Much of the saving, of course, was in the energy recovered under braking, energy that would have otherwise gone to waste in the form of heat out of the exhaust, but in adopting electric motor/generator technology there is so much more potential for efficiency than many might at first think. Take the turbocharger compressor wheel design for instance, and the potential for efficiency savings in compressing the intake charge.       

Powered by an exhaust gas-driven turbine or the electric motor of the motor/generator unit, the engine intake air is drawn into the centre of a centrifugal compressor wheel and accelerated radially outwards, increasing the kinetic energy of the intake gas. Having left the perimeter of the wheel, the rapidly moving air is slowed down again, or ‘diffused’, so that the kinetic energy is converted into pressure energy – the intake manifold boost pressure. The design and angle of the blades of the compressor wheel, the diffuser and the scroll of the compressor housing all work together to generate the compression characteristics of the system in the form of a compressor ‘map’, examples of which are shown in Fig. 1.  

Essentially a plot of pressure ratio against the mass flow, the left-hand side of the operating envelope is referred to as the ‘surge’ line. At this point the aerodynamic elements of the compressor wheel create reverse flow effects, leading to stress reversals in the compressor blades and a ‘coughing’ type of sound as the airflow stalls. At the other side of the map, towards the right-hand side of the envelope, the limit is one of compression efficiency. Normally taken to be around 60%, at these values excessive heating of the air intake charge takes place, the mass flow drops significantly and the compressor is effectively ‘choked. In between, the map consists of a series of contours connecting points of equal compression efficiency, rather like the height contours on a map, and superimposed on all this are the lines of constant compressor wheel speed.

The operating range, or ‘width’ of the map, is in part a function of the compressor wheel design – the type and the number of blades and their angle of twist. When designed to have a degree of what is called ‘backsweep’, these impeller blades create maps with higher peak compression efficiencies at the expense of being narrower and therefore more difficult to match to engine applications, particularly those used in applications with variable speed and load. In most automotive applications, therefore, the running position of the compressor is governed by the boost pressure which, once achieved, is regulated by the turbine wastegate.

However, if you now throw in the potential to drive the compressor using, say, an electric motor/generator then you now have the opportunity to match the compressor to the peak efficiency point using the electric motor when insufficient exhaust is available or when there is too much gas, to absorb the excess power and feed some of it back into the battery storage system. Either way, the compressor can be redesigned to operate at a more efficient point in its range than would otherwise be the case, producing the minimum heating to the engine intake air and resulting in smaller intercoolers and a more efficient vehicle aerodynamic package.

So not only are the new-for-2014 direct injected engines producing impressive fuel economy, the opportunities available in powering the compressor using an electric motor can make the overall engine vehicle package even more efficient.

Fig. 1 - Typical turbocharger maps: a) conventional wastegated approach; and b) using an electric motor/generator unit to give higher compression efficiency

Written by John Coxon

Back then, and much like 2014 in some respects, one team dominated. In 1988 it was McLaren. Winning all but one of the races that year using a V6-configured engine; there the similarities end though. In 1988, the winning engines (the Honda 1.5 litre RA168E, for thus it was designated) were reputed to deliver something like 504 kW (685 PS) at 12,500 rpm on 2.5 bar boost using a fuel consisting of 84% toluene and 16% normal heptane. Of course, regulation in Formula One was much less restrictive back then, and so long as the fuel used bore some resemblance to road-based or ‘pump’ fuels – in that it had a Research Octane Number (RON) no greater than 102 (the Honda fuel was 101.8) – then all was well. The lack of low boiling point constituents in some fuels, which meant they had to be heated to around 75 C before being injected into the engine, wasn’t seen as an issue, and neither was the reportedly evil-smelling brews of other fuels, but hey, this was the 1980s and Formula One was pushing the boundaries.

In 2014, the engines could appear to the uninitiated to be very similar to those used in 1988. These days we still have V6 engines – this time 1.6 litres – and we now have turbochargers again, a single unit as opposed to most teams using twin units in ’88, but the ‘forecourt’ fuel of 2014 is totally different from that used in 1988. Indeed, even though Article 19 of the technical regulations remains unchanged the fuel used in 2014 will be significantly different from that used in 2013.

In designing a fuel for any engine, fuel technologists will look at many aspects. The heating value, the stoichiometry and even the density of the fuel in some cases will all be considered. But the fuel requirements of a 2.4 litre naturally aspirated V8 revving to 18,000 rpm will be totally different from those of a 1.6 litre turbocharged V6 doing not much more than 12,000 rpm. So from 2013 to 2014, although the fuel regulations did not change so far as the make-up the fuel is concerned, the precise blend of hydrocarbons within it almost certainly will have.

