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2014 Audi R18 e-tron Quattro Le Mans racer consumes about 40% less fuel than first TDI engine at Le Mans in 2006

Audi is racing three R18 e-quattros at Le Mans. Click to enlarge.

The Audi R18 e-tron quattro diesel hybrids (earlier post) that will race at Le Mans this coming weekend (14-15 June) are the lightest and most fuel efficient LMP1 racers has yet to bring to the track. New WEC regulations require up to 30% less fuel use this year.

For the powertrain, Audi, in the 25th year of the TDI engine, has developed a new diesel 4.0-liter V6 unit for Le Mans. It has been purposefully designed for efficiency and, together with many other optimizations of the race car, such as aerodynamics, helps save energy. Compared with the 2006 5.5-liter V12 Audi R10 TDI, the first TDI engine used at Le Mans, the current race car consumes about 40% less fuel while achieving comparable lap times.

Specifically, 138.7 megajoules of fuel energy are available to the new R18 e-tron quattro per lap at Le Mans. This amounts to 6.16 liters less per 100 kilometers than the gasoline engines of the challengers, Toyota and Porsche, are allowed to consume.

Top: The LMP1 rules define energy classes for different powertrain systems. Bottom: The flow of energy and the amount of energy for ERS systems are also specified precisely by the rules. Click to enlarge.

If the best teams, as last was the case in the 2012 season that saw only brief safety car periods, covered 378 laps, then Audi’s high-performance TDI engine would have 317.52 liters less fuel available in the course of 24 hours than the gasoline units.

The situation at Le Mans is aggravated by the sum of all ratings. A complex set of rules assesses the various technical concepts. Through energy allocations and fuel flow quantities, as well as the pit stop intervals resulting from fuel consumption and fuel tank capacity, the regulations aim to achieve an “equivalence of technology.”

In addition to the new, more efficient internal combustion engine, the 2014 R18 powertrain concept, for the first time, features the integration of two hybrid systems: ERS-K and ERS-H.

  • ERS-K. As before, during braking events at the front axle a Motor-Generator-Unit (MGU) recovers kinetic energy flows into a flywheel energy storage system. A fundamentally new Motor Generator Unit (MGU) sits in the monocoque together with a differential, which are both level with the front axle. A pair of driveshafts connect the system to the front axle. Under braking, the kinetic energy of the wheels is converted into electric energy, which is stored in a new, optimized flywheel accumulator mounted in the cockpit alongside the driver. The recovered energy is reconverted during acceleration by the MGU and powers the front wheels.

  • ERS-H. For the first time, the engine’s turbocharger is linked to an electrical machine, which makes it possible to convert the thermal energy of the exhaust gas flow into electric energy—e.g., when the boost pressure limit has been reached. This energy also flows into the flywheel energy storage system. When the car accelerates, the stored energy can either flow back to the MGU at the front axle or to the innovative electric turbocharger, depending on the operating strategy.

Audi has been competing at Le Mans since 1999 in order to achieve sporting success with technological innovations. Since 2012, the diesel hybrid drive of the R18 e-tron quattro has been unbeaten at La Sarthe.

Sibling rivalry. This year, Audi is welcoming its Volkswagen Group sibling Porsche back to Le Mans as well—the first outing there for Porsche after an absence of 16 years. Porsche will be racing its 919 Hybrid (earlier post).

Porsche has registered the 919 Hybrid for the 6-megajoule category, which means that the LMP1 prototype can use exactly 1.67 kilowatt hours (kWh) of energy per lap on the “Circuit des 24 heures”, since 3.6 megajoules is equivalent to 1 kilowatt hour (kWh). In this category, the WEC rules allow a gasoline engine with more than 500 hp a consumption of only 4.78 liters per lap (or about 35 liters/100 km—the circuit is 13.629 kilometers long) in Le Mans.

The Porsche 919 Hybrid drive system is based on a 2.0-liter V-4 gasoline engine that is compact and lightweight. The engine is a structural component of the chassis, and reaches a maximum engine speed of approximately 9,000 rpm. It features direct injection, a single turbocharger and thermodynamic recovery capabilities. The compact unit outputs around 500 hp (373 kW).

