Exhaust gas
The Stuart engine is of four cycle design. During the intake stroke (1), fresh air is inducted into the cylinder through a mechanically operated intake valve. Simultaneously, oil is injected into the vapouriser. The vapour of the oil is almost entirely confined to the vapouriser chamber. This cloud of hot oil vapour is too rich to support combustion. On the compression stroke (2) of the piston, the fresh air is forced through the narrow neck and into the vapouriser. Just as compression is completed, the mixture is just right to support combustion and ignition occurs to push the piston during expansion stroke (3). Exhaust gas is released then during stroke (4).