Engine Oils evolve with modern emission systems

B. El Asri

20 Sep, 2024

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.

Explore the impact of modern exhaust after-treatment systems (ATS) on engine oil formulation, selection, and maintenance

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 emergence of these complex ATS has necessitated significant changes in engine oil formulations. Traditional oils with high levels of sulfur, phosphorus, and ash-forming metallic additives are no longer suitable. Modern engine oils must balance engine protection, performance, and ATS compatibility.

The key factors influencing engine oil formulation for ATS-equipped engines include:

Low SAPS Technology: Low SAPS (Sulphated Ash, Phosphorus, and Sulfur) oils are specifically formulated to minimize the buildup of ash, which can clog DPFs and poison catalytic converters in DOC, TWC, and LNT systems. These oils use ashless detergents, dispersants, and anti-wear agents to maintain engine cleanliness and protection.
Optimized Additive Chemistry: Modern oils use advanced additive packages that provide robust protection against wear, oxidation, and corrosion while being compatible with ATS. The formulation includes reduced levels of zinc, phosphorus, and other metallic elements that can harm catalysts.
Soot Handling and Dispersancy: EGR systems increase soot levels in engine oil, which can lead to sludge formation, oil thickening, and engine wear. Modern engine oils are formulated with high-performance dispersants to keep soot finely suspended, preventing agglomeration and ensuring proper oil flow.
Volatility and Oil Consumption: High volatility oils can lead to increased oil consumption and deposits on ATS components, reducing their efficiency. Low volatility base oils, such as Group III and IV, are preferred for modern engines to minimize oil consumption and ensure ATS longevity.
Oxidation and Thermal Stability: High operating temperatures in modern engines and ATS require engine oils with excellent oxidation and thermal stability. These properties help prevent oil breakdown, sludge formation, and deposit buildup, ensuring longer oil drain intervals and engine protection.

Lubricant Analysis and Monitoring for ATS-Equipped Engines

Regular lubricant analysis is crucial for ATS-equipped engines to ensure optimal performance and longevity of both the engine and the ATS components.

Key parameters to monitor include:

Soot Levels: High soot levels can indicate EGR-related issues or incomplete combustion. Effective dispersant action is necessary to manage soot in the oil.
Oxidation and Nitration: Increased oxidation and nitration levels can result from high operating temperatures and EGR systems. Monitoring these parameters helps determine oil condition and the need for oil changes.
Sulfur, Phosphorus, and Metal Content: Monitoring these elements is essential to assess the potential impact on ATS components. High levels may indicate contamination or the use of incorrect oil.
Viscosity: Oil viscosity changes due to fuel dilution, oxidation, or soot accumulation can affect lubrication performance and engine protection.
Base Number (BN) Depletion: BN depletion can occur due to acidic by-products from combustion and EGR. Monitoring BN helps assess the oil’s ability to neutralize acids and prevent corrosion.

ATS-Equipped engines

A real-world example of the impact of ATS on engine oils involves a fleet of heavy-duty trucks equipped with DPF, SCR, and EGR systems. The fleet operator noticed an increase in DPF clogging and active regeneration cycles, leading to higher fuel consumption and maintenance costs. Upon analyzing the used oil samples, elevated levels of soot, sulfur, and phosphorus were detected, indicating the use of a non-compliant oil formulation.

By switching to a low SAPS engine oil with enhanced dispersant technology and lower sulfur and phosphorus content, the operator observed a significant reduction in DPF clogging and regeneration frequency. The optimized oil formulation helped maintain ATS efficiency, reduce maintenance costs, and extend oil drain intervals, ultimately improving the fleet's overall operational efficiency.

Future Trends

As emissions regulations continue to evolve, future ATS technologies will become even more advanced, requiring further refinements in engine oil formulations. Some of the future trends and considerations for engine oils in ATS-equipped engines include:

Hybrid and Electric Powertrains: While hybrid and electric vehicles reduce the dependence on internal combustion engines, they still require advanced lubricants to manage unique challenges such as electric motor cooling and battery thermal management.
Biofuels and Alternative Fuels: The use of biofuels and alternative fuels can impact oil degradation and compatibility with ATS. Engine oils will need to be formulated to handle the specific by-products and contaminants associated with these fuels.
Enhanced Additive Technologies: The development of new additive chemistries that provide superior protection and performance while minimizing ATS poisoning will be crucial. Nanotechnology and other innovative approaches may offer solutions for enhancing lubricant performance.
Real-Time Oil Condition Monitoring: Advancements in sensor technology and data analytics will enable real-time monitoring of oil condition and ATS performance, allowing for predictive maintenance and optimized oil change intervals.

Modern exhaust after-treatment systems have transformed the landscape of engine oil formulation, selection, and maintenance. Understanding the complex interplay between ATS components, engine design, and lubricant chemistry is essential for lubrication professionals and maintenance engineers.

By optimizing engine oil formulations to meet ATS compatibility requirements, we can ensure compliance with emissions regulations, enhance engine performance, and extend the service life of both the engine and the ATS components.

In this rapidly evolving field, staying informed about the latest developments in ATS technologies and lubricant formulations will be key to achieving sustainable and efficient engine operation.

As the industry moves towards cleaner and more efficient powertrains, the role of advanced engine oils in supporting this transition will remain pivotal.

Engine Oils evolve with modern emission systems