Home Tech Explained F1 - Tech Explained How F1 Exhausts work
How F1 Exhausts work
Gemma Hatton - Deputy Editor
F1 exhausts don't just extract the exhaust gases from the engine, but can also be used to optimise engine, aerodynamic and turbocharger performance.
A puff of vapour from the Mercedes W11 exhaust
How do exhausts work?
The journey of the exhaust gases begins once combustion has occurred. Then, during the exhaust stroke as the piston moves back up the cylinder, the exhaust valve opens and the burnt gases are expelled from the combustion chamber. The gases then travel into a set of primaries or headers, with one primary per cylinder (red, purple, blue). The three primaries coming from each bank of the engine then join together in a three-to-one primary collector (orange) and then a secondary pipe (yellow). The two secondaries (one from each side of the engine) then go into the turbocharger.
The primaries (red, purple, blue), collector (orange) and secondaries (yellow) on the 2018 Honda RA618H power unit
Depending on the engine manufacturer, the primaries, collector and secondaries can either be all one piece and integrated into the turbocharger, or separate pieces. A tailpipe (blue) from the turbocharger then carries the exhaust gases from the turbo out the rear of the car. While there is also a wastegate which controls the speed of the turbo and consists of either one or two wastegate pipes (red) that come off the secondaries and bypass the turbine housing, exiting at the rear of the car.
The tailpipe (blue) and wastegate (red) layouts of the four different power units. Top left: Mercedes (Racing Point RP20). Top right: Ferrari SF1000. Bottom left: Honda (Red Bull RB16). Bottom right: Renault (McLaren MCL35)
Despite the concept of an exhaust system appearing relatively simple, there is an entire science behind parameters such as pipe length, diameter and layout which can be manipulated to tune the torque and power band of the engine.
The more compact you can get the exhaust system, the tighter you can make the bodywork, which gives an aerodynamic benefit. But with exhaust gasses reaching temperatures of 1,000degC and pipes that are within a millimetre of bodywork, new insulation strategies and thermal coatings have had to be developed. Overall, an effective exhaust design is one which strikes the perfect balance between exploiting engine and turbo performance within the smallest package possible, without damaging the surrounding components.
Tighter packaging of the exhaust allows the rear end to be a 'coke-bottle' shape (red arrow) which improves the overall aerodynamic performance. Racing Point RP19 pictured.
At the beginning of the turbo-hybrid era, in 2014, teams initially positioned the compressor at the front of the engine block and the turbo at the rear. Some manufacturers opted for a compact manifold and short primaries, with a longer secondary pipe going from the collector to the turbo. However, the optimal design in terms of packaging was to have long primary pipes which consequently not only decreased the size of the sidepods, but also meant that the 'coke bottle' shape of the rear of the car could be emphasised; improving aerodynamics. To ensure that these longer pipes were as tight as possible to the engine, they often had to be of unequal length, which for turbocharged engines is less of an issue.
'In the early turbo days teams went for more conventional manifolds with equal length primaries,' highlights Nick Henry, Engineering Director at SST technology who manufactures F1 exhausts. 'But the traditional benefits of equal length systems aren't as great with turbochargers because the turbo helps to draw the exhaust gases out, rather than relying on the pistons to push the exhaust gases out. So, the aerodynamic advantages of being able to package the exhaust system tighter outweigh the benefits of equal primary lengths for these hybrid powertrains.'
The benefits of equal length primaries are less with turbocharged engines, making packaging even more important. Mercedes W11 pictured.
Tightly packaging the exhaust system is a challenging process, with many factors to consider. 'When you are laying out the car the [first requirement is the] compressor output position [which] is defined by the power unit so there is a discussion there on engine architecture,' highlights Jody Egginton, Technical Director at Alpha Tauri. 'Then there is the S-bend which goes from the compressor to the tailpipe and you need to make sure that you've got a geometry that optimises performance so there's a chunk of CFD work involved there. The geometry is never perfect, because the perfect geometry is straight which is impossible. Then you need to consider the tailpipe diameter which needs to be within the legality box as well as how that [flow] interacts with the rear wing pylon. Again you want a nice clear path but the aero guys want minimum blockage through the engine cover so you don't want to have to move the flow around wishbones because aero is king, so you're trying to find the best tailpipe position and how to best orientate the wastegates,' Egginton continues.
'It's a mixture of suspension design, packaging and power unit performance but the overall view is aero and the best overall package. If you had a straight tailpipe which is good from a power unit performance perspective, but you have a ridiculous hole in the back of the engine cover and the flow around the rear wing pylons is horrible with flow separation, then you wouldn't do that. It's all about the global car performance.'
The position of the tailpipe (blue) and wastegates (red) is critical in optimising aerodynamics. Alfa Romeo C39 pictured.
