Testing Tomorrow: Gasoline Particulate Filters and Emerging Technology

Whitepaper

Testing Tomorrow: Gasoline Particulate Filters and Emerging Technology Huifang Shao, Joseph E. Remias and Joseph W. Roos Afton Chemical, Richmond VA, US

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Summary

Our industry faces a critical tipping point. As pollution continues to harm people and the environment, new legislation has created strict vehicle fuel economy and CO² emissions regulations. As manufacturers develop and bring into play technologies to meet these existing standards, the chemists and engineers at Afton have prepared solutions for the future.

Collaborating with industry leaders and academic experts, we developed mold breaking methods to determine how gasoline particulate filters (GPF) impact pollutant emissions in gasoline direct injection (GDI) vehicles. Our patent application, US 16/121,225 is the first accelerated aging test to determine how GPFs will interact with ash-forming oil lubricants over an engine’s full useful life.

By using a range of oils, including Afton’s own products, we discovered exciting results: not only do GPFs maintain performance, oil-produced ash and soot actually help GDIs meet emission standards.

Our researchers at Afton have uncovered key GPF performance details and ensured GDI can continue to meet future demands for cleaner vehicles.

2019 © Afton Chemical Corporation, All Rights Reserved. Not to be copied, shared, or reproduced in any media without the express written permission of Afton Chemical Corporation.

1. Tracking Trends 2

GDI Technology and Emissions Regulations Globally, emissions regulations are becoming more stringent. To meet CO² and fuel economy standards, manufacturers continue to turn to GDI engines in new vehicle designs. In fact, adoption of GDI engines is rising across the three major GDI markets, as detailed in Figure 1.

continues, vehicle manufacturers will need to account for stricter regulations.

Compared to conventional port fuel injection engines, GDIs produce high levels of particulate matter (PM) that includes carbon (soot) and inorganic material (ash). To reduce potential risk to the environment and our health, legislators have already taken measures to tighten the emission standards on motor vehicles.

Figure 2 shows the worldwide light-duty emission regulation timeline. In the future, legislation requirements and target deadlines for meeting those standards will tighten.

Figure 1: GDI production and forecast - GDI technology continues to grow despite stringent emissions regulations

By 2025, analysts predict that vehicles with GDI technology will pass 80% of new vehicle sales in all major markets. However, as this trend

With GDI popularity showing no signs of slowing, it is essential to prepare for tomorrow’s particulate emissions standards. While GPFs have emerged as a cost-effective system to meet particulate matter emission limits, we needed to evaluate its performance and interaction with ash-producing lubricants.

Figure 2: Global trends to tighten emissions regulations will continue through 2025 2019 © Afton Chemical Corporation, All Rights Reserved. Not to be copied, shared, or reproduced in any media without the express written permission of Afton Chemical Corporation.

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2. Addressing the Particulates GPF Soot and Ash Emissions From in-cylinder control to exhaust emission reduction, automotive engineers have explored a range of potential solutions designed to lower particulate matter. Our research and results continue to point to GPF technology as the most viable, cost-effective leader for particulate emissions control.

How GPF Works By thoroughly understanding the filtration processes, and associated aging mechanisms, we developed new methods to test how GPFs will perform over time when interacting with ashproducing lubricants.

Figure 3 depicts the GPF’s general structure and operation. The channels in the GPF alternate between being closed at the front or at the exit.

The exhaust gas containing particulate matter (PM) enters the open front channels. The PM is

filtered out of the exhaust as the exhaust moves through the wall to an adjacent channel that has an open exit. Designed as a monolith, GPF filtration is based on two major mechanisms that represent the two stages of filtration: 1. Stage One | Bed Filtration: After installing the GPF, exhaust gas must pass through a porous wall, the filter bed, which gradually traps PM (Figure 4, top diagram). This stage is characterized by lower filtration efficiency and rapid increase in back pressure.

2. Stage Two | Cake Filtration: Soot and ash build up along the interior channel wall and act as the primary filtration method after PM fill the pores in the channel’s wall (Figure 4, middle). This stage is characterized by higher efficiency and relatively slower increase in back pressure.

