Steady-State Thermal Flows in an Air-Cooled, Four-Stroke Spark-Ignition Engine 1999-01-0282
Measurements of the instantaneous heat flux at three positions on the cylinder head surface, and the steady-state cylinder head temperatures at four positions on the cylinder head have been obtained. Engine tests were performed for a range of air-fuel ratios including regimes rich of stoichiometric, stoichiometric, and lean of stoichiometric. In addition, ignition timing was advanced in increments from 22° BTDC to 40° BTDC.
All tests were run with the throttle either fixed in the wide open position, or fixed in a position that produced 75% of the maximum power with the standard ignition timing and an air-fuel ratio of 13.5. This was done to ensure that changes in air mass flow rate were not influencing the results. In addition, all tests were performed with a fuel mixture preparation being provided by system designed to deliver a homogeneous premixed charge to the inlet port. This was done to ensure that mixture preparation issues were not confounding the results.
Based on the results of the heat flux measurements, a phenomenological model for spatially resolved predictions of the steady-state heat flux to the cylinder head was developed. This model allows prediction of the changes in steady state flux to the cylinder head occurring as a result of changes in air-fuel ratio, load, and ignition timing.
The phenomenological model was used in a finite element prediction of energy flows in the nonmoving parts of the engine. In-cylinder boundary conditions were determined using the phenomenological model. Comparisons of steady state temperatures predicted from the finite element analysis with those measured in the engine tests showed good agreement.