At 18,000 rpm the fuel has about 0.001 s in which to burn from the point of ignition to the opening of the exhaust valve. As it burns progressively across the bore, if the fuel ignites in front of the flame front then detonation will occur. This will cause a sudden increase in local pressure and temperature in the cylinder which, if allowed to continue, will damage the piston. At 18,000 rpm the speed of burn and the motion within the cylinder is such that there is generally insufficient time for this to occur. At this speed, this resistance to detonation (or ‘knock’) governed by the fuel’s octane number is therefore not so important.

However, at 12,000 rpm – the typical top speed of the new V6 engines –the time available for this flame front to move across the bore is now 50% greater, which is a lot more time for any stray pockets of end gas from previous combustion cycles to ignite any fuel-air charge in front of the flame front and cause detonation. At these speeds, and at the increased charge temperatures and pressures in the combustion chamber of a turbocharged engine over that of a naturally aspirated unit, the resistance to detonation of the fuel typified by its octane number is therefore more significant.

So while the 2013 fuels may have been blended more for their rapid speed of burn, in 2014 the emphasis is more likely to be on the resistance of the fuel to detonation. And as each species of hydrocarbon – be it aromatic, olefin, paraffin or naphthene – will have its own speed of burn and blending octane, so the optimum fuel for each engine made up from varying amounts of these will almost certainly vary.

Fig. 1 - Comparative flame speeds of some commonly used aromatic hydrocarbons

Written by John Coxon

In the original KERS battery pack of 2009, storing only a mere 400 kJ of electrical energy was never really a problem. The issue at the time was how to deploy the 60 kW of the push-to-pass energy for 6.67 s per lap. Thus the size of the battery in terms of kW-hours per kg was not considered much of an issue. More of an issue perhaps was the power density in terms of kW per kg and the size of the electric motor to use it. For 2014, however, the amount of energy that can be stored has increased tenfold to 4 MJ, but the maximum electrical power available to the rear wheels has been increased only twofold, to 120 kW. That would seem to put greater emphasis on electrical storage over simple outright performance compared with earlier designs, and so represents quite a pivotal moment.

But battery technology has moved on a long way in the past ten years. Whereas in the early 2000s the only practical technology might have been traditional lead-acid batteries – as fitted even these days by just about every vehicle manufacturer – for the current crop of Formula One teams the only serious option, according to many is lithium-ion technology. Since lithium is the highest placed metal in the electrochemical series, and much lighter than lead or indeed any other battery technology, it is easy to understand why.

Consisting simply of an anode, electrolyte and a cathode, in many cases the anode is principally carbon or carbon-based. Most ongoing development therefore would appear to be based around the electrolyte and the cathode, and in particular the choice of lithium-based compounds. Because of its relatively high voltage output per cell (around 3.6-3.7 V), early designs were developed around lithium-cobalt chemistry. Further developments led to the introduction of manganese and nickel, which reduced the internal resistance of the cell and offered higher current flow and faster charging but at the expense of lower energy density. These days, the favoured cathode would seem to be based around nanophosphate technology which, although generating a reduced voltage (around 3.2-3.3 V), can accept higher currents and increased capacity at the expense of shorter overall battery life. In Formula One, where chassis parts (including the battery) can be replaced frequently, that is not the problem it might be in other electric vehicle applications.  

In the end though, battery development in Formula One is not just about voltage per cell or indeed energy storage, it is in effect about designing an efficient system, from harvesting all the way through to re-powering the electric motor and making maximum use of the 100 kg of fuel available. That is why Mercedes-Benz is running away from the rest of the field at the moment.

To this end, teams might already be looking at potential new developments in lithium-sulphur technology which, although offering only 1.9 V per cell if early reports are to be believed, offer vastly greater storage capacity per kilogramme.

Fig. 1 - The Periodic Table

Written by John Coxon

So at a time while many may be looking at what has been brought in for 2014, as an engineer I am looking more to what has been left out.

Perhaps the most fundamental characteristic of any engine – be it diesel, gasoline, two- or four-stroke – is its combustion system, and while the Formula One power unit regulations for 2013 specified only port injection fuelling systems, for 2014 this restriction is left out. So while previously in the formula direct injection has been specifically excluded, starting in March this year it must surely be the only way to go. Two little letters, DI  – such a fundamental change to the sport but totally hidden from the rest of the world!