Particulate matter continuously builds on the

Figure 3 — The porous wall helps filter particulates from exhaust entering a GPF. 2019 © Afton Chemical Corporation, All Rights Reserved. Not to be copied, shared, or reproduced in any media without the express written permission of Afton Chemical Corporation.

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cake, comprised of soot products and engine oil derived ash. With high enough temperatures and sufficient oxygen levels, the soot will oxidize, regenerating the filter. Ash, however, does not oxidize and will gradually deposit inside the filter and leave a cake (Figure 4, lower image).

Figure 4 — As exhaust flows into the GPF, particle matter builds up.

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3. Developing a Method: Testing GPF Historically, determining how engine oil combustion products affect GPF performance over the full useful life (FUL) of a GDI required significant time and money.

Now, with Afton’s US 16/121,225 patent, we can apply our newly developed accelerated aging method to accurately address how soot and ash impact GPF durability and efficiency.

Accelerated Aging We used several popular accelerated aging techniques in new and unique ways to address the conditions of an engine over its FUL.

Figure 5a: Exhaust temperature engine map - Contour Plot of Fuel consumption rate vs Torque, Engine speed

Our goal was to realistically deteriorate a GPF quickly with minimum cost. To do so, we considered several key elements: • Thermal Aging: caused by exposure to high temperature exhaust • Ash Loading: derived from lubricant and other sources, including wear • Soot Generation and Regeneration: attributed to incomplete combustion and system operations To support this test, we developed an accelerated GPF durability method using a GDI engine (Shanghai Automotive Industry Corp., MGE Model, 2.0L, 4 cylinder). By running the engine under various conditions, we collected data to develop a comprehensive engine mapping and emission control system protocol.

Figure 5b: Fuel consumption engine map - Contour Plot of PN vs Torque, Engine speed

To do so, we monitored the backpressure and temperature profiles with installed pressure transducers and thermocouples. We also used emission instruments to measure soot and particle emission levels.

Figure 5c: Particle Number engine map - Contour Plot of Exhaust Temperature vs Torque, Engine speed 2019 © Afton Chemical Corporation, All Rights Reserved. Not to be copied, shared, or reproduced in any media without the express written permission of Afton Chemical Corporation.

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Figure 5d: Exhaust temperature engine map - Contour Plot of Fuel consumption rate vs Torque, Engine speed

Figure 5 illustrates the engine map for key parameters: 1.

Exhaust Temperature 2.

Fuel Consumption 3.

Particle Number 4.

Soot Level These maps helped determine how to run hightemperature thermal aging, as well as the low to moderate temperatures required for ash accumulation and cake buildup.

Throughout our method, we took extra caution to balance realistic GPF aging with reasonable test times and capabilities. We also ensured that our accelerated aging process would not produce unrealistic conditions or results.

Stage 1

Stage 2

Stage 3

Speed (rpm)

High

Medium

Low

Torque (N*m)

Medium

High

Low

Power (kW)

Medium

High

Low

Fuel Flow kg/hr

Medium

High

Low

Exhaust T (°C)

Medium

High

Low

PN (#/cm3)

Low

Medium

High

FSN

Low

Medium

High

Oil Doping

Yes

Yes

No

Primary Role

Ash loading Secondary Role Thermal Aging

Thermal Soot Aging Loading Engine Maintenance

Table 1: Our new GPF test methodology included a threestage process to identify GPF performance in various situations

The accelerated aging and cake build up in the three stages accurately reflects the FUL of a vehicle in consumer use. This protocol helped us realistically assess system performance durability, hardware technology, and lubricant oil interactions.

Three-Stage Protocol The accelerated GPF durability and performance protocol we developed involves a three-stage process based on testing targets and engine operating characteristics (Table 1).

Each of the three stages simultaneously ages the catalyst and builds the amount of ash and soot that would accumulate over the vehicle’s life.

2019 © Afton Chemical Corporation, All Rights Reserved. Not to be copied, shared, or reproduced in any media without the express written permission of Afton Chemical Corporation.

4. Using Chemistry 7

Lubricant and GPF Interactions A properly designed lubricant is essential for engine durability and performance. With GDI and GPF popularity on the rise, engineers and manufacturers need a balanced oil to help reduce emissions and increase fuel efficiency.

