Adiabatic

The achilles heel of the conventional metal internal combustion engine is heat. An engine develops a massive amount of heat; indeed to a certain extent its efficiency is dependent upon that heat. But with conventional engine building materials there is a breaking point. If the heat is allowed to build up unabated, serious damage is caused to the engine components, and so the cooling of an engine becomes a vital part of the process. Heat is channelled away from the engine by water, air and oil, but since heat is energy this presents a significant handicap to the potential power output of the unit, and thus your conventional engine is caught in a ‘Catch 22’ situation.

Recent developments in ceramic technology might just point to a way out of this difficulty. Ceramics have several significant advantages over metals, not least their abilities to withstand high temperatures, and their resistance to corrosion and wear. Yet in this strength lies a fundamental weakness, that only recent developments have offered any hope of overcoming.

Drop a tea-cup on the floor and it shatters. Ceramics can withstand heat, chemicals and corrosion, but because of their atomic structure they cannot deform; instead a crack develops and the component may break up dramatically.

Traditional ceramics remain far too brittle for industrial processes such as machining, let alone the stresses components are subject to in an internal combustion engine. Major advances began in the 1940s when new ceramics were developed that were oxides of metal, such as Alumina. Although vastly improved they still remained insufficiently strong. However in the 1970s ceramics such as Silicon Nitride, and Silicon Carbide, which are not oxides of metal, were developed with a strength greater than that of iron. Brittleness still remained a problem, but can now be overcome in several ways. One is to toughen the ceramic with fibres, which can disperse the energy of a fracture. Another is known as stress toughening, and consists of creating the ceramic out of two types of crystals. As a crack develops stresses cause one type of crystal to expand, and thus close the gap. Kazuo Inamori, Chairman of the Kyocera Corporation in Japan, says that brittleness can also be overcome by a precise mix of ceramic powders, in clean rooms with no contamination.

The Kyocera Corporation in conjunction with lsuzu is at the spearhead of ceramic engine research, and together they have reached a stage where the astonishing advantages of ceramic technology have actually been realised in an almost completely ceramic engine. The engine itself is nothing stunning to look at, although it is certainly unusual and has a certain beauty of its own, but one particular feature, or lack of it, would certainly attract your attention: there is no radiator. Nor is it air-cooled.

This engine, the all ceramic P306Y, is based on the Aska diesel engine, and has already completed some 3000 miles of high-speed testing. Tests already indicate that a ceramic engine will last some five times as long as a metal engine, and in principle will provide 30% better fuel efficiency and 30% more power.

So what exactly are the beneficial properties of ceramics that can result in such a seemingly efficient engine? Fundamentally ceramics have outstanding strength at high temperatures, high corrosion and wear resistance, as well as light weight. There are many types of ceramics, all possessing different qualities. Silicon Nitride, and Silicon Carbide exceed the strength of iron, and can withstand stress greater than 100kg/mm. The low thermal conductivity of Zirconia means that it is an excellent insulating material. One of the main features of all ceramics is their low coefficient of expansion, resulting in low distortion at high temperatures. Both Silicon Nitride and Silicon Carbide have coefficients one third of that of iron.

The necessary characteristics for the materials out of which an engine is built are heat resistance, heat insulation, wear resistance, high rigidity and light weight. Although ceramics possess all of these properties, no one ceramic combines all of them. For example the materials surrounding the combustion chamber require heat resistance/insulation, as well as strength, but no ceramic material satisfactorily combines these properties. (Although the development of such a material is in progress). The solution at the moment is to build the engine head and cylinder walls in a composite structure of various ceramics each positioned according to their relative properties. If the engine is carefully designed in this way it is possible to obviate the cooling system.

The walls of the combustion chamber itself, the valves, and the surface of the piston are constructed with high strength ceramic materials. Surrounding the wall of the combustion chamber, and at the skirt of the piston, is a ceramic material of low thermal conductivity. The cylinder wall itself is constructed of a ceramic with a low coefficient of friction. With such a construction it is possible for the combustion chamber to run at temperatures of up to 800°C while the outside of the engine remains at 100°C or below. The engine thus harbours the heat wasted in more conventional engines, and therefore increases its fuel efficiency and power.

In addition these high operating temperatures produce other advantages: for example exhaust emissions are vastly reduced and the engine is able to run on substitute fuels such as coal or vegetable oil. The development process, however, was not without its problems in this respect. The high temperatures also caused reduced volumetric efficiency, and a reduction in the detonation delay period. These problems were mainly caused by the injection system, the combustion chamber, and the airflow not being adapted specifically for ceramic materials.

It is now common practice that the ceramic engine components are completely redesigned to suit the particular properties of the ceramic materials, and this has redressed many of the problems caused by copying designs that had been evolved to suit metal components. Ceramics then, may well be the face of the future: extremely light, and running at a fuel and power efficient 800°C. The lack of cooling equipment would mean extremely low and compact engine bays, but more significantly there would be no cumbersome radiators in the airstream. Will we see arrow-thin Formula One cars, completely shorn of the now customary sidepods that house all of the cooling equipment? Indeed, it would be interesting to know just how far this technology has crept into the world of motor racing, for the advantages seem too obvious to be passed over. CSR-W