Παρασκευή 10 Αυγούστου 2012
Sulfated Ash and DI Engines
Τρίτη 11 Αυγούστου 2009
oil test 2004
Engine Oil Testing
Chemical and physical analysis on commercial lubricants.
Oxidation tests
The combined effects of ambient oxygen and temperature affect lubricant aging; this phenomenon is known as oxidation. In laboratory oxidation tests, temperatures are selected in accordance with those encountered during equipment operation.
Corrosion tests
One of a lubricant's main functions is protection against corrosion. Accordingly, the reactions between the lubricant and various metal surfaces need to be determined and, where appropriate, modified.
Chemical compatibility tests
These tests are used to determine the behavior of various materials when in contact with oil. For example, specific tests are conducted to ensure the compatibility of a lubricant with seals.
Storage stability tests
Some lubricant combinations are formed by the association of products that are not fully miscible in oil. In this case, final stability representative of changes during storage needs to be checked.
Dispersion tests
The purpose of these tests is to determine the ability of an oil to maintain in suspension solids likely to pollute it during operation. For example, combustion engines produce carbon residues (soot), some of which are found in the oil. The latter must be able to maintain the soot in suspension and prevent deposits that could result in fouling or even clogging.
Shear tests
These tests determine how well lubricants withstand mechanical loads that can cause the molecules of some components to break up.
Pressure tests
There is no device available that can directly measure the ability of an oil film to withstand pressure. In the laboratory, the various properties (unctuosity, film strength, high pressure, extreme pressure) can only be assessed by their effects, using test benches that vary, one after the other, the factors that could influence them. The same types of test are carried out for greases as for oils, using special devices: four-ball machine, Timken, etc.
Bench tests
Laboratory tests are supplemented by bench tests on machines very similar to real ones and which operate under controlled conditions.
Engine tests
Engine tests are designed to determine the behaviour of oils on either gasoline or diesel engines. Each test is performed in such a way as to highlight one or more lubricant properties. No engine test enables all properties to be tested at the same time.
Bench tests are carried out either on standard automotive multi-cylinder engines or on single-cylinder engines.
Gear tests
These tests check, on real gears, the internal cohesion and pressure withstanding properties of lubricants. Various methods are used depending on the type of gear and test conditions.
Power
To test and determine the efficiency of the oil in being able to provide both, peak and smoothness of power delivery. Ability proven on engine dyno.
Reduction in friction
To show the absolute lubricating properties of the oil and the correlation in power production.
Anti-wear ability
Laboratory testing to highlight the mass and size of metal particles with in the sample of oil after 100 hours of testing.
Testing in operation
Lubricants cannot be developed without laboratory and bench tests. But these tests are specialized and, however carefully done, cannot be considered to be fully comprehensive: only operating tests can provide the final word on whether a lubricant is suitable for a given application.
Operating tests have two advantages :
they allow manufacturers to keep up with changes in the lubrication needs of various types of machinery and in the strength of the lubricants developed for them ;
they provide valuable information for adjusting bench testing methods used in the preliminary stages of development.
Operating tests are usually long and expensive, since they have to be carried out statistically on a variety of machines of the same category. Sometimes individual tests have to be repeated in order to allow for mechanical component failure, which often occurs.
The test findings are based on :
observations made throughout the duration of tests by specialized engineers,
routine analyses of lubricants sampled during operation,
examination of mechanical components once the test has been completed.
I strongly advise that you read the results that were found very, very, very carefully. Look at the properties that are important for the application that you are using it for. For example, just because a certain oil didn’t rank well overall, does not mean that it is not the best for a certain use. In the competition section, castrol ranked the poorest overall, but how it stores and how long it lasts are not issues for a racing driver, and infact would rate as being one of the best as a purpose race oil. So take notice of the aspects that reflect the use of a certain products. It would be stupid to look at a product as number 1 or 2 and say “yep that’s what I’ll get next”…..cost is also a big factor and value for money might be a deciding factor.
Group Number (1): Fully synthetic, light grade 4-stroke engine oils
Agip evolution 0W40
Agip evolution 5W40
Castrol formula r 0W40
Castrol formula r 5W30
Elf Excellium 0W40
Elf Excellium 5W40
Mobil 1 0W40
Mobil 1 5W50
Motul e-tech 8100 0W40
Motul e-tech 8100 0W30
Redline 5W30
Oxidation
8
6
8
5
9
8
9
9
8
7
6
Corrosion
8
8
9
8
10
9
10
7
7
7
8
Chemical Compatibility
8
9
9
9
9
9
9
8
8
9
9
Storage
9
9
8
6
7
7
8
10
8
8
8
Dispersion
9
8
9
7
10
9
10
7
10
9
9
Shear Tests
8
7
7
7
9
9
8
6
7
8
7
Pressure resistance
7
8
7
6
8
8
7
9
9
8
Power conversion
8
9
8
9
9
9
9
7
8
9
8
Reduction in friction co-efficient
8
8
8
9
9
9
9
8
8
8
9
Anti-wear
8
8
8
7
10
10
10
7
8
7
8
Rankings:
1. Elf Excellium 0W40
2. Mobil 1 0W40
3. Elf Excellium LDX 5W40
4. Agip evolution 0W40 / Castrol Formula r 0W40
6. Motul E-tech 8100 0W40
7. Agip evolution 5W40 / Redline 5W30
9. Mobil 1 5W50
10. Castrol Formula r 0W30
11. Motul E-tech 8100 0W30
Group Number (2): Fully synthetic, medium grade 4-stroke engine oils
Agip sint 2000 10W40
Castrol formula r 10W60
Elf Excellium 10W50
Mobil 1 5W50
Motul 6100 10W40
Penzoil GT 15W40
Redline 10W40
Shell Helix Ultra 5W40
Oxidation
8
8
9
9
9
6
7
8
Corrosion
9
8
9
7
7
6
8
8
Chemical Compatibility
8
7
8
8
8
9
8
9
Storage
7
6
7
10
6
8
7
9
Dispersion
9
8
9
7
9
7
8
7
Shear Tests
8
7
8
6
8
5
7
8
Pressure resistance
8
10
10
9
7
8
8
8
Power conversion
9
8
9
7
9
6
9
8
Reduction in friction co-efficient
9
8
9
8
8
7
8
8
Anti-wear
10
7
9
7
9
6
9
8
Rankings:
1. Elf Excellium 10W50
2. Agip Sint 2000 10W40
3. Shell Helix Ultra 5W40
4. Motul 6100 10W40
5. Redline 10W40
6. Mobil 1 5W50
7. Castrol Formula R 10W60
8. Penzoil GT 15W40
Group Number (3): Fully synthetic, full competition purpose 4-stroke engine oils
Agip GPX N1 10W40
Castrol formula SLX 0W30
Elf HTX833 10W50
Mobil 1 0W40
Motul 300V 10W40
Redline Raceoil 5W40
Royal Purple 5W30
Oxidation
7
6
8
9
7
7
7
Corrosion
8
8
9
10
8
8
8
Chemical Compatibility
9
6
7
9
7
7
8
Storage
6
5
7
8
7
6
7
Dispersion
10
10
10
10
10
10
10
Shear Tests
10
9
10
8
10
9
9
Pressure resistance
9
7
10
7
8
8
7
Power conversion
10
10
10
9
10
9
9
Reduction in friction co-efficient
10
10
10
9
10
9
10
Anti-wear
10
10
10
10
10
10
9
Rankings:
1. Elf HTX833 10W50
2. Mobil 1 0W40
3. Agip SZ N1 10W40
4. Motul 300V 10W40
5. Royal Purple 5W30
6. Redline Raceoil 5W40
7. Castrol Formula SLX
Group Number (4): Fully synthetic, gearbox and differential oils
Agip Rotara LSX 75W90
Castrol Syntrax 75W90
Elf HTX729 75W90
Mobil SHC 75W90
Mobil XHP 75W90
Motul Gear300 75W90
Redline NS 75W90
Shell SGO 75W90
Oxidation
8
9
9
8
6
9
9
7
Corrosion
9
9
9
9
10
9
8
8
Chemical Compatibility
8
9
9
8
10
9
10
8
Storage
10
10
10
10
10
10
10
10
Dispersion
10
9
10
9
9
10
10
9
Shear Tests
10
9
10
10
7
10
8
8
Pressure resistance
10
9
9
9
6
10
8
8
Power conversion
8
9
10
8
8
10
9
7
Reduction in friction co-efficient
9
10
10
9
9
10
9
8
Anti-wear
9
10
9
9
7
10
9
9
Rankings:
1. Motul Gear300 75W90
2. Elf HTX729
3. Castrol Syntrax 75W90
4. Agip Rotara LSX 75W90
5. Mobil SHC 75W90 / Redline NS 75W90
6 Redline NS 75W90
7. Mobil XHP 75W90 / Shell SGO 75W90 "
Chemical and physical analysis on commercial lubricants.