Two different energy recovery systems harness energy to replenish the batteries and provide power. The first system is the recovery of thermal energy by an electric generator powered by exhaust gases. The second hybrid system is a motor on the front axle utilizing brake recuperation to convert kinetic energy into electric energy.

For the recuperation of thermodynamic energy from exhaust gases, the system uses an extra turbine generator unit instead of a wastegate valve, which normally allows excess energy from exhaust gasses that are not required to drive the compressor to escape into the atmosphere.

Porsche utilizes this excess energy from exhaust gases to a second turbine, which in turn drives a generator that generates electrical energy. The new technology recuperates energy that has always been lost in other systems. This use of energy from exhaust gases allows the Porsche 919 Hybrid to recuperate energy not only when it brakes but also when it accelerates.

The electric energy is then stored in liquid-cooled lithium-ion battery packs from A123 Systems. When the driver needs the stored power, the front motor drives the two front wheels through a differential during acceleration. This gives the Porsche 919 Hybrid a temporary all-wheel drive system, because the gasoline engine directs power to the rear wheels, just like the 918 Spyder.



This is old table table (appendix B) in the article the current one can be found here (page 50):

The difference in consumption between petrol and diesel prototypes in litres seems huge but when you look at fuel energy the difference is only 0.6 % (139.5 MJ/lap vs. 138.7 MJ/lap).

So technically Audi is correct they are the most fuel efficient, but only by 0.6 % or to put it another way: all prototypes will consume the amount they are allowed by the rules, from that old table in article they clearly were not the most efficient (137.2 vs. 140.2) with the same car ;) but they were 2 s faster than anyone else at test day at Paul Ricard.


This is a little bit of apples and oranges comparison. The best comparison is at the same level of hybridization. For example, at a “hybridization level” (ERS option) of <6 MJ/lap, the gasoline engines can use 139.5 MJ/lap while diesel engines can use 131.7 MJ/lap, i.e. a much bigger difference than cited. Audi has chosen the option of <2 MJ/lap and can for that reason use 138.7 MJ/lap. Car mass is the same in both cases.

While we know that an increased hybridization most likely has an advantage according to these rules, it is surprising to find that Audi has chosen a lower level of hybridization than the others. I think it is simply that they do not want to develop a new engine. If they would go for maximum hybridization, weight would increase and the engine should be downsized somewhat to compensate for this. Apparently, they think that they are competitive after all, perhaps due to that the efficiency of the diesel engine might be higher than foreseen in the rules.

The rationale for such complex rules as in this case can be questioned. If the purpose is to promote hybrids, they could set the same energy use for all levels of hybridization. It can never be 100 % equal in any case between the options and the question is: why should it? The same is with diesel and gasoline. If a max energy and fuel flow is set equal to both, everyone would opt for a diesel engine. If they do not like to favour diesel engines, why not forbid them, just as in F1?


The rule makers equalize both diesel and bigger ERS classes, all the cars are equipped with torque, fuel flow and bunch of other sensors. On the first test day they collected best in class BSFC for petrol and diesel and came with a bigger factor than first anticipated (7,4 % vs 6,1 %) but still with this penalty it lets some of the diesel advantage in the same ERS class. And also ERS is just free energy that would be otherwise thrown out by the friction brakes, but higher ERS classes are penalised with less fuel.

IMHO, when you make a minimum weight restriction and limit fuel usage per lap, you will get very equal results from any system, may it be heavier efficient engine and lighter ERS or lighter engine and heavier hybrid system. And in the end it came to exactly that, almost the same MJ per lap usage.

The controversial thing is that the final table (appendix B) was released long after all the manufacturers already built and homologated their cars, maybe if Audi had the final table earlier they would make a different car, who knows?


In my opinion, the whole idea to equalize both diesel and various ERS classes is wrong. It can never be equal. The more parameters that are included in the rules, the more difficult it will become to equalize everything. If they want as close completion as possible, they should limit the choices, e.g. gasoline and ERS <8 MJ/lap (or any other combination). If they simply want highest efficiency, it is logical that a diesel hybrid will be chosen by anyone who wants to be competitive. Of course, the higher the hybridization, the more the added weight will be a penalty. Consequently, if ERS limit would be set very high, the optimum might be at a lower level of hybridization.

Finally, we now have the results and do not have to speculate any more. Audi won again!

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