The engine may be worked by multiple expansion by admitting to the high-pressure cylinder a portion only of the fuel necessary to consume the oxygen of the air charge, and the remainder to the low-pressure cylinder.
The fuel may be heated by the exhaust to a temperature below the igniting temperature, and the quantity admitted is determined by the load.
Illuminating gas or producer gas may be used, and liquid of pulverised fuels; steam, Oxygen, or inert gases may be mixed with the charge.