Combustion engine oil additives are functional chemical formulations specifically developed for the lubrication needs of internal combustion engines (including gasoline engines, diesel engines, and hybrid internal combustion engines). As the core functional component of internal combustion engine oil, they are mixed with base oils (mineral oil, synthetic oil) to solve the unique lubrication challenges brought by the high-temperature, high-pressure, and complex combustion environment of internal combustion engines. Unlike general automotive lubricant additives, combustion engine oil additives focus more on addressing issues such as carbon deposit formation, acid corrosion, friction and wear of key components, and oxidation degradation of oil products caused by fuel combustion. With the continuous upgrading of internal combustion engine technologies (such as turbocharging, direct injection, high compression ratio) and increasingly strict emission standards, the performance requirements for combustion engine oil additives are moving towards higher efficiency, environmental protection, and specialization. This article will systematically explore the definition, core value, main types and functional mechanisms, key performance requirements, typical applications, and future development trends of combustion engine oil additives, providing a comprehensive interpretation of their important role in ensuring the efficient and durable operation of internal combustion engines.
1. Definition and Core Value of Combustion Engine Oil Additives
Combustion engine oil additives refer to a class of high-performance chemical compounds that are added to internal combustion engine base oils in a certain proportion (usually 8%-35% of the total mass of engine oil) to optimize, enhance, or endow specific lubrication performance of engine oil. The working environment of internal combustion engines is extremely harsh: the temperature of the cylinder wall can reach 200-300℃ during operation, the pressure in the combustion chamber can exceed 10MPa, and the combustion of fuel will generate a large amount of acidic substances, soot, and carbon deposits. These factors will accelerate the degradation of base oils and cause severe wear, corrosion, and carbon deposition of key components (such as pistons, cylinder liners, crankshafts, and valve trains). Combustion engine oil additives are designed to target these pain points, making up for the performance defects of base oils and ensuring the stable operation of internal combustion engines under complex working conditions.
The core value of internal combustion engine oil additives lies in adapting to the unique combustion environment of internal combustion engines, extending engine life while ensuring efficient operation. This can be summarized in five key aspects: First, controlling carbon deposits and sludge. Effectively cleaning and dispersing carbon deposits, sludge, and oil residues generated by fuel combustion and oil oxidation, preventing oil passage blockage and component wear; Second, reducing friction and wear. Forming a stable protective film on the surfaces of critical friction pairs (piston ring-cylinder liner, crankshaft-bearing), reducing direct contact and wear under high temperature and pressure; Third, neutralizing acidic substances. Neutralizing acidic products (such as sulfuric acid and nitric acid) generated by fuel combustion and oil oxidation, preventing acid corrosion of metal parts; Fourth, inhibiting oxidation and deterioration. Delaying the oxidative aging of engine oil under high temperature and high oxygen conditions, extending the service life of the engine oil; Fifth, optimizing lubrication performance. Adjusting the viscosity-temperature characteristics, low-temperature fluidity, and foam stability of engine oil, ensuring effective lubrication during cold starts and high-temperature operation. For internal combustion engines, high-quality internal combustion engine oil additives are key to balancing power output, fuel economy, and component durability.
2. Main Types and Functional Mechanisms of Combustion Engine Oil Additives
Combustion engine oil additives are classified according to their functional orientation, and each type of additive has a unique chemical structure and functional mechanism that adapts to the combustion environment of internal combustion engines. In actual engine oil formulation, multiple additives are usually compounded to achieve comprehensive performance optimization, avoiding antagonistic effects between additives and maximizing synergistic effects. The main types of combustion engine oil additives include detergent-dispersants, anti-wear additives, antioxidants, rust and corrosion inhibitors, viscosity index improvers, pour point depressants, and defoamers, among which detergent-dispersants and anti-wear additives are the core types for adapting to combustion conditions.
