The control equipment (13) for the engine (1) has a system for detection of fluctuations in the engine output and a combustion limit controller for closed loop control of an engine control parameter which contributes to the combustion conditions. This enables the output fluctuations to approach a permissible maximum limit. A control parameter switching circuit switches and adjusts the parameter according to the engine operating conditions. The output fluctuation detection can be based on integrating the cylinder pressure over a specific time interval i.e. an angular interval after top dead centre.
