Alternative Fuels: How Do They Affect Lubrication in Heavy-Duty Vehicle Engines?

Ambitious EU goals for reducing CO82 emissions in heavy vehicles are increasing the popularity of alternative fuels.

This process is slow, and the vast majority of newly registered heavy-duty vehicles in EU countries still have low-emission diesel engines. At the same time, the number of heavy-duty vehicles powered by alternative fuels is gradually increasing, and the strategy to reduce CO82 emissions also creates enormous development pressure on OEM manufacturers. Although Poland is not currently leading in the number of vehicles powered by alternative fuels, this trend will not pass us by. Together with experts from Mobil Delvac oil manufacturer, we explain what requirements different alternative fuels impose on lubricants.

Market Realities and the Popularity of Alternative Fuels

Reducing CO82 emissions by 90% in heavy-duty vehicles by 2040 is one of the EU’s environmental priorities. According to estimates by the European Automobile Manufacturers’ Association ACEA, achieving the intermediate goal of a 45% emission reduction by 2030 would require the introduction of 400,000 zero-emission trucks and the registration of at least 100,000 such vehicles each year. This is undoubtedly an ambitious goal, as according to ACEA data, in 2022, about 97% of new trucks sold were powered by diesel, with the remainder using alternative fuels.

So what alternative fuels are used in trucks to reduce emissions and improve fuel efficiency? Among them is the popular biodiesel, natural gas, as well as newer families of alternative fuels like hydrogen, synthetic fuels, and electricity.

Oil Requirements and Compatibility with Various Fuels

The impact of alternative fuels on engine lubrication varies depending on the type of fuel used. Let’s look at specific cases.

Biodiesel

It can be used alone or in diesel fuel, which makes it widely available at fuel stations. Biodiesel is produced from various raw materials affecting its properties and quality. Higher biodiesel content can increase the risk of engine oil dilution by fuel and result in faster degradation of the lubricant product.

As Esin Yilmaz, Technology Solution Professional, ExxonMobil, emphasizes, potential risks from using fuels with a high content of biocomponents include faster oil oxidation, deposit formation on the pistons, changes in flow temperature, and oil viscosity. “When using biofuels, it’s worth asking your lubricant supplier whether the proposed product has been tested for compatibility with biodiesel. At ExxonMobil, we have conducted oxidation stability, low-temperature pumpability, and piston cleanliness maintenance tests for Mobil Delvac oils working in the presence of biodiesel. Biodiesel can enter the lubricant, and the nature of this fluid can potentially accelerate oil oxidation. That’s why ExxonMobil conducted tests burdening engine oil with biodiesel at high temperatures. The aim was to demonstrate the engine oil’s resistance to oxidation. This allows us to advise customers on which lubricants are compatible with this fuel.” Information about oil compatibility with biodiesel-powered engines is available on the front label of selected Mobil Delvac lubricants. One of them is Mobil Delvac Modern 5W-30 Extreme Protection.

Natural Gas

Compared to diesel, it emits several percent less CO82 and combusts more cleanly, reducing soot and acid production. These conditions place less strain on oil life and lubrication systems, but there is another side to the coin. Natural gas generates higher engine temperatures, increasing oil stability requirements to minimize ash deposits in the combustion chamber.

“A good engine oil, compatible with a CNG engine, should feature high resistance to oxidation and nitration. Besides, natural gas engines require oils with low ash content because high ash content can lead to deposit build-up in the combustion chamber and on valve seats, potentially causing valve recession. We consider all these requirements when developing our oil formulations, compatible with gas-powered engines,” explains a Mobil Delvac expert.

Hydrogen

This fuel is gaining more interest among OEM manufacturers and provides real benefits to owners of hydrogen-powered vehicles. Refueling time is comparable to diesel-powered vehicles. The range per refuel is significantly greater compared to EV vehicles, and most importantly for the environment, water is the only emission. Due to the challenges associated with combustion in a hydrogen engine, including higher combustion chamber temperature, pre-ignition, and water presence, entirely new lubricant solutions were necessary. Recent collaboration between ExxonMobil and an H2 engine manufacturer has resulted in the development of high-quality oils for hydrogen units, with their effective protection confirmed by tests. In the future, as hydrogen engines become more popular, such lubricants will find broader application, including in heavy vehicles.

Electricity

Heavy-duty vehicles powered by electricity are still a distant prospect. Between 2020-2022 their sales volume in the European Union grew by 0.1% annually, reaching 0.6%. Of course, electric vehicles (EVs) do not require engine oil used in combustion units, but other lubrication challenges arise.

“I sometimes hear opinions that the lubricant industry will stagnate in the era of electromobility. That’s certainly not true. And while the vision of electric freight fleets on European highways is still distant, we are already developing a range of Mobil EV fluids for electric passenger, delivery, and heavy-duty vehicles,” comments Esin Yilmaz. Mobil EV Therm Elite 701, a state-of-the-art product designed for direct, immersive cooling of batteries in electric vehicles, is an excellent example of transitioning from concept to new technology ensuring more efficient heat dissipation and temperature control of cells.

Regardless of the type of alternative fuel used, employing high-quality oils, greases, or additives is essential. This is especially important for fleets transitioning from fossil to alternative fuels, as their lubrication needs may vary significantly. When making such a change, it is worth consulting with a lubricant supplier and following the good advice of Mobil Delvac specialists, who encourage treating the purchase of lubricants as an investment that helps reduce the vehicle’s total cost of ownership (TCO).