Crankcase dilution

Last updated

Crankcase dilution is a phenomenon of internal combustion engines in which unburned diesel or gasoline accumulates in the crankcase. Excessively rich fuel mixture or incomplete combustion allows a certain amount of fuel to pass down between the pistons 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.

Contents

When a mixture of air and fuel enters the cylinder of an engine, it is entirely possible for condensation of fuel to occur on the cooler parts of the cylinders. The condensate may wash the lubricating oil 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 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, [1] the fuel oil will condense and have a higher chance to end up in the crankcase. [2] Another way that the fuel oil can end up in the crankcase is because there is too much wear on the piston compression rings. [1] The job of the piston compression ring is to keep the oil and the exhaust gases from entering the crankcase, 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. [1] “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. [3] Another cause of crankcase dilution is a slow or delayed injection cycle. [2] 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. [1] 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. [4] These substances getting into the lube oil can accelerate the effects of crankcase dilution.

Piston compression ring wear. 47mm piston rings.jpg
Piston compression ring wear.

Effects

Fuel oil in the crankcase lube oil can cause the oil to chemically degrade. This means that the oil loses viscosity and is less effective when lubricating. [5] 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 over time. [5]

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. [1] The viscosity that they recommended was 500-575 sec. Another thing that can reduce the effects of crankcase dilution is changing the piston compression rings 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 of the oil and compare it to the brand of lube oil. [5] 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 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. [5] SAW stands for surface acoustic wave.

Biodiesel and crankcase dilution

Biodiesel 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 than regular fuel and is less likely to evaporate out causing it to stay in the crankcase for a longer period of time. [6] Also, the longer that the biodiesel stays inside of the crankcase, it degrades the organic acids 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 . [7] There are ways that these effects can be reduced. Chevron created additives to reduce the effects of the biodiesel. [7]

See also

Related Research Articles

A lubricant 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, transporting foreign particles, or heating or cooling the surfaces. The property of reducing friction is known as lubricity.

Piston Moving component of reciprocating engines that is contained by a cylinder and is made gas-tight by piston rings

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-tight by piston rings. In an engine, its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod. In a pump, the function is reversed and force is transferred from the crankshaft to the piston for the purpose of compressing or ejecting the fluid in the cylinder. In some engines, the piston also acts as a valve by covering and uncovering ports in the cylinder.

Two-stroke engine Internal combustion engine type

A two-strokeengine is a type of internal combustion engine that completes a power cycle with two strokes of the piston during one power cycle, this power cycle being completed in one revolution of the crankshaft. A four-stroke engine requires four strokes of the piston to complete a power cycle during two crankshaft revolutions. In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with the intake and exhaust functions occurring at the same time.

Exhaust gas recirculation NOx reduction technique used in gasoline and diesel engines

In internal combustion engines, exhaust gas recirculation (EGR) is a nitrogen oxide (NOx) emissions reduction technique used in petrol/gasoline, diesel engines and some hydrogen engines. EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. This dilutes the O2 in the incoming air stream and provides gases inert to combustion to act as absorbents of combustion heat to reduce peak in-cylinder temperatures. NOx is produced in high temperature mixtures of atmospheric nitrogen and oxygen that occur in the combustion cylinder, and this usually occurs at cylinder peak pressure. Another primary benefit of external EGR valves on a spark ignition engine is an increase in efficiency, as charge dilution allows a larger throttle position and reduces associated pumping losses. Mazda's turbocharged SkyActiv engine uses recirculated and cooled exhaust gases to reduce combustion chamber temperatures, thereby permitting the engine to run at higher boost levels before the air-fuel mixture must be enriched to prevent engine knocking.

