PSA looks for the right balance

Challenges and constraints impact future lubricant performance requirements

As emissions limits right across the world tighten, OEMs are introducing new hardware technologies across the powertrain to ensure their vehicle fleets comply. Dr Gérald Crepeau, battery & aftertreatment functional design & fuels expert at PSA Peugeot Citroen, talks to Insight about how he expects these changes to impact lubrication requirements and discusses the new PSA low-speed pre-ignition test.

Tightening emissions limits are one of the key drivers of change to vehicle hardware and in turn to lubricant performance requirements. Euro 5, which has been obligatory for all vehicles produced since January 2011, introduced strict limits for particulate matter. These limits made the use of diesel particulate filters (DPF) on all diesel models essential.

DPF introduction at PSA

Dr Gérald Crepeau, PSA Peugeot Citroen Infineum International Limited

At Groupe PSA the particulate filter on our vehicles was already deployed by 2000, and more widely introduced since 2008. Following Euro 5, diesel vehicles emit fewer particles than the best petrol vehicles.

Three years later, in 2014, the Euro 6 standards imposed, inter alia, new tougher limits to control emissions of nitrogen oxides (NOx). However, there are differences between the emissions characterised ‘on cycle’ and those generated in real driving conditions. “To reduce this gap,” Gérald explains, “legislators have imposed more dynamic test cycles called the Worldwide Harmonised Light Vehicle Test Procedure and the Real Driving Emissions test, which came into force for Euro 6.d TEMP in 2017.

Impact of emissions regulations on lubricants

Dr Gérald Crepeau, PSA Peugeot Citroen Infineum International Limited

This hardening will result in a reduction of the emissions from the vehicle of 80% vs the vehicles of former generations! The engine oils will thus be formulated to ensure durability of all the different aftertreatment systems like oxidation catalysts, DPF, gasoline particulate filters (GPF), selective catalytic reduction (SCR) and passive NOx absorbers (PNA).

The second key driver that Gérald sees impacting lubricant technology is vehicle electrification, which introduces new thermal and dilution stresses. “To meet CO2 emissions reduction targets I believe the market share of electric vehicles will grow. In Europe, we are targeting 15% of plug in hybrids and electric vehicles in 2025 along with a very strong increase in mild and other hybrids.”

Along with these emission reduction drivers, Gérald also sees fuel diversity as a key driver for change in lubricant performance. “This does not just mean the ability to cope with an increase in the different types of biofuel being used in different concentrations, but also the use of a wider variety of compounds, such as aniline and butyl acetate, in the global fuels mix.”

Ensuring these drivers are transferred into lubricant formulations so that emerging constraints can be met is a complex business.

PSA response to market drivers

Dr Gérald Crepeau, PSA Peugeot Citroen Infineum International Limited

For all these drivers a lot of R&D projects were and are required to ensure the durability of the engine oil and the engine and the post treatment systems. Improvements of the engine calibration and the hardware are also necessary so as not to put all the efforts on the engine oil formulations.

In addition to these R&D efforts, PSA has taken the majority of the different key drivers into account in their lubricant specifications. “As the formulation window closes, it is necessary for us to pursue our efforts within these constraints and to keep our chemistries at the appropriate levels. To ensure aftertreatment durability, for example, particularly because the chemistry differs from system to system, it is necessary to limit sulphated ash, phosphorus and sulphur (SAPS) in the formulation.”

One of the key challenges is achieving a good balance between improved fuel economy and longer oil drain intervals. “In my view, as we move to lower lubricant viscosities, we will need to work on finding the right balance of Group IV and V base stocks and suitable additives. But, we also need to ensure these formulations are robust so that they continue to provide sufficient engine durability.

Achieving a balance

Dr Gérald Crepeau, PSA Peugeot Citroen Infineum International Limited

More and more constraints on the engine oils formulation is a real challenge. To achieve improved fuel economy and post treatment / engine robustness and durability requires more and more interaction between additive company and car manufacturer to do research together to have a better understanding of current and future needs.

LSPI is the latest challenge

The challenges do not stop there, PSA is also looking at new problems being experienced in the field – the latest of which is low-speed pre-ignition (LSPI). “Many passenger car drivers have observed intermittent pre-ignition in their turbocharged gasoline engines, particularly at low speeds and medium-to-high loads,” Gérald explains. “At these elevated loads, pre-ignition usually results in severe engine knock that can damage the engine.”

Gérald goes on to outline the complex LSPI phenomenon: “Pre-ignition in a flame propagation (or ‘spark-ignition’) engine describes an event wherein the air/fuel mixture in the cylinder ignites before the spark plug fires. It is initiated by an ignition source other than the spark plug, such as hot spots in the combustion chamber.” However, as Gérald points out, pre-ignition can be initiated in a number of ways including:

  • Hot deposits within the combustion chamber.
  • Elevated levels of lubricant vapour from the PCV (positive crankcase ventilation) system.
  • Oil seepage past the turbocharger compressor seals.
  • Auto-ignition of oil and/or fuel droplets.

In his view, the current LSPI tests fall short of PSA's requirements for LSPI protection.

PSA's new LSPI test

Dr Gérald Crepeau, PSA Peugeot Citroen Infineum International Limited

The current LSPI tests look at the propensity of a new engine oil to create LSPI events. But in fact it is a bath curve. At the first kilometers it is possible for an engine oil to create reactive species due to mechanical and chemical shearing. But the ageing of the engine oil and higher pressure increase in the combustion chamber creates more LSPI events. Moreover the dispersant detergent nature can impact the number and the size of the fuel/ engine oils droplets and so the LSPI events. That’s why Groupe PSA developed a LSPI test, which covers all the different driving life which generate LSPI in the field and with aged oils.

Clearly, the lubricant has a role to play in minimizing LSPI events. “Although we have seen hardware and engine software improvements, in the fight against LSPI I think that dedicated anti-LSPI engine oils will continue to be required.”

We concluded by asking what Gérald expects as a result of all the uncertainty stemming from these tightening constraints, high levels of complexity and the next generation of challenges. His answer was simple: “I think it means we still have a lot of work in front of us!”

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Passenger cars

SN PLUS and beyond

23 May 2018

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