Analysis: F1 Fuel System

One of the great pieces of unseen technology in the F1 car is the fuel system. Comprised of complicated fuel tank and an array of pumps, the system is taken for granted. The super safe and highly efficient fuel system delivers the F1 cars 160kg of fuel during a race with barely any reliability issues.
Historically fuel tanks were simply metal tanks formed to fit in wherever they could be fitted. Often prone to puncturing during accidents and impacts, the fuel could easily spill and cause a huge fire. Major fires in F1 car are now thankfully rare. It’s fair to say the biggest leap in F1 safety has probably been the advent of the flexible fuel cell. Flexible bags to house the fuel have been part of the regulations for decades, There’s been no major fuel tank fire at an F1 race since Berger Imola crash in 1989 and no fire related deaths since Ricardo Palletti in Canada in 1982, or in testing with Elio De Angelis in 1986.

Anatomy

Fuel systems in F1 are split into two areas; the fuel tank itself and the fuel pump system that delivers fuel to the engine.

Design
The first point in the fuel cell’s design, starts back at the F1 teams design office. The size of the fuel tank capacity is agreed and the then the length of the fuel tank area is defined as a fundamental parameter in the cars layout. Fuel cells cannot extend more than 400mm from the cars centerline, so tanks are limited to being just 800mm wide. Additionally teams want the fuel as low in the car as possible so the shape of the monocoque will be altered to achieve the design capacity, while fitting in with the length and width demands. Nowadays, teams need to consider the packaging for the engine oil tank in the back of the monocoque, the Accident Data Recorder mounted towards the front of the tank area and the KERS batteries commonly mounted under the fuel tank area.

The tank has to conform to the shape inside the monocoque, including clearance for the engine oil tank

The resulting void inside the monocoque is the starting point the fuel cell design. This shape and several mounting points will be provided to ATL for the design work on the tank to start. The outer skin is relatively straightforward, largely needing to fit into the void. But the fuel cells design goes far deeper than its outer skin. Inside the skin there are two systems that need to be packaged; the baffles and the fuel pump system.

Tank Baffle System

Baffle system simplified: the inside of the tank is crossed with baffles with one way trap doors to direct fuel to the rear centre compartment.

The baffle system is required, as although F1 cars now start the race with full tanks, for Practice, Qualifying and part way into the Race; the fuel load will be smaller than the tanks capacity. Fuel will tend to move around in all directions, from the forces created by lapping quickly. Fuel moving around inside the tank, or fuel ‘slosh’ as it’s known, creates two problems. Firstly the weight of the fuel will alter the balance of the car and secondly the fuel needs to be centered on the fuel pump to ensure fuel is constantly delivered to the engine. So the teams design baffle systems within the tank, to damp out of the movement of the fuel and direct it towards the fuel pumps. This system of baffles, trap doors and collectors is now designed in CFD.

This ATL CAD drawing of a real F1 tank shows the complexity of the vent, baffle and trap door system

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Looking inside a Honda RA107 fuel tank through the fuel filler opening, the complex arrangement of baffles is apparent.

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Trap Door detail: Despite the overall complexity, the actual parts within an F1 tank are relatively simple

Taking account of the all the loads the cars see at different tracks. Spa is a good example of tracks demands on fuel slosh. There’s heavy braking, heavy acceleration, high G turns left and right, not to mention the vertical loads from through Eau Rouge.
As well as controlling fuel slosh, there is also the consideration for internal venting, so that the fuel fills and drains the tank without causing pressure variations. This is now less of an issue since mid-race refueling was banned. When refuelling was allowed, it pumped in fuel in at a rate of 12 litres per second, meant this that the air needed to be vented out of the tank at the same rate. Inside the fuel tank tall breather vents were created and a snorkel vented air from the top of the tank back down to the refueling coupling. As the Intertechnique refueling rig also served to extract the vented air from the tank, back down the double walled refueling hose.

Teams may also build a dummy tank for rig testing at the factory. Mounted to a shaker rig, the tank is fitted with Perspex windows to observe the fuel inside tank. The rig moves the tank with the same forces as seen on track, this will show if the baffle system is working effectively.
Both CFD and physical testing should correlate to ensure assumptions are correct with both methods. Baffles will be in three planes vertical baffles to control fuel slosh on turns, lateral baffles to control movement under acceleration\braking, then horizontal baffles to stop fuel rising upwards.

To serve their secondary purpose, the baffles will need to direct fuel into one compartment to be collected by the fuel pump system. As the fuel load lightens, the fuel will be directed towards a compartment at the bottom rear of the tank, gravity pulls the fuel down, down while acceleration forces the fuel backwards to the rear of the tank. At first it might seem logical for the stronger braking forces to be used to force fuel forwards in the tank. But the car sees more frequent and consistent acceleration around the majority of circuits, making this a more reliable method, than fewer more violent braking loads. Baffles will feature one way trap-doors to allow the fuel to move from one compartment to the next. Fuel will cascade down the horizontal and vertical baffles towards the rear of the tank. In this final compartment the fuel system will pick up almost all of the fuel remaining in the tank at the end of the race. F1 cars do not feature reserve tanks. One of the first tasks during testing is the team running the fuel tank to empty to see what level of fuel remains in the tank. This will be taken into account when fueling the car for qualifying and the races.

Construction
The FIA have a range of regulations on the design construction and placement of fuel cells. In terms of the supply of FIA approved F1 fuel cells there is only one supplier, ATL. Each year, every team goes to ATL to help design and manufacture their fuel cells. Despite having to maintain commercial confidentiality to each client, ATL were able to provide me with information on the generic design and construction of the modern F1 fuel cell.