Packaging is without doubt the most difficult element of modern F1 exhaust design. 'Our part of the problem is packaging the set of primaries and the entry to the turbine on the side of the engine and adjacent to the front of the gearbox. Then trying to get the exit air from the radiators upstream,' says Rob Taylor, Chief Designer at Haas F1 Team. 'We have lots of radiators and we're constantly trying to find creative spaces to put them. Sometimes you wonder 'why am I putting something that is meant to be cooling adjacent to something that is really hot?' because that's the only space you've got. One of our central coolers is adjacent to the tailpipe – why would you do that? Because you have to.'
In addition to optimising the packaging for sleeker, narrower bodywork for aero gain, teams also utilise the energy of the exhaust flows to improve aerodynamic performance. The most renowned example of this was the blown diffusers of 2010 which was first showcased on the Red Bull Racing RB6. The regulations then changed in 2012 and the teams response led to the development of Coanda exhausts which exploited the 'Coanda effect'.
Exhaust blowing shown on the Red Bull RB6 back in 2010. CREDIT: XPB
Teams have also experimented with miniature rear wings or monkey seats which are positioned rearwards of the exhaust tailpipe and direct the exhaust flow to the underside of the rear wing. This has two main benefits; firstly by increasing the speed of the flow in this region, the pressure decreases leading to a larger pressure differential between the upper (high pressure) and lower (low pressure) surfaces of the rear wing; improving downforce. Secondly the high energy flow is less likely to separate so blowing it underneath the rear wing allows teams to run a more cambered wing that would otherwise stall.
The monkey seat (blue) on the Haas VF-16. Credit: XPB
'A few years ago we had various winglets appearing adjacent to the exhaust outlet but with the FIA restrictions on flow rates and throttle positions this has largely declined,' explains Taylor. 'In the past it was about making more of a cascade between the diffuser, the intermediate wing and the main wing to make them all act together. The more you can do that, the more tolerant the wings are to onset flow, detachment and therefore stalling. If you look at the size of that little wing and the stalks they're on they're not producing a great deal of downforce in themselves, but they had a beneficial effect on the bigger elements because it meant you could put more camber into the wing above it as it wouldn't detach as early.'
With monkey seats now banned, teams now run low T-wings (blue) to help recover some downforce. Top left: Renault RS20. Top right: Ferrari SF1000. Bottom left: Alpha Tauri AT01. Bottom right: Mercedes W11.
When the regulations changed the position of the exhaust tailpipe and this monkey seat, teams then started to point the exhaust tailpipe towards the rear wing by the maximum allowable angle of five degrees as specified by the regulations. This can be seen on the Renault RS18 from 2018 where a thermal barrier coating was also applied to the underside of the rear wing to protect the carbon fibre from the heat of the exhaust plume.
'At the end of the day a tailpipe in a racecar sticks out the back, so it is a wetted surface and subject to aero flows so we are constantly trying to optimise it and minimise any deficit we get from its effect on the flow coming out of the back of the car or off the rear tyre jet,' highlights Egginton. 'If there's a way that we can make the tailpipe and wastegate flows useful then we do it, but the amount of usefulness is reducing compared to years ago and everyone has probably found all the big gains now.'
The tailpipe on the Alpha Tauri AT01
F1 Exhaust Gallery
The primaries, collectors and secondaries highlighted on the 2018 Honda RA618H power unit
Tighter packaging of the exhaust allows the rear end to be a 'coke-bottle' shape (red arrow) which improves the overall aerodynamic performance. Racing Point RP19 pictured.
Further detail of the tailpipe (blue) and wastegate pipe (red) on the Alfa Romeo C29
Exhaust blowing shown on the Red Bull RB6 back in 2010
With monkey seats now banned, teams now run low T-wings to help recover some downforce. Top left: Renault RS20. Top right: Ferrari SF1000. Bottom left: Alpha Tauri AT01. Bottom right: Mercedes W11.
The monkey seat (blue) on the Haas VF-16
Find out more on F1 Exhausts in our November 2019 issue:
https://www.racecar-engineering.com/wp-content/uploads/2020/04/F1-Exhaust-November-2019-issue.mp4
Get yours here!
F1 power unit
Gemma has a BEng in Mech Eng from Bath University and an MSc in Advanced Motorsport Eng from Cranfield University. She has worked trackside in BTCC, GT and F1 as a Tyre Engineer for Pirelli and then Manor F1. She has been writing for Racecar since 2010, using her engineering experience to unravel modern motorsport technology.
2022 Hindsight: The Mercedes AMG F1 W13
Receive the latest news, in-depth features, interviews and analysis in a monthly email put together by the magazine's editorial team.
I consent to receiving monthly updates from Racecar Engineering