Adrian Hill, technology manager at Morris Lubricants, discusses the role engine oil plays in reducing emissions.
In the world of passenger cars, the challenge of reduced emissions is being addressed continually with new technologies and the latest innovations that deliver significant improvements. However, there are many pieces to this ‘emissions’ jigsaw and each must be in place, for the true overall benefits to be realised. Engine oil has a part to play in this jigsaw and in its mission to reduce emissions.
Since the 1990s, legislation has continued to drive vehicle emissions down, resulting in an evolution of engine and exhaust systems. A variety of emission reduction technologies have been introduced over the years to control the levels of NOx gases, carbon dioxide and particulate matter (harmful solid debris). The continued effectiveness of these systems has always depended strongly on the quality and performance of the oils and lubricants used.
NOx gases can be controlled using exhaust gas recirculation and selective catalytic reduction systems (Adblue). EGR, whether in diesel or petrol engines, creates a severe engine environment, with spent exhaust gases being introduced into the fuel/air mixture. This reduces the amount of free oxygen available to convert nitrogen in the air to NOx compounds. However, the side effect is incomplete combustion, which can lead to undesirable levels of soot.
Soot is not only abrasive, but also affects the flow properties of the oil. Without the correct level of oil performance, the engine will experience accelerated wear and oil thickening, which could lead to catastrophic failure. Correctly formulated engine oils control this wear and thickening and help the engine to run at optimum efficiency, contributing to the reduction of emissions.
The SCR systems (Adblue) rely on the effectiveness of a catalyst fitted to the exhausts of diesel cars. Adblue, a solution of urea, is sprayed into the exhaust gas stream and is carried into the catalyst, where a chemical reaction takes place to remove NOx gases, by converting them to nitrogen and water vapour.
However, when the engine oil lubricates the compression rings, valve stems and valve guides, a small amount of lubricant is burnt, releasing sulphur and phosphorous from certain compounds. These elements find their way into the catalyst and poison the active sites where the reaction takes place, making the catalyst unusable. Engine oils must be correctly formulated to ensure the additive chemistry and formulation provides suitable levels of wear and corrosion protection, while ensuring the maximum service life from the catalyst.
Balancing act
In effect, it is a chemical balancing act. A poorly functioning catalyst will not only be unable to control emission levels, but engine management systems may put the vehicle into reduced power mode (or limp mode) until the situation has been remedied.
Diesel particulate filters are installed in the exhaust system to catch particulate matter (soot) and to prevent it from entering the atmosphere where it can cause health and environmental issues. Sensors monitor the working pressure across the unit and when it drops to a defined value, a regeneration cycle is initiated. This usually involves unburnt fuel entering the unit, causing a temperature spike that oxidises the soot (solid) to carbon dioxide (gas). Carbon dioxide flows out and the unit is good to go again.
In petrol engines, the introduction of direct fuel injection has again made big improvements in fuel efficiency due to higher injection pressures and vastly improved atomisation of the fuel. The high level of atomisation in TGDI (turbocharged gasoline direct injection) engines essentially increases the available surface area of the fuel, which, although providing a better burn, can lead to the formation of carbon (soot).
In the same way that carbon (soot) in diesel engines passes through the exhaust system, carrying harmful by-products of combustion, carbon generated in TGDI engines can do the same. This has led to the introduction of gasoline particulate filters (GPFs) to catch this carbon and to stop it entering the atmosphere.
As mentioned previously, a small amount of lubricant is burnt during engine operation and this creates a metallic ash, from certain additives, that is swept into the DPF or GPF. However, the metallic ash that is generated remains behind during regeneration and eventually the DPF or GPF will be unable to reach normal pressure ranges. Again, the vehicle will click into reduced power mode until the situation is remedied.
Using the correct engine oil with the correct formulation will protect the engine components and ensure that the DPF or GPF has the best possible service life. When the DPF or GPF are working at their optimum levels, particulate emissions are controlled more effectively. Poorly formulated and low-quality oils will lead to the premature blocking of diesel and gasoline particulate filters, resulting in expensive replacement and time in the garage.
Another strategy to reduce emissions is to improve fuel efficiency. If less fuel is used, then emissions are also reduced. Improvements in fuel efficiency can be made by using engine oils that produce thinner oil films in the bearings and where the compression ring travels along the cylinder liner. These thinner oil films result in less drag and therefore offer more useable energy that can be directed to the wheels.
To ensure that component integrity is not compromised, these thinner engine oil films are fortified with polymer chemistry to ensure there is no metal-to-metal contact. New low viscosity engine oils, such as 0W-8, 0W-16, 5W-20 and 0W-20s, contribute to significant improvements in fuel efficiency.
The modern passenger car engine is complex and is still evolving. New hardware technologies, engine designs and fuelling strategies produce real world emission reductions, but they will only achieve this if they are fitted with new generation engine oils, which are as critical as any other component.
Morris Lubricants’ Multivis is a range of superior quality automotive engine oils that use the latest synthetic technology products and oil formulations required in the operation of these low emission engine designs and specifications. The chemical profiles in the Multivis range are carefully tailored to ensure maximum after-treatment device compatibility found with petrol, diesel & hybrid engines.
