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Passage of unburned fuel and combustion gases past the piston rings of internal combustion engines, resulting in fuel dilution and contamination of the crankcase oil.

Related Terms


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


A pump mechanism that sprays fuel into the cylinder of an internal combustion engine at the appropriate part of the cycle.


Nitration products are formed during the fuel combustion process in internal combustion engines. Most nitration products are formed when an excess of oxygen is present. These products are highly acidic, form deposits in combustion areas and rapidly accelerate oxidation.


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


A prime mover in which the fuel is burned within the engine and the products of combustion serve as the thermodynamic fluid, as with gasoline and diesel engines.


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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Ignition of a charge of fuel vapor and air in an internal combustion engine by passing a high-voltage electric electron flow.


A combined internal combustion engine and pump in which the metal piston has been replaced by a column of water.


System for removing blow-by gases from the crankcase and returning them through the intake manifold to the combustion chamber where the recirculated hydrocarbons are burned. A PCV valve controls the flow of gases from the crankcase to reduce hydrocarbon emissions.


A diaphragm which surrounds the piston rod of a crosshead-type engine and separates the crankcase from the lower portion of the cylinder.

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