Stirling engine with at least four piston assemblies

A method of operating an engine, the method comprising the steps of:

• (i) providing a Stirling engine, the engine comprising:
• at least four piston assemblies, wherein each piston assembly comprises:
• a first cylinder comprising a piston configured to separate at least two expansion or compression chambers of the first cylinder;
• a second cylinder comprising a piston configured to separate at least two expansion or compression chambers of the second cylinder;
• wherein the pistons of the first and second cylinders are connected, such that the first and second cylinders form each piston assembly;
• wherein a first chamber of the first cylinder of a first piston assembly is fluidly connected to a first chamber of a first cylinder of a second piston assembly;
• and wherein a second chamber of said first cylinder is fluidly connected to a second chamber of a first cylinder of the second piston assembly;
• and
• wherein a first chamber of the second cylinder of the first piston assembly is fluidly connected to a first chamber of a second cylinder of a third piston assembly, and
• wherein a second chamber of the second cylinder of the first piston assembly is fluidly connected to a chamber of a second cylinder of the third piston assembly;
• and
• wherein a first chamber of the second cylinder of the second piston assembly is fluidly connected to a first chamber of a second cylinder of a fourth piston assembly, and wherein a second chamber of the second cylinder of the second piston assembly is fluidly connected to a second chamber of the second cylinder of the fourth piston assembly;
• such that a working fluid to be compressed/expanded can flow between the fluidly connected chambers of the respective piston assemblies;
• wherein each piston assembly is a free piston assembly, wherein at least one free piston assembly is rigidly couplable by a coaxially connecting rod to a linear generator or alternator assembly to generate electricity;
• and
• (ii) providing a temperature difference between the fluidly connected expansion and compression cylinders, such that the pistons of each cylinder oscillate.