All base lubricants — synthetic or derived from crude — need additive packages to meet engine performance requirements. As shown in Figure 6, these additive packages deliver the full range of features demanded by modern engines.

With engines becoming increasingly complex, the demand for well-balanced lubricants is even greater. Contemporary engine oil performance specifications, like GF-6 oils, require even better wear protection, cleanliness, and fuel efficiency

than the previous generation GF-5 oils. Further, new tests and performance requirements target: • Low speed pre-ignition (LSPI) prevention • Air retention reduction as the lubricant is used more for hydraulic applications Addressing each of these requirements in isolation is relatively easy. When taken as a whole, however, the various aspects begin to conflict with each other. Therefore, lubricants — like GPFs — must be designed and evaluated as part of the whole engine, fluid, and emission system.

In this context, we studied the relationship between lubricants and GPFs. The two major areas are:

Figure 6 — With the increasing need to meet high-performance levels, lubricants must cover an ever-broadening range of operating requirements.

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1. Study Focus: Ash Loading Lubricant/GPF relationship primarily determined by: • Lubricant ash content • Lubricant oil consumption rate • Trap design • Vehicle mileage 2. Study Focus: Ash Impact on GPF Performance Lubricant/GPF Relationship affected by: • Ash loading • GPF properties • Lubricant chemistry • Vehicle operation During normal engine operation, a small amount of lubricant combusts and, due to the inorganic content present in oil additives, forms ash. While the additive levels vary based on the formulation, these additional components are crucial to the lubricant’s full functionality.

Example components include: • ZDDPs: efficiently deliver antiwear and antioxidant benefits to the system • Metal-Containing Detergents: ensure cleanliness and neutralize acidic species introduced by the lubricants, including combustion by-products To develop balanced, highly functional lubricants, we studied lubricants with standard ash and reduced ash levels. We set out to determine how and at what levels ash would prevent GPFs from meeting durability requirements.

High- and Low-Ash Oil Testing and Results To understand the technology’s extremes, we assessed how high- and low-ash–producing lubricants affected emission performance across new and aged GPFs. With an ash-level range from 0.6 – 1.25%, our tests covered most oils in the lubricant market. In addition, with a total ash load of 50 g/L at a normal oil consumption rate,

Figure 7 — Both high- and low-ash–producing lubricants met emission requirements.

we used a high-ash oil at the equivalent of more than 320,000 km. The charts in Figure 7 show the results for GPF performance and vehicle fuel economy from some of our vehicle testing.

During our testing, we evaluated key criticalperformance metrics, including: • Backpressure • Fuel Consumption • Particulate Mass (PM) • Particle Number (PN) We first observed that PN and PM remained comparable for high- and low-ash oils in both new and aged GPFs. When we looked at particulate emissions from new and aged GPFs, both oils showed improved filtration efficiency.

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Further, while the backpressure increases as the cake builds up, the ash loading ultimately raises filtration efficiency — and does not affect performance or fuel consumption.

These findings tell us that ash cake buildup can help boost GPF performance while keeping emission levels well below the regulation limit.

With the highs and lows covered, we turned to lubricant oils that produce mid-level ash buildup.

2. A balanced detergent formulation that met the LSPI compliance threshold (Oil B) When using a total ash load of 42 grams — equivalent to 200,000 km of on-road operation at a normal oil consumption rate — GPFs easily met emissions requirements. Figure 8 illustrates PN and PM trends in both Oil A and Oil B over the entire accelerated aging test.

To better understand the early filtration process, we studied PNs and PMs both upstream and downstream of the GPF. Our research showed that as ash loading continued, filtration efficiency improved the ability to lower particulate emissions.

Soot Oxidation Additionally, we explored the impact of these oils on GPF soot oxidation. Using eight oils with varying amounts of ash, we built a system to asses each lubricant’s soot oxidation rate.

Figure 9 illustrates the relationship between the detergents used — whether Magnesium (Mg) or Calcium (Ca) based — and the levels of ZDDP and sulfated ash.

Figure 8 — Ash caking in reduced SAP lubricants help keep particulate emissions low.

