Internal combustion engine

Abstract

 A means of improving the performance of internal combustion engines by coating the surfaces of combustion chambers, such as cylinder heads, inlet and outlet valves, and piston crowns, and inlet and exhaust valve ports with a layer of low thermal mass formed from a suitable combination of thermally conducting and thermally insulating materials.

Description

[0001] This invention relates to internal combustion engines.

[0002] In conventional internal combustion engines, a proportion of the heat generated by combustion of the fuel-air charge is lost to the surfaces of the combustion chamber, therefore reducing the temperature of the combustion products, power output and fuel efficiency. In addition, heat lost to the surfaces of the combustion chamber, ie. the walls of the combustion chamber, the crown of the piston and any inlet and outlet valves fined, can heat the incoming fuel-air charge so effectively reducing the mass of fuel-air charge available for combustion and reducing the available power output in an engine of a given size. In general terms the weight of charge admitted to naturally aspirated engines decreases by about 1% per 3 - 4 C° increase in fuel-air charge temperature prior to compression. That is, heat lost to the surfaces of the combustion chamber reduces the power output by both reducing the temperature of the fuel-air charge following combustion and by reducing the mass of fuel-air charge available for combustion. Heat lost to the surfaces of the combustion chamber increases the heat rejection load imposed on the engine cooling system.

[0003] A number of techniques have been applied to reducing heat loss to the surface of the combustion chamber. One effective technique is to coat such surfaces with a suitable heat insulating ceramic material. However, such treatment has limited operational lifetimes, typically of the order of 1,000 hours. While adequate for race engines which are regularly stripped following each race, such limited lifetime would be unsuitable for vehicles or other equipment used for normal industrial, commercial or domestic purposes.

[0004] The effect of coating engine surfaces with thermally insulating materials effectively coats the surfaces with a material with low thermal mass.

[0005] A mechanically robust coating of low thermal mass can be obtained by covering the surfaces of interest with a thin layer of thermally resistant metal backed by a layer of thermal insulation between the thin metal layer and the surface being coated so that the metal layer is supported by the insulation and the insulation is protected against damage by the metal surface. The metal layer can consist of thermally resistant metals such as nickel or chromium. The insulation layer can consist of the ceramic material currently sprayed onto combustion chamber surfaces or of suitable minerals such as mica or pearlite powder. The thickness of the metal layer is minimised to reduce its thermal mass. The metal layer is suitably bonded to the surface being coated to provide a robust protection to the thermal insulation below, the thickness of the metal is made small compared to the distance to any point of bonding to the underlying surface so that heat conduction along the metal coating is small compared with heat transfer between the metal surface and the underlying surface through the insulation layer.

[0006] A specific embodiment of the invention will now be described by way of example only with reference to Figure 1 which shows application of the invention to a piston crown.

[0007] Modified Piston Crown 10 is formed on Piston 11 in the form of a 0.5 mm thick layer of Mineral Insulation 12 covered by Cup 13 of a 0.2 mm thickness of a nickel/chromium high temperature alloy. Cup 13 is welded at Circumference 14 to a suitable alloy Ring 15 located in a slot in Piston 11 such as provided for Piston Rings 16 and 17. The outside diameter of welded Circumference 14 is slightly smaller than the outside diameter of Piston Rings 16 and 17 so that there is no contact between Cup 13 and the walls of the cylinder.

[0008] The thickness of the metal of Cup 13 is selected such that the Cup has sufficient physical strength when supported by Mineral Insulation 12 to withstand the detonation of the fuel-air charge in the cylinder and such that the overall thermal conduction from the upper surface of the Cup to Piston 11 is small compared with thermal conduction through Mineral Insulation 12. That is, overall heat transfer to Piston 11 is controlled by Mineral Insulation layer 12.

[0009] The reduced heat load on Piston 11 potentially enables the overall mass of the piston to be reduced thus improving engine fuel efficiency.

Claims

1. A means of improving the performance of internal combustion engines by coating the surfaces of combustion chambers, such as cylinder heads, inlet and outlet valves, and piston crowns, and inlet and exhaust valve ports with a layer of low thermal mass formed from a suitable combination of thermally conducting and thermally insulating materials.

2. A means of improving the performance of internal combustion engines as described in Claim 1) in which the layer of low thermal mass consists of an outer layer of thermally conducting robust materials resistant to high temperatures physically supported by a layer of mechanically robust thermally insulating materials.

3. A means of improving the performance of internal combustion engines as described in Claims 1 and 2) in which the layer of low thermal mass consists of a layer of thermally conducting robust materials resistant to high temperatures physically supported by a layer of mechanically robust thermally insulating materials and in which the thickness of the thermally conducting layer is selected such that thermal conduction along the thermally conducting layer is small compared to thermal conduction through the thickness of the thermally insulating layer.

Drawing