Page 49 - Energize August 2021

TECHNICAL

The base oil itself cannot protect against the detrimental effects of choice in modern SCR systems. Most people know DEF by its
of oil oxidation and for this reason engine oils contain antioxidants. more commercialised name of AdBlue or, in South Africa, Air 1
These are a group of additives that minimise oxidation and deposit- which is supplied by Engen Petroleum.
formation by targeting particular steps in the oxidation reaction. Air 1 is aqueous urea solution which comprises 32,5% urea
They decompose reactive hydroperoxides and free radicals before and 67,5% deionized water. The water acts as a solvent to ensure
they lead to oxidation of the base oil. the solid urea, which is in the form of colourless crystals, becomes
There are two types of antioxidants: primary and secondary a liquid solution. Air 1 is non-toxic, odourless and perfectly safe
antioxidants. Primary antioxidants are free radical scavengers to handle.
typically comprised of aromatic amines and hindered phenolics. The Air 1 is injected from the vehicle’s dedicated storage
Secondary antioxidants are peroxide decomposers typically tank into the exhaust pipe, which is usually situated in front
composed of phosphates and certain sulphur-containing compounds. of the SCR catalyst, but downstream of the engine. As it is
With the restriction in phosphorus-containing additives like heated in the exhaust, the Air1 changes into ammonia (NH₃)
ZDDP and increased oxidation control requirements, formulators and carbon dioxide (CO₂). When the nitrogen oxide (NOx)
have turned to incorporating higher levels of ashless antioxidants in gases from the exhaust pipe react inside the catalyst with the
their blends. NH₃, the harmful NOx molecules in the exhaust are converted
Ashless-type oxidation inhibitors have helped to replace into harmless nitrogen (N2) and water, which is released to the
the oxidation performance of ZDDPs, with recent additive atmosphere as steam.
systems making use of aminic and phenolic chemistries. The Air 1 consumption varies depending on the particular
use of molybdenum-based chemistry for improved anti-oxidancy aftertreatment system of the exhaust gases, but also on driving
performance has also gained popularity in recent years. style and driving conditions. Air 1 dosing into the exhaust system
Given the ever-changing landscape in the lubricant industry is typically between 3 to 5% of the fuel consumed.
and these stringent oil quality requirements, it became apparent Purity requirements for SCR catalyst reductants are high
that a new heavy-duty engine oil category would be required. As and among the specific requirements, metals such as sodium,
a result of this, the API introduced two new standards to take the potassium, calcium, magnesium, copper, zinc, iron or chromium
latest technology in diesel engines into account. API CK-4 and FA-4 – as well as the content of ash-forming phosphates – must be
first appeared in the API service symbol donut in 2017. These new kept at low levels in SCR-grade urea. As a result of these purity
service categories improve upon existing standards by providing requirements, storage and handling of these reductants is of
enhanced protection against oil oxidation, engine wear, piston utmost importance.
deposits, shear stability as well as providing better compatibility Urea-based DEFs do have some drawbacks, including low
with emission-controlling devices. freezing temperatures (-11°C) and the necessity to carry the weight
API CK-4 was introduced to reflect the upgraded performance of the liquid. However, with widespread adoption of highly efficient
benefits beyond API CJ-4 for engine lubricants with a minimum SCR systems, diesel engines are likely to become a more significant
HTHS viscosity of 3,5 cP. New API CK-4 lubricants must pass source of urea demand globally.
more stringent oxidation and aeration limits with increased
shear stability, providing greater protection for heavy-duty diesel There is no “plan B”
engines. CK-4 is backward-compatible with older API categories It is widely acknowledged that there is more to be done in the drive
like CJ-4. to further reduce harmful gases, improve air quality and mitigate
The API FA-4 fuel efficiency category requires lubricants to pass the effects of global warming. Limits on emissions in the heavy-
the same performance tests as API CK-4, with the addition of a duty engine sector are expected to become more stringent in the
HTHS viscosity limit of between 2,9 and 3,2 cP, to deliver increased future and further engine hardware changes, the expansion of
fuel efficiency benefits whilst maintaining engine protection. The current technologies and the introduction of new emission control
FA-4 category is not backward-compatible. devices are among the options being explored. The road to zero
Evolutionary approaches will continue to play a role in lubricant harmful emissions is not going to be an easy one, but it is one that
formulations of the future. However, real step-out changes in the we, as a civilisation, must travel in order to safeguard the future of
additive technologies are currently taking place to address the this beautiful blue marble we call home. As former UN secretary
longer-term needs of the industry. Hopefully, it can be seen that General Ban Ki-moon famously said during the 2016 United
such changes will affect not just one or two classes of additives, but Nations Climate Change Conference- “There is no plan B because
every major type of additive component used in oil formulations. All there is no planet B”.
of this makes for trying times in the lube kitchen. Diesel engine emissions standards introduced around the world
have undoubtedly had a major impact on reducing pollutants so
DEF it’s not all doom and gloom. To give you an idea of how far we
And finally, a new addition to the buffet on offer to the most have come – 30 years ago, one heavy on-highway truck produced
discerning of diesel engines is diesel exhaust fluids (DEF). As the same level of particulate matter as 100 heavy goods vehicles
already mentioned, SCR technology uses a reductant known as produced in 2019. Now isn’t that a breath of fresh air? n
a DEF, which is injected into the exhaust gas to help reduce NOx
emissions, over a catalyst. Aqueous urea is the preferred reductant Send your comments to rogerl@nowmedia.co.za

energize | August 2021 | 47