In motorsport, however, direct injection is nothing new. Winning the world championships in 1954 and ’55, the Mercedes Grand Prix racer used a mechanical system to inject the fuel through the side of the cylinder in its straight eight-cylinder M196. Reintroduced into automotive technology in 1996 by Mitsubishi using electronic means, in 2001 Audi was next and brought its twin-turbo 3.6 litre V8 to the technology, winning Le Mans that year. By this time of course, many other manufacturers began to see the advantages of increased power (up to 5%) and better fuel consumption (up to15%). But like many things in life, such improvements don’t come easily, and while the potential benefits of improved cylinder filling and better mixture preparation are highly attractive, to achieve them takes a lot of painstaking development work.

In a port-injected engine the fuel can be injected over much of the four-stroke cycle, with injection ending as the intake valve closes. At, say, 10,000 rpm this injection period may be something of the order of 12 ms. In a DI unit, however, injection can’t even start until the inlet valve opens, and then only when there is no chance of the fuel escaping through the exhaust valve during valve overlap. Start of injection will therefore be at or close to exhaust valve closing for that cylinder. After that, the fuel has to be given sufficient time to evaporate to create a combustible mixture before it can be fired by the spark. At this same 10,000 rpm, the time for this to happen falls to somewhere nearer 1.6 ms.

This in itself is not a problem, since under the new regulations fuel rail pressures are considerably higher (up to 500 bar). However, getting the correct air-fuel mixture at the correct time in the engine cycle sequenced to the position of the piston, and ensuring that this mixture burns quickly and completely, takes a great deal of understanding of the airflow in the cylinder. This, as well as the progression of the flame front across the combustion chamber, requires much more knowledge of the in-cylinder flows at any particular instant than with our port-injected engine. Little wonder then that in the past two years or more, countless hours of CFD work will have been undertaken to model both air and fuel mixing to get to where we are now. Increasing the engine speed to the maximum of that now allowed (15,000 rpm) reduces this time for evaporation and mixing still further, and you now begin to see the nub of the problem.

By the time you read this, how well individual engine manufacturers are faring may be all too visible, but there is one thing of which you can be certain. If, as of 28 January 2014, we can say the starting pistol has been fired, there will be a lot more CFD activity in darkened rooms around the world until the first race in March. The Formula One season may not have officially started yet, but the race to extract maximum performance out of 100 kg of the fuel allowed certainly has. As of that date Formula One suddenly got interesting again!

Fig. 1 - Such little time!

Written by John Coxon

And so, by allowing teams to ‘harvest’ other forms of wasted energy on the vehicle, rather than being simply a tyre-shredding spectacle relying on aerodynamic downforce, from 2014 Formula One will be all about efficiency – efficiency in the generation of engine power, and at the same time efficiency in using it.

Under the current rules, energy recovery from the 2.4 litre V8 engines has been restricted to the use of a single device, a motor/generator (otherwise known as an e-machine) or (in theory at least) a flywheel arrangement, capturing energy under vehicle braking. Subject to a recovery rate of no more than 2 kW and a release rate of no greater than 60 kW, this is released for a maximum of 6.67 s per lap at maximum power output. Such a system, while potentially great for overtaking and thus adding to the spectacle, has little real benefit in the road vehicle world.

For 2014, however, the rules are much more far-reaching, for in addition to a limit on the fuel flow rate and the ability to capture the vehicle’s kinetic energy, the energy that might otherwise be wasted in the exhaust gas of the now 1.6 litre turbocharged unit can be harnessed as well.

So as well as doubling the power of the e-motor directly to the engine and a tenfold increase in the amount of energy released per lap (up to 4 MJ), teams have the ability to harvest as much energy as they wish from any left over in the engine exhaust system by introducing yet another e-motor attached to the shaft of the turbocharger.

And so from a period when getting as much air as possible into the engine was the guiding principle, the introduction of a fuel flow limit of 100 kg/h and a maximum tank size of 100 kg moves the formula to a place where maximum fuel efficiency is the aim.

This introduces a number of options for the engine designers, and yet more so for the teams during the race. Computer modelling of the systems so far has indicated that the KERS unit will be operating for much of the time. The power for this will come partly from the energy harvested under braking but mostly from that harvested from the e-machine linked to the turbocharger. At times during the race, excess energy will be harvested from the turbocharger turbine to top up the battery energy store. At other times, however, at low engine speed say, the energy from the battery could be used to spin up the compressor to maintain the boost.

