Mercedes-Benz dominated Formula One in 2017, and part of its success was no doubt due to its latest F1 powertrain. The big news surrounding the engine is the fact it achieves a 50-percent thermal efficiency.
What's so special about that? Jason Fenske of Engineering Explained is here to tell us.
Thermal efficiency is the percentage of the energy content of gasoline that's actually provided as torque to the transmission. Racing engines must extract as much useful work as possible during the combustion process, to conserve their fuel supply and require fewer pit stops.
Most road cars hover around 30-percent thermal efficiency, and the best Atkinson Cycle engines used in hybrid-electric vehicles now surpass 40 percent, but Mercedes' racing engine is more efficient yet.
One way engineers were able to extract more efficiency from the powertrain is by using a motor-generator unit heat, which recaptures waste heat from the exhaust and converts it to electric power. That wasted exhaust heat spools up a compressor that spins an electric motor, which sends electricity to a battery that powers another electric motor to add torque to the rear wheels. Mercedes also pioneered the split turbocharger, which keeps the unit cooler and allows the car to use a smaller intercooler design with less intake piping.
Second, and more importantly, Mercedes engineers improved the pre-chamber combustion. In its 1.6-liter turbocharged V-6 engine, a spark plug ignites a rich mixture of air and fuel in a pre-chamber, which then spews a fiery mixture into the larger standard combustion chamber, which contains a much leaner mixture.
Doing this, Mercedes-Benz can use less fuel and extract more work from the engine. Readers old enough to recall the Honda Compound Vortex Controlled Combustion, or CVCC, engines of the 1970s will be familiar with the concept of pre-chamber combustion spreading into the main combustion chamber.
The interesting catch is that we don't know exactly how Mercedes has achieved this. F1 regulations say the race cars can run only one fuel injector per cylinder, which means Mercedes seems to have found a clever way to use it to inject fuel for both the pre-chamber and the normal chamber. That's the magic behind the scenes.