2.1 Detergent-Dispersants: Core for Carbon Deposition and Sludge Control
Detergent-dispersants are the most important type of additives in combustion engine oil, accounting for 30%-50% of the total additive amount. Their core function is to control the carbon deposition, varnish, and sludge generated during the combustion process of internal combustion engines, which is the key to ensuring the cleanliness of engine components. The main types include sulfonates (calcium alkyl benzene sulfonate, magnesium alkyl benzene sulfonate), phenates (calcium phenate, magnesium phenate), and salicylates (calcium salicylate). Among them, calcium alkyl benzene sulfonate is widely used in gasoline and diesel engine oils due to its excellent cleaning ability, acid neutralization performance, and cost-effectiveness; magnesium-based sulfonates and salicylates are more suitable for high-end engine oils that require low ash content and high-temperature stability.
The functional mechanism of detergent-dispersants is closely linked to the combustion environment of internal combustion engines: First, cleaning effect. The polar groups in the additive molecule can strongly adsorb on the surface of carbon deposits and varnish on the piston, cylinder wall, and valve stem, and peel off and decompose these solid impurities through chemical solubilization and thermal decomposition (adapting to high-temperature conditions of engines); second, dispersion effect. The non-polar alkyl chains of the additive are compatible with base oils, dispersing the peeled impurities and newly generated sludge into small particles (less than 1μm) and suspending them in the engine oil, preventing aggregation and deposition (avoiding blockage of oil passages and oil filters); third, acid neutralization effect. Most detergent-dispersants are alkaline (with a total base number TBN of 10-40 mgKOH/g), which can neutralize the acidic substances generated by the combustion of sulfur-containing fuel and the oxidation of engine oil (such as sulfuric acid generated by diesel combustion), reducing acid corrosion of metal components. For example, calcium alkyl benzene sulfonate can form a dense protective film on the metal surface while cleaning carbon deposits, and its alkaline groups can quickly neutralize acidic substances, achieving the integration of cleaning, dispersion, and anti-corrosion.
2.2 Anti-Wear Additives: Protection for Key Friction Pairs Under High Temperature and High Pressure
Anti-wear additives are used to protect the key friction pairs of internal combustion engines (piston ring-cylinder liner, crankshaft-axis瓦, camshaft-tappet) from severe wear, scuffing, and seizure under high temperature, high pressure, and boundary lubrication conditions (such as cold start and full-load operation). The main types include zinc dialkyldithiophosphate (ZDDP), molybdenum disulfide (MoS₂), tungsten disulfide (WS₂), and borate esters. ZDDP is the most commonly used anti-wear additive in combustion engine oil due to its excellent anti-wear, anti-oxidation, and anti-corrosion comprehensive performance; molybdenum-based additives are suitable for high-end engine oils that require low friction and fuel economy.
The functional mechanism of anti-wear additives adapts to the harsh friction conditions of internal combustion engines: First, chemical reaction film formation. Under high temperature (above 150℃) and high pressure (above 5MPa) conditions, additive molecules (such as ZDDP) decompose and react with the metal surface (iron) to form a dense chemical reaction film (phosphate film, sulfide film) with high hardness (HV 300-500) and good lubricity. This film can isolate the direct contact between friction pairs, even under boundary lubrication conditions; second, physical adsorption film formation. Under low-temperature conditions (such as cold start), the polar groups of the additive molecules are adsorbed on the metal surface through electrostatic interaction to form a physical adsorption film, reducing the friction coefficient during cold start; third, solid lubrication effect. Solid anti-wear additives (MoS₂, WS₂) have a layered crystal structure, which can form a solid lubrication film on the friction surface. The layers slide relative to each other under the action of load, reducing friction and wear. For example, ZDDP can decompose to generate phosphate radicals and sulfur-containing radicals under high temperature conditions of the engine, forming a mixed protective film of iron phosphate and iron sulfide on the piston ring and cylinder wall, which can effectively resist wear under full-load and high-temperature conditions.
2.3 Antioxidants: Extending Oil Life Under High Temperature Combustion
The high-temperature combustion environment of internal combustion engines (cylinder wall temperature up to 300℃) will significantly accelerate the oxidation of base oils, leading to increased oil viscosity, increased acid value, sludge generation, and reduced lubrication performance. Antioxidants are used to inhibit the oxidation chain reaction of engine oil, delay oil degradation, and extend the service life of engine oil. The main types include phenolic antioxidants (2,6-di-tert-butyl-p-cresol, BHT), amine antioxidants (diphenylamine, phenyl-α-naphthylamine), and composite antioxidants (phenolic-amine composite, metal-containing antioxidants).