This latter could encourage engines to run at lower engine speeds than the maximum of 15,000 rpm, where friction is lower, efficiency is higher and the amount of heat rejected into the atmosphere through heat exchangers much less. And whereas current 2013 engines work best at minimal exhaust back-pressures, future V6 turbocharged units will experience greater back-pressures and may need to be less sensitive to them, so as not to downrate performance.    

But whatever approach is used, things like the aerodynamic set-up (and hence drag of the vehicle), the heat rejected from the engine and the sensitivity to the increased back-pressures generated – not forgetting of course the amount of fuel still left in the tank – will all feature in the race strategy.

If all this is uncertain, of one thing I am sure: there will be road vehicle power unit designers all over the world looking at the outcome.

Fig. 1 - Formula One engine schematic for 2014

Written by John Coxon

By the 1920s, blends of Grand Prix fuel are reported to have consisted of mixtures of ethanol, benzol (a mixture of benzene, toluene and xylene) and the gasoline of the day. Later, and by the late ’30s, ethanol was replaced by the higher specific energy and increased blending octane of methanol, but by the 1980s, after general improvements to gasoline, the discovery of the anti-knock additive TEL (tetra-ethyl lead), the sport went back to using exotic blends based on high levels of toluene for its turbocharged engines. 

But times change, and in Formula One after the banning of TEL and the progressive restriction of other environmentally hazardous components in forecourt fuels, politics and the winds of change overtook the sport. Rather than the exotic but highly toxic brews of the past, the fuel used in the sport was required to be similar to that found at your roadside filling station. Indeed, by 2008 any fuel complying with the then current Formula One regulations would automatically comply with the European standard EN 228 for automotive fuels and therefore be totally road legal.

Article 19 of the Formula One Technical Regulations of that year tried to dictate not only the physical properties of the fuel but also, within fairly narrow bands, its composition. Controlling the volatility curve by setting upper and lower bounds, and by putting limits on the density of the fuel as well as adding a maximum octane level of 102 (not required by EN 228), any fuel thus described would very closely follow that of a typical forecourt fuel. Additionally, fearing the excessive introduction of any of the power-boosting hydrocarbons, the so-called PONA components (paraffins, olefins, napthenes and aromatics) were heavily restricted by carbon number and category.

So while Article 19 described a typical forecourt fuel of the time it did little to encourage research into new fuels, and so in 2008 the FIA, pre-empting European Union legislation for 2010, encouraged more environmental awareness, and stipulated that fuels should include a minimum of 5.75% by mass of “components derived from biological sources”. At a stroke, and seeking environmental attributes, the colour ‘green’ was applied to fuels in Formula One.

In 2010, however, after another iteration of the regulations scarcely reported anywhere else and although seemingly very similar to those of 2008, Article 19 was changed to allow much freer blending opportunities. While still basically conforming to EN 228 and therefore road legal in most respects, the revised rules allowed much more potential for the chemists. Gone were the limitations on the volatility curve, and the only volatility now is represented by the Reid Vapour Pressure (RVP) and final boiling point (FBP). Gone too was the maximum research octane rating of 102 as well as the minimum value of 95. Instead a minimum of 87 was applied to the value (RON + MON) ÷ 2, which is the way many other countries prefer to express their octane requirements. Finally the fuel density requirement of between 720 and 775 kg/m³ of EN 228 was discarded, giving teams much greater opportunity to explore the wider bands of fuel technology.

Importantly, however, the 5.75% minimum of bio-components was retained, and while initially this was restricted to oxygenates such as ethanol or methanol, the way forward is signposted to move towards more useful hydrocarbon components generated from environmentally friendly biomass sources.

Thus from the ethanol of the 1920s, having come full circle, fuels are moving on again.

Fig. 1 - The well-thumbed pages of the 2014 Formula One Technical Regulations – Article 19: Fuel

Written by John Coxon

That we no longer see such incidents is a testament to the efforts of the FIA and the concept of the ‘survival cell’ encompassing both driver cockpit and fuel tank. So whereas the fuel tank of Bandini’s Ferrari was made entirely of aluminium and ruptured during the accident, modern Formula One fuel tanks consist of a flexible bladder surrounded by a crushable structure within the carbon fibre bodywork of the vehicle, and are therefore much more robust.

