Thermal Periodic Contact of Exhaust Valves

Abstract

Internal combustion engines generate exhaust gases at extremely high temperatures and pressures. As these heated gases exit through the exhaust valve, the valve and valve seat insert achieve comparable temperatures. To avoid damage, heat is transferred from the exhaust valve to the valve seat insert as they come into contact with each other during the opening and closing cycle. Modern engine management systems regulate the thermal process through coolant and/or airflow rates, fuel injection, and ignition timing, and exhaust gas recirculation contributions to achieve satisfactory tradeoffs between power, emissions, and efficiency for various engine speeds and loads. One of the primary functions of the engine control unit is the prevention and detection of abnormal combustion to prevent severe engine damage. The online estimation of cylinder component temperatures offers an opportunity for greater engine control measures. A nonlinear dynamic thermal model is presented to describe the transient and steady-state phenomena in the engine's cylinder using a lumped parameter resistance-capacitance network. The model prediction of the engine's thermal behavior establishes a foundation to explore thermal periodic contact issues. Representative experimental and numerical results will be presented and discussed.