Engine oils are the lifeblood of combustion engines, lubricating, cooling, and protecting engine components. Based on environmental sustainability and technological advancements, modern engines necessitate exhaust after-treatment systems (ATS) to reduce harmful emissions.
This evolution in engine design has influenced the formulation, selection, and maintenance of its oils, making it important for lubrication professionals and maintenance engineers to comprehend the relationship.
Users must understand the modern exhaust after-treatment systems, their components and functions, their impact on engine oil properties and performance, the relationship between oil additives and engine design and how lubrication experts can optimize formulations to meet emissions standards while maintaining engine durability and performance.
Exhaust after-treatment system components
Exhaust after-treatment systems reduce harmful emissions from internal combustion engines (ICEs) by treating the exhaust gases before they are released into the atmosphere.
Global emissions regulations in Euro 6 Europe, Tier 3 United States, and China VI have prompted the development of advanced after-treatment systems (ATS) to combat pollutants like nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HC), and particulate matter (PM),
Modern ATS comprises various components of pollutants, including diesel particulate filters (DPF), selective catalytic reduction (SCR) Systems, diesel oxidation catalysts (DOC), exhaust gas recirculation (EGR) Systems, three-way catalysts, and lean NOx traps (LNT).
Diesel Particulate Filters
Diesel Particulate Filters (DPF) are designed to capture and store particulate matter (PM) or soot from diesel engine exhaust gases, preventing these harmful particles from being emitted into the atmosphere.
Over time, soot accumulates and burns off through regeneration. This regeneration can be passive, occurring naturally during high-temperature operation, or active, where fuel is injected to raise the exhaust stream temperature and burn off soot.
DPF regeneration can dilute engine oil with diesel fuel, increasing oil degradation risk and lubricity issues. Therefore, SAPS (Sulphated Ash, Phosphorus, and Sulfur) oils are vital for DPF-equipped engines, as they minimize DPF clogging risk and prolonged service life.
Selective Catalytic Reduction Systems
Selective Catalytic Reduction (SCR) systems decrease NOx emissions in diesel engines by injecting urea-based solution called Diesel Exhaust Fluid (DEF) or AdBlue into the exhaust stream. The ammonia reacts with NOx, forming harmless nitrogen and water vapor.
SCR systems efficiency is influenced by engine operating conditions and fuel quality, with detergent and dispersant packages for injector fouling and maintaining engine cleanliness indirectly supporting the SCR's performance.
Diesel Oxidation Catalysts (DOC)
Diesel Oxidation Catalysts (DOC) reduce PM emissions and facilitate DPF regeneration by increasing the exhaust gas temperature. However, their effectiveness can be impacted by oil-derived elements like phosphorus and zinc .
To maintain DOC efficiency, modern engine oils should be formulated with reduced levels of these catalyst-poisoning elements for the safety of the catalyst.
Exhaust Gas Recirculation Systems
Exhaust Gas Recirculation (EGR) systems reduce NOx emissions by recirculating exhaust gas back into the combustion chamber, lowering oxygen concentration and combustion temperature.
However, this increases soot loading in engine oils, leading to oil degradation, increased viscosity, and potential sludge formation.
EGR-equipped engines require high dispersant levels to manage soot and prevent sludge for engine longevity and cleanliness.
Three-Way Catalysts
Three-Way Catalysts (TWC) reduce gasoline engines NOx, CO, and HC emissions. They require precise air-fuel mixture control but are sensitive to phosphorus and other catalyst-poisoning elements. Modern engine oils must have low phosphorus content to ensure compatibility with TWCs, reducing efficiency.
Lean NOx Traps (LNT)
Lean NOx Traps (LNT) lean-burn gasoline and diesel engines to reduce NOx emissions. They absorb NOx during lean operation and release it during reach operation, converting it to nitrogen. LNTs are sensitive to sulphur in engine oils, making low-sulphur engine oils for longevity and effectiveness.
Engine oils for modern ATS compatibility
The development of after-treatment systems (ATS) has necessitated changes in engine oil formulations, requiring modern oils to balance engine protection, performance, and compatibility with ATS.
ATS-equipped engine oil formulations include low SAPS (sulphurated ash, phosphorus, and sulphur) oils. They minimize ash buildup, which clogs DPFs and poisons catalytic converters in DOC, TWC, and LNT systems , by using ashless detergents, dispersants, and anti-wear agents for engine cleanliness and protection.
Modern oils also use advanced additive packages for robust protection against wear, oxidation, and corrosion. These packages are compatible with ATS and contain reduced levels of zinc, phosphorus, and other metallic elements that can harm catalysts.
EGR systems increase soot levels in engine oil to prevent sludge formation, oil thickening, and engine wear. Modern engine oils use high-performance dispersants to maintain soot suspension and ensure proper oil flow.
High-volatility oils can increase oil consumption and reduce efficiency in ATS components, making low-volatility base oils like Group III and IV preferred for modern engines to reduce oil consumption and increase longevity.
Modern engines and ATS require oxidation and thermal stability engine oils to prevent breakdown, sludge formation, and deposit buildup. It ensures longer oil drain intervals and engine protection.
ATS-Equipped engines
Regular lubricant analysis is important for an ATS-equipped engine’s optimal performance and longevity. Parameters to monitor include soot levels, oxidation and nitration, sulphur, phosphorus, metal content, oil viscosity, and Base Number (BN) depletion. High soot levels can indicate EGR-related issues or incomplete combustion, while increased oxidation and nitration can result from high operating temperatures and EGR systems. Monitoring these parameters determines soil conditions and the need for oil changes. High levels may indicate contamination or incorrect oil use.
The impact of ATS on engine oils in heavy- duty trucks with DPF, SCR, and EGR systems was observed to increase fuel consumption and maintenance costs. Oil samples showed elevated levels of soot, sulphur, and phosphorus,
indicating non-compliant oil formulations, highlighting the need for oil formulations.Monitoring also assesses the oil’s ability to neutralise acids and prevent corrosion.
Future Trends
Future advanced ATS technologies will necessitate refinements in engine oil formulations. While hybrid and electric vehicles reduce the dependence on internal combustion engines, they require advanced lubricants to manage challenges such as battery thermal management. The use of biofuels and alternative fuels affects oil degradation and its compatibility with ATS. Engine oils must be formulated to account for the by-products and contaminants associated with these fuels.
Advancements in sensor technology and data analytics will enable real-time monitoring of oil conditions and ATS performance, enabling predictive maintenance and optimised oil change intervals.
Modern exhaust after-treatment systems have altered the landscape of engine oil formulation, selection, and maintenance. Lubrication and maintenance engineers must understand the complicated interplay of ATS components, engine architecture, and lubricant chemistry.