Conforming to regulation FIA/FT5-1999, the bladder itself is made from Kevlar, a proprietary product developed by the chemical giant DuPont in the 1960s, the same basic material now for anti-stab or bullet-proof vests. It consists of aramid fibres (a bit like nylon but far stronger) which are woven into a cloth-like material and coated with a fuel-resistant elastomer on both sides. Assembled, bonded and cured, the bladder has to be flexible enough to be inserted into the void within the survival cell through a small aperture, generally on the underside of the chassis. The exact process, elastomers and bonding agents used are a closely guarded secret, since they affect the degree to which the cell can be compressed and hence the size of the aperture needed. The greater the size of the aperture the more this will affect the ultimate stiffness of the tub, and so, as in anything concerning Formula One, the pressure is on to make the aperture as small as possible.

Once inside the tub though, and located by the fuel filler aperture and the flange required to run the mechanical fuel pump inside the tank – and maybe one or two other fasteners – final assembly is rather like putting a model ship in a bottle. For in order to control the movement of the fuel under the forces of acceleration, braking and cornering, various baffles and one-way trapdoors have to be inserted once the bladder is in position. Placed horizontally to prevent the fuel from rising up, and vertically to control its lateral movement, these ensure that the fuel can be pumped from any part of the tank to the collector tank feeding the main high-pressure fuel pump under all and particularly low fuel conditions. Partially assembled while the bladder is in manufacture, these baffles are made from a similar but slightly more flexible material than the bladder itself, and finally erected once the bladder is in place. The trapdoors so necessary to swing open and then trap the fuel as it attempts to flow back are made from a rigid carbon fibre.

With its low-pressure scavenge pumps, high-pressure mechanical fuel pump, filler pipes, breather systems, and return hoses, as well as the system of baffles and trapdoors, a modern Formula One fuel tank weighing something in the region of 5 kg is a complex affair. But since it was 1989 when Gerhard Berger was the last driver to be burned in an on-track incident, something somewhere must be right. So while the FIA may be criticised for its continual interference with the rules and regulations of the sport, thank heavens for the fuel tank safety bladder.

Fig. 1 - Formula One safety cell

Written by John Coxon

Thus the new engine regulations for 2014 specify 1.6 litre turbocharged V6 engines and, unlike many other turbocharged formulae, engine performance will not be limited by the inlet manifold ‘boost’ pressure but rather indirectly by the fuel flow rate, according to the formula Q (the flow rate in kg/h) =  0.009 x N (engine speed in rpm) + 5. This, it is stated, will encourage engine designers to extract every last bhp out of the fuel allowed at all engine speeds, and by so doing add to the general pool of knowledge available to the roadcar engine designer. With no maximum intake manifold pressure set as such, and for overall engine fuel efficiency, it is expected therefore that engines will be only mildly boosted to something around 2-3 bar.

Fuel efficiency, however, means different things to the road engine designer than the race engine designer. The former concentrates mainly on the specific legislative test cycles used to determine the engine tailpipe emissions of unburned hydrocarbons, carbon monoxide, oxides of nitrogen and of course carbon dioxide, which these days seems to the villain in the story. At these conditions, engines will be running almost totally under low-speed, part-throttle conditions, where the mechanical friction is low and the advantages of direct injection – better, more precise control over the combustion and the lack of wall wetting in the intake port zone – are undisputed.

By their very nature though, race engines run more towards the wide-open throttle envelope of their performance, and while fuel economy is just as important, this has to be delivered at altogether higher speeds and loads with total disregard for exhaust gas emissions. So while the 2.4 litre V8s were effectively mandated to run as port-injected devices (a 50 bar limit on fuel injection pressure), the 2014, V6 power units appear to be able to use either port or direct injection depending on the precise fuelling characteristics needed at the time. The only provisos as written in the 2014 Formula One technical regulations are a limit on the injector supply fuel pressure of 500 bar, only one direct injector per cylinder, and that according to rule 8.5.2 (page 24 of 77): “Over 80% of the maximum permitted fuel flow rate, at least 75% of the fuel flow must be injected directly into the cylinders.” With no emissions to worry about, and cycle-to-cycle variations under cold start, idle and warm-up, the challenge for the race engine designer is exacting but still very much different from that for a roadcar engine.

So while there may be many other areas where the red-hot technology of powertrain design may be helpful to the roadcar designer, in the case of the 2014 V6 base engine – at least in the beginning – the initial direct-injection knowledge may come from the road engine guys.

Fig. 1 - How Formula One engines used to be – the BRM 16-cylinder ‘H’ configuration engine

Written by John Coxon