Blowing New Life Into Downsized Engines: The Face and Future of Turbocharging

Before the 2014 Formula One season had even kicked off in Australia, race followers were already decrying the lack of a screaming exhaust note from the 1.6 liter turbocharged V6 engines. The fact that these little powerhouses were putting out more than 450 kW from the ICE, with a further 120 kW from the electric motor seems to have gone unnoticed in the general outcry.

After running for a full season, with most polls showing viewership dropping sharply, Bernie Ecclestone prompted the teams to look at increasing the noise levels to pacify the growing dissent. However, no amount of tinkering with exhaust systems, megaphones, and outlet angles did much to make the pinnacle of motor car technology sound any more like their predecessors.

The F1 regulators had come up against one of the most tested laws of the universe: Energy cannot be created or destroyed (or words to that effect). The exhaust energy was now being put to useful work in driving the compressor to boost the inlet charge, whilst also recovering the heat energy through the Heat Energy Recovery System (MGU-H). There simply wasn’t enough energy left to please the crowds baying for more noise!

Modern day turbo developments

Living up to expectations, the F1 racing teams have pushed the envelope of turbo development to eke out the last pony in the herd:

Honda introduced the “Axial Flow” turbine, where the exhaust gas is redirected to drive the turbine along its axis instead of radially as is common. Mercedes-Benz split the compressor and the turbine to reduce the inlet-charge temperature. The ‘Motor Generator Unit – Heat’ also stores the heat energy which is then used to spool up the turbo, thereby reducing turbo-lag. (The MGU-H also acts as a wastegate, thus saving weight) While F1 seeks to extract the maximum horsepower out of an engine, the World Rally Championship cars have fitted theirs with a standardized 33 mm restrictor plate to restrict the inlet airflow.

According to M-Sport's engine guru Tom Flynn, rally cars require precise throttle response with no or, at the very least, minimal turbo-lag. In a recent interview with reporters Flynn explained the technology teams use to achieve this: "When you come off the throttle, we open a valve, which releases air into the exhaust pre-turbo," says Flynn, explaining what's imaginatively known as the 'anti-lag system.' "You retard the ignition at the same time and inject the fuel. That then explodes right through the turbo, keeping it spinning off-throttle. So basically, there's no lag at all."

[inlinead]

But it’s not only motorsport that’s advancing the technology at breakneck speed, the pressure of meeting ever tightening emissions regulations has also seen significant development claw back some of the performance lost in downsizing.

In a 2016 Autelligence expert survey on the future of powertrain, forced induction was voted in the top 5 most critical technologies for achieving powertrain objectives in the next 10 years, clearly showing that much is still expected of the technology.

Take Audi’s 2017 SQ7 for example: The 4.0-liter diesel V8 makes 325 kW by employing two turbochargers as well as, for the first time ever in a production car, an electric supercharger.

Although Audi demonstrated this setup on an RS5 TDI prototype in 2014, the long-awaited promise of turbocharged engines with zero lag has finally arrived. Unlike a conventional supercharger, which is powered via a pulley attached to the crankshaft, Audi’s electric unit is spooled by a 7 kW DC motor essentially replacing an exhaust gas driven turbocharger’s turbine.

The motor is connected to the compressor via a shaft, and it’s neither exhaust-driven like a turbocharger nor crank-driven like a supercharger. Driven by the electric motor, it can spin up to 70,000 rpm in less than a quarter of a second.

A conventional 12 Volt system would never be able to supply the current required to drive the motor, so the SQ7 also becomes one of the first mass series-production vehicles to run a 12/48 V dual voltage electric network. The 48volt lithium-ion battery under the cargo floor can produce up to 13 kilowatts of electrical power at a moment’s notice.

While Audi’s achievement is noteworthy, Thomas Wasserbaech, Development Director of Boxer Engines at Porsche would like to take electric supercharging even further: Not just pre-fill like Audi but fully engaged fulltime electric forced induction.

Recognizing the opportunity, French supplier Valeo recently demonstrated a full-time electric turbo system, which dispenses with exhaust gasses altogether. Using a 48 volt drive to ‘idle’ the turbo's impeller at 10,000 rpm, with the capability of spooling the compressor to over 70,000 rpm in under a second, hesitation and turbo-lag are all but eliminated.

Valeo more correctly refers to the technology as an electric supercharger, and the system has drawn widespread industry interest. Besides Porsche and Audi, BMW, Mercedes-Benz, and General Motors have all claimed to be studying the technology.

There’s no doubt that turbocharging has come a long way since Alfred Büchi’ fitted the first turbocharger to a radial piston aircraft engine in 1915, but with electrification gaining ground, does that mean its days are numbered?

Possibly not: With fuel cell technology still a contender in the race to sustainable mobility, the electric supercharger may still have a place: Hydrogen fuel cells, as with their ICE counterparts deliver significantly improved performance if the atmospheric air intake is pressurized.

Unlike the ICE versions of turbocharging, there is insufficient energy in the exhausted air to drive a turbine, so fuel cell powered vehicles will likely settle for the electric supercharger.

So even if, in the future, turbochargers don’t harvest energy from the unproductive exhaust gas, they’re likely to be with us for years to come.

Sources:

Clifford Atiyeh; Car and Driver; 2017 Audi SQ7 TDI: The High-Voltage Diesel SUV; March 2016; http://www.caranddriver.com/news/2017-audi-sq7-tdi-diesel-photos-and-info-news Greg Stuart; RedBull.com; How WRC turbochargers work; March 2016; http://www.redbull.com/en/motorsports/offroad/stories/1331665126891/turbocharging-world-rally-championship Andy Enright; Wheels; Porsche to boost future with fully electric turbocharging; April 2016; https://www.wheelsmag.com.au/news/1604/porsche-to-boost-future-fully-electric-turbocharging