Four-stroke engine Internal combustion engine type

A four-strokeengine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed:

  1. Intake: Also known as induction or suction. This stroke of the piston begins at top dead center (T.D.C.) and ends at bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position while the piston pulls an air-fuel mixture into the cylinder by producing vacuum pressure into the cylinder through its downward motion. The piston is moving down as air is being sucked in by the downward motion against the piston.
  2. Compression: This stroke begins at B.D.C, or just at the end of the suction stroke, and ends at T.D.C. In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke (below). Both the intake and exhaust valves are closed during this stage.
  3. Combustion: Also known as power or ignition. This is the start of the second revolution of the four stroke cycle. At this point the crankshaft has completed a full 360 degree revolution. While the piston is at T.D.C. the compressed air-fuel mixture is ignited by a spark plug or by heat generated by high compression, forcefully returning the piston to B.D.C. This stroke produces mechanical work from the engine to turn the crankshaft.
  4. Exhaust: Also known as outlet. During the exhaust stroke, the piston, once again, returns from B.D.C. to T.D.C. while the exhaust valve is open. This action expels the spent air-fuel mixture through the exhaust valve.
Motor oil Lubricant used for lubrication of internal combustion engines

Motor oil, engine oil, or engine lubricant is any one of various substances used for the lubrication of internal combustion engines. They typically consist of base oils enhanced with various additives, particularly antiwear additives, detergents, dispersants, and, for multi-grade oils, viscosity index improvers.. The main function of motor oil is to reduce friction and wear on moving parts and to clean the engine from sludge and varnish (detergents). It also neutralizes acids that originate from fuel and from oxidation of the lubricant (detergents), improves sealing of piston rings, and cools the engine by carrying heat away from moving parts.

Knocking in spark ignition internal combustion engines occurs when combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignited by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel-air charge is meant to be ignited by the spark plug only, and at a precise point in the piston's stroke. Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive.

Synthetic oil Lubricant consisting of artificially made chemical compounds

Synthetic oil is a lubricant consisting of chemical compounds that are artificially made. Synthetic lubricants can be manufactured using chemically modified petroleum components rather than whole crude oil, but can also be synthesized from other raw materials. The base material, however, is still overwhelmingly crude oil that is distilled and then modified physically and chemically. The actual synthesis process and composition of additives is generally a commercial trade secret and will vary among producers.

Internal combustion engine cooling uses either air or liquid to remove the waste heat from an internal combustion engine. For small or special purpose engines, cooling using air from the atmosphere makes for a lightweight and relatively simple system. Watercraft can use water directly from the surrounding environment to cool their engines. For water-cooled engines on aircraft and surface vehicles, waste heat is transferred from a closed loop of water pumped through the engine to the surrounding atmosphere by a radiator.

Homogeneous Charge Compression Ignition (HCCI) is a form of internal combustion in which well-mixed fuel and oxidizer are compressed to the point of auto-ignition. As in other forms of combustion, this exothermic reaction releases energy that can be transformed in an engine into work and heat.

Crankcase

A crankcase is the housing for the crankshaft in a reciprocating internal combustion engine. In most modern engines, the crankcase is integrated into the engine block.

Piston ring Part of a reciprocating engine

A piston ring is a metallic split ring that is attached to the outer diameter of a piston in an internal combustion engine or steam engine.

Wet stacking is a condition in diesel engines in which unburned fuel passes on into the exhaust system. The word "stacking" comes from the term "stack" for exhaust pipe or chimney stack. The oily exhaust pipe is therefore a "wet stack".

Lubricity is the measure of the reduction in friction and or wear by a lubricant. The study of lubrication and wear mechanisms is called tribology.

Oil additives are chemical compounds that improve the lubricant performance of base oil. The manufacturer of many different oils can utilize the same base stock for each formulation and can choose different additives for each specific application. Additives comprise up to 5% by weight of some oils.

Emulsified Fuels are emulsions composed of water and a combustible liquid, either oil or a fuel. Emulsions are a particular example of a dispersion comprising a continuous and a dispersed phase. The most commonly used emulsion fuel is water-in-diesel emulsion. In the case of emulsions, both phases are the immiscible liquids, oil and water. Emulsion fuels can be either a microemulsion or an ordinary emulsion. The essential differences between the two are stability and particle size distribution. Microemulsions are isotropic whereas macroemulsions are prone to settling and changes in particle size over time. Both use surfactants and can be either water-in-oil, or oil-in-water or bicontinuous.

