A split cycle
internal combustion engine comprising a compression cylinder accommodating a compression
piston; a
combustion cylinder accommodating a
combustion piston; a
crossover passage between the compression cylinder and the
combustion cylinder arranged to provide
working fluid to the combustion cylinder; a controller arranged to determine a peak temperature of combustion in the combustion cylinder based on a received indication of a peak temperature of combustion in the combustion cylinder; and a
coolant system arranged to regulate a temperature of the
working fluid supplied to the combustion cylinder; wherein, in response to determining that the peak temperature of combustion exceeds a selected threshold, the controller is configured to control the
coolant system to regulate the temperature of the
working fluid supplied to the combustion cylinder so that a peak temperature of combustion in the combustion cylinder is less than the selected threshold.