Oxidation tests
The combined effects of ambient oxygen and temperature affect lubricant aging; this phenomenon is known as oxidation. In laboratory oxidation tests, temperatures are selected in accordance with those encountered during equipment operation.
Corrosion tests
One of a lubricant's main functions is protection against corrosion. Accordingly, the reactions between the lubricant and various metal surfaces need to be determined and, where appropriate, modified.
Chemical compatibility tests
These tests are used to determine the behavior of various materials when in contact with oil. For example, specific tests are conducted to ensure the compatibility of a lubricant with seals.
Storage stability tests
Some lubricant combinations are formed by the association of products that are not fully miscible in oil. In this case, final stability representative of changes during storage needs to be checked.
Dispersion tests
The purpose of these tests is to determine the ability of an oil to maintain in suspension solids likely to pollute it during operation. For example, combustion engines produce carbon residues (soot), some of which are found in the oil. The latter must be able to maintain the soot in suspension and prevent deposits that could result in fouling or even clogging.
Shear tests
These tests determine how well lubricants withstand mechanical loads that can cause the molecules of some components to break up.
Pressure tests
There is no device available that can directly measure the ability of an oil film to withstand pressure. In the laboratory, the various properties (unctuosity, film strength, high pressure, extreme pressure) can only be assessed by their effects, using test benches that vary, one after the other, the factors that could influence them. The same types of test are carried out for greases as for oils, using special devices: four-ball machine, Timken, etc.
Bench tests
Laboratory tests are supplemented by bench tests on machines very similar to real ones and which operate under controlled conditions.
Engine tests
Engine tests are designed to determine the behaviour of oils on either gasoline or diesel engines. Each test is performed in such a way as to highlight one or more lubricant properties. No engine test enables all properties to be tested at the same time.
Bench tests are carried out either on standard automotive multi-cylinder engines or on single-cylinder engines.
Gear tests
These tests check, on real gears, the internal cohesion and pressure withstanding properties of lubricants. Various methods are used depending on the type of gear and test conditions.
Power
To test and determine the efficiency of the oil in being able to provide both, peak and smoothness of power delivery. Ability proven on engine dyno.
Reduction in friction
To show the absolute lubricating properties of the oil and the correlation in power production.
Anti-wear ability
Laboratory testing to highlight the mass and size of metal particles with in the sample of oil after 100 hours of testing.
Testing in operation
Lubricants cannot be developed without laboratory and bench tests. But these tests are specialized and, however carefully done, cannot be considered to be fully comprehensive: only operating tests can provide the final word on whether a lubricant is suitable for a given application.
Operating tests have two advantages :
they allow manufacturers to keep up with changes in the lubrication needs of various types of machinery and in the strength of the lubricants developed for them ;
they provide valuable information for adjusting bench testing methods used in the preliminary stages of development.
Operating tests are usually long and expensive, since they have to be carried out statistically on a variety of machines of the same category. Sometimes individual tests have to be repeated in order to allow for mechanical component failure, which often occurs.
The test findings are based on :
observations made throughout the duration of tests by specialized engineers,
routine analyses of lubricants sampled during operation,
examination of mechanical components once the test has been completed.
I strongly advise that you read the results that were found very, very, very carefully. Look at the properties that are important for the application that you are using it for. For example, just because a certain oil didn’t rank well overall, does not mean that it is not the best for a certain use. In the competition section, castrol ranked the poorest overall, but how it stores and how long it lasts are not issues for a racing driver, and infact would rate as being one of the best as a purpose race oil. So take notice of the aspects that reflect the use of a certain products. It would be stupid to look at a product as number 1 or 2 and say “yep that’s what I’ll get next”…..cost is also a big factor and value for money might be a deciding factor.
Group Number (1): Fully synthetic, light grade 4-stroke engine oils
Agip evolution 0W40
Agip evolution 5W40
Castrol formula r 0W40
Castrol formula r 5W30
Elf Excellium 0W40
Elf Excellium 5W40
Mobil 1 0W40
Mobil 1 5W50
Motul e-tech 8100 0W40
Motul e-tech 8100 0W30
Redline 5W30
Oxidation
8
6
8
5
9
8
9
9
8
7
6
Corrosion
8
8
9
8
10
9
10
7
7
7
8
Chemical Compatibility
8
9
9
9
9
9
9
8
8
9
9
Storage
9
9
8
6
7
7
8
10
8
8
8
Dispersion
9
8
9
7
10
9
10
7
10
9
9
Shear Tests
8
7
7
7
9
9
8
6
7
8
7
Pressure resistance
7
8
7
6
8
8
7
9
9
8
Power conversion
8
9
8
9
9
9
9
7
8
9
8
Reduction in friction co-efficient
8
8
8
9
9
9
9
8
8
8
9
Anti-wear
8
8
8
7
10
10
10
7
8
7
8
Rankings:
1. Elf Excellium 0W40
2. Mobil 1 0W40
3. Elf Excellium LDX 5W40
4. Agip evolution 0W40 / Castrol Formula r 0W40
6. Motul E-tech 8100 0W40
7. Agip evolution 5W40 / Redline 5W30
9. Mobil 1 5W50
10. Castrol Formula r 0W30
11. Motul E-tech 8100 0W30
Group Number (2): Fully synthetic, medium grade 4-stroke engine oils
Agip sint 2000 10W40
Castrol formula r 10W60
Elf Excellium 10W50
Mobil 1 5W50
Motul 6100 10W40
Penzoil GT 15W40
Redline 10W40
Shell Helix Ultra 5W40
Oxidation
8
8
9
9
9
6
7
8
Corrosion
9
8
9
7
7
6
8
8
Chemical Compatibility
8
7
8
8
8
9
8
9
Storage
7
6
7
10
6
8
7
9
Dispersion
9
8
9
7
9
7
8
7
Shear Tests
8
7
8
6
8
5
7
8
Pressure resistance
8
10
10
9
7
8
8
8
Power conversion
9
8
9
7
9
6
9
8
Reduction in friction co-efficient
9
8
9
8
8
7
8
8
Anti-wear
10
7
9
7
9
6
9
8
Rankings:
1. Elf Excellium 10W50
2. Agip Sint 2000 10W40
3. Shell Helix Ultra 5W40
4. Motul 6100 10W40
5. Redline 10W40
6. Mobil 1 5W50
7. Castrol Formula R 10W60
8. Penzoil GT 15W40
Group Number (3): Fully synthetic, full competition purpose 4-stroke engine oils
Agip GPX N1 10W40
Castrol formula SLX 0W30
Elf HTX833 10W50
Mobil 1 0W40
Motul 300V 10W40
Redline Raceoil 5W40
Royal Purple 5W30
Oxidation
7
6
8
9
7
7
7
Corrosion
8
8
9
10
8
8
8
Chemical Compatibility
9
6
7
9
7
7
8
Storage
6
5
7
8
7
6
7
Dispersion
10
10
10
10
10
10
10
Shear Tests
10
9
10
8
10
9
9
Pressure resistance
9
7
10
7
8
8
7
Power conversion
10
10
10
9
10
9
9
Reduction in friction co-efficient
10
10
10
9
10
9
10
Anti-wear
10
10
10
10
10
10
9
Rankings:
1. Elf HTX833 10W50
2. Mobil 1 0W40
3. Agip SZ N1 10W40
4. Motul 300V 10W40
5. Royal Purple 5W30
6. Redline Raceoil 5W40
7. Castrol Formula SLX
Group Number (4): Fully synthetic, gearbox and differential oils
Agip Rotara LSX 75W90
Castrol Syntrax 75W90
Elf HTX729 75W90
Mobil SHC 75W90
Mobil XHP 75W90
Motul Gear300 75W90
Redline NS 75W90
Shell SGO 75W90
Oxidation
8
9
9
8
6
9
9
7
Corrosion
9
9
9
9
10
9
8
8
Chemical Compatibility
8
9
9
8
10
9
10
8
Storage
10
10
10
10
10
10
10
10
Dispersion
10
9
10
9
9
10
10
9
Shear Tests
10
9
10
10
7
10
8
8
Pressure resistance
10
9
9
9
6
10
8
8
Power conversion
8
9
10
8
8
10
9
7
Reduction in friction co-efficient
9
10
10
9
9
10
9
8
Anti-wear
9
10
9
9
7
10
9
9
Rankings:
1. Motul Gear300 75W90
2. Elf HTX729
3. Castrol Syntrax 75W90