Reduced Ash Oil Testing and Results

Figure 9 — Building a matrix of eight oils helped us begin to understand their soot-oxidation levels.

Expanding on our testing, we also researched two reduced ash lubricant oils: 1. A modern product meeting ACEA C3 (Oil A)

We assessed the carbon oxidation rate for soot samples generated in an engine using each of the eight oils. The soot samples we tested

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contained both carbon content and ash from the combusted lubricants.

by reducing the total soot load over a GPF’s full useful life (FUL) or between regeneration events.

Figure 10 below demonstrates the rates at which the soot’s carbon portion oxidized for the different oils. These results show that the ash from lubricants can impact soot’s oxidation rate. Further, they may carry practical benefits

GPF and DPF Similarities and Differences While details like purpose and working principles are similar, GPFs and DPFs vary greatly in how they function. The combustion systems of each type of engine sets them uniquely apart. Table 2 lists the similarities and differences between GPF and DPF, covering: • Durability • Functionality • Integration • System Specification As the chart demonstrates, GPFs and DPFs are quite different in how they function. Of particular note, DPFs use fuel injections or heat sources to increase oxidation and clean soot from the trap. Meanwhile, current GPFs rely on passive regeneration to remove soot.

Figure 10 — Testing soot oxidation rates revealed that lubricant ash can positively benefit GPFs

Similarities

Categories

GPF

Purpose

Particulate filtration (Catalytic conversion)

System Integration

Packaging concerns for LD

Backpressure requirement

Needs to be reduced

Working principle

Three-mode filtration

Cost Configuration Exhaust temperature

Differences

DPF

Comparable UF, CC, FWC

UF

High

Low

02 in the exhaust

Low

High

Soot/ash production rate

Low

High

Relatively lower

Relatively higher

Not available

OBD integrated

Regeneration is needed, most likely as passive

Regeneration is needed, can be either active or passive

Cleaning strategy

No physical cleaning

Physical cleaning needed for HD, not for LD

Technical maturity

+

++

Ash density Control strategy Regeneration strategy

Table 2 — Though similar in concept, GPF and DPF systems are not interchangeable.

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Passive Regeneration The active-regeneration approach found in DPFs is much less likely to occur in GPFs. As such, we understand how ash build up can enhance oxidation and benefit the system.

Soot regeneration does have a potential to harm GPFs if not well handled. This harm could include: • Elevated backpressure due to the soot loading • Undesirable thermal shock due to regenerating excessive soot • High immediate emission of small particles due to uncontrolled soot burnoff

The plot in Figure 11 illustrates the transition of filtration stages. As the initial bed-filtration stage gives way to cake filtration, GPF efficiency rises. These behaviors are critical to real-world applications, as GPF technology is still new and within the low-mileage range.

Our findings clearly indicate that ash and soot levels in current lubricant technology should not affect GPF performance. As the industry trends toward reduced ash oils, engineers and manufacturers alike will need GPF technology to continue meeting emissions regulations.

Our goal is to identify a solution that helps GPFs overcome these problems. As we have found, when we formulate additives for lubricant oil, we can use its inherent physical and chemical makeup to benefit the entire system.

Test Results Afton’s patent — US 16/121,236 — has proven that we can use ash loading and oxidation to improve GPF efficiency. While others look for ways to reduce ash, we understand that using ash intentionally can help meet durability and emissions requirements.

Figure 11 — From bed filtration to cake filtration, Afton technology can help improve GPF efficiency.

Specifically, fresh GPFs have a lower filtration efficiency than aged GPFs which use ash cakes to assist the filtration process. Thus, controlling the early ash-loading phase is crucial to meet emission regulations. Otherwise, without sufficient cake built from soot and ash, lowfiltration efficiency can lead the vehicle to fail emission testing.

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5. Configuring Systems:

Optimizing GPF Performance With so much potential, GPF technology needs to work across a variety of vehicle emission systems. Our research further demonstrates how GPFs can fit within engine platforms for broader applications.

Figure 12 shows different gasoline emissioncontrol systems and how GPFs can be implemented.

Depending on system configurations and performance requirements, GPFs are sometimes coated with a catalyst. They can be closecoupled with TWCs or placed under the floor.