The Cummins X-series engine is an Inline (Straight)-6 diesel engine produced by Cummins for heavy duty trucks and motorcoaches, replacing the N14 in 2001 when emissions regulations passed by the EPA made the engine obsolete. Originally called the "Signature" series engine, the ISX uses the "Interact System" to further improve the engine. This engine is widely used in on highway and vocational trucks and is available in power ranging from 430 hp all the way to 620 hp 2050 lb-ft. The QSX is the off-highway version of the ISX with the Q standing for Quantum. The QSX is used for industrial, marine, oil & gas and other off-highway applications. Cummins also produced a 650 hp and 1950 lb-ft version for the RV market.

Internal combustion engine Engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber

An internal combustion engine is a heat engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is applied typically to pistons, turbine blades, a rotor, or a nozzle. This force moves the component over a distance, transforming chemical energy into useful kinetic energy and is used to propel, move or power whatever the engine is attached to. This replaced the external combustion engine for applications where weight or size of the engine is important.

Low-speed pre-ignition (LSPI), also known as stochastic pre-ignition (SPI), is a pre-ignition event that occurs in gasoline vehicle engines when there is a premature ignition of the main fuel charge. LSPI is most common in certain turbocharged direct-injection vehicles operating in low-speed and high-load driving conditions.

An oil catch tank or oil catch can is a device that is fitted into the cam/crankcase ventilation system on a car. Installing an oil catch tank (can) aims to reduce the amount of oil vapors re-circulated into the intake of the engine.

References

  1. 1 2 3 4 5 Wilson, Robert E.; Wilkin, Robert E. (January 1926). "A Suggested Remedy for Crankcase-Oil Dilution". SAE Technical Paper Series. Vol. 1. Warrendale, PA. doi:10.4271/260006.
  2. 1 2 Hu, Tingjun; Teng, Ho; Luo, Xuwei; Lu, Chun; Luo, Jiankun (2015-09-29). "Influence of Fuel Dilution of Crankcase Oil on Ignitability of Oil Particles in a Highly Boosted Gasoline Direct Injection Engine". SAE Technical Paper Series. Vol. 1. doi:10.4271/2015-01-2811.
  3. ↑ Nanjundaswamy, Harsha; Tatur, Marek; Tomazic, Dean; Koerfer, Thomas; Lamping, Matthias; Kolbeck, Andreas (2009-04-20). "Fuel Property Effects on Emissions and Performance of a Light-Duty Diesel Engine". SAE Technical Paper Series. Warrendale, PA: SAE International. 1. doi:10.4271/2009-01-0488.
  4. ↑ "The Effect of Evaporative Cooling in Saddle Fuel Tanks on Diesel Engine Operation", Diesel Fuel Oil, ASTM International, 1967, pp. 25–25–17, doi:10.1520/stp46056s, ISBN   9780803166325
  5. 1 2 3 4 Walsh, D. and Price, R. "Fuel dilution in engine crankcases: a fast field method for the workshop". spectrosci.com/product/q6000/?fileID=8a8081894ccb3b72014d104badbb2999.{{cite web}}: CS1 maint: multiple names: authors list (link)
  6. ↑ He X., Williams A.M., Christensen E.D., Burton J.L. and McCormick R.L. (2011). "Biodiesel impact on the engine lubrication oil dilution" (PDF). energy.gov/sites/prod/files/2014/03/f8/p-11_he.pdf.{{cite web}}: CS1 maint: multiple names: authors list (link)
  7. 1 2 Durbin T.D., Miller J.W. and Jiang S.M. (2010). (PDF) https://www.arb.ca.gov/fuels/diesel/altdiesel/biodieseldurabilityreport2010_08_11.pdf.{{cite web}}: Missing or empty |title= (help)
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.