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A laboratory test simulator has been developed to analyze the intake-valve deposit formation mechanism. The characteristics of the deposits formed with the simulator were compared with those of the real engine deposits. This comparison verified that the simulator deposits ILLEGIBLE nearly equal to those of engines. The influence of each parameter such as valve temperature, oil or gasoline quality was tested individually using this simulator. The intake valve temperature influenced the location and quantity of the deposits. The deposit formation significant in the temperature range of about 0-350 °C. The high-boiling components of oil ILLEGIBLE increased the deposits. The increase oxidation products and the decrease of antioxidants in used oil caused a significant increase of deposits. The commercial premium gasoline in Japan containing practical detergents ILLEGIBLE down and decreased the deposits. Another premium gasoline affected the oil quality, in increasing the deposits.

The purposes of this series of studies are to examine the characteristics of intake-valve deposits and to clarify their formation mechanism. This paper discusses the chemical compositions and physical states of the deposits on the basis of the results obtained by chemical analyses. The results indicate that the deposits mainly originate from engine oil, and suggest that the main reaction route of the deposit formation is the carbonization of oxidized engine oil. Namely, low boiling point (light) fractions in the engine oil easily evaporate from the valve surface. On the other hand, the remaining heavy fractions are subjected to deposit forming reactions. These final states are amorphous and carbonaceous aggregates. The deposit has a tendency to form in the temperature range of about 230 to 350 °C. The location of accumulating deposit depends on the valve surface temperature.