Compressed-gas Fuel Practicable
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AMONGST the alternative fuels suggested for operating oil and petrol engines is coal gas, which has the advantage that it is available almost anywhere in the country, and has at its back the immense capacity of our mines.
As an emergency measure, gas in flexible containers was used to a considerable extent between 1915-19, when liquid fuel became scarce as a result of the greatly increased demand for military purposes and the reduction in supplies consequent 'upon the submarine campaign.
A new development in this connection has been announced by the United Kingdom Gas Corporation, which controls coal-gas-producing units over large areas throughout Great Britain. The work has been carried out in association with the National Gas and Oil Engine Co., Ltd., which has been working for some time on the Erren patents. It is claimed that the new development is so successful as to justify the conversion of oil and petrol engines on grounds of performance and economy alone.
Two types of engine have been evolved, each with an efficiency hitherto unknown in gas-engine design, and capable of operating equally well on either gas or oil. The first is a compressionignition type, mainly for large stationary plant, but also adaptable to mobile uses, whilst the other, known as the Erren, is intended particularly for motor vehicles and boats.
Almost Any Gas Will Do.
These engines will run not only on coal gas, but on gas from sewage, coke ovens, blast furnaces or natural sources. The big engine is identical in operation, except for a new type of carburetter, with the ordinary stationary Diesel engine, and oil engines of any make can be quickly converted to the new principle without loss of efficiency.
At present, from 5 to 10 per cent, of the total fuel requirements take the form of oil fuel for ignition purposes, but it is anticipated that all sizes will be available soon to operate entirely on gas by the addition of an electric ignition system.
The old type of gas engine had a compression ratio of about 6 to 1; the new type has the unusually high compression of 15 to 1. The result is a great increase in thermal efficiency.
The Erren type sucks in air on the Diesel principle, and then supercharges gas at a pressure of 60-70 lb. per sq. in., the gas-air mixture being then ignited under a maximum pressure of 400-500 lb. per sq. in. This high concentration of fuel gives the engine an important increase in power output for the size of cylinder, and for it is claimed the satisfactory thermal efficiency of 34 per cent.
It is stated that the ordinary oil engine, as used for road transport, can be converted to the use of gas on this principle by the attachment of a simple mechanical gear, costing about £60 for a large bus engine of about 100 h.p.
Tests Show Excellent Results.
Tests with a small " three-way " engine, which can be operated at will as an ordinary oil engine, high-compression gas engine, or supercharged gas engine, have shown that on oil fuel it develops 9 b.h.p., on high-compression gas 10 per cent., and on supercharged gas 11 per cent. Comparative b.m.e.p. of the old-type gas engine with the new National and the Erren are 80, 100 and 120, respectively.
As to the use of compressed gas fuel for ordinary petrol engines, however, there is the one great difficulty that vehicles must be supplied from roadside filling stations, and the compressed gas must be stored in cylinders delivered from the gas depot, but once development has really begun, this problem should not be unsolvable. It is believed, however, that in urban areas the stage will be reached when the filling station, taking its supply direct from the main, will feed the gas-equipped vehicle by flexible tubes, in the same way as, to-day, tyres are inflated by compressed air. The progress attained so far is a result of experiments covering many years, but it appears likely that they may, at last, be crowned with success.