The heat release rates of an engine with divided combustion chambers have been calculated up to now from the indicated pressures of both chambers (called the gas-flow method here). The enthalpy transfer is estimated by the gas flow, the error of which increases if the pressure ratio between the chambers becomes close to 1. Such a pressure ratio often occurs when the passageway is thick. Because the gas-flow method cannot be applied in such cases, one of the authors has proposed a new method (called the distribution method), suitable when the pressure ratio lies in the vicinity of unity. the relation of the boundary between these methods are, however, not yet clear. The purpose of this paper is to investigate the relations in the boundary region and obtain knowledge about the application limits of both methods by computation and experiments.
