The present invention relates to an engine which employs circulating compressed gas to drive a turbine to provide energy output.

A wide variety of engines are well known, from conventional internal combustion engines, through to engines driven by compressed air, wind, water power and other sources. All such engines are driven by the need to provide energy output whilst minimising energy consumption and also minimise emissions that may be harmful to the environment. Furthermore, they often have the need to have simple control of their output, as well as the desire to have a long useable life through the use of a minimal amount of moving components and the provision of components with minimal wear and tear to reduce maintenance requirements.

The present invention seeks to provide an engine which is highly efficient, which is highly controllable in terms of its output, and yet which is simple and easy to maintain and has a long useable lifetime with minimal maintenance.

According to the present invention there is provided an engine comprising a compressor and a closed fluid circuit connected to the input and output of the compressor such that compressed gas can be driven through the circuit by the compressor, the output of the compressor being connected, through the fluid circuit to a turbine component comprising at least one set of turbine blades connected to a rotating shaft that acts as the output of the engine in use; a condenser for receiving fluid in the circuit that has passed through the turbine component and arranged to reduce the temperature and pressure of the compressed gas, the outlet of the condenser being connected to the inlet of the compressor.

The turbine may comprise plural sets of blades arranged along a common axis, the number of blades in each set, and their relative positions being configured to control flow of the compressed gas through the turbine component and control the output power of the engine.

A check valve may be located at the input to compressor to control flow of expanded circulating gas to the input of the compressor to improve its efficiency and optimise performance of the engine for a given load.

The circulating gas in the engine may be ammonia, of more preferably, for safety and operational efficiency reasons, may be carbon dioxide.

The condenser component may be attached to energy recovery means for recovering heat energy that can be converted into electrical energy to drive the compressor and improve the efficiency of the engine. The turbine shaft may be connected to a generator which provides a proportion of the energy required to generate the compressor in order to control the overall performance of the engine.

One example of the present invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a schematic view of an engine according to the present invention; and Figure 2 is a schematic diagram showing the flow of circulating gas within the engine of Figure 1.

Referring to Figure 1 , an engine 1 has a gas circuit 2 to hold compressed gas. The gas may be carbon dioxide, ammonia or any other appropriate gas that can be held at the appropriate compression pressure, dependent upon the output required in the engine, as well as other requirements such as overall weight, preferred operating pressure, and the temperature thresholds of the components forming the circuit and other parts of the engine. A compressor 3 is provided which, in use, compresses gas in the circuit and drives it from a compressor outlet 4 towards a turbine component 5. The compressor in this example is electrically powered but may have an alternative power source. The diameter of the compressor outlet 4 controls the pressure and flow rate of the compressed gas as it arrives at the turbine 5. High efficiency is provided if the pressure and temperature of the gas is at its critical point in this section of the fluid circuit. A heater (not shown) can be incorporated adjacent to the compressor 3 to heat the compressed gas to aid in achieving this. As gas passes from the compressor outlet 4 into the turbine component 5 it passes over sets of blades 6, 7 and 8, expanding as it does so and driving the series of blades and a central shaft 9 to which the sets of blades 6, 7, 8 are attached. In this example three sets of blades 6, 7, 8 have been provided, although the number of sets, together with the number of blades in each set, and their angle of configuration, can be selected dependent upon the pressure at which the gas resides in the turbine component 5, as well as flow rate. The shaft 9 acts as an output, and can be connected through a gear box to a mechanical component to be driven.

In this example it is shown connected to an electrical generator 10 which is linked to control components 1 1 and 12. These control components can receive electrical power from the generator 10 to control the output load on the shaft 9, the operating output of the generator 10, and also potentially to control feedback of electricity generated from the generator 10 to the compressor 3, again to control overall operating output of the engine to optimise its energy efficiency. It may be that in addition, or as an alternative, the generator 10 is mechanically connected to the compressor 3 so that it can be operated as a motor to start the compressor 3. It may also be that components from the generator 10 and turbine components are integrated into a single unit to reduce size and mechanical losses associated with connection of the two.

In one example the generator generates AC at 400Hz, to provide high efficiency, yet also has stepping components to drop it to 50Hz for use with standard electrical components. After passing over the turbine blade sets 6, 7, 8, the gas, now at a very much lower pressure, passes out of the turbine component 5 through a condenser 13. In this example the condenser is a series of pipes and dissipates residual heat in the gas that it is left following its expansion. In one example, the condenser 13 can act as a heat exchanger so that the heat energy there can be recovered and potentially converted into other forms of energy, potentially even electrical energy, to improve the efficiency of the electrical output of the engine or indeed to provide supply to control components or to the compressor 3. The output of the condenser 13 is then fed through a further pressure reducing component 14, which is optional, and through a check valve 15, which is also optional, and back to be compressed once more by the compressor 3. The check valve 15 ensures gas flow in a single direction and can help ensure correct flow of gas through the system, particularly during start-up, and can be used to regulate the output of the engine through flow of the gas, therefore optimising efficiency of the engine.

The check valve 15 can also be used to regulate the pressure differential across the compressor 3 to optimise its operational efficiency.

A relief valve (not shown) may be placed at an appropriate point in the fluid circuit to release unwanted pressure build up if necessary for safety reasons.

In one example of operation the pressure differential across the compressor 3 is controlled at around 22 bar with C0 ₂ as the driven gas (30 bar at compressor input and 52 at output).

Figure 2 shows, in schematic form, the flow of gas through the engine 1 , with the location of gas in the closed circuit within the relevant components, as outlined in Figure 1 having the corresponding numbering. From this it can be seen that the loss of gas within the circuit is absolutely minimal, meaning that the gas can be cycled over a long period with minimal moving parts in the engine as a whole and extremely low environmental damage with no consumption of gas that is used within the circuit. As will be appreciated from the above, by simple control of the compressor 3 and its output through the compressor outlet 4, the generator 10 can be powered to optimise the output of the engine 1 with high levels of efficiency and a minimal number of moving parts to reduce maintenance and improve operation. The configuration is such that the noise output of the engine is minimal when operating the engine, and that the engine can be controlled to have a wide variety of power outputs with minimal adaptation thereto through appropriate operation of the compressor 3, feedback of generated electricity to the compressor 3, and appropriate energy recovery from the exchanger 13 as well as appropriate control of the check valve 15.