ALMS to reduce diesel fuel flow rate

Yesterday, the ACO released news that they are to restrict the size of the fuel tanks in diesel cars for next year's Le Mans 24 Hours, so they carry the same amount of energy in a tank as their petrol-equivalents.

Diesel fuel is more energy-rich than regular gasoline, allowing the R10 to last longer between pitstops than petrol-powered cars.

Now, the International Motorsports Association, which runs the ALMS, plans to shrink the size of the fuel nozzle from 38mm to 33mm. This is being mandated as an interim step before the fuel tanks are restricted in accordance with the ACO's wishes.

This means that the pitstops for the Audi R10, competing in the ALMS for the second time this season in Utah this weekend, will take longer than their petrol equivalents.

"There is an overall desire by the organising bodies to work toward a situation where all cars, no matter what fuel they choose to use, have the same amount of energy on board," said Tim Mayer, chief operating officer of IMSA.

"However, that is not the situation with the current regulations. So as an interim step, we have restricted the R10 so that it cannot receive more energy in the tank in a given time frame.

"We notified the team of this change at the Lime Rock Park event. However, because of a variety of test and calculation methods that are possible to determine the energy content of fuels, we chose to hold the public release of the bulletin until we had verification of the numbers."

Diesel cars have been previously allowed the wider nozzle to account for a thicker viscosity of the fuel, meaning a slower flow-rate into the fuel tank.

"The original intent was to permit the full volume of the tanks to be filled in the same time," said Mayer. "However, diesel is a more energy-rich fuel for any given volume.

"The change that we have implemented means that the energy delivered will be similar, for the diesel versus gasoline, for the same length of refuelling.

"The goal is to ensure that competitors have the opportunity to compete without a quirk in the physics of the fuels creating a particular advantage. We are currently working with the ACO to come up with a formula for tank sizes for a variety of different fuels."