The best engine that will ever exist? Ultimate efficiency of F1's hybrid

Racing tech

It's the most efficient engine in the world. And with the advent of a cost cap, plus a global switch to electric cars, Formula 1's hybrid power unit could well remain the pinnacle of petrol power for good

Mercedes V6 hybrid F1 engine

Mercedes' V6 hybrid has dominated the current era

Mercedes

135 years of innovation: making of the internal combustion engine, Part 8

We’ve travelled from the first sparks of the internal combustion engine over more than a century’s worth of engineering brilliance in this series, examining the finest race engines constructed. However, none of these come close to the current engineering marvels that power Formula 1. More emotive, maybe, but for sheer ingenuity and mechanical marvel, nothing can match the current generation ‘power units’ which blend technology with efficiency and phenomenal power.

The raw figures speak for themselves. The last generation 2.4-litre V8s put out around 850 bhp with the KERS electrical system in full swing. The current power units produce over 1000 bhp, yet consume approximately a third less fuel over a race distance. Whereas the old engines were, on a good day, maybe a shade off 30% thermal efficiency (the measure of how much potential energy in the fuel is actually converted to motive power), the current hybrids are in excess of 50%, and even more efficient when the hybrid contribution is taken into account.

The introduction of the current formula can be traced back to the idea of a ‘global race engine’ or GRE, first touted by Audi engine guru Ulrich Baretzky and others, then picked up on by the FIA in 2009. The concept was for a single, four-cylinder engine architecture that could be scaled for any series: Formula 1, Formula 3, GP2, sports prototypes of all flavours, touring and rally. Formula 1 was supposed to get a GRE with a hybrid system, cutting costs considerably and making the series relevant to as many manufacturers are possible.

Ultimately, Ferrari and Mercedes could not stomach racing with a four-cylinder, and there were also legitimate concerns about how such an engine could be used reliably as a stressed unit. So it was that in 2011, a vote was called by the FIA and the current V6 configuration adopted. As an aside, Cosworth had already done a full design concept for an I4 F1 unit.

Mercedes F1 powertrain with battery

V6 power unit and battery were introduced to F1 in 2014

Mercedes

“I was involved from the beginning on the definition of the rules,” said Luca Marmorini, former head of Ferrari’s engine operation shortly, speaking after his departure from the team in 2015. “Looking back, if you were to ask have the rules been a success from a sporting point of view? The answer is probably no, have they improved the show? Also no, but from a technical point of view they have been a huge success. People now claim these rules were designed for Mercedes, but that is completely wrong. It was a committee of representative manufacturers. The basic idea was that we should do a regulation set that was road relevant, moving towards hybrid systems and working on efficiency. Unfortunately, the domination of Mercedes did not help the image of the new regulations, though I have to say, they deserve their results.”

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The power units are fiendishly complex and truly push the limits of engineering to levels never before imagined. “If you asked someone in 2013 about the possibility of that an engine could be that efficient, most people, myself included, would just smile at you because we would not have thought it possible,” added Marmorini.

The power unit is made up of a direct injected and turbocharged 1.6-litre, V6 to which is coupled a Kinetic Energy Recovery system (the MGU-K) in the form of a motor/generator unit (MGU) with its power output capped at 120kW. This recovers energy usually lost as heat under braking, and drives the wheels when accelerating.

The second form of energy recovery comes from the MGU-H (Heat), with an output of around 90-100kW (from a motor barely bigger than a coke bottle that spins at 120,000 rpm), which is driven by the turbocharger and shares a common shaft with the turbo compressor and turbine wheels. There is then a battery (the capacity isn’t limited but per lap energy output is capped at 4MJ per lap) and the power electronics that control the motors.

Honda hybrid F1 engine diagram

Two MGUs, turbo, battery, control electronics, and V6 engine make up F1’s current power unit

Honda

The key to being fast in the hybrid era is squeezing every drop of energy from the available fuel, the flow of which is limited to 100kg/hr with an overall maximum fuel load to 110kg, while also packaging the myriad of components in the most integrated way possible, shrink wrapped under the bodywork. Mercedes was undoubtedly the team that achieved this integration most successfully from the outset and was rewarded for the time and resource it dedicated to development in the run up to 2014. In the case of Ferrari, it was not able to dedicate all of its resources to the new engine’s development until the end of 2013, with the team intent on fighting for that season’s championship.

