[abstFig src='/00280005/07.jpg' width='300' text='Adaptive engine combustion control system' ] This paper deals with a combustion control system design problem of diesel engine. For a combustion model of diesel engine, which has been provided for on-board control, an adaptive control system based on an adaptive output feedback control with a simple adaptive feedforward input will be proposed based on the “almost strictly positive real-ness” (ASPR-ness) of the controlled system. A simple parallel feedforward compensator (PFC) design scheme, which renders the resulting augmented controlled system ASPR, will also be proposed based on basic combustion model properties to design stable adaptive control system for the diesel engine combustion control. The effectiveness of our proposal is confirmed through numerical simulation.