While GPF technology can support a range of modern vehicles, Afton studied its performance across a variety of the system configurations (Figure 12).

We demonstrated that regardless of GPF layout or catalyzation, our lubricant additives maintain performance and durability.

Our broad insights and deep understanding of GDI and GPF systems will help us deliver sustainable solutions to future needs.

To determine where and how a GPF fits in, one must identify its properties and the engine operation strategy. In some cases, GPFs can integrate into TWCs as a single piece to meet compact design standards.

Figure 12 — GPF specifications can work with a variety of gas vehicle emission control systems. (Ref. [7]) 2019 Š Afton Chemical Corporation, All Rights Reserved. Not to be copied, shared, or reproduced in any media without the express written permission of Afton Chemical Corporation.

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6. Reviewing Our Results: The Takeaway With growing environmental concerns and the rise of GDI systems in vehicles, the industry needs a solution to meet our emissions goals.

By developing patent US 16/121,225— a mold breaking accelerated aging method used to test lubricants — our researchers have paved the way for full useful life assessment of GPF technology. Not only are ash and soot derived from oils integral to the process, our research proves that they each can help GPF emissions fall well-below future standards (US 16/121,236).

In short, the future’s path toward meeting fuel efficiency and lower emissions is here today.

We understand that new technology needs investigating. By collaborating with global experts, Afton Chemical will continue to design and implement mold breaking methods and strategies to find answers to tomorrow’s questions.

2019 © Afton Chemical Corporation, All Rights Reserved. Not to be copied, shared, or reproduced in any media without the express written permission of Afton Chemical Corporation.

Bibliography 14

1. Zhan, R., Eakle, S. T., Weber, P., “Simultaneous Reduction of PM, HC, CO and NOx Emissions from a GDI Engine”, SAE 2010-01-0365 2. Ito, Y., Shimoda, T., Aoki, T., Yuuki K., et al., “Next Generation of Ceramic Wall Flow Gasoline Particulate Filter with Integrated Three Way Catalyst”, SAE 2015-01-1073 3. Seong, H., Choi, S., Ash-Durable Catalyzed Filters for Gasoline Direct Injection (GDI) Engines, 2016 DOE-Crosscut Lean/Low-temperature Exhaust Emissions Reduction Simulation (CLEERS) Workshop, April, 2016 4. Lambert, C., “Gasoline Particle Filter Development”, 2016 DOE-Crosscut Lean/Low-temperature Exhaust Emissions Reduction Simulation (CLEERS) Workshop, April, 2016 5. Shao, H., Lam, W., Remias, J., Roos, J., et al., “Effect of Lubricant Oil Properties on the Performance of Gasoline Particulate Filter (GPF)”, SAE 2016-01-2287 6. Miao, S., Luo, L., Liu, Y., and Zhan, Z., “Development of a Gasoline Particulate Filter for China 6(b) Emission Standards”, SAE 2017-24-0135 7. Joshi, A., “Progress and Outlook on Gasoline Vehicle Aftertreatment Systems”, Johnson Matthey Technology Review, 2017, 61(4), 311-325 8. Choi, S., Seong, H., “Lube Oil-dependent Ash Chemistry on Soot Oxidation Reactivity in a Gasoline Direct-injection Engine”, Combustion and Flame, 174 (2016): 68-76 9. Xia, W., Zheng, Y., “Catalyzed Gasoline Particulate Filter (GPF) Performance: Effect of Driving Cycle, Fuel, Catalyst Coating”, SAE 2017-01-2366 10. Lambert, C.K., “Gasoline Particulate Filter Development”, API DAP meeting, Detroit, December 12th, 2017 11. Shao, H., Carpentier, G., et al., “Engine Accelerated Aging Method Developed to Study the Effect of Lubricant Formulations on Catalyzed Gasoline Particulate Filter Durability”, SAE 2018-01-1804 12. US 16/121,225 “Predictive Methods for Emissions Control Systems Performance” 13. US 16/121,236 “Gasoline Particulate Filters with High Initial Filtering Efficiency and Methods of Making Same” 14. Figure 2: Delphi - Worldwide Emissions Standards. Passenger Cars and Light Duty Vehicles 20172018

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