Still engine

The Still engine was a piston engine that simultaneously used both steam power from an external boiler, and internal combustion from gasoline or diesel, in the same unit. The waste heat from the cylinder and internal combustion exhaust was directed to the steam boiler, resulting in claimed fuel savings of up to 10%. The inventor, William Joseph Still was not the first in this field. A similar, but not identical, system was patented in 1903 by Paul Lucas-Girardville and Louis Mékarski.

The inventor, William Joseph Still, patented his device in 1917 and on 26 May 1919 in London he announced it at a meeting, chaired by steam turbine inventor Charles Algernon Parsons, at the Royal Society of Arts. Still described a continuous process by which a double-acting cylinder is powered on one side by internal combustion and on the other by steam from a boiler heated principally by the waste heat from the water jacket and exhaust gases. He explained how the reserve of energy represented by the steam pressure in the boiler provided for any occasional overload which would defeat a standard internal combustion engine of the same power. Independent heating of the boiler was occasionally used, to provide extra power for exceptional conditions, and in the first stage of operation to allow the engine to start itself from steam power alone, even against a load.

In 1924 Scotts Shipbuilding and Engineering Company of Greenock, Scotland, put a diesel-fuelled marine version, the Scott-Still regenerative engine, into production, with the first pair of engines installed in the twin-screw M. V. Dolius. The requirement to carry marine engineering officers certified with both steam and motor qualifications, meaning extra crew members and wages, and the extra complexity with consequent higher maintenance costs, offset the fuel savings and conventional diesel engines were later installed in their place.

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