FR2811017A1 - LOW TEMPERATURE EXTERNAL COMBUSTION THERMAL ENGINE - Google Patents

Abstract

The invention concerns an external combustion heat engine operating at low temperatures using the physical properties of carbon dioxide. The engine can be used for producing electrical power by using renewable energy resources and in particular solar energy. The arrangement of the inventive thermal machine comprises: a high temperature fluid source (HT); a low temperature fluid source (LT); two carbon dioxide containers communicating with two cylinders containing two pistons in contra-position; two separate circuits for circulating the HT and LT fluids; a device for using and storing the mechanical energy produced. For each operating cycle the pressure difference between the carbon dioxide heated in a container and the gas cooled in the other container produces mechanical energy, which is then stored by a flywheel. Since the system is reversible, the following cycle is obtained by reversing the temperatures of the containers: the cold compressed gas is heated and expanded and, simultaneously, the hot gas is cooled and compressed. The inventive thermal machine drives an alternator. The alternator generates electricity which is used either directly or via storage batteries.

Description

-1 - The present invention relates to a combustion engine

  external operating at low temperatures (close to ambient temperatures). The engine can be used for the production of electrical energy using renewable energies and in particular solar thermal energy. The heat engine presented makes it possible to exploit the physical characteristics of the carbon dioxide contained in a

  closed circuit for the transformation of thermal energy into mechanical energy.

  The physical characteristics of carbon dioxide at determined densities allow very high pressures to be released for small temperature variations in a temperature range around its critical point (30.92 C). This property of C02 allows us to use as external hot source, apart from the different types of conventional fuels, solar energy by means of a solar thermal collector in which a fluid can easily be heated to a temperature between 70 and 80 sufficient to obtain significant working pressures. Other "ecological" features of the present invention are

  absence of pollutant emissions and reduction of noise pollution.

  In relation to the state of the art, the internal combustion engine which is the subject of the present invention should not be confronted with the engines used today for internal combustion which have much greater technical performance (even if with the known problems at the level environmental). The present invention must be framed in a global ecological system for exploiting renewable energies for the production of electricity. In this context, the proposed engine presents innovations and can open up avenues of research in the fields of electrical energy production through a more diffuse system in the region, such as

  it occurs today with wind and photovoltaic.

  The first aim of the present invention is therefore to obtain an electrical energy production with a low-cost and environment-friendly system by using renewable resources including solar energy: a simple and solid machine capable of operating at very high pressures, to rotate continuously through a thermodynamic system that saves primary energy and to exploit the physical characteristics of carbon dioxide making it possible to supply

  mechanical energy at low temperatures.

  To achieve these objectives, in a first embodiment which represents its most synthetic form, the proposed thermal machine consists of: a source of high temperature fluid (H.T.); a low temperature fluid source (B.T.); two gas containers (the gas will be designated hereinafter by "working fluid") in communication with two counter-placed cylinders containing two pistons integral with each other, either directly or by means of a crankshaft; two separate circuits which make it possible to circulate the fluids at H.T. and B.T. around the containers to alternate the temperatures of the working fluid by creating the pressure differences necessary for the expansion and the compression of the working fluid; a device

  for the use and storage of the mechanical energy produced.

  The operation of the machine is carried out through the following phases: the fluid coming from the HV source convection heats the working fluid in a container and, at the same time, the fluid coming from the LV source cools the working fluid in the other container; being the containers in communication with the two cylinders, the pressure difference between the two containers, produced by the different temperatures of the gas, will produce the expansion of the gas in a cylinder and consequently the displacement of the piston which, being forced against the piston of the other cylinder, will produce gas compression in the temperature and pressure container

  lower; at the end of the piston stroke the circulations of fluids at H.T. and B.T.

  are inverted by a system of valves, controlled by the movement of the pistons,

  to repeat the previous cycle in reverse and so on.

  The working fluid, contained in an enclosed space, undergoes the following stages: - the cold working fluid is compressed - the cold compressed working fluid is heated - the heated compressed working fluid is expanded - the expanded heated working fluid is cooled

  the cooled working fluid is compressed and so on.

