Thin end of the wedge
Very low-viscosity oils can improve fuel consumption and emissions but meeting OEMs’ volatility and durability specifications will be challenging
- Published in Features.
Shell's 0W-10 concept oil can improve fuel consumption by 4.6% on the combined cycle
Meeting fleet average CO2 targets means that improvements in combustion engine efficiency have to come through more quickly than in the past. This means optimising everything, not just downsizing, deleting cylinders or hybridisation.
The lubrication circuit is coming under closer scrutiny now. Variable flow oil pumps are becoming more common – only moving as much oil as you need, at the pressure you need, reduces parasitic losses. But there’s an increasing focus on the oil itself.
Reducing the viscosity reduces friction losses, which lowers fuel consumption. But only up to a point – go too far and the extra pumping losses cancel out some of the gains. Volatility is higher – that could increase evaporative emissions.
And OEMs have tough requirements on durability and oil drain intervals. Striking the right balance will not be straightforward. Shell has developed what it calls an ultra-low viscosity concept oil.
Instead of the typical 10W-30 grade, this engine lubricant is formulated to 0W-10. Tested in a Gordon Murray design T.25 city car prototype, the fuel consumption improvements are 6.5% on the urban cycle and 4.6% on the NEDC cycle.
Shell draws an analogy with a concept car – it shows what’s possible. Some of the features will reach the market; others won’t.
“We wanted to demonstrate that there are further fuel consumption improvements available than with today’s engine oils,” says Simon Dunning, Shell’s technology manager for passenger car motor oils. “We wanted to see what we could achieve by applying new technologies to lubricant formulation.
“Clearly, durability is one of the other aspects we’re working on. Partnerships with OEMs are key to co-developing the optimum solution in terms of the oil and the engine.”
Now the hard work comes in developing ultra-low viscosity engine oils for series production applications. This won’t be easy.
OEMs want to reduce CO2 emissions but also want to reduce oil consumption and maintain or increase oil drain intervals. And all at a time when engines will require better performance from oil, especially as downsizing becomes more extreme.
Making the oil thinner could affect durability. Investigating this trade-off is a big part of Shell’s test and development work for the future. Stability is another. Thinner oils are more volatile – this tends to increase evaporative emissions and oil consumption.