Renault was not in a much better position and at a dinner with (former) Renault engine head Rob White and Mercedes Andy Cowell at Monza in 2014, Cowell quipped “Rob always used to joke that he had one person working on it and I had loads,” judging by White’s response, this was not far from the truth. Ferrari was also hobbled by the fact that its chassis team demanded too much from the engine department in terms of packaging, to the detriment of performance. Though its reliability was acceptable, it was well down on power compared to Merc.

So what makes the power units so complex? There are too many individual factors to list them all, but a few do stand out. The first is the efforts taken to refine the combustion process; the key to making power is efficiency with these engines and that means running exceptionally lean. The leaner the engine runs, the greater the issues with knock (where the fuel/air mix starts to combust ahead of the flame front, leading to unstable combustion and expensive noises). This means precise control is needed over combustion conditions which is where one of the more public innovations comes to light, pre-chamber ignition.

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First revealed as being part of Ferrari’s package, this relies on a small chamber within the main combustion chamber which is filled with rich mixture and then ignited. The burning mixture is expelled from the chamber via nozzles to the main combustion chamber, igniting the much leaner mixture within. The result is an (almost) simultaneous ignition of all of the mixture, negating the problems of pre-ignition found with a standard spark and allowing the engine to run very lean.

Making these systems work is complicated, particularly within the constraints of the rules. There are also times when some pre-ignition is desired, effectively controlled knock, as Andy Cowell once alluded to. “We use a conventional spark to start our combustion. Does the pressure increase that then occurs as a consequence of combustion cause spontaneous combustion, as opposed to flame front combustion? The answer is ‘yes’. Do we welcome that? Sometimes it’s welcome, sometimes unwelcome combustion? I think that is the challenge of taking combustion to another level.”

Next up in the mind-blowing complexity stakes are the electrical elements of the hybrid system. The rules now specify minimum weights for the various components, which give some idea of the levels power unit manufacturers had reached before they were reigned in. The MGU-K, which has an output of 120kW (161 bhp) is pegged at 7kg, giving an astounding 17kW/kg power density; the most cutting-edge motors available commercially are about 10kW/kg. The MG-H is even more nuts, with a minimum weight of 4kg, and output of 90-100kW they sit at around 22.5kW/kg. The MGU-H is also used as an active boost control system for the turbo, meaning lag is non-existent as the turbo can be kept spinning even off throttle (also handy for exhaust blowing the rear wing and diffuser).

Lewis Hamilton leads Nico Rosberg in 2014 F1 Mercedes 1-2

Mercedes concentrated on getting its engine right in 2014 - with spectacular results

Grand Prix Photo

Ferrari engine parts from 2017

Ferrari engine parts in 2017: many secrets remain untold

DPPI

As with the IC engine, efficiency is king for the hybrid system, losses, both mechanical and electrical have been aggressively reduced, ensuring that as much of the permitted battery energy per lap is fed to the MGU-K (energy flow form the H to K is unregulated, so power is also fed from one to the other, meaning the cars deploy more than this over a lap). Control of the MGUs relies on extremely high-speed electronic switching via silicon-carbide power semiconductors in the inverter, again, optimised to cut losses and reduce cooling requirement (which help the aero department).

There are many, many secrets of the current engines that we still don’t know, from the use of 3D printed steel pistons (Ferrari are rumoured to run these and Mercedes’ Cowell has hinted that this was perfectly feasible) to the various tricks allegedly used to circumvent the fuel flow regulations. Not to mention the phenomenally complex strategies needed to manage the energy flows throughout the powertrain.

Given the direction the automotive industry is moving, it is quite possible that this era of Formula 1 represents peak internal combustion engine. Of course, the pinnacle of motorsport is going to stick with combustion for a while yet, with a switch to 100% sustainable fuel on the cards. However, it is likely that the new engine rules when they arrive will do away with the MGU-H and costs will be more tightly constrained, meaning the incredible efficiency levels seen today may never be beaten.

135 years of innovation: making of the internal combustion engine