An air heating system for a compression ignition engine comprises a combustion chamber which includes a burner through which fuel is supplied to the combustion chamber. A two stage fuel pump is provided to supply fuel to the burner with the output of the second stage being connected to the burner and the input of the second stage being connected to the output of the first stage. Valve means is provided to ensure that there is substantially no pressure drop across the second stage of the pump and control means is provided to control the speed of operation of the pump so that the rate of fuel delivery to the combustion chamber can be closely controlled.