Starting from the outside and the fuel cells most important feature is the skin material. This puncture proof ballistic material is a mix of a Kevlar fabric coated with rubber to be both strong and flexible. ATL’s F1 material is called 818-D (Issue 2003) and conforms to all FIA FT5-1999 requirements (see below).
Minimum FIA Requirements FT5-1999From 1/1/99

Tensile Strength 2000 lb (8.90 KN)
Tear Strength 350 lb (1.56 KN)
Puncture Strength 400 lb (1.78 KN)
Seam Strength 2000 lb (8.90 KN)

Constructing the baffle system is a challenge. Not so much as the baffles are complex, but because how the tank is fitted into the car. To make the monocoque as stiff as possible, there is only a small aperture under the car to fit the fuel cell in through. The fuel cell has to be folded, crumpled up and forced through this small hole. If the entire tank and baffle system was bonded permanently inside the tank it would never fit. So the baffles are partly removable, they meet the skin of the cell with Velcro and zips to allow the entire assembly to be collapsed for fitting. The baffles themselves are made from a lighter weight version of ATL’s proprietary rubber coated fabric, while the precision engineered trap-doors tend to be made from carbon fibre.
Once all of the sections are assembled, bonded and cured, the tank is rigorously tested. Teams will go through 6 or so tanks each year.

The machined bulkhead that covers the fuel tank area is visible below this Honda monocoque

Once squeezed through the small aperture in the bottom of the monocoque, the Fuel tank is secured in position by a few small fasteners as well at as the refueling plate and fuel pump mount. Fuel is delivered into the tank by a specialist rig. The fuel trolley is used by all teams; this stores a tank fuel of fuel and can pump fuel accurately into and out of the tank. To be sure the car is filled with the correct weight of fuel; the fuel rig will first empty the tank and then refill it. This pipe fits to the fuel cover plate under the fuel flap. The fuel rig monitors the weight of fuel rather than its volume, as the fuel will expand when its gets warmer, so weight is more accurate and stable measurement.

Fuel pump system

Simplified the fuel pump systems comprises: the collector (grey), lifter pumps (yellow) and high pressure pump (red)

In simple terms the fuel pump system needs to collect fuel from the tank and deliver it to the engine, the regulations now demand a maximum fuel pressure of 100bar at the fuel rail. But as we’ve already explained, the fuel is not static within the cell and the entire systems needs to be able collect the fuel and constantly pump it to the engine. The precision high pressure fuel pump will be wrecked if it runs dry; equally the engine will stop if no fuel is delivered. Already the fuel cell itself is designed to lead the fuel into a single compartment. Inside this compartment two or three lifter pumps will pick up the fuel and send it to a carbon fibre collector.

The Lifter pumps are used to take fuel from the bottom of the tank to the collector

Being more robust electric pumps, the lifter pumps can safely run if there’s no fuel for them to pick up. They are relatively cheap items (in F1 terms at £500 ach) teams may design and manufacture their own buy them in from specialist suppliers such a Marelli. Each Lifter pumps work at lower pressures of around 1bar (15psi) to feed the collector tank.

Fuel collector tank: the carbon tank also houses the regulator (made here in a rapid protoype material). Picture taken at the Williams F1 musuem

The collector tank  holds around 1-2 litre of fuel. There’s enough fuel to feed the engine for 30s second or more. This should be more than enough time for the cornering loads to keep fuel from reaching the final compartment, such as around long high G turns like as R130 at Suzuka. Sensors will detect if the lifter pumps are not delivering fuel, when all three show that no fuel is being delivered, the team and driver will be warned that the car is imminently going to run out of fuel. Although sensors may check the level of fuel in the tank, this will not be accurate when lapping the track or when fuel levels are very low. Additionally teams need to allow 1litre of fuel to be drained from the tank for FIA inspection at all times.

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From the collector a constant feed of fuel will reach the high pressure pump. Again typically design and manufactured to very high tolerances by the teams or engine manufacturer this pump is some ten times more expensive than the lifter pumps. It’s driven off the engine usually via a shaft connecting with the water pump drive. The interface between the monocoque, fuel cell and high pressure pump is critical, as this is one of the few openings in the lower part of the tank and preventing leaks is critical.

The high pressure fuel pump drive passes through the tank.

Limited to 100bar the fuel delivered by the high pressure pump is controlled by a regulator mounted on the collector. The pipe work from the regulator needs to route up to the fuel rail and then the fuel injectors. The fuel delivery pipes are aerospace grade braided hoses; they have a dry break coupling where they exit the monocoque. If the engine should become detached in a crash this keep the fuel safely in the tank. This pipe work also has a one way valve; this maintains pressure in the fuel system, which makes starting the car easier.
Lastly fuel delivery to the fuel rail is managed by a pressure relief valve (PRV) at the end of the fuel rail. Fuel bypassing through the PRV goes back into the fuel tank. It was this PRV that lead to Lewis Hamilton’s fuel leak in the garage before the 2011 Chinese Grand Prix.

I have to extend my thanks to Giles Dawson & Steve Lissamore from ATL for their assistance in creating this article.

More info on F1 fuel loads by Brain Jee and F1PitRadio.com

Fuel slosh video
This video shows the extreme amount of movement the fuel sees while cornering in an f1 car.  courtesy of the ‘The Flying Lap’ and Willem Toet from the Sauber F1 team