GB2376507A

GB2376507A - An engine where the working gases in the cylinder are heated by injection of hot liquid

Info

Publication number: GB2376507A
Application number: GB0110943A
Authority: GB
Inventors: Anthony Gregory Smith; David Michael Thomas; Matthew James Culley Stobart
Original assignee: S & C Thermofluids Ltd
Current assignee: S & C Thermofluids Ltd
Priority date: 2001-05-03
Filing date: 2001-05-03
Publication date: 2002-12-18
Also published as: GB0110943D0

Abstract

An engine where a working liquid from sump 1 is first heated in heat exchanger 5 and then pumped and injected into the engine cylinder 2 through atomiser 6. The atomised liquid transfers heat to the working gas in the cylinder causing it to expand and force piston to move. The liquid then collects on the top surfaces of the piston and is allowed to drain away to the sump via pipe 9. The liquid may then be cooled in the low temperature heat exchanger 11 and then pumped into the engine cylinder 2 through atomiser 13. The cooler liquid may then extract heat from the gas causing it to contract so that the piston continues its motion. The engine could, for example, be of the stirling type.

Description

PATENT SPECIFICATION IMPROVEMENTS TO STIRLING ENGINE HEAT TRANSFER EFFICIENCY Stirling engines make use of a cylinder containing a piston and a closed volume of working fluid such as pressurised helium. Work is obtained from the engine by repeatedly heating and cooling the working gas. The heating of the gas increases the pressure which causes the volume to increase to equalise the pressure. The change in volume is achieved by movement of the piston and this movement is transferred into work. Cooling the gas causes its pressure to reduce, the opposite motion thus being created.

It is an essential feature of the Stirling engine that the working fluid is not expelled as in the case of an internal combustion engine. The transfer of heat to and from the gas from external heat sources is achieved through the cylinder wall of the engine. This heat transfer is therefore highly dependent upon the convective heat transfer coefficients between the heating/cooling fluid and the cylinder walls and the working fluid and the inner cylinder walls.

In the outer parts of the cylinder, liquid is often used to achieve higher heat transfer coefficients. In the case of the internal working fluid of the Stirling engine, a liquid cannot be used because it is incompressible.

The following patent application describes a technique for increasing the heat transfer efficiency for the working fluid inside a Stirling engine.

In the present embodiment, liquid (the working liquid) is injected into the Stirling engine cylinder and atomised in order to achieve high rates of heat transfer to the working fluid-from now on referred to as the working gas.

The working liquid which may have a high boiling point is first heated in a higher temperature heat exchanger. The high temperature liquid is then injected and atomised (but not vaporised) as it enters the cylinder. The atomised liquid transfers heat to the working gas causing it to expand and resulting in work from the movement of the piston. The liquid then collects on the top surfaces of the piston and is allowed to drain away to a sump. A scavenge pump may be used to help with the removal of the working liquid.

The working liquid is then cooled in a low temperature heat exchanger. This heat exchanger may be air cooled. The cooler liquid is then again atomised (but not vaporised) as it is injected into the working gas of the Stirling engine. High rates of heat transfer are then used to cool the working gas causing it to contract.

The invention is more particularly described by way of Figure 1.

Variations within this invention include heating and cooling the outer casing of the engine as well as using liquid injection.

Claims

IMPROVEMENTS TO STIRLING ENGINE HEAT TRANSFER EFFICIENCY CLAIMS 1. A Stirling engine in which liquid is injected into the working gas of the engine in order to transfer heat from the liquid stream to the working gas.
2. A Stirling engine according to claim 1 in which the liquid is heated so that its temperature is above that of the working gas of the engine.
3. A Stirling engine according to claim 1 in which the liquid is cooled so that its temperature is below that of the working gas of the engine.
4. A Stirling engine according to claim 1 in which the liquid first injected into the working gas is at a temperature above that of the working gas and is then followed by liquid at a temperature below that of the working gas.
5. A Stirling engine according to any of the preceding claims, in which the injection of the liquid is the main method by which heat is transferred to the working gas.
6. A Stirling engine according to claims 1 to 4, in which heat is transferred to the working gas through the cylinder walls as well as by the liquid entering the gas.
7. A Stirling engine according to any of the preceding claims in which the liquid is injected into the working gas through an atomiser in order to produce small droplets which can transfer heat more readily between the liquid and the working gas.
8. A Stirling enging according to claim 7 which uses a more that a single atomiser.
9. A Stirling engine according to any of the preceding claims in which the liquid is collected from the cylinder and recirculated through to the working gas.
10. A Stirling engine as shown in Figure 1.