Abstract: The present invention provides a method of operating an engine (14) having one or more cylinders (16) each having a piston (18) within the cylinder (16) and each piston (18) having an expansion stroke and a return stroke and a top dead center (TDC) position and a bottom dead center position (BDC) and said engine (14) employing a working fluid (WF) and a heat exchange fluid (HEF), comprising the steps of: introducing the HEF during the return stroke of the engine; introducing the working fluid (WF) during the expansion stroke of the engine; causing the exhaust valve to be opened at or near bottom dead center of the piston BDC; delivering the HEF to the cylinder (16) after the exhaust valve has been opened; and closing the exhaust valve before TDC, such as to allow the working fluid to be compressed by the piston within the cylinder. The invention also provides an engine (14) capable of being operated in accordance with the method.

Abstract: The present invention provides a method of operating an engine (14) having one or more cylinders (16) each having a piston (18) within the cylinder (16) and each piston (18) having an expansion stroke and a return stroke and a top dead centre (TDC) position and a bottom dead centre position (BDC) and said engine (14) employing a working fluid (WF) and a heat exchange fluid (HEF), comprising the steps of: introducing the HEF during the return stroke of the engine; introducing the working fluid (WF) during the expansion stroke of the engine; causing the exhaust valve to be opened at or near bottom dead centre of the piston BDC; delivering the HEF to the cylinder (16) after the exhaust valve has been opened; and closing the exhaust valve before TDC, such as to allow the working fluid to be compressed by the piston within the cylinder. The invention also provides an engine (14) capable of being operated in accordance with the method.