Porsche is entering this year’s Le Mans race with their 919 Hybrid – their self-titled most complex Porsche race car ever created. But what makes this car special? Their new hybrid drivetrain recovers energy lost in exhaust gasses and uses it to make the car more efficient.
Many technological advances that we see in ‘normal’ everyday cars have come from the world of car racing where the constant climb for a competitive edge, or the need to meet ever stricter race rules has led to engineering breakthroughs. For example this year at Le Mans, racers are only allowed to use 4.78 litres fuel per lap forcing manufacturers to look at ways to make their cars even more efficient.
On top of this, the amount of pure electrical energy independent from the traditional engine each driver can use per lap at Le Mans delivered as a boost is limited. The rules specify four classes of energy levels ranging from 2 to 8 megajoules (MJ). Porsche has registered the 919 Hybrid for the 6 megajoule category, which means that the car can use exactly 1.67 kilowatt hours (kWh) of energy per 13.629 km (8 mile) long lap on the Circuit des 24 Heures, since 3.6 megajoules is equivalent to 1 kilowatt hour (kWh). But what does this mean in real terms?
In 2013, the Le Mans winner covered 348 laps. Calculated over the same distance the new 919 Hybrid needs to generate and use 581.2 kilowatt hours (kWh). That’s enough to cover 4,576 km in the most efficient electric car that is currently available in the compact class, the new Volkswagen e-Golf – which would take you across the USA from coast to coast, from New York to Los Angeles.
Alexander Hitzinger, Technical Director LMP1, said: “The recuperation of kinetic braking energy at the front axle has great potential with the axle load being dynamically shifted to the front when you brake, so a system that exploits this was a logical step. In favour of this solution we gave up a KERS on the rear axle. If you start with a naturally aspirated engine, KERS is the only option you have. But using turbocharging gave us another option, which is why we opted for using the energy from exhaust gases from the turbocharger.”
This principle basically uses an extra turbine generator unit instead of what is called the wastegate. This valve normally allows excess energy from exhaust gasses, that are not required to drive the compressor, to escape into the atmosphere.
Porsche uses this excess energy from exhaust gases to drive a second turbine, which in turn drives a generator that produces electrical energy. The new technology recuperates energy that has always been lost in other systems. This use of energy from exhaust gases makes the Porsche 919 Hybrid the only car in the field that recuperates energy not only when it brakes but also when it accelerates. Both systems direct kinetic and thermal energy converted into electrical energy back to a liquid cooled lithium ion battery.
What do you think of this new way to capture energy from an hybrid system? Is this something you could see being adapted to work on non-race cars? Let us know what you think.
You can also support us directly as a monthly supporting member by visiting Patreon.com.