Starting a compression ignition free piston internal combustion engine having multiple cylinders

A method for starting a free piston, internal combustion engine includes supplying an air charge to a space in a combustion cylinder, and reciprocating the piston in the cylinder so that the maximum pressure of the air charge in the space cyclically increases. Air and fuel are cyclically admitting to the cylinder to produce an air-fuel mixture, and spark ignition is used to produce cyclic combustion of the air-fuel mixture. The air-fuel ratio of the mixture is increasing when a maximum pressure in the cylinder occurs within a predetermined period following a TDC position of the piston. Spark ignition is discontinued, and cyclic compression ignition (HCCI) of the air-fuel mixture occurs.