Rankine Cycle With Linear Generator


The Company has a developed proprietary technology that can make use of low grade heat from gaseous or aqueous sources, using the temperature difference provided by a cooler source, to generate electricity. Waste heat can be derived from a number of industrial sources including; combustion processes, reciprocating engines, steam processes, and nuclear processes. Alternatively, natural sources can also be used as a heat source including; geothermal, near surface water, solar or steam. Depending on the temperature differential, thermal to electricity conversion efficiency of 50% or more is achievable (See Fig. 2.1A). This device gains its efficiency and operational cost advantages by replacing turbines and rotary generators with a novel, proprietary, free piston and linear generator combination.

Fig. 2.1A—Comparison Between Conventional Generation Efficiencies and the M-Power Generator

Fig. 2.1B—Fundamental Components of WHRG

Existing heat recovery technologies, typically utilizing rotary turbines, possess a number of inherent barriers to market uptake, including:

  • Requirement for high waste heat and operational temperatures/pressures
  • Narrow temperature/pressure operating range
  • Low efficiencies, particularly at sub MW scales
  • High capital and operating/maintenance costs

M-Power Generators specifically address all these shortcomings and focus primarily on the capture and conversion of the vast amount of low temperature wasted heat that current technologies are incapable of capturing.

The fundamental components of the M-Power Waste Heat Recovery Generator (WHRG) are:

  • Heat Capture Loop
  • Organic Working Fluid
  • Free Piston/Gas Spring
  • Linear Generator
  • Rotary Valve
  • Computer Control System

The elegance of the WHRG is that it combines a suite of exiting technologies and components with proprietary control systems into a package that addresses the key weaknesses of other waste heat recovery systems (see Fig. 2.1A). Incremental advances in each of these technologies, and manufacturing capabilities, has allowed for both the realization and cost-effective production of WHRG. This system is easily adaptable to Geothermal sources of energy creating one of the most efficient Geothermal Electricity Production Systems (GEPS) currently available in the market.


The heat capture loop of the WHRG operates using a traditional Organic Rankine Cycle Engine (ORC) (see Fig. 2.1C). An organic working fluid is pressurized and pumped through a heat exchanger, which collects heat from a geothermal source , a low-grade waste stream (or other) source. The heat energy is sufficient to vaporize/boil the organic working fluid, transforming it into a gas. The pressurized gas is then precisely fed into the engine, in this case a free-piston system, which translates the potential energy of the gas into work/motion. Once through the engine, the gas is condensed, using a cooling loop and then it returns to the liquid phase for reuse in the cycle.

Fig. 2.1C—Organic Rankine Cycle Engine Schematic

Fig. 2.1D—Simplified Free Piston Engine Schematic


Traditional free-piston engines consist of a linear, ‘crankless’ engine, in which the motion of the piston is determined by the interaction of forces from the combustion gases, a rebound device (e.g., a piston in a closed cylinder) and a linear alternator as a load device (see Figure 2.1D). A number of variations on this theme exist. Considerable interest surrounds this technology for use in hybrid-electric automotive applications in which a free piston, powered by internal combustion, would be used to drive a linear alternator, and the resulting energy would be used to drive electric motors . Linear free pistons have the capability to increase engine efficiency by 40%. They eliminate mechanical losses associated with the conversion of linear motion to rotational motion.

WHRG’s Free Piston Generator uses expanding gases from the ORC in place of combustion of conventional fuels to provide compression to the piston. Piston motion is stopped through the use of highly efficient, dynamically tuned, valves that conserve and reuse energy, in the form of gas pressure, to rebound the piston. Tremendous efficiencies are achieved by precise control of gas ingress and egress from the cylinder chambers using these proprietary valves and the related control system. Free piston engines are attractive as they are simple in design, using fewer moving parts, have reduced frictional losses, and have resultant low maintenance costs.


A linear alternator is a device that directly converts mechanical energy into electrical energy by reciprocal linear motion. All alternators operate on the principle of electromagnetic induction whereby a magnet moves in relation to a wire coil and induces a varying magnetic flux/current through the coil. Conventional alternators operate using rotational motion, requiring a linkage that converts a reciprocating motion to a rotary motion resulting in loss of efficiency. The alternator used in WHRG consists of a central structure (the reactor) on which a series of powerful permanent magnets are mounted (see Figure 2.1E). The reactor is attached to the free piston and moves reciprocally with its motion through a series of windings creating a magnetic flux. The design of the alternator assembly is proprietary to the Company and is optimized to produce the maximal electrical output to the inverter or storage system.

Fig. 2.1E—Simplified Schematic of Linear Alternator

Fig. 2.1F— A 100kW M-Power Generator 3D CAD Model Design

Fig. 2.1G—100kW M-Power Generator Pre-Production Model on test stand