The air intake and airbox is one of the most distinctive features of a modern F1 car. Situated just above the driver’s head, the oval-shaped air intake hole dictates not only the shape of the engine cover but also the flow of air into the engine. In this latest feature we explain what it does in detail, but also what goes on underneath the bodywork and inside the RS27.
Explain in simple terms what the airbox is.
The airbox and intake system govern the maximum amount of air pumped by the engine, and therefore the amount of fuel it can burn and the level of power that it can produce. The air intake we see above the driver’s head is just the tip of the iceberg with regards to the engine’s inlet system. At high speed, the air is pushed into the hole above the driver’s head and down into a hollow tube that opens out to a horn shape at its base, where the air filter is situated. The air arrives at the air filter at a pressure higher than atmospheric as a consequence of the dynamic pressure created by the car’s velocity. An efficient air ‘horn’ will keep as high a percentage of this dynamic pressure as possible before the air meets the air filter.
The air filter’s job is then to stop any airborne particles or foreign material such as sand or grit from entering the engine. The ‘clean’ air is ingested into the eight trumpets where the throttles are located. If the throttles are closed, the air will go no further, but if the throttles are open, the air will pursue its journey and be mixed with the fuel. Ultimately this fuel-air mixture passes into the combustion chamber via the valves, where it is ignited by the spark plug and drives the piston down, creating torque.
Why is the air system so important for car performance?
Air – or rather oxygen – is an essential part of the combustion process and having enough airflow at maximum possible pressure will maximize the amount of torque produced. Delivering this optimum therefore depends on the constituent parts of the system. Firstly, the shape of the airbox governs how much air can be taken into the engine unit. If the inlet is too small, the engine will be ‘starved’ of air and therefore produce less power. If it is too large, however, the engine will not be more efficient on a linear scale – more air does not mean more power; exactly the correct amount must be introduced. This relates back to trying to try to keep the total pressure as high as possible. To achieve this we need to keep as much dynamic pressure created from the car speed as possible. This is of course a compromise with the adverse effect on the aerodynamics of having a giant airbox, which would create turbulence for the rear wing so we look to the airbox to keep as high a percentage of dynamic pressure as we can.
The air filter also needs to be very robust. Have too tight a filter and the flow of oxygen is hindered, or the total pressure drops. But have too little and you run the risk of having foreign bodies enter the engine, which can cause irreparable damage to the pistons and other engine internals. For this reason, engine suppliers work on the ‘tightness’ of the air filter but also on its capability to retain debris.
What are the technical regulations governing air filters?
Surprisingly, there are very few technical regulations governing air filters. The principal ones forbid any system that decreases the temperature of the engine intake air, and the restriction of any systems that increase the volume of oxygen ingested above the percentage found in air (20%). Then there are the general aerodynamic prescriptions, which is actually why you see a lot of variations in the designs of air intakes: some are round, while others are split by a central pillar. Even between Renault Sport F1’s teams the designs are very different according to each team’s priorities. But in any case, there can be no compromise on the air filter characteristics, which need to protect the engine.
Teams and engine manufacturers therefore work in unison to develop the air horn and airbox as it is another area where aerodynamic and engine performance can be found.
How has the design of the airbox and air filter evolved over the history of the V8?
The evolution of the airbox has been mainly driven by aerodynamics. The shape has evolved to suit drag reduction systems and narrower bodywork, but has also been affected by the installation of coolers close to the rear end of the air duct. In the era of the F-Duct we also saw some big changes, while nowadays with DDRS the air from the intake is used for aero purposes down to the rear wing.
The insulation of the airboxes has also moved forward since the bodywork of the cars has become tighter. Tighter bodywork gives less opportunity for the heat to escape so preventing the overheating of the air that goes into the engine becomes crucial as lower temperatures ultimately mean more power.
For the air filter, a fair bit of work has been done to improve the quality of the air ingested by the engine by running clever systems to separate debris up front rather than at the base of the air horn. Furthermore, when engine life was extended, the air filter was developed in parallel: a better filtration means a higher average power output.
Without the engine freeze, what would we be seeing now with regards to airbox design?
It is very difficult as it is closely linked to the internals, but it is fair to say that these boxes would certainly have been much more complex, possibly incorporating variable geometry, for example. It is even possible to think we could have had different designs changing race to race. We could have developed a single throttle butterfly system at the top of the airhorn beneath the roll hoop – in fact we looked into this at one point, but the benefits of having eight separate throttles rather than one were more advantageous, especially due to the extra weight of the latter.
Any interesting stats and facts…
At the end of the straight in China where the car is travelling at close to 330kph with DRS open, the air pressure hitting the air filter will be close to 1,070 millibar – normal ambient air pressure is around 1,020 millibar. This means the engine produces around 5% more power – equivalent to 40 bhp – than at ‘walking speed’.
Also the combination of the air pressure inside the air horn and resonance generated by the high frequency wave of the engine pitch is such that the physical structure of the air horn needs to be adequate – or robust enough – to cope with the airbox wall deformation. To give an example of how much it physically deforms, if you were to film inside the air horn with a high speed camera you would pick up a change of approx. 10mm! You could compare this to the behaviour of a bottle on take-off and landing in a plane - expanding at high ambient pressure, and contracting at low pressure.
The Renault Sport F1 air filter is also based on those used in desert rallies – fine enough to stop fine dust and sand, but overall open enough not to restrict maximum power.