4. Agip Rotara LSX 75W90
5. Mobil SHC 75W90 / Redline NS 75W90
6 Redline NS 75W90
7. Mobil XHP 75W90 / Shell SGO 75W90 "
Σάββατο 25 Απριλίου 2009
ESTERS IN SYNTHETIC LUBRICANTS
By T. G. Schaefer
In the simplest terms, esters can be defined as the reaction products of acids and alcohols. Thousands of different kinds of esters are commercially produced for a broad range of applications. Within the realm of synthetic lubrication, a relatively small but still substantial family of esters have been found to be very useful in severe environment applications. This paper shall provide a general overview of the more common esters used in synthetic lubricants and discuss their important benefits and utilities.
Esters have been used successfully in lubrication for more than 60 years and are the preferred stock in many severe applications where their benefits solve problems or bring value. For example, esters have been used exclusively in jet engine lubricants worldwide for over 50 years due to their unique combination of low temperature flowability with clean high temperature operation. Esters are also the preferred stock in the new synthetic refrigeration lubricants used with CFC replacement refrigerants. Here the combination of branching and polarity make the esters miscible with the HFC refrigerants and improves both low and high temperature performance characteristics. In automotive applications, the first qualified synthetic crankcase motor oils were based entirely on ester formulations and these products were quite successful when properly formulated. Esters have given way to PAOs in this application due to PAOs lower cost and their formulating similarities to mineral oil. Nevertheless, esters are often used in combination with PAOs in full synthetic motor oils in order to balance the effect on seals, solubilize additives, reduce volatility, and improve energy efficiency through higher lubricity. The percentage of ester used can vary anywhere from 5 to 25% depending upon the desired properties and the type of ester employed.
The new frontier for esters is the industrial marketplace where the number of products, applications, and operating conditions is enormous. In many cases, the very same equipment which operates satisfactorily on mineral oil in one plant could benefit greatly from the use of an ester lubricant in another plant where the equipment is operated under more severe conditions. This is a marketplace where old problems or new challenges can arise at any time or any location. The high performance properties and custom design versatility of esters is ideally suited to solve these problems. Ester lubricants have already captured certain niches in the industrial market such as reciprocating air compressors and high temperature industrial oven chain lubricants. When one focuses on temperature extremes and their telltale signs such as smoking and deposits, the potential applications for the problem solving ester lubricants are virtually endless.
Ester Chemistry
In many ways esters are very similar to the more commonly known and used synthetic hydrocarbons or PAOs. Like PAOs, esters are synthesized from relatively pure and simple starting materials to produce predetermined molecular structures designed specifically for high performance lubrication. Both types of synthetic basestocks are primarily branched hydrocarbons which are thermally stable, have high viscosity indices, and lack the undesirable and unstable impurities found in conventional petroleum based oils. The primary structural difference between esters and PAOs is the presence of oxygen in the hydrocarbon molecules in the form of multiple ester linkages (COOR) which impart polarity to the molecules. This polarity affects the way esters behave as lubricants in the following ways:
1) Volatility: The polarity of the ester molecules causes them to be attracted to one another and this intermolecular attraction requires more energy (heat) for the esters to transfer from a liquid to a gaseous state. Therefore, at a given molecular weight or viscosity, the esters will exhibit a lower vapor pressure which translates into a higher flash point and a lower rate of evaporation for the lubricant. Generally speaking, the more ester linkages in a specific ester, the higher its flash point and the lower its volatility.
2) Lubricity: Polarity also causes the ester molecules to be attracted to positively charged metal surfaces. As a result, the molecules tend to line up on the metal surface creating a film which requires additional energy (load) to wipe them off. The result is a stronger film which translates into higher lubricity and lower energy consumption in lubricant applications.
3) Detergency/Dispersency: The polar nature of esters also makes them good solvents and dispersants. This allows the esters to solubilize or disperse oil degradation by-products which might otherwise be deposited as varnish or sludge, and translates into cleaner operation and improved additive solubility in the final lubricant.
4) Biodegradability: While stable against oxidative and thermal breakdown, the ester linkage provides a vulnerable site for microbes to begin their work of biodegrading the ester molecule. This translates into very high biodegradability rates for ester lubricants and allows more environmentally friendly products to be formulated.
Another important difference between esters and PAOs is the incredible versatility in the design of ester molecules due to the high number of commercially available acids and alcohols from which to choose. For example, if one is seeking a 6 cSt synthetic basestock, the choices available with PAOs are a straight cut 6 cSt or a “dumbbell” blend of a lighter and heavier PAO. In either case, the properties of the resulting basestock are essentially the same. With esters, literally dozens of 6 cSt products can be designed each with a different chemical structure selected for the specific desired property. This allows the “ester engineer” to custom design the structure of the ester molecules to an optimized set of properties determined by the end customer or application. The performance properties that can be varied in ester design include viscosity, viscosity index, volatility, high temperature coking tendencies, biodegradability, lubricity, hydrolytic stability, additive solubility, and seal compatibility.
As with any product, there are also downsides to esters. The most common concern when formulating with ester basestocks is compatibility with the elastomer material used in the seals. All esters will tend to swell and soften most elastomer seals however, the degree to which they do so can be controlled through proper selection. When seal swell is desirable, such as in balancing the seal shrinkage and hardening characteristics of PAOs, more polar esters should be used such as those with lower molecular weight and/or higher number of ester linkages. When used as the exclusive basestock, the ester should be designed for compatibility with seals or the seals should be changed to those types which are more compatible with esters.
Another potential disadvantage with esters is their ability to react with water or hydrolyze under certain conditions. Generally this hydrolysis reaction requires the presence of water and heat with a relatively strong acid or base to catalyze the reaction. Since esters are usually used in very high temperature applications, high amounts of water are usually not present and hydrolysis is rarely a problem in actual use. Where the application environment may lead to hydrolysis, the ester structure can be altered to greatly improve its hydrolytic stability and additives can be selected to minimize any effects.
The following is a discussion of the structures and features of the more common ester families used in synthetic lubrication.
