Method of operating a free piston internal combustion engine with high pressure hydraulic fluid upon misfire or initial start-up

A method of operating a free piston internal combustion engine, comprising the steps of:

• providing a housing including a combustion cylinder and a second cylinder;
• providing a piston including a piston head reciprocally disposed within said combustion cylinder, a second head reciprocally disposed within said second cylinder, and a plunger rod interconnecting said piston head with said second head, said second head and said second cylinder defining a variable volume pressure chamber on a side of said second head generally opposite said interconnecting plunger rod;
• pulsing a supply of hydraulic fluid from a high pressure hydraulic accumulator into said pressure chamber during a beginning portion of a compression stroke to cause said piston head to move toward a top dead center position in said combustion cylinder;
• decoupling said high pressure hydraulic accumulator from said pressure chamber after said pulsing step;
• coupling a low pressure hydraulic accumulator with said pressure chamber during a remaining portion of said compression stroke;
• coupling said high pressure hydraulic accumulator with said pressure chamber when said piston head is traveling toward a bottom dead center position in said combustion cylinder during a return stroke;
• providing a sensor for sensing a position of said piston in said combustion cylinder which is one of at and near said bottom dead center position and providing a corresponding signal;
• and
• maintaining said coupling between said high pressure hydraulic accumulator and said pressure chamber for a period of time, dependent upon said sensor signal and a length of said return stroke.