Lubricant additives have played a crucial role in lubricant development since the introduction of petroleum-based lubricants in 19 century. These additives are continuously researched and developed to meet evolving specifications and deliver optimal performance. Today, all lubricants contain additives to meet various performance requirements.
The main purpose of engine oil is to protect engine parts from friction, wear, corrosion, deposits, and oxidation. To achieve this, different types of additives are used. Anti-wear agents protect metal surfaces from wear when in close contact. Antioxidants maintain oxidation stability and minimize oxidative decomposition. Friction modifiers reduce friction coefficients, improving fuel economy and preventing wear. Detergents keep the engine clean by removing combustion contaminants and impurities. Dispersants suspend and separate insoluble particles from fuel combustion or oil degradation. Viscosity modifiers provide flexibility to meet the requirements of lower viscosity oils for improved fuel economy. Pour point depressants enhance flow properties at low temperatures. Emulsifiers prevent phase separation when the engine oil is contaminated with water. These additives are essential for optimal lubricant performance, ensuring smooth engine operation and durability.
While additives are necessary to meet performance requirements, certain chemical components can directly or indirectly affect emission levels or the functionality of emission control systems. For example, zinc dialkyl dithiophosphate (ZDDP) is a widely used anti-wear agent and antioxidant. However, the presence of phosphorous from ZDDP can negatively impact emission control catalysts. Controlling the level of ZDDP in the lubricant can mitigate this effect. Detergents, typically containing calcium and magnesium, are used to maintain engine cleanliness. However, these metals can form compounds with phosphorous and sulfur during combustion, which can be harmful to emission control catalysts. Specific compounds can scavenge these harmful elements, reducing their negative impact. Industry specifications regulate the levels of phosphorous to mitigate risks. Calcium also acts as an oxidation catalyst, assisting in the oxidation of particulates in the exhaust.
Research has demonstrated the compatibility between lubricant formulations and emission control systems. Gasoline particulate filters (GPF) are used in gasoline-powered vehicles to reduce particulate emissions. The accumulation of ash from lubricant combustion in the filter can impact its operation. Accelerated aging protocols were developed to simulate real-world conditions and assess ash accumulation. The protocols consider thermal load, soot accumulation, and regeneration dynamics. Testing with two different oil formulations showed that the ash loading rates matched the field-aged profile. Vehicle emission performance was evaluated during periodic testing, and it was found that lubricant oils with a specific ash level were compatible with GPF technology, meeting emission requirements.
In conclusion, lubricant additives are essential for optimal lubricant performance. While some additives can impact emissions or emission control systems, industry standards and careful formulation can mitigate these effects. Research has demonstrated the compatibility of lubricant formulations with emission control systems, ensuring compliance with emission regulations.
Particle emissions (PN and PM) during WLTC durability testing are influenced by the interaction between lubricants and emission control systems, particularly in terms of ash levels and catalyst performance. Excessive ash accumulation in the filter can increase backpressure, leading to reduced fuel efficiency. Specific chemical components in engine oil can have harmful effects on emission control catalysts, causing catalyst poisoning and inefficiency. To optimize performance, it is crucial to understand the interaction between lubricant chemistry and particulate emissions, specifically soot oxidation.
In the study mentioned, an engine bench test was conducted to assess the impact of lubricant formulation on GPF performance and PM oxidation. A naturally aspirated 2.4 L 4-cylinder GDI engine was used, and the fuel was doped with 2% lubricant oil before injection into the engine combustion chamber. A prototype bench-scale GPF (2 inches in diameter and 6 inches in length) was placed in the exhaust sampling line. Ash loading on the GPF was accelerated through oil dosing. Flow control valves were used to adjust the flow rates for the main exhaust and the partial exhaust for GPF testing. Compressed air was mixed with the partial exhaust and preheated to reach an inlet temperature of 600 degrees Celsius for PM oxidation testing. Cold air was supplied for backpressure and filtration efficiency measurement. Particle emission analyzers were employed to measure mass and number, while filtration efficiency was calculated based on emissions upstream and downstream of the GPF. The study varied the type and amount of detergent metal (calcium or magnesium) and the amount of ZDDP, while other essential components remained constant. The lubricant oils used were fully formulated and had the same SAE grade of 5W-20.
The evaluation of oil properties on GPF performance showed that the use of Mg-based detergent (blue line) had minimal impact on PM oxidation rate. However, higher levels of Ca/P increased the PM oxidation rate for calcium-based detergent oil (green line). This difference can be attributed to the detergent chemistry, as the other factors were kept constant. Calcium, acting as an oxidation catalyst, facilitated better PM combustion compared to magnesium. The Ca/P ratio influenced the oxidation and reduction process dynamics, potentially altering catalytic activity and affecting the overall PM oxidation rate.
Engine emissions technology is a complex system that requires effective coordination of various components to achieve optimal performance. Over the past two decades, significant advancements have been made in intellectual property to address vehicle emission requirements, highlighting the crucial role of lubricants and fuels. To ensure the emissions system functions optimally, both the combustion and emission control processes must be taken into account, with lubricant and fuel additives playing a vital role in enhancing overall emissions performance.
Controlling particulate emissions is a key focus in vehicle emissions control. Factors such as particulate mass, number emissions, particle characteristics, and secondary organic aerosols all influence emissions and should be considered as part of the comprehensive system. The composition of fuel directly and indirectly impacts vehicle emissions performance. Fuel additives contribute to improved combustion properties, leading to better emissions performance across the entire system. By reducing the aromatic content in fuel, noticeable reductions in particulate emissions and secondary organic aerosols can be achieved.
The ash content in lubricants is a crucial consideration for vehicles equipped with gasoline particulate filter (GPF) systems. Initially, there were concerns that high ash levels might limit the GPF's useful life. However, research has demonstrated that even at an ash content of 0.8% SAPS (Sulfated Ash, Phosphorus, and Sulfur), the GPF's durability and performance remain intact. Moreover, the accumulation of ash in the filter has been shown to have a positive impact on filtration performance. Additionally, detergents present in lubricants can help reduce soot buildup in the GPF by catalyzing its combustion, potentially enhancing system performance.
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