Diesters
Diesters were the original ester structures introduced to synthetic lubricants during the second World War. These products are made by reacting monohydric alcohols with dibasic acids creating a molecule which may be linear, branched, or aromatic and with two ester groups. Diesters which are often abbreviated DBE (dibasic acid esters) are named after the type of dibasic acid used and are often abbreviated with letters. For example, a diester made by reacting isodecyl alcohol with adipic acid would be known as an “adipate” type diester and would be abbreviated “DIDA” (Diisodecyl Adipate).
Listed below are the more common families of diesters used in synthetic lubricants, and the alcohols most commonly employed.
Adipates are the most widely used diesters due to their low relative cost and good balance of properties. They generally range from about 2.3 to 5.3 cSt at 100°C and exhibit pour points below -60°C. The viscosity indices of adipates usually run from about 130 to 150 and their oxidative stability, like most of the diesters, are comparable to PAOs. The primary difference between adipate diesters and PAOs is the presence of two ester linkages and the associated polarity benefits outlined previously. The most common use of adipate diesters is in combination with PAOs in numerous applications such as screw compressor oils, gear and transmission oils, automotive crankcase oils, and hydraulic fluids. Adipates are also used as the sole basestock where biodegradability is desired or high temperature cleanliness is critical such as in textile lubricants and oven chain oils.
Azelates, Sebacates, and Dodecanedioates are similar to adipates except that in each case the carbon chain length (backbone) of the dibasic acid is longer. This “backbone stretching” significantly increases viscosity index and improves the lubricity characteristics of the ester while retaining all the desirable properties of the adipates. The only downside to these types of diesters is price which tends to run about 50 - 100+% higher than adipates at the wholesale level. This group of linear DBEs are mainly used in older military specifications and where the lubricity factor becomes an important parameter.
Phthalates are aromatic diesters and this ring structure greatly reduces the viscosity index (usually well below 100) and eliminates most of the biodegradability benefit. In all other respects, phthalates behave similar to other diesters and are about 20 - 30% lower in cost. Phthalates are used extensively in air compressor lubricants (especially the reciprocating type) where low viscosity index is the norm and low cost clean operation is desirable.
Dimerates are made by combining two oleic acids which creates a large branched dibasic acid from which interesting diesters are made. Dimerates exhibit high viscosity and high viscosity indices while retaining excellent low temperature flow. Compared to adipates, dimerates are higher in price (30 - 40%), have marginal biodegradability, and are not as clean in high temperature operations. Their lubricity is good and they are often used in synthetic gear oils and 2-cycle oils.
The alcohols used to make diesters will also affect the properties of the finished esters and thus are important factors in the design process. For example, three of the common alcohols used to make diesters each contain eight carbons, and when reacted with adipic acid, all create a dioctyl adipate. However, the properties are entirely different. The n-octyl adipate would have the highest viscosity and the highest viscosity index (about 50% higher then the 2-ethylhexyl adipate) but would exhibit a relatively high freeze point making their use in low temperature applications virtually impossible. By branching the octyl alcohol, the other two DOAs exhibit no freeze point tendencies and have pour points well below -60°C. The isooctyl adipate offers the best balance of properties combining a high viscosity index with a wide temperature range. The 2-ethylhexyl adipate has a VI about 45 units lower and a somewhat higher volatility. These examples demonstrate the importance of combining the right alcohols with the right acids when designing diester structures and allows the ester engineer a great deal of flexibility in his work. In addition, the alcohols may be reacted alone or blended with other alcohols to form coesters with their own unique properties.
Polyol Esters
The term “polyol esters” is short for neopentyl polyol esters which are made by reacting monobasic acids with polyhedric alcohols having a neopentyl structure. The unique feature of the structure of polyol ester molecules is the fact that there are no hydrogens on the beta-carbon. Since this “beta-hydrogen” is the first site of thermal attack on diesters, eliminating this site substantially elevates the thermal stability of polyol esters and allows them to be used at much higher temperatures. In addition, polyol esters usually have more ester groups than the diesters and this added polarity further reduces volatility and enhances the lubricity characteristics while retaining all the other desirable properties inherent with diesters. This makes polyol esters ideally suited for the higher temperature applications where the performance of diesters and PAOs begin to fade.
Like diesters, many different acids and alcohols are available for manufacturing polyol esters and indeed an even greater number of permutations are possible due to the multiple ester linkages. Unlike diesters, polyol esters (POEs) are named after the alcohol instead of the acid and the acids are often represented by their carbon chain length. For example, a polyol ester made by reacting a mixture of nC8 and nC10 fatty acids with trimethylolpropane alcohol would be referred to as a “TMP” ester and represented as TMP C8C10. The following is a list of the more common types of polyol esters:
Neopentyl Glycols (NPGs) - 2 Hydroxyls
Trimethylolpropanes (TMPs) - 3 Hydroxyls
Pentaerythritols (PEs) - 4 Hydroxyls
DiPentaerythritols (DiPEs) - 6 Hydroxyls
Each of the alcohols shown above have no beta-hydrogens and differ primarily in the number of hydroxyl groups they contain for reaction with the fatty acids. The difference in ester properties as they relate to the alcohols are primarily those related to molecular weight such as viscosity, pour point, flash point, and volatility. The versatility in designing these fluids is primarily related to the selection and mix of the acids esterified onto the alcohols.
The normal or linear acids all contribute similar performance properties with the physicals being influenced by their carbon chain length or molecular weight. For example, lighter acids such as C5 may be desirable for reducing low temperature viscosity on the higher alcohols, or the same purpose can be achieved by esterifying longer acids (C10) onto the shorter alcohols. While the properties of the normal acids are mainly related to the chain length, there are some more subtle differences among them which can allow the formulator to vary such properties as thermal stability and lubricity.
Branched acids add a new dimension since the length, location, and number of branches all impact the performance of the final ester. For example, a branch incorporated near the acid group may help to hinder hydrolysis while multiple branches may be useful for building viscosity, improving low temperature flow, and enhancing thermal stability and cleanliness. The versatility of this family is best understood when one considers that multiple acids are usually co-esterified with the polyol alcohol allowing the ester engineer to control multiple properties in a single ester. Indeed single acids are rarely used in polyol esters because of the enchanced properties that can be obtained through co-esterification.
Polyol esters can extend the high temperature operating range of a lubricant by as much as 50 - 100°C due to their superior stability and low volatility. They are also renowned for their film strength and increased lubricity which is useful in reducing energy consumption in many applications. The only downside of polyol esters compared to diesters is their higher price tag, generally 20 - 70+% higher on a wholesale basis.
The major application for polyol esters is jet engine lubricants where they have been used exclusively for more than 40 years. In this application, the oil is expected to flow at -65°C, pump readily at -40°C, and withstand sump temperature over 200°C with drain intervals measured in years. Only polyol esters have been found to satisfy this demanding application and incorporating even small amounts of diesters or PAOs will cause the lubricant to fail vital specifications.Polyol esters are also the ester of choice for blending with PAOs in passenger car motor oils. This change from lower cost diesters to polyols was driven primarily by the need for reduced fuel consumption and lower volatility in modern specifications. They are sometimes used in 2-cycle oils as well for the same reasons. In industrial markets polyol esters are used extensively in synthetic refrigeration lubricants due to their miscibility with non-chlorine refrigerants. They are also widely used in very high temperature operations such as industrial oven chains, tenter frames, stationary turbine engines, high temperature grease, fire resistant transformer coolants, fire resistant hydraulic fluids, and textile lubricants.
In general, polyol esters represent the highest performance level available for high temperature applications at a reasonable price. Although they cost more than many other types of synthetics, the benefits often combine to make this chemistry the most cost effective in severe environment applications. The primary benefits include extended life, higher temperature operation, reduced maintenance and downtime, lower energy consumption, reduced smoke and disposal, and biodegradability.