The functional mechanism of antioxidants is aimed at the oxidation characteristics of engine oil under combustion conditions: First, free radical scavenging. Phenolic and amine antioxidants can quickly capture the alkyl free radicals and peroxy free radicals generated during the oxidation of base oils (accelerated by high temperature and metal catalysts such as iron and copper), terminating the oxidation chain reaction and inhibiting further oxidation; second, peroxide decomposition. Sulfur-containing and phosphorus-containing antioxidants (such as ZDDP) can decompose the peroxides generated during oxidation into stable alcohols and ketones, preventing peroxides from decomposing into more harmful acidic substances and free radicals; third, metal deactivation. Some antioxidants (such as benzotriazoles) can chelate with metal ions (iron, copper) in the engine oil, reducing the catalytic oxidation effect of metal ions on base oils. For example, BHT is widely used in gasoline engine oils because of its stable anti-oxidation effect under high temperature conditions and good compatibility with other additives.
2.4 Rust and Corrosion Inhibitors: Protection Against Acid and Moisture Corrosion
Rust and corrosion inhibitors are used to prevent metal components of internal combustion engines from rusting and corroding due to contact with moisture (from air and fuel combustion), acidic substances (from combustion and oxidation), and harmful gases (such as carbon dioxide). The main types include sulfonates (calcium alkyl benzene sulfonate, sodium alkyl benzene sulfonate), carboxylic acid salts (fatty acid calcium, fatty acid magnesium), amines (octadecylamine, cyclohexylamine), and borate esters. Among them, calcium alkyl benzene sulfonate is widely used due to its dual functions of anti-corrosion and detergent-dispersion.
The functional mechanism of rust and corrosion inhibitors adapts to the corrosion environment of internal combustion engines: First, adsorption film formation. The polar groups of the additive molecules are adsorbed on the metal surface through electrostatic interaction and chemical bonding to form a dense adsorption film (thickness 5-20 nm), isolating the metal surface from moisture, oxygen, and acidic substances; second, chelate film formation. Amine compounds and borate esters can form stable chelates with metal ions on the metal surface, further enhancing the compactness and stability of the protective film (adapting to the alternating high and low temperature environment of engines); third, acid neutralization and passivation. Alkaline inhibitors (such as calcium alkyl benzene sulfonate) can neutralize residual acidic substances in the engine oil, and passivate the metal surface to form a passive film (such as iron oxide passivation film), reducing the corrosion rate of metal.
2.5 Other Key Additives for Combustion Engine Oil
- Viscosity index improvers: Mainly polymers such as polymethacrylates and polyisobutenes. They can improve the viscosity-temperature performance of engine oil: under high temperature (engine full-load operation), the polymer molecules stretch to increase oil viscosity (ensuring lubrication film thickness); under low temperature (engine cold start), the molecules curl to reduce oil viscosity (reducing startup resistance). They are essential for adapting to the large temperature fluctuation range of internal combustion engines (from -30℃ cold start to 300℃ high-temperature operation).
- Pour point depressants: Mainly polyacrylates and polyalphaolefins. They can inhibit the crystallization of paraffin in base oils under low temperature conditions (below 0℃), reducing the pour point of engine oil (usually by 10-20℃) and ensuring that engine oil can flow normally during cold start (avoiding dry friction due to oil flow blockage).
- Defoamers: Mainly silicone oils and polyethers. During the operation of internal combustion engines, the violent stirring of engine oil and the mixing of combustion gases will generate foam. Foam will reduce the lubrication effect, cause cavitation (damaging axis tiles and hydraulic components), and block oil passages. Defoamers can quickly break foam and inhibit foam generation, ensuring the stability of the lubrication system.
3. Key Performance Requirements of Combustion Engine Oil Additives
The performance requirements of combustion engine oil additives are more stringent than those of general automotive lubricant additives, which must fully adapt to the high-temperature, high-pressure, and complex combustion environment of internal combustion engines, and meet the requirements of engine technology upgrading and emission standards. The key performance requirements mainly include thermal stability, chemical stability, anti-wear performance, detergent-dispersant performance, acid neutralization capacity, compatibility, and environmental friendliness.
