CPC Pitches PAOs for E-fluids

“These e-fluids will offset the loss of the passenger car motor oil market space and accelerate the quality shift toward ultra-low synthetic viscosity grades and premium base oil and lubricant products,” Sharbel Luzuriaga, a project manager in Kline’s energy practice, told ACI’s European Base Oils and Lubricants conference in November.  

Novel base stocks will have to address heat transfer, electrical conductivity, material compatibility and durability challenges unique to electrified vehicles, both hybrid and pure battery.

>Read more about EV fluid requirements here.

“The emerging EV lubricant formulations can be achieved with Group III, Group III+ base stocks, PAOs and synthetic esters. Fluor-based fluids and low conductivity glycol-base stocks are also in play for use in transmission systems,” Luzuriaga said.

Dedicated fluids for dielectric applications have been in use for at least four decades, said Ken Hope of Chevron Phillips Chemical. They are commonly found in applications such as computer cooling, bitcoin mining and 5G mobile phone network systems, which use large amounts of energy.

“Their product stability and ability to shed water are their inherent advantages,” Hope said.

First and foremost, the ideal base oil for these applications, including battery thermal management and hybrid vehicle transmission, needs to have low viscosity, thinks Hope.

“With low viscosity means less energy to move the fluid, while low viscosity and higher density of the fluid is beneficial for heat transfer. Oxidative stability and thermal conductivity relates to cooling efficiency, by the ability to move that heat around,” he said.

The base oil also has to be hydrolytically stable, Chevron Phillips found in tests. 

“It means that it have to repel water and other impurities, which are contaminants for dielectric fluids. It also have to resist hydrolysis. The liquid hydrolyses is related to resulting products that can be flammable, corrosive and to cause electrical problems,” he said.

The ideal base oil for a dedicated e-fluid should also have material compatibility to such products as elastomers and insulation components, be shear stable because of the high-speed bearings found in EVs, have flash and fire point within limits, good freeze point, low foaming/aeration properties and be biodegradable.

Base stocks have different properties and if compared, silicate esters have issues with hydrolysis, while aromatics have issues with flash point and biodegradation, according to Hope. Mineral oils have fewer issues all round but PAOs excel in all aforementioned properties, Hope added.

“PAOs have very good frictional properties and it is demonstrated by our bench tests. Low friction generates less heat. They also have much better thermal conductivities compared to hydrocracked and mineral base oils.” 

Chevron Phillips’ bench tests have shown that temperature reduction has been related to specific heat differences. 

All of these inherent differences are believed to be responsible for and are working in concert to provide finished lubricants with increased oil life and reduced energy consumption, he concluded, giving a thumbs up to the fact that PAOs are in an undisputed lead position in the search for ideal E-fluid formulation.