Closed loop scroll expander

An engine to convert heat into mechanical output using a working fluid in a closed-circulating system, the engine comprising:

• a variable displacement pump configured to raise a fluid pressure of the working fluid from a first pressure to a second pressure;
• a heat receiving portion of a regenerative heat exchanger configured to receive the working fluid from the variable displacement pump, the regenerative heat exchanger configured to add heat to the working fluid;
• a heating device configured to supply additional heat to the working fluid to raise a fluid temperature of the working fluid to a desired working temperature that is above a critical temperature of the working fluid;
• a scroll expander having an inlet coupled to the heating device and an outlet, the scroll expander configured to generate the mechanical output through the expansion of the working fluid from the inlet to the outlet of the scroll expander;
• a heat transmitting portion of said regenerative heat exchanger configured to receive the expanded working fluid from the outlet of the scroll expander and pass it therethrough;
• a condenser coupled between an outlet of the heat transmitting portion and the variable displacement pump to reduce the fluid temperature to a low-cycle temperature;
• and
• a power control valve to adjust the mechanical output of the engine by adjusting a mass flow of the working fluid in the closed circulating system;
• wherein the variable displacement pump is configured to compensate for the adjustment of the mass flow rate by maintaining the second pressure in a specified range.

A method of converting heat into mechanical output using a working fluid in a closed-circulating system, comprising:

• supplying a working fluid at a low-cycle temperature;
• raising a fluid pressure of the working fluid with a variable displacement pump from a first pressure to a second pressure;
• adding heat to the working fluid at substantially its second pressure to raise a fluid temperature of the working fluid to a high-cycle temperature above a critical temperature of the working fluid;
• expanding the working fluid through a scroll expander to generate the mechanical output and reduce the fluid pressure;
• cooling the working fluid to reduce the fluid temperature substantially down to a low-cycle temperature;
• transferring heat contained in an expanded portion of the working fluid to a pressurized portion of the working fluid using a regenerative heat exchanger during the cooling of the working fluid;
• controlling the mechanical output of the engine by regulating a mass flow rate of the working fluid;
• and
• compensating, by the variable displacement pump, for adjustments to the mass flow rate of the working fluid to maintain the second pressure in a specified range.