  A point analysis will be made on the working fluid. The driving fluid consists of carbon dioxide. The present invention uses the physical characteristics of the carbon dioxide preferably used at concentrations between 1.4 g. / cm3 and 2.2 g. / cm3 to obtain large pressure variations for small temperature differences which are easy to reach because they are close to room temperature (at 1.4 g / cm3 the pressure is 58.5 bars at 20 C .; 116.5 bars at 35 C .; from 215.9 bars at 50 C.). To have good performance, the ratio between the volume of the compressed fluid and its volume after its expansion must allow

  maintain the gas in the indicated concentrations.

  The active phase of the cycle, unlike internal combustion engines, with its brief and very rapid useful phases, is characterized by large displacements of the piston and constant high useful pressures throughout the entire stroke of the piston. The linear force developed can be transformed at the mechanical level into a circular movement of a free flywheel capable of storing the energy produced by doubling the dead times between the phases. In a second embodiment, the containers of the working fluid, of cylindrical shape, are placed in continuation of the -3 cylinders and in direct communication with the pistons. This embodiment makes it possible to limit the pressure losses due to the passage of the working fluid between the

containers and cylinders.

  In the embodiments described, the gas container is made of a material with low thermal inertia to allow rapid temperature variations following the alternation of the passages of the HV and LV fluids on the external surface of the container. In order to limit the consumption of calories lost in the reversals of the temperatures of the containers, and to reduce the times of inversion of the temperatures of the working fluid, a variant is proposed in a third mode of

production.

  Another characterization of the heat engine of the present invention is the "reversibility" of the elements constituting the machine. There is not a displacement of the gas, as in Stirling cycle engines, from a cold zone to a hot zone and vice versa, but are the same zones which are once cold and once hot and

  vice versa according to the phases of the cycle.

  In a third embodiment, a device described below makes it possible to obtain this temperature inversion through a system which always maintains

  constant the temperatures on specific surfaces of the containers.

  The containers of the working fluid are constituted by elements which are maintained at high temperature and by elements which are maintained at low temperature through the continuous circulation of the fluids at H.T. and B.T. on the external surfaces of these elements. The entire surface of the container is made up of one half of the HT surface and the other half of the LV surface. Inside each cylindrical container, a device consisting of a "heat shield" allows the alternating insulation of the high temperature elements and low temperature elements to allow variations in the temperatures of the working fluid contained in the containers to be obtained. Said device which makes it possible to isolate alternately the elements at high temperature and the elements at low temperature is controlled directly or indirectly by the movement of the piston at each end of the stroke of the piston itself. The mechanical energy produced is stored in a free flywheel. In this embodiment, the materials constituting the containers have high thermal inertia to better conserve the given temperatures and exchange them.

  then with the working fluid inside the containers.

  The heat engine object of this invention can, among other uses,

  drive an alternator for the production of electrical energy.

  The features of the present invention will be more evident from the

  description with reference to the accompanying drawings according to its third embodiment:

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  Figure 1 shows the general diagram of the invention.

  Figure 2 shows in longitudinal section the details of the cylinder - piston assembly

  - container - heat shield during the gas expansion phase.

  Figure 3 shows in longitudinal section the details of the cylinder - piston - container - heat shield assembly at the end of the gas compression phase. Figure 4 shows in longitudinal section the details of the cylinder - piston assembly

  - container - heat shield at the end of the gas expansion phase.

  In the variant relating to the third embodiment, the machine proposed has significant advantages: reduction of thermal losses due to the need, for each cycle, to reverse the temperatures of the containers of the working fluid and elimination of the pressure losses due to the passage of the engine fluid

containers to cylinders.

  The main components of the heat engine in this third embodiment are: - two containers (3) for the high density engine fluid communicating with two cylinders (4) equipped with two counter-placed pistons (5); - a system for circulating hot and cold fluids around the cylinders to heat or cool the working fluid inside the cylinders (6); - thermal insulation (13) of the hot and cold fluid circuits; - a device for reversing the temperatures inside the cylinders (7); - a source of hot fluid (1); - a source of cold fluid (2);

  - a device for the use (8) and storage of the mechanical energy produced (9).

