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Internal Combustion Engine

  There are basically two kinds of internal combustion engine. In one the fuel burns within a cylinder, exerting pressure on a piston which is generally connected to a crank to produce rotation; the other is the gas turbine where the combustion produces hot gases under pressure which are guided by vanes to the impellers of the turbine, producing rotation according to the same fundamental laws as govern the windmill.

Gaseous hydrocarbon from oilfields, or produced from coal and liquid fuels from oil wells, coal or fermented sugar, can be used in both kinds of engines. On a small scale sewage gases and methane from cattle manure have been used.

Credit for inventing the internal combustion engine is generally given to Nikolaus Otto who in 1867 designed and produced the Otto reciprocating engine. In this, a mixture of gas and air is drawn into the cylinder on the downstroke. The valves close and the piston moving upwards compresses the mixture heating it until combustion starts at a ‘hot spot’ on the cylinder head. The mixture then burns, increasing the cylinder pressure four- or fivefold, pushing the piston down in the ‘working stroke’ and giving a power output. After this stroke the inlet valve opens, the piston moves up again ready to restart the cycle with air/fuel induction. Benz in 1885 developed the use of petrol, producing the first internal combustion powered wheeled vehicle. The operation of these engines was greatly simplified by the development of the carburettor to give a uniform mixture of air and fuel vapour, ascribed to Maybach in 1892, and the application by Daimler of the sparking plug to ignite the fuel and air mixture at a precise time in the engine cycle.

The compactness of the internal combustion engines and its high power-to-weight ratio were big advantages over the steam engine, which had dominated industry and transport until this time. In the USA, Ford produced the Model T automobile, making personal powered vehicles widely available at low cost. Buses had existed from the early 19th century and progressed from horse traction to steam, but they only really made headway with the application of electrical power in tramways and the internal combustion engine as we know it now.

Present-day buses, trucks and lorries are generally powered by the engine developed by Diesel (1892). This has no electrical ignition system. Air is drawn into the cylinder and compressed to a pressure of up to 600lb/in2 (4MPa; 40 atmospheres). Diesel fuel oil is then injected into the cylinder where it burns immediately and rapidly because of the temperature of the compressed air. Because of the high pressures developed Diesel engines require to be stronger and therefore heavier than petrol or gas engines. Their virtues however are long life, less frequent maintenance requirements, rugged construction, and economy due to use of cheaper fuel.

The first aircraft used internal combustion petrol engines, initially with the cylinders in line as in present cars but soon in a more compact lighter form with the cylinders placed on the radius of a circle centred on the crankshaft. During World War II the UK and Germany developed almost simultaneously the concept of the gas turbine. This has proved so successful that nearly all planes are now powered by ‘jets’ rather than reciprocating combustion engines. Gas turbines are used also for ships and for electric power production. The advantage of the gas turbine over conventional coal-fired steam turbine generators is its compact size and its very rapid start up time, allowing it to be brought into service quickly to keep the electrical supply in balance with sudden changes in the power requirements. There will always be controversy over the use of gas turbines which are dependent on the availability of limited supplies of natural gas compared to the much greater stocks of coal. AA

Further reading D.I. Ruquhart, The Internal Combustion Engine and How It Works.



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