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That pressure developed in a reciprocating piston engine at the end of the compression stroke without combustion of fuel.

Related Terms


The ratio of the absolute pressure at the discharge from a compressor divided by the absolute pressure at the suction. For internal combustion engines compression ration is absolute pressure at the end of compression stroke divided by absolute pressure at beginning of this stroke


An internal combustion engine cycle in which the heat of compression ignites the fuel.


The blades of a turbine in the outlet exhaust flow of an engine are driven by the gases flowing over them. Compressor blades at the other end of the same axle are spun in the inlet flow, drawing large volumes of air into the cylinders. This enables faster combustion than naturally aspirated engines and increases power of the engine.


The phase of a positive displacement engine or compressor in which the motion of the piston compresses the fluid trapped in the cylinder.


The top of the piston in an internal combustion engine above the fire ring, exposed to direct flame impingement.


An instrument which makes a plot of pressure in the cylinder of an engine as a function of piston (or volume) displacement, making use of magnification by optical systems and photographic recording; for example, the small motion of a pressure diaphragm may be transmitted to a mirror to deflect a beam of light.


Circular metallic elements that ride in the grooves of a piston and provide compression sealing during combustion.
Piston Rings are made of alloying cast iron with chromium, molybdenum, vanadium, titanium, nickel and copper. They are harder than the cylinder liner in which they run to give them a maximum life. Piston rings seal the gas space by expanding outwards due to the gas pressure acting behind them. They also spread the lubricating oil up and down the cylinder liner and transfer heat to the liner walls.
When overhauling the piston, it is important to check the ring grooves for wear and the piston ring condition. The axial and butt clearances should be measured and recorded.
The function of the piston ring is to give a gas-tight sealing of the clearance between the piston and cylinder liner. This seal is brought about by the gas pressure above and behind the piston ring, which forces it downwards, against the bottom of the ring groove, and outwards against the cylinder wall. In-order to ensure optimum sealing, it is therefore important that the piston rings, the grooves, and the cylinder walls, are of proper shape, and that the rings can move freely in the grooves (since the piston will also make small horizontal movements during the stroke). The lubrication of the piston rings influences the sealing as well as the wear and deposits.
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A combined internal combustion engine and pump in which the metal piston has been replaced by a column of water.


An internal combustion engine cycle completed in four piston strokes; includes a suction stroke, compression stroke, expansion stroke, and exhaust stroke.


Ignition produced by compression of the air in a cylinder of an internal combustion engine before fuel is admitted.

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