Other esters
While diesters and polyol esters represent the most widely used ester families in synthetic lubrication, two other families are worth mentioning. These are monoesters and trimellitates.
Monoesters are made by reacting monohydric alcohols with monobasic fatty acids creating a molecule with a single ester linkage and linear or branched alkyl groups. These products are generally very low in viscosity (usually under 2 cSt at 100°C) and exhibit extremely low pour points and high VIs. The presence of the ester linkage imparts polarity which helps to offset the high volatility expected with such small molecules. Hence, when compared to a hydrocarbon of equal molecular weight, a monoester will have a significantly higher flash point giving it a broader temperature range in use. Monoesters are used primarily for extremely cold applications such as in Arctic hydraulic oils and deep sea drilling. They can also be used in formulating automotive aftermarket additives to improve cold starting.
Trimellitates are aromatic triesters which are similar to the phthalates described under diesters but with a third ester linkage. By taking on three alcohols, the trimellitates are significantly more viscous then the linear adipates or phthalates. Viscosities range from about 9 to 20 cSt at 100°C. Like phthalates, trimellitates have a low viscosity index and poor biodegradability with a price range between adipates and polyols. Trimellitates are generally used where high viscosity is needed as in gear lubricants, chain lubricants, and grease.
Summary
Esters are a broad and diverse family of synthetic lubricant basestocks which can be custom designed to meet specific physical and performance properties. The inherent polarity of esters improves their performance in lubrication by reducing volatility, increasing lubricity, providing cleaner operation, and making the products biodegradable. A wide range of available raw materials allow an ester designer the ability to optimize a product over a wide range of variables in order to maximize the performance and value to the client. They may be used alone in very high temperature applications for optimum performance or blended with PAOs or other synthetic basestocks where their complementary properties improve the balance of the finished lubricant. Esters have been used in synthetic lubricants for more than 60 years and continue to grow as the drive for efficiency make operating environments more severe. Because of the complexity involved in the designing, selecting, and blending of an ester basestock, the choice of the optimum ester should be left to a qualified ester engineer who can better balance the desired properties.
In the simplest terms, esters can be defined as the reaction products of acids and alcohols. Thousands of different kinds of esters are commercially produced for a broad range of applications. Within the realm of synthetic lubrication, a relatively small but still substantial family of esters have been found to be very useful in severe environment applications. This paper shall provide a general overview of the more common esters used in synthetic lubricants and discuss their important benefits and utilities.
Esters have been used successfully in lubrication for more than 60 years and are the preferred stock in many severe applications where their benefits solve problems or bring value. For example, esters have been used exclusively in jet engine lubricants worldwide for over 50 years due to their unique combination of low temperature flowability with clean high temperature operation. Esters are also the preferred stock in the new synthetic refrigeration lubricants used with CFC replacement refrigerants. Here the combination of branching and polarity make the esters miscible with the HFC refrigerants and improves both low and high temperature performance characteristics. In automotive applications, the first qualified synthetic crankcase motor oils were based entirely on ester formulations and these products were quite successful when properly formulated. Esters have given way to PAOs in this application due to PAOs lower cost and their formulating similarities to mineral oil. Nevertheless, esters are often used in combination with PAOs in full synthetic motor oils in order to balance the effect on seals, solubilize additives, reduce volatility, and improve energy efficiency through higher lubricity. The percentage of ester used can vary anywhere from 5 to 25% depending upon the desired properties and the type of ester employed.
The new frontier for esters is the industrial marketplace where the number of products, applications, and operating conditions is enormous. In many cases, the very same equipment which operates satisfactorily on mineral oil in one plant could benefit greatly from the use of an ester lubricant in another plant where the equipment is operated under more severe conditions. This is a marketplace where old problems or new challenges can arise at any time or any location. The high performance properties and custom design versatility of esters is ideally suited to solve these problems. Ester lubricants have already captured certain niches in the industrial market such as reciprocating air compressors and high temperature industrial oven chain lubricants. When one focuses on temperature extremes and their telltale signs such as smoking and deposits, the potential applications for the problem solving ester lubricants are virtually endless.
Ester Chemistry
In many ways esters are very similar to the more commonly known and used synthetic hydrocarbons or PAOs. Like PAOs, esters are synthesized from relatively pure and simple starting materials to produce predetermined molecular structures designed specifically for high performance lubrication. Both types of synthetic basestocks are primarily branched hydrocarbons which are thermally stable, have high viscosity indices, and lack the undesirable and unstable impurities found in conventional petroleum based oils. The primary structural difference between esters and PAOs is the presence of oxygen in the hydrocarbon molecules in the form of multiple ester linkages (COOR) which impart polarity to the molecules. This polarity affects the way esters behave as lubricants in the following ways:
1) Volatility: The polarity of the ester molecules causes them to be attracted to one another and this intermolecular attraction requires more energy (heat) for the esters to transfer from a liquid to a gaseous state. Therefore, at a given molecular weight or viscosity, the esters will exhibit a lower vapor pressure which translates into a higher flash point and a lower rate of evaporation for the lubricant. Generally speaking, the more ester linkages in a specific ester, the higher its flash point and the lower its volatility.
2) Lubricity: Polarity also causes the ester molecules to be attracted to positively charged metal surfaces. As a result, the molecules tend to line up on the metal surface creating a film which requires additional energy (load) to wipe them off. The result is a stronger film which translates into higher lubricity and lower energy consumption in lubricant applications.
3) Detergency/Dispersency: The polar nature of esters also makes them good solvents and dispersants. This allows the esters to solubilize or disperse oil degradation by-products which might otherwise be deposited as varnish or sludge, and translates into cleaner operation and improved additive solubility in the final lubricant.
4) Biodegradability: While stable against oxidative and thermal breakdown, the ester linkage provides a vulnerable site for microbes to begin their work of biodegrading the ester molecule. This translates into very high biodegradability rates for ester lubricants and allows more environmentally friendly products to be formulated.
Another important difference between esters and PAOs is the incredible versatility in the design of ester molecules due to the high number of commercially available acids and alcohols from which to choose. For example, if one is seeking a 6 cSt synthetic basestock, the choices available with PAOs are a straight cut 6 cSt or a “dumbbell” blend of a lighter and heavier PAO. In either case, the properties of the resulting basestock are essentially the same. With esters, literally dozens of 6 cSt products can be designed each with a different chemical structure selected for the specific desired property. This allows the “ester engineer” to custom design the structure of the ester molecules to an optimized set of properties determined by the end customer or application. The performance properties that can be varied in ester design include viscosity, viscosity index, volatility, high temperature coking tendencies, biodegradability, lubricity, hydrolytic stability, additive solubility, and seal compatibility.
As with any product, there are also downsides to esters. The most common concern when formulating with ester basestocks is compatibility with the elastomer material used in the seals. All esters will tend to swell and soften most elastomer seals however, the degree to which they do so can be controlled through proper selection. When seal swell is desirable, such as in balancing the seal shrinkage and hardening characteristics of PAOs, more polar esters should be used such as those with lower molecular weight and/or higher number of ester linkages. When used as the exclusive basestock, the ester should be designed for compatibility with seals or the seals should be changed to those types which are more compatible with esters.
Another potential disadvantage with esters is their ability to react with water or hydrolyze under certain conditions. Generally this hydrolysis reaction requires the presence of water and heat with a relatively strong acid or base to catalyze the reaction. Since esters are usually used in very high temperature applications, high amounts of water are usually not present and hydrolysis is rarely a problem in actual use. Where the application environment may lead to hydrolysis, the ester structure can be altered to greatly improve its hydrolytic stability and additives can be selected to minimize any effects.
The following is a discussion of the structures and features of the more common ester families used in synthetic lubrication.