3.1 High Thermal Stability: Adapt to High-Temperature Combustion Environment
The cylinder wall and piston top of internal combustion engines work under high temperature conditions (200-300℃), and the engine oil in contact with these components must have excellent thermal stability. Combustion engine oil additives must not decompose, volatilize, or generate harmful substances (such as coke and toxic gases) under high temperature conditions, and must maintain stable functional performance (such as cleaning, anti-wear, and oxidation resistance). The thermal decomposition temperature of additives should be above 250℃ (preferably above 300℃) to avoid failure under extreme high-temperature conditions (such as engine overheating). For example, ZDDP must maintain stable anti-wear performance at 200℃, and calcium alkyl benzene sulfonate must not decompose and lose acid neutralization capacity at high temperatures.
3.2 Excellent Detergent-Dispersant Performance: Control Carbon Deposition and Sludge
The combustion of fuel in internal combustion engines will generate a large amount of carbon deposits and soot (especially diesel engines), and the oxidation of engine oil will generate sludge. These impurities will cause wear of components, blockage of oil passages, and reduction of engine power. Therefore, combustion engine oil additives must have excellent detergent-dispersant performance: the cleaning ability should be able to peel off existing carbon deposits and varnish, and the dispersion ability should be able to stably disperse impurities in the engine oil (avoiding aggregation and deposition). The detergent-dispersant performance is usually evaluated by tests such as piston cleanliness test (ASTM D5500) and sludge dispersion test (ASTM D2783).
3.3 Strong Acid Neutralization Capacity: Resist Acid Corrosion
The combustion of sulfur-containing fuel (especially diesel) and the oxidation of engine oil will generate a large amount of acidic substances, which will corrode the metal components of the engine (such as cylinder liners, crankshafts, and valve trains). Therefore, combustion engine oil additives (especially detergent-dispersants) must have strong acid neutralization capacity, usually characterized by total base number (TBN). Gasoline engine oil additives usually require a TBN of 8-15 mgKOH/g, and diesel engine oil additives (adapting to high-sulfur fuel) require a TBN of 15-40 mgKOH/g. The acid neutralization capacity must be maintained during the service life of the engine oil to avoid acid corrosion.
3.4 Reliable Anti-Wear Performance: Protect Key Friction Pairs
The key friction pairs of internal combustion engines (piston ring-cylinder liner, crankshaft-axis瓦) bear large loads (up to 10MPa) and work under boundary lubrication conditions (cold start, full load). Combustion engine oil additives must have reliable anti-wear performance, which can form a stable protective film on the friction surface to prevent scuffing and seizure. The anti-wear performance is usually evaluated by four-ball wear test (ASTM D4172) and Timken wear test (ASTM D2783). For turbocharged engines, additives must also have anti-wear performance under high temperature and high speed conditions (protecting turbocharger bearings).
3.5 Good Compatibility and Environmental Friendliness
Compatibility: Combustion engine oil additives must have good compatibility with base oils and other additives, without precipitation, stratification, or antagonistic effects. For example, detergent-dispersants and anti-wear additives must have synergistic effects (improving both cleaning and anti-wear performance), and must not react with each other to reduce performance. Environmental friendliness: With the increasingly strict emission standards (such as Euro VI and China National VI), combustion engine oil additives must be low-toxic, biodegradable, and free of harmful substances (such as heavy metals, chlorine, and polycyclic aromatic hydrocarbons). At the same time, low-ash additives (ash content less than 1.0%) must be used to avoid clogging of diesel particulate filters (DPF) and gasoline particulate filters (GPF).
4. Typical Applications of Combustion Engine Oil Additives by Engine Type
Different types of internal combustion engines (gasoline engines, diesel engines, hybrid internal combustion engines) have different working conditions and performance requirements, so the type and compound ratio of combustion engine oil additives are also different. The formulation of additives must be targeted to ensure the optimal matching between engine oil and engine performance.