  The container for the working fluid consists of elements (10), steel crowns in its simplest form, separated by a seal (11) acting as thermal insulator. These elements, with great thermal inertia, have, on the outside, a jagged surface (12) along which circulate the HV or LV fluids. The container is therefore composed of a succession of "hot elements" and " cold elements "insulated from each other by a thermal seal, thus making it possible to have a cylinder / container having inside 50% of surface at HT and 50% of surface at LV In adhesion with the internal walls of the cylinder / container an element made of insulating material, acting as a "heat shield" (7), moves to position itself alternately once on the "hot" surfaces allowing the cold surfaces to lower the temperature of the gas and once on the surfaces "cold" allowing hot surfaces to increase the temperature of the gas inside the cylinder / container. The cylindrical container is completed by a safety valve (14). The containers of the working fluid are placed in continuity with the cylinder I piston assemblies (4-5) completely open on the cylinders. The assemblies constituted by a container, a cylinder and a piston is placed in counter position between them in direct linear connection (or through a system of connecting rods and crankshaft) so that to a phase of gas expansion in an assembly corresponds a phase compression in the other. The movements of the heat shields are controlled directly by the pistons. A metal bar (15) internal to the container and integral with the piston allows, through an adjustable blocking system (16), the displacement of the thermal screen and its positioning at each end of the piston stroke by causing

Inversion of the cycle.

  The two counter-posed cylinders represent the base module of the machine.

  The performances can be increased with the addition of other modules making it possible inter alia to limit the dead times due to the inversions of the temperatures of the working fluid. The hot source which heats the working fluid can be of different types and in particular, given the low temperatures necessary to operate

the machine, solar energy.

  The cold source can also be of different types with temperatures

  close to room temperature.

  The devices for the use of the mechanical energy supplied by the machine can be of conventional types, comprising a flywheel for the conservation of

  energy before its direct use.

  The application of this thermal machine for the production of electrical energy implies that the mechanical energy produced drives an alternator. This alternator can be of the rotary type connected to the flywheel or of the linear type driven directly or indirectly by the rectilinear movement of the pistons. The alternator generates electricity which is used either directly or through

storage batteries.

  The invention presented is not limited to the embodiments described and shown but, without departing from the scope of the invention, numerous technological variants are possible, in particular in the choice of the materials most suited to

each use.

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Claims (7)

  1) Closed circuit external combustion engine characterized in that it comprises: a source of high temperature fluid (H.T.); a low temperature fluid source (B.T.); two gas containers (working fluid) in communication with two counter-placed cylinders containing two pistons integral with each other, either directly or by means of a crankshaft; two separate circuits that allow the fluids to circulate at high and low over the containers to alternate the temperatures of the working fluid by creating pressure differences   necessary for the expansion and compression of the working fluid.   2) A heat engine according to claim 1 characterized in that it uses, as the working fluid, carbon dioxide at high concentrations. As   non-limiting example, these concentrations can vary between 1.4 gr./cm3 and 2.2 gr./cm3.   3) A heat engine according to claim 2 characterized in that the containers of the working fluid are of cylindrical shape and are placed in continuation   cylinders and in direct communication with the pistons.   4) A heat engine according to claim 1 or claim 2 characterized in that the containers of the working fluid consist of elements which are maintained at high temperature and elements which are maintained at low temperature through the continuous circulation of fluids at HT and to BT on surfaces of these elements.   ) A heat engine according to claim 3 characterized in that inside each cylindrical container a device constituted by a "heat shield", allows to alternately isolate the elements at high temperature and the elements at low temperature to allow to obtain the variations fluid temperatures engine contained in the containers.   6) A heat engine according to claim 5 characterized in that said device which makes it possible to isolate alternatively the elements at high temperature and the elements at low temperature is controlled directly or indirectly by the   piston movement at each end of the piston stroke itself.   7) A heat engine according to any one of claims 1 to 6 characterized   in that the mechanical energy produced is stored in a free flywheel   8) A heat engine according to any one of claims 1 to 7 characterized   in that it drives an alternator for the production of electrical energy.