Diesters
Diesters were the original ester structures introduced to synthetic lubricants during the second World War. These products are made by reacting monohydric alcohols with dibasic acids creating a molecule which may be linear, branched, or aromatic and with two ester groups. Diesters which are often abbreviated DBE (dibasic acid esters) are named after the type of dibasic acid used and are often abbreviated with letters. For example, a diester made by reacting isodecyl alcohol with adipic acid would be known as an “adipate” type diester and would be abbreviated “DIDA” (Diisodecyl Adipate).
Listed below are the more common families of diesters used in synthetic lubricants, and the alcohols most commonly employed.
Adipates are the most widely used diesters due to their low relative cost and good balance of properties. They generally range from about 2.3 to 5.3 cSt at 100°C and exhibit pour points below -60°C. The viscosity indices of adipates usually run from about 130 to 150 and their oxidative stability, like most of the diesters, are comparable to PAOs. The primary difference between adipate diesters and PAOs is the presence of two ester linkages and the associated polarity benefits outlined previously. The most common use of adipate diesters is in combination with PAOs in numerous applications such as screw compressor oils, gear and transmission oils, automotive crankcase oils, and hydraulic fluids. Adipates are also used as the sole basestock where biodegradability is desired or high temperature cleanliness is critical such as in textile lubricants and oven chain oils.
Azelates, Sebacates, and Dodecanedioates are similar to adipates except that in each case the carbon chain length (backbone) of the dibasic acid is longer. This “backbone stretching” significantly increases viscosity index and improves the lubricity characteristics of the ester while retaining all the desirable properties of the adipates. The only downside to these types of diesters is price which tends to run about 50 - 100+% higher than adipates at the wholesale level. This group of linear DBEs are mainly used in older military specifications and where the lubricity factor becomes an important parameter.
Phthalates are aromatic diesters and this ring structure greatly reduces the viscosity index (usually well below 100) and eliminates most of the biodegradability benefit. In all other respects, phthalates behave similar to other diesters and are about 20 - 30% lower in cost. Phthalates are used extensively in air compressor lubricants (especially the reciprocating type) where low viscosity index is the norm and low cost clean operation is desirable.
Dimerates are made by combining two oleic acids which creates a large branched dibasic acid from which interesting diesters are made. Dimerates exhibit high viscosity and high viscosity indices while retaining excellent low temperature flow. Compared to adipates, dimerates are higher in price (30 - 40%), have marginal biodegradability, and are not as clean in high temperature operations. Their lubricity is good and they are often used in synthetic gear oils and 2-cycle oils.
The alcohols used to make diesters will also affect the properties of the finished esters and thus are important factors in the design process. For example, three of the common alcohols used to make diesters each contain eight carbons, and when reacted with adipic acid, all create a dioctyl adipate. However, the properties are entirely different. The n-octyl adipate would have the highest viscosity and the highest viscosity index (about 50% higher then the 2-ethylhexyl adipate) but would exhibit a relatively high freeze point making their use in low temperature applications virtually impossible. By branching the octyl alcohol, the other two DOAs exhibit no freeze point tendencies and have pour points well below -60°C. The isooctyl adipate offers the best balance of properties combining a high viscosity index with a wide temperature range. The 2-ethylhexyl adipate has a VI about 45 units lower and a somewhat higher volatility. These examples demonstrate the importance of combining the right alcohols with the right acids when designing diester structures and allows the ester engineer a great deal of flexibility in his work. In addition, the alcohols may be reacted alone or blended with other alcohols to form coesters with their own unique properties.
Polyol Esters
The term “polyol esters” is short for neopentyl polyol esters which are made by reacting monobasic acids with polyhedric alcohols having a neopentyl structure. The unique feature of the structure of polyol ester molecules is the fact that there are no hydrogens on the beta-carbon. Since this “beta-hydrogen” is the first site of thermal attack on diesters, eliminating this site substantially elevates the thermal stability of polyol esters and allows them to be used at much higher temperatures. In addition, polyol esters usually have more ester groups than the diesters and this added polarity further reduces volatility and enhances the lubricity characteristics while retaining all the other desirable properties inherent with diesters. This makes polyol esters ideally suited for the higher temperature applications where the performance of diesters and PAOs begin to fade.
Like diesters, many different acids and alcohols are available for manufacturing polyol esters and indeed an even greater number of permutations are possible due to the multiple ester linkages. Unlike diesters, polyol esters (POEs) are named after the alcohol instead of the acid and the acids are often represented by their carbon chain length. For example, a polyol ester made by reacting a mixture of nC8 and nC10 fatty acids with trimethylolpropane alcohol would be referred to as a “TMP” ester and represented as TMP C8C10. The following is a list of the more common types of polyol esters:
Neopentyl Glycols (NPGs) - 2 Hydroxyls
Trimethylolpropanes (TMPs) - 3 Hydroxyls
Pentaerythritols (PEs) - 4 Hydroxyls
DiPentaerythritols (DiPEs) - 6 Hydroxyls
Each of the alcohols shown above have no beta-hydrogens and differ primarily in the number of hydroxyl groups they contain for reaction with the fatty acids. The difference in ester properties as they relate to the alcohols are primarily those related to molecular weight such as viscosity, pour point, flash point, and volatility. The versatility in designing these fluids is primarily related to the selection and mix of the acids esterified onto the alcohols.
The normal or linear acids all contribute similar performance properties with the physicals being influenced by their carbon chain length or molecular weight. For example, lighter acids such as C5 may be desirable for reducing low temperature viscosity on the higher alcohols, or the same purpose can be achieved by esterifying longer acids (C10) onto the shorter alcohols. While the properties of the normal acids are mainly related to the chain length, there are some more subtle differences among them which can allow the formulator to vary such properties as thermal stability and lubricity.
Branched acids add a new dimension since the length, location, and number of branches all impact the performance of the final ester. For example, a branch incorporated near the acid group may help to hinder hydrolysis while multiple branches may be useful for building viscosity, improving low temperature flow, and enhancing thermal stability and cleanliness. The versatility of this family is best understood when one considers that multiple acids are usually co-esterified with the polyol alcohol allowing the ester engineer to control multiple properties in a single ester. Indeed single acids are rarely used in polyol esters because of the enchanced properties that can be obtained through co-esterification.
Polyol esters can extend the high temperature operating range of a lubricant by as much as 50 - 100°C due to their superior stability and low volatility. They are also renowned for their film strength and increased lubricity which is useful in reducing energy consumption in many applications. The only downside of polyol esters compared to diesters is their higher price tag, generally 20 - 70+% higher on a wholesale basis.
The major application for polyol esters is jet engine lubricants where they have been used exclusively for more than 40 years. In this application, the oil is expected to flow at -65°C, pump readily at -40°C, and withstand sump temperature over 200°C with drain intervals measured in years. Only polyol esters have been found to satisfy this demanding application and incorporating even small amounts of diesters or PAOs will cause the lubricant to fail vital specifications.Polyol esters are also the ester of choice for blending with PAOs in passenger car motor oils. This change from lower cost diesters to polyols was driven primarily by the need for reduced fuel consumption and lower volatility in modern specifications. They are sometimes used in 2-cycle oils as well for the same reasons. In industrial markets polyol esters are used extensively in synthetic refrigeration lubricants due to their miscibility with non-chlorine refrigerants. They are also widely used in very high temperature operations such as industrial oven chains, tenter frames, stationary turbine engines, high temperature grease, fire resistant transformer coolants, fire resistant hydraulic fluids, and textile lubricants.
In general, polyol esters represent the highest performance level available for high temperature applications at a reasonable price. Although they cost more than many other types of synthetics, the benefits often combine to make this chemistry the most cost effective in severe environment applications. The primary benefits include extended life, higher temperature operation, reduced maintenance and downtime, lower energy consumption, reduced smoke and disposal, and biodegradability.