4.1 Gasoline Engine Oil Additives
Gasoline engines (especially turbocharged direct injection engines) have the characteristics of high speed, high temperature, and high compression ratio, and are prone to generate carbon deposits on the intake valve, piston top, and fuel injector. The core requirements for additives are cleaning performance, anti-wear performance, and oxidation resistance. The main additive formula: detergent-dispersants (calcium alkyl benzene sulfonate + calcium salicylate, addition amount 15%-25%), anti-wear additives (ZDDP, addition amount 0.5%-1.5%), antioxidants (phenolic-amine composite, addition amount 0.3%-0.8%), viscosity index improvers (polymethacrylates, addition amount 3%-8%), pour point depressants (polyacrylates, addition amount 0.1%-0.3%), and defoamers (silicone oil, addition amount 0.001%-0.01%). For turbocharged gasoline engines, molybdenum disulfide is added to improve anti-wear performance and reduce friction (protecting turbocharger bearings).
4.2 Diesel Engine Oil Additives
Diesel engines (especially heavy-duty diesel engines) have the characteristics of high load, high sulfur content in fuel (some regions), and large amount of soot generation. The core requirements for additives are acid neutralization performance, soot dispersion performance, and anti-wear performance. The main additive formula: detergent-dispersants (high-base number calcium alkyl benzene sulfonate + calcium phenate, addition amount 20%-30%), anti-wear additives (ZDDP + sulfur-phosphorus extreme pressure additives, addition amount 1.0%-2.0%), antioxidants (amine-based antioxidants, addition amount 0.5%-1.0%), viscosity index improvers (polyisobutenes, addition amount 4%-10%), pour point depressants (polyalphaolefins, addition amount 0.2%-0.5%), and defoamers (silicone oil, addition amount 0.001%-0.01%). For low-sulfur diesel engines (sulfur content less than 10ppm), low-base number additives (TBN 8-12 mgKOH/g) are used to adapt to emission standards and avoid DPF clogging.
4.3 Hybrid Internal Combustion Engine Oil Additives
Hybrid internal combustion engines (including mild hybrid, strong hybrid) have the characteristics of frequent start-stop, low engine operating temperature (long-term low-load operation), and compatibility with electric drive systems. The core requirements for additives are low-temperature fluidity, anti-wear performance (adapting to frequent start-stop), and electrical insulation (avoiding damage to electric drive components). The main additive formula: detergent-dispersants (low-ash calcium salicylate + magnesium sulfonate, addition amount 12%-20%), anti-wear additives (ZDDP + borate esters, addition amount 0.8%-1.2%), antioxidants (phenolic antioxidants, addition amount 0.4%-0.8%), viscosity index improvers (low-shear polymethacrylates, addition amount 2%-6%), pour point depressants (polyacrylates, addition amount 0.3%-0.6%), and defoamers (low-volatility silicone oil, addition amount 0.001%-0.01%). The additive formula must ensure that the engine oil has good electrical insulation (volume resistivity above 10¹² Ω·cm) to avoid short circuits in the electric drive system.
5. Future Development Trends of Combustion Engine Oil Additives
Driven by both the upgrading of internal combustion engine technology (high efficiency and low emissions) and the development of hybrid power, the internal combustion engine oil additive industry is showing five major development trends: greening (low ash content, environmentally friendly), high efficiency (long-lasting, low dosage), specialization (targeted formulations), multi-functionality (integrated functions), and adaptation to hybrid power operating conditions. These trends will drive the continuous upgrading of additive technology and meet the increasingly stringent requirements of internal combustion engines.
5.1 Greenization: Low Ash, Environmental Protection, and Compliance with Emission Standards
With the implementation of strict emission standards (Euro VI, China National VI) and the popularization of particulate filters (DPF/GPF), low-ash and ashless additives will become the mainstream. Traditional high-ash calcium sulfonates will be gradually replaced by low-ash magnesium salicylates and ashless detergents; lead-containing, chlorine-containing, and other harmful additives will be completely eliminated. At the same time, bio-based additives derived from renewable resources (such as vegetable oil-based sulfonates, natural phenolic antioxidants) will be developed and promoted, improving the biodegradability of additives and reducing environmental pollution.
