All About Engines

248 All About Engines from 12 to 20 knots, or perhaps even more than this, for over the details of the latest types is drawn the impenetrable veil of official secrecy. The first practicable submarine vessel became possible towards the close of last century by the invention of the petrol motor. But petrol, producing a highly inflammable vapour, was an extremely danger- ous substance to be kept in such a limited space, and there was more than one terrible explosion, accom- panied by loss of life. Steam engines with special soda boilers were tried in France, but without much success; and though it is possible that some sub- marines to-day are fitted with steam engines and oil-fired boilers, the majority are equipped with twelve-cylinder Diesel engines for surface cruising and electric power for propulsion when submerged. For some purpose or another, then, the Diesel engine has come to stay. It will be used to a greatly increasing extent in those parts of the world where petroleum is found, and where the heavy oils re- maining after distillation are plentiful and cheap. But the extent to which it is used in districts remote from the oilfields depends upon the way in which we and other countries dependent upon coal decide to use that fuel. If we decide to burn less of it in ordinary boiler grates and open fireplaces, and to make and consume more gas, then in the tar oils produced by gas manufacture we shall find an ex- cellent fuel for Diesel engines, which may become almost as familiar as the ubiquitous gas engine is to-day.