Other esters
While diesters and polyol esters represent the most widely used ester families in synthetic lubrication, two other families are worth mentioning. These are monoesters and trimellitates.
Monoesters are made by reacting monohydric alcohols with monobasic fatty acids creating a molecule with a single ester linkage and linear or branched alkyl groups. These products are generally very low in viscosity (usually under 2 cSt at 100°C) and exhibit extremely low pour points and high VIs. The presence of the ester linkage imparts polarity which helps to offset the high volatility expected with such small molecules. Hence, when compared to a hydrocarbon of equal molecular weight, a monoester will have a significantly higher flash point giving it a broader temperature range in use. Monoesters are used primarily for extremely cold applications such as in Arctic hydraulic oils and deep sea drilling. They can also be used in formulating automotive aftermarket additives to improve cold starting.
Trimellitates are aromatic triesters which are similar to the phthalates described under diesters but with a third ester linkage. By taking on three alcohols, the trimellitates are significantly more viscous then the linear adipates or phthalates. Viscosities range from about 9 to 20 cSt at 100°C. Like phthalates, trimellitates have a low viscosity index and poor biodegradability with a price range between adipates and polyols. Trimellitates are generally used where high viscosity is needed as in gear lubricants, chain lubricants, and grease.
Summary
Esters are a broad and diverse family of synthetic lubricant basestocks which can be custom designed to meet specific physical and performance properties. The inherent polarity of esters improves their performance in lubrication by reducing volatility, increasing lubricity, providing cleaner operation, and making the products biodegradable. A wide range of available raw materials allow an ester designer the ability to optimize a product over a wide range of variables in order to maximize the performance and value to the client. They may be used alone in very high temperature applications for optimum performance or blended with PAOs or other synthetic basestocks where their complementary properties improve the balance of the finished lubricant. Esters have been used in synthetic lubricants for more than 60 years and continue to grow as the drive for efficiency make operating environments more severe. Because of the complexity involved in the designing, selecting, and blending of an ester basestock, the choice of the optimum ester should be left to a qualified ester engineer who can better balance the desired properties.
Δευτέρα 29 Δεκεμβρίου 2008
Oil consumption; why some, not others?
At least one study found a major cause of oil consumption to be reverse blow-by. The oil gets sucked and flung into the combustion chambers.
High fuel dilution makes the oil more easily combustible so that will increase consumption as well.
Low tension rings increases it.
Piston and piston ring deposits decreases ring seal and ability of the rings to scrape oil from the cylinder walls. That increases oil consumption.
Some oil enters the CC past the valves when their is a partial vacuum in the CC.
Some oil is sucked through the PCV system and burned in the CC.
If by consume I think you mean burn essentially. Only really 2 place for oil to get into cylinder where then burned up; first along valve guide, down stem, around valve head, and then into combustion chamber. The amount thru this route is very small unless very worn out guides. That leaves the second route: around the ring pack. This is the big variable and will allow a lot more oil into cylinder. Some manufactures use low tension rings for either hp or mileage benefit. The looser rings have less friction, and seal up less well, and scrape off less excessive oil film on cyclinder walls. I think this why some use oil and some don't in a otherwise mechanically sound engine.
High fuel dilution makes the oil more easily combustible so that will increase consumption as well.
Low tension rings increases it.
Piston and piston ring deposits decreases ring seal and ability of the rings to scrape oil from the cylinder walls. That increases oil consumption.
Some oil enters the CC past the valves when their is a partial vacuum in the CC.
Some oil is sucked through the PCV system and burned in the CC.
If by consume I think you mean burn essentially. Only really 2 place for oil to get into cylinder where then burned up; first along valve guide, down stem, around valve head, and then into combustion chamber. The amount thru this route is very small unless very worn out guides. That leaves the second route: around the ring pack. This is the big variable and will allow a lot more oil into cylinder. Some manufactures use low tension rings for either hp or mileage benefit. The looser rings have less friction, and seal up less well, and scrape off less excessive oil film on cyclinder walls. I think this why some use oil and some don't in a otherwise mechanically sound engine.
Σάββατο 17 Νοεμβρίου 2007
What Is Normal Oil Consumption?
What Is Normal Oil Consumption?
Oil consumption is normal and necessary for internal combustion engines to run properly. At what level does oil consumption become abnormal, you may ask? This question is difficult to answer since different engine designs may lead to different levels of “normal” consumption.
Picture a car with an oil consumption problem. Most would imagine a car belching a smoke-screen for several blocks. Others might envision a vehicle which leaks a lake of oil on the driveway.
Neither of the above examples describe our typical call relating to oil consumption. The typical car we hear about consumes around 2 to 3 quarts of oil every 3000 miles. Is this normal consumption?
Possibly, but one needs to investigate further.
First, where did the oil go? Oil is lost by either an external or internal oil leak. What may appear to
be a small external loss could actually turn out to be excessive. Did you know that one drop leaking
every minute from an engine would add up to 7 gallons in a year? Also, one drop of oil leaking from
a vehicle every 20 feet would lead to 1 quart of oil lost every 100 miles, which equals 7.5 gallons
every 3000 miles! Since a small leak may often go undetected, it is very important to carefully and
thoroughly investigate external leaks before looking for other possibilities.
External leaks may be due to leaky valve cover gaskets, oil pan gaskets, front or rear main seals or
cracks in the crankcase or valve covers. To make leak detection easier, clean the engine before you
start searching. Using special dyes in the oil may also help identify evasive leaks. Keep in mind that
the evidence of a leak may not be found near the actual source. A clogged or inoperative Positive
Crankcase Ventilation (PCV) system may lead to oil consumption indirectly by increasing crankcase
pressures and forcing oil from the gaskets and seals. Crankcase breather elements, PCV valves, hoses
and related items should be inspected and replaced as needed, or as recommended by the
manufacturer, to prevent these problems. If there are no signs of external oil loss, the leak is probably
internal and will be more difficult and expensive to locate and repair.
Blue smoke exiting the tail pipe signals an internal oil consumption problem. Even if blue exhaust
smoke is not apparent, internal oil consumption may still exist. If an engine burns as much as one
drop of oil on every firing stroke it will use more than a quart of oil every two miles! The most likely
sources of internal oil consumption are worn valve guides and worn piston rings. If you think you
have an internal oil consumption problem, check with your local mechanic about performing a
leakdown test, a compression test or a ring seal (blow-by) test. A qualified mechanic will use these
tests to pinpoint the source of internal oil consumption. Other possibilities of internal and external
consumption are listed below.
Internal Oil Consumption
Improper oil levels Valve cover gaskets
Incorrect engine oil viscosity Oil pan gasket
Clogged PCV System Front and rear main seals
Worn valve stems and guides Cracks in the crankcase
Worn, broken or stuck piston rings Leaking oil drain plug
Improperly installed piston rings Porous crankcase casting
Worn ring grooves Cylinder Head Gasket
Cracked or broken piston lands
Incorrect pistons
Improperly honed cylinders
Distorted cylinders
Worn or damaged main bearings
Worn or damaged cam shaft bearings
Bent or misaligned connecting rods
Excessive oil pressure
Blown cylinder head gasket
Clogged oil passageways
Fuel dilution of the engine oil
Clogged crankcase breather element
Intake manifold leak
External Oil Consumption
Valve cover gaskets
Oil pan gasket
Front and rear main seals
Cracks in the crankcase
Leaking oil drain plug
Porous crankcase casting
Cylinder Head Gasket
An increase in oil consumption is most likely due to a combination of several of the above items.
Also, oil loss can be masked by other conditions such as fuel dilution. In this case, the fuel will
evaporate if the vehicle is driven under highway conditions for an extended period of time giving the
appearance of excessive oil consumption. In reality, the drop in oil level was a result of a change in
operating conditions and evaporation of the fuel in the oil.
