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the cylinder (known as Bottom Dead Centre or BDC) the exhaust valve starts to open. As the piston now moves up the cylinder, the hot gases (consisting mostly of nitrogen, carbon dioxide, water vapour and unused oxygen) are expelled from the cylinder. As the Piston approaches TDC again the inlet valve starts to open and the cycle repeats itself.
1 Plume (hydrodynamics) , the form of effluent in water or emissions in air. 2  Eruption column, or volcanic plume, a column of volcanic ash and gas emitted into the atmosphere during an eruption. 3  Mantle plume, an upwelling of hot rock within the Earth's mantle that can cause volcanic hotspots.