high speed video camera shows that the smoke emitted from the engine is not continuous. Smoke is emitted like a pulse wave and the pulse wave become more obvious at decelerating. It was found that the engine heat release rate is well correlated with the opacity variations. The opacity at high heat release ratio cycle is higher than that at low heat release ratio cycle. This reveals that at low heat release ratio cycle the engine doesn't combust so the unburned oil will accumulate in the muffler. Engine speed and heat release ratio are the main factors that affect the smoke opacity.
Finally we compare the smoke opacity by using fully synthetic oil and mineral oil. The fully synthetic oil has better effect on reducing the opacity. Another method to reduce the opacity is to add petrol injection cleaner in the fuel. After driving about 84 km the opacity is reducing 15% .
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