5.2 High Efficiency: Long Oil Change Cycle and Low Addition Amount
To reduce the operating and maintenance costs of internal combustion engines (especially commercial vehicles), the oil change cycle of engine oil is gradually extended (from 5,000km to 10,000km, even 20,000km). This requires combustion engine oil additives to have higher efficiency: high-efficiency antioxidants (extending oil life), high-efficiency detergent-dispersants (maintaining cleanliness for a long time), and high-efficiency anti-wear additives (reducing addition amount while ensuring performance). For example, high-purity calcium alkyl benzene sulfonate (purity above 99%) can reduce the addition amount by 20%-30% while ensuring cleaning performance; nanomolybdenum disulfide (particle size 50-100nm) can improve anti-wear performance by 40% with an addition amount of only 0.1%-0.3%.
5.3 Specialization: Targeted Formulation for Engine Technology Upgrading
With the upgrading of internal combustion engine technologies (turbocharging, direct injection, high compression ratio), specialized additive formulas will be developed for different engine types and working conditions. For example, additives for turbocharged direct injection gasoline engines will focus on carbon deposition control (intake valve, fuel injector) and turbocharger protection; additives for heavy-duty diesel engines will focus on soot dispersion and acid neutralization; additives for hybrid engines will focus on low-temperature fluidity and electrical insulation. At the same time, additive manufacturers will cooperate with engine manufacturers to develop customized additive formulas (original equipment manufacturer (OEM) specifications), achieving precise matching between engine oil and engine performance.
5.4 Multifunctionalization: Integrated Functions to Simplify Formulation
Single-function additives can no longer meet the complex performance requirements of modern internal combustion engines. Multifunctional composite additives that integrate multiple functions will become an important development trend. For example, composite additives integrating detergent-dispersion, anti-wear, and anti-oxidation functions (such as calcium alkyl benzene sulfonate + ZDDP + phenolic antioxidants) can simplify the engine oil formula, reduce the number of additives, avoid antagonistic effects, and improve comprehensive performance. In addition, multifunctional additives that integrate anti-wear and friction reduction functions (such as molybdenum-based composite additives) can improve fuel economy while protecting components.
5.5 Adaptation to Hybrid Internal Combustion Engines: Meeting New Working Conditions
The rapid development of hybrid internal combustion engines has put forward new requirements for combustion engine oil additives. Hybrid engines have frequent start-stop, low operating temperature, and compatibility with electric drive systems, so additives must adapt to these new working conditions: improving low-temperature fluidity (ensuring lubrication during frequent cold starts), enhancing anti-wear performance (reducing wear caused by start-stop), and ensuring electrical insulation (avoiding damage to electric drive components). At the same time, additives must have good compatibility with fuel (ethanol-gasoline, biodiesel) to avoid performance degradation.
Conclusion
Internal combustion engine oil additives are the core functional components of internal combustion engine oils, playing an irreplaceable role in adapting to the high temperature, high pressure, and complex combustion environment of internal combustion engines, controlling carbon deposits and sludge, reducing friction and wear, neutralizing acidic substances, and extending the service life of engines and engine oils. With the continuous upgrading of internal combustion engine technology and increasingly stringent emission standards, the performance requirements for internal combustion engine oil additives are developing towards greener, more efficient, more professional, more multifunctional, and more adaptable to mixed operating conditions.
In the future, combustion engine oil additive manufacturers will focus on optimizing molecular structures, developing new materials and new technologies (such as nanotechnology, bio-based technology), and compounding high-performance additives to meet the needs of modern internal combustion engines. For engine oil manufacturers and users, understanding the types, functional mechanisms, performance requirements, and development trends of combustion engine oil additives is the key to selecting suitable engine oil, ensuring the efficient and durable operation of internal combustion engines, and balancing power output, fuel economy, and environmental protection. Even in the era of new energy vehicles, internal combustion engines (especially hybrid internal combustion engines) will still occupy an important position in the automotive and commercial vehicle fields, and combustion engine oil additives will continue to play a key supporting role in the development of internal combustion engine technology.