CONJUGATE CONDUCTION-CONVECTION HEAT TRANSFER MODEL FOR THE VALVE FLOW-FIELD REGION OF FOUR-STROKE PISTON ENGINES

Abstract

A multidimensional method has been devised to solve the conjugate conduction-convection heat transfer process at the surface of a moving valve of finite thickness within the flow field of an operating four-stroke internal combustion (IC) engine. Heat exchange processes between the valve and the gases adjacent to these boundaries were also computed during the portions of the engine cycle when the valve was closed. Boundaries of the solution scheme were extended fixed distances into the piston and cylinder liner. The valve was simulated as having a small but measurable thickness for the purpose of heat transfer calculations and as being immeasurably thin for the purpose of other flow-field calculations. The effects of fluid entrainment caused by valve motion were also considered and modeled. The implicit finite-difference solution of the governing equations for the primitive variables in the flow field was conducted in three regions: one fixed in space and time, one using a stretching and compressing computational mesh, and one that moved with time without stretching or compressing. Valve, cylinder liner, and piston head energy equation solutions were obtained in a fourth region (nonflow-field region), which was matched to the three adjacent flow-field regions. This work reports use of the model to simulate a portion of an exhaust stroke for an axisymmetric four-stroke engine piston. For final runs, a 20 × 26 mesh was used to solve the conjugate heat transfer problem in the fluid flow field, valve, piston top, and cylinder liner. A 17 × 20 mesh was used for other flow-field calculations.