Crankcase dilution is a phenomenon of

internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combus ...

s in which unburned

diesel Diesel may refer to: * Diesel engine, an internal combustion engine where ignition is caused by compression * Diesel fuel, a liquid fuel used in diesel engines * Diesel locomotive, a railway locomotive in which the prime mover is a diesel engin ...

gasoline Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic co ...

accumulates in the

crankcase In a piston engine, the crankcase is the housing that surrounds the crankshaft. In most modern engines, the crankcase is integrated into the engine block. Two-stroke engines typically use a crankcase-compression design, resulting in the fuel/a ...

. Excessively rich fuel mixture or

incomplete combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combusti ...

allows a certain amount of fuel to pass down between the

piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tig ...

s and cylinder walls and dilute the engine oil. It is more common in situations where fuel is injected at a very high pressure, such as in a direct-injected

diesel engine The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is a so-call ...

. When a mixture of air and fuel enters the cylinder of an engine, it is entirely possible for

condensation Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor to ...

of fuel to occur on the cooler parts of the cylinders. The condensate may wash the

lubricating oil A lubricant (sometimes shortened to lube) is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, t ...

from the cylinder walls, travel past the piston rings and collect in the oil pan, thus increasing wear and also diluting the lubricating oil. Since the less volatile components of the fuel will have the greatest tendency to condense, the degree of crankcase-oil dilution is directly related to the end volatility temperatures of the mixture.

Causes

Crankcase dilution occurs when the fuel oil from the engine gets into the

lube oil A lubricant (sometimes shortened to lube) is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, t ...

of the engine. This can be caused by the walls being wetted due to the fuel condensing in the cylinder. If the engine is cold, or there is an excess amount of cooling around the cylinder, the fuel oil will condense and have a higher chance to end up in the crankcase. Another way that the fuel oil can end up in the crankcase is because there is too much wear on the

compression rings. The job of the piston compression ring is to keep the oil and the exhaust gases from entering the

, but when there is too much wear it can no longer do its job. Other than the piston rings, “blow-by” gases can push the fuel oil past the rings and into the crankcase. “Blow-by” gases are a mix of fuel oil and exhaust gases that push past the piston rings. Crankcase dilution is caused more when the lube oil is fresher. Another cause of crankcase dilution is a slow or

delayed injection cycle Delay (from Latin: dilatio) may refer to: Arts, entertainment, and media * ''Delay 1968'', a 1981 album by German experimental rock band Can * '' The Delay'', a 2012 Uruguayan film People * B. H. DeLay (1891–1923), American aviator and ac ...

. This causes the timing to be thrown off and the oil is most likely to enter the crankcase at this point. Water and dirt can also further the effects of crankcase dilution. Also, soot getting into the lube oil can cause crankcase dilution, but there are additives that can keep the soot at the top of the lube oil. Soot that collects in the crankcase fully goes away when the lube oil is changed out of the engine. Additives can be added to the oil to cause the soot to stay on top of the engine lube oil. These substances getting into the lube oil can accelerate the effects of crankcase dilution. 47mm_piston_rings

Effects

Fuel oil in the crankcase lube oil can cause the oil to chemically degrade. This means that the oil loses

viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...

and is less effective when lubricating. The loss of viscosity of the lube oil causes the oil to not fully connect and lubricate the moving parts of the engine. This lack of lubrication can cause the engine to have an increased amount of

wear Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion) or chemical (e.g., corrosion). The study of wear and related processes is referred to as tribology. Wear in m ...

over time.

Reducing Crankcase dilution

There are many ways to reduce the amount of crankcase dilution that occurs in an engine. One of the ways is to counteract the loss of viscosity by using a heavier oil. The viscosity that they recommended was 500-575 sec. Another thing that can reduce the effects of crankcase dilution is changing the piston

compression ring A compression fitting is a fitting used in plumbing and electrical conduit systems to join two tubes or thin-walled pipes together. In instances where two pipes made of dissimilar materials are to be joined (most commonly PVC and copper), the ...

s when they become worn. This would reduce the amount of blow-by gases and overall reducing the effects. Another thing that can be done is to change the car's oil regularly to avoid the wear on your engine from crankcase dilution.

Detecting Crankcase dilution

Detecting crankcase dilution can help reduce the effects that it will have on your engine. There are many ways to detect crankcase dilution. One of the ways is to check the

flash point The flash point of a material is the "lowest liquid temperature at which, under certain standardized conditions, a liquid gives off vapours in a quantity such as to be capable of forming an ignitable vapour/air mixture". (EN 60079-10-1) The fl ...

of the oil and compare it to the brand of lube oil. The way to test the flash point of the oil is to manually take a sample and use a testing kit. When the fuel leaks into the lube oil the

chemical makeup A chemical composition specifies the identity, arrangement, and ratio of the elements making up a compound. Chemical formulas can be used to describe the relative amounts of elements present in a compound. For example, the chemical formula for ...

is different than the normal lube oil. Another way to test for crankcase dilution is to use a SAW to test the concentration of fuel oil in the crankcase oil. SAW stands for surface acoustic wave.

Biodiesel and crankcase dilution

Biodiesel Biodiesel is a form of diesel fuel derived from plants or animals and consisting of long-chain fatty acid esters. It is typically made by chemically reacting lipids such as animal fat (tallow), soybean oil, or some other vegetable oil with ...

is vegetable oil or animal fats that are mixed with lipids to produce alcohol that can be burned. The alcohol that is produced is the biodiesel. Engines that run on biodiesel have the same problem as regular fuel engines. The biodiesel fuel finds its way into the crankcase of the engine and mixes with the lube oil. When biodiesel leaks into the crankcase, it has more problems than with more traditional fuel. The biodiesel has a higher

boiling point The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding envir ...

than regular fuel and is less likely to

evaporate Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when humidi ...

out causing it to stay in the crankcase for a longer period of time. Also, the longer that the biodiesel stays inside of the crankcase, it degrades the

organic acid An organic acid is an organic compound with acidic properties. The most common organic acids are the carboxylic acids, whose acidity is associated with their carboxyl group –COOH. Sulfonic acids, containing the group –SO2OH, are rel ...

s in the lube oil and then reacts with the crankcase wall. After reacting, it causes deposits of the reacted biodiesel in the walls of the crankcase . There are ways that these effects can be reduced. Chevron created additives to reduce the effects of the biodiesel.

References