Audi has opted for the 6 MJ hybrid subclass for its all-new R18 because it feels the top hybrid power category, which LMP1 rivals Porsche and Toyota will utilize in this year’s FIA World Endurance Championship, could potentially be a disadvantage for diesel-powered cars.
According to Audi Sport technical director Joerg Zander, the current Equivalence of Technology tables does not provide any performance advantage, as seen with gasoline-powered cars, when factoring in the heavier diesel powerplant to the mix.
“You would have a weight issue if you go to the 8 MJ diesel concept but it’s not worthwhile understanding the EoT category at the moment,” Zander told Sportscar365. “You should not gain any advantage, and if anything, it would be a disadvantage.
“One thing you have to consider, whilst the diesel has a more efficient combustion process, as we know, the petrol cars get more fossil energy to compensate that. They have more energy per lap available to balance this kind of effect.
“On the other end, a bit of a drawback is because of the much larger combustion pressures — the working pressures you get with this combustion process — you have to ask for a different level of structural integrity, which means the components would be heavier.
“Of course we get a certain amount of additional energy to compensate for the extra weight… But you would [still] not get any additional energy if you have 8 MJ ERS system in the car. There’s still difference in weight, so what are you going to do with it?”
Zander said the K Technology Factor, a function to calculate the difference between allocated energy and maximum instantaneous fuel flow, has made it difficult to yield any potential gains with a step up to 8 MJ.
LMP1 hybrids are regulated to a 0.980 K Factor for the 2 and 4 MJ subclasses per lap of Le Mans, with a slight change to 0.979 for 6 MJ but a considerable leap to 1 K Factor for the top hybrid power category.
Additionally, a move to 8 MJ, Zander said, would have resulted in a 30-40 kg increase in the R18’s weight, which would have put it well over the 875 kg overall minimum.
“I don’t want to say it was a no-brainer, because you still have to look at it, but it’s not worthwhile,” Zander said.
“We discussed this with the FIA and ACO because they may think there should still be a strive to go for the 8 MJ class, but clearly, we can explain to them that it doesn’t make sense at the moment.
“The energies we transfer on the track, we would end up with an overall concept that’s too heavy and doesn’t make sense.”
Audi has gone with a complete overhaul of its R18 for 2016, not only stepping up from the 4 to 6 MJ hybrid subclass but utilizing battery storage instead of its previous flywheel design.
Zander said they’ve been able to recover most of the FIA’s class-wide reduction in fuel flow, as witnessed by lap times set in last month’s official pre-season Prologue test at Paul Ricard.
“The major focus we put on this car concept was to increase efficiency, all over,” he said.
“Because of the energy reductions, what we wanted to achieve is to develop the car in all areas and to balance the losses with the gains of development. Hopefully we can have a similar car like last year’s car.”
While there’s a significant increase in electric power, with up to 350 kW now transferred, compared to last year’s 150-200 kW, Audi has remained with a single motor unit, attached to the front wheels, instead of the maximum two hybrid systems allowed per rules.
Zander said weight and the added complexity of balancing motors at both axles played a factor into their decision.
“At this stage of the project, we said 6MJ, we can recuperate it with just system in place,” he said. That’s why we’re doing it. It’s more efficient at the end of the day.”