Colloidal fuel is an emulsion of powdered coal in kerosene or fuel oil.
It was used in World War I aboard ships as kerosene supplies ran low.
[1] Development continued after the war, and in 1932 the Cunard liner Scythia made a round-trip transatlantic voyage partly powered by colloidal fuel containing 40% coal.
Advantages over oil included cost and energy density.
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