Steps to Identify Abnormal Oil Consumption
1. Consider the year and model of vehicle, the type of engine, the type of service the
vehicle is driven in and how the engine was maintained.
2. Was there a drastic change in consumption? A part may have broken.
3. Were there recent changes in operating conditions?
4. Check for external leaks. Small leaks can lead to big losses.
5. Then, check for internal leaks.
Obviously, most engines begin to consume more oil as they wear. We recommend three basic steps
to minimize oil consumption for the life of your car. First, provide proper preventative maintenance.
Next, use a quality motor oil meeting your automobile’s manufacturer’s specifications. Finally,
change the oil and filter every 3000 miles or three months, whichever comes first. There is no way to
completely eliminate all oil consumption. In fact, that would be harmful for an engine. Problems
with oil consumption can be greatly reduced, however, by following the above advice.
Oil consumption is normal and necessary for internal combustion engines to run properly. At what level does oil consumption become abnormal, you may ask? This question is difficult to answer since different engine designs may lead to different levels of “normal” consumption.
Picture a car with an oil consumption problem. Most would imagine a car belching a smoke-screen for several blocks. Others might envision a vehicle which leaks a lake of oil on the driveway.
Neither of the above examples describe our typical call relating to oil consumption. The typical car we hear about consumes around 2 to 3 quarts of oil every 3000 miles. Is this normal consumption?
Possibly, but one needs to investigate further.
First, where did the oil go? Oil is lost by either an external or internal oil leak. What may appear to
be a small external loss could actually turn out to be excessive. Did you know that one drop leaking
every minute from an engine would add up to 7 gallons in a year? Also, one drop of oil leaking from
a vehicle every 20 feet would lead to 1 quart of oil lost every 100 miles, which equals 7.5 gallons
every 3000 miles! Since a small leak may often go undetected, it is very important to carefully and
thoroughly investigate external leaks before looking for other possibilities.
External leaks may be due to leaky valve cover gaskets, oil pan gaskets, front or rear main seals or
cracks in the crankcase or valve covers. To make leak detection easier, clean the engine before you
start searching. Using special dyes in the oil may also help identify evasive leaks. Keep in mind that
the evidence of a leak may not be found near the actual source. A clogged or inoperative Positive
Crankcase Ventilation (PCV) system may lead to oil consumption indirectly by increasing crankcase
pressures and forcing oil from the gaskets and seals. Crankcase breather elements, PCV valves, hoses
and related items should be inspected and replaced as needed, or as recommended by the
manufacturer, to prevent these problems. If there are no signs of external oil loss, the leak is probably
internal and will be more difficult and expensive to locate and repair.
Blue smoke exiting the tail pipe signals an internal oil consumption problem. Even if blue exhaust
smoke is not apparent, internal oil consumption may still exist. If an engine burns as much as one
drop of oil on every firing stroke it will use more than a quart of oil every two miles! The most likely
sources of internal oil consumption are worn valve guides and worn piston rings. If you think you
have an internal oil consumption problem, check with your local mechanic about performing a
leakdown test, a compression test or a ring seal (blow-by) test. A qualified mechanic will use these
tests to pinpoint the source of internal oil consumption. Other possibilities of internal and external
consumption are listed below.
Internal Oil Consumption
Improper oil levels Valve cover gaskets
Incorrect engine oil viscosity Oil pan gasket
Clogged PCV System Front and rear main seals
Worn valve stems and guides Cracks in the crankcase
Worn, broken or stuck piston rings Leaking oil drain plug
Improperly installed piston rings Porous crankcase casting
Worn ring grooves Cylinder Head Gasket
Cracked or broken piston lands
Incorrect pistons
Improperly honed cylinders
Distorted cylinders
Worn or damaged main bearings
Worn or damaged cam shaft bearings
Bent or misaligned connecting rods
Excessive oil pressure
Blown cylinder head gasket
Clogged oil passageways
Fuel dilution of the engine oil
Clogged crankcase breather element
Intake manifold leak
External Oil Consumption
Valve cover gaskets
Oil pan gasket
Front and rear main seals
Cracks in the crankcase
Leaking oil drain plug
Porous crankcase casting
Cylinder Head Gasket
An increase in oil consumption is most likely due to a combination of several of the above items.
Also, oil loss can be masked by other conditions such as fuel dilution. In this case, the fuel will
evaporate if the vehicle is driven under highway conditions for an extended period of time giving the
appearance of excessive oil consumption. In reality, the drop in oil level was a result of a change in
operating conditions and evaporation of the fuel in the oil.
Steps to Identify Abnormal Oil Consumption
1. Consider the year and model of vehicle, the type of engine, the type of service the
vehicle is driven in and how the engine was maintained.
2. Was there a drastic change in consumption? A part may have broken.
3. Were there recent changes in operating conditions?
4. Check for external leaks. Small leaks can lead to big losses.
5. Then, check for internal leaks.
Obviously, most engines begin to consume more oil as they wear. We recommend three basic steps
to minimize oil consumption for the life of your car. First, provide proper preventative maintenance.
Next, use a quality motor oil meeting your automobile’s manufacturer’s specifications. Finally,
change the oil and filter every 3000 miles or three months, whichever comes first. There is no way to
completely eliminate all oil consumption. In fact, that would be harmful for an engine. Problems
with oil consumption can be greatly reduced, however, by following the above advice.
Τετάρτη 7 Νοεμβρίου 2007
stokes and poise
Stokes are the way kinematic viscosity is measured and basically measures how fast a steel ball bearing falls through a solution. Poise is a measure of the internal resistance of a liquid and basically tells us how fast it flows . The difference between Stokes and Poise is that Stokes is Poise divided by the specific gravity of the liquid.
Πέμπτη 1 Νοεμβρίου 2007
fuel dilution
1) fuel dilution will naturally cause viscosity thinning due to the mixture of a low viscosity fluid (fuel) with a higher viscosity fluid.
2) Fuel in the oil will volatize. Some will be recycled through the combustion chamber and burn off. Some non-volatile components will be left behind as solids. These will tend to thicken the oil.
3) Fuel chemical interaction with the oil will cause increased oxidative thickening. For some oils, this thickening will tend to offset the thinning due to fuel dilution.
4) There are some highly active aromatic hydrocarbon molecules in fuel that do nasty things to some oil and VII molecules, snipping the long chain molecules apart. This seems to happen with some oils that use VIIs and causes what Terry Dyson calls chemical shear or aromatic damage to the oil.
5) Fuel is a solvent, and as such will soften the tribological additive layers on the bearings. This softening or washing causes an increase in additive depletion and increased wear of some bearing metals in some engines.
As a side note, if fuel does indeed cause aromatic damage to the VIIs, that would also subsequently cause a reduction in HT/HS, since HT/HS is primarily adjusted using VIIs in many oils.
2) Fuel in the oil will volatize. Some will be recycled through the combustion chamber and burn off. Some non-volatile components will be left behind as solids. These will tend to thicken the oil.
3) Fuel chemical interaction with the oil will cause increased oxidative thickening. For some oils, this thickening will tend to offset the thinning due to fuel dilution.
4) There are some highly active aromatic hydrocarbon molecules in fuel that do nasty things to some oil and VII molecules, snipping the long chain molecules apart. This seems to happen with some oils that use VIIs and causes what Terry Dyson calls chemical shear or aromatic damage to the oil.
5) Fuel is a solvent, and as such will soften the tribological additive layers on the bearings. This softening or washing causes an increase in additive depletion and increased wear of some bearing metals in some engines.
As a side note, if fuel does indeed cause aromatic damage to the VIIs, that would also subsequently cause a reduction in HT/HS, since HT/HS is primarily adjusted using VIIs in many oils.
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