On the mechanism of exhaust gas recirculation valve sticking in diesel engines

Research was conducted on a means of responding to the issue of sticking of exhaust gas recirculation valves resulting from the occurrence of high concentrations of hydrocarbons when the exhaust gas recirculation operating range is expanded. The chemical components responsible for the phenomenon were identified, and exhaust gas and deposits were analyzed. From the tendency of deposition and the results of analyses of deposits, it was conjectured that the type of hydrocarbons present, and their dew points, were the major factors in the sticking of exhaust gas recirculation valves. In order to confirm that the dew points of the hydrocarbons were the major factor, tests were conducted to synthesize deposits in a batch furnace. When the hydrocarbons involved in deposit-forming reactions reached their dew points and did liquefy, the chemical reactions were checked. The conditions in which valve sticking occurs in engines were determined to correlate with the dew points of the hydrocarbons in question. The relationship between the dew points of the hydrocarbons and exhaust gas recirculation valve wall temperature was studied, and a method of avoiding valve sticking by applying control to maintain the temperature of the valve walls above the dew points was proposed.