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Y. Cao et al.
in order to neutralize these substances, detergents are added to the lubricating oil.
Detergents are mostly alkaline which can neutralize the acids produced by the oxidation of lubricating oils and prevent them from further oxidative condensation.
Detergent has a role in promoting dissolution. Because they can dissolve and wash
the materials such as colloidal substances and carbon deposits produced by the oxidation of lubricating oils. Detergents are rarely used singly in oils. They are often
used in combination with dispersants [41].
Carbonaceous sludge forms in the combustion chamber due to incomplete combustion. This sludge accumulates to form an oil-insoluble substance. Dispersant
additives can disperse the sludge particles and keep them suspended in the oil [39].
The main function of the dispersant is similar to that of the detergent. Both dispersants and detergents play a part in dispersing and solubilizing, but the performance
of dispersant is better than that of detergent. This is because the dispersant provides
a larger oil-soluble group, which makes carbon deposits and colloidal substances
harder to aggregate. The dispersant can directly interact with the carbonyl, carboxyl,
hydroxyl, nitro, sulfate of the sludge. These polar groups are dissolved and dispersed
in oil in the form of small particles thus preventing the clogging of the screen.
Commonly used dispersants and detergents include metal sulfonate, ash-less sulfonate, overbased sulfonate, salicylates, alkyl phenolates, overbased carboxylate,
polyisobutylene succinimides, glycidol modified succinimides, Mannich adducts,
polyethylene glycol esters, polyol poly- (12-hydroxy stearic acid), phosphates and
phosphonates [39].
Antioxidants
Lubricants inevitably undergo oxidation during use and storage. Oxidation is the
main cause of deterioration of the lubricating oil. In order to solve this problem,
it is necessary to add a certain amount of antioxidant to extend the working time
of the lubricating oil. Antioxidants have two mechanisms: one is the capture of
free radicals generated during the oxidation process to terminate the oxidation process; the other one is decomposing the peroxide and yielding a stable compound.
Therefore, according to these two mechanisms, antioxidants can be divided into two
categories: free radical trapping agents and peroxide decomposition agents. Among
the commonly used antioxidants, the radical capturing agents are mainly phenol
antioxidants and amine antioxidants. And the peroxide decomposition antioxidants
are mainly dialkyldithiophosphates e.g., dialkyl zinc dithiophosphate and dialkyl
dithiocarbamate [36], etc.
Extreme Pressure and Anti-Wear Additives
Extreme pressure and anti-wear additives play a role in preventing metal surface from
abrasion, scratching, and sintering under high load on the metal surface. Chlorine,
phosphorus, and sulfur are typically contained in extreme pressure and anti-wear
Y. Cao et al.
in order to neutralize these substances, detergents are added to the lubricating oil.
Detergents are mostly alkaline which can neutralize the acids produced by the oxidation of lubricating oils and prevent them from further oxidative condensation.
Detergent has a role in promoting dissolution. Because they can dissolve and wash
the materials such as colloidal substances and carbon deposits produced by the oxidation of lubricating oils. Detergents are rarely used singly in oils. They are often
used in combination with dispersants [41].
Carbonaceous sludge forms in the combustion chamber due to incomplete combustion. This sludge accumulates to form an oil-insoluble substance. Dispersant
additives can disperse the sludge particles and keep them suspended in the oil [39].
The main function of the dispersant is similar to that of the detergent. Both dispersants and detergents play a part in dispersing and solubilizing, but the performance
of dispersant is better than that of detergent. This is because the dispersant provides
a larger oil-soluble group, which makes carbon deposits and colloidal substances
harder to aggregate. The dispersant can directly interact with the carbonyl, carboxyl,
hydroxyl, nitro, sulfate of the sludge. These polar groups are dissolved and dispersed
in oil in the form of small particles thus preventing the clogging of the screen.
Commonly used dispersants and detergents include metal sulfonate, ash-less sulfonate, overbased sulfonate, salicylates, alkyl phenolates, overbased carboxylate,
polyisobutylene succinimides, glycidol modified succinimides, Mannich adducts,
polyethylene glycol esters, polyol poly- (12-hydroxy stearic acid), phosphates and
phosphonates [39].
Antioxidants
Lubricants inevitably undergo oxidation during use and storage. Oxidation is the
main cause of deterioration of the lubricating oil. In order to solve this problem,
it is necessary to add a certain amount of antioxidant to extend the working time
of the lubricating oil. Antioxidants have two mechanisms: one is the capture of
free radicals generated during the oxidation process to terminate the oxidation process; the other one is decomposing the peroxide and yielding a stable compound.
Therefore, according to these two mechanisms, antioxidants can be divided into two
categories: free radical trapping agents and peroxide decomposition agents. Among
the commonly used antioxidants, the radical capturing agents are mainly phenol
antioxidants and amine antioxidants. And the peroxide decomposition antioxidants
are mainly dialkyldithiophosphates e.g., dialkyl zinc dithiophosphate and dialkyl
dithiocarbamate [36], etc.
Extreme Pressure and Anti-Wear Additives
Extreme pressure and anti-wear additives play a role in preventing metal surface from
abrasion, scratching, and sintering under high load on the metal surface. Chlorine,
phosphorus, and sulfur are typically contained in extreme pressure and anti-wear