It may look like a collection of basic metal tubes, but an F1 exhaust system is a carefully crafted component of the car. The engineering challenges involved in the designing, shaping, and manufacturing of each part stretches the limits of the science of materials and their uses.
In F1, the main problem concerning exhaust systems is the heat. When the engine ignites, the exhaust gases are released at 900 degrees Celsius. The turbocharger adds another 1000 degrees Celsius which is enough to melt and oxidize most metals. Even the most basic automotive stainless steel would already be glowing and degrading within a few minutes. F1 exhaust systems need more capable materials.
That is the problem Inconel helps solve. Inconel is a family of nickel and chromium alloys originally made for jet engines and gas turbines. For F1 exhaust systems, Inconel is ideal because of its strength and resistance to oxidation. It can even be worked with at a red hot state. The only con for Inconel is the amount of money and energy spent in order to manipulate it. It is more difficult to work with than even titanium and even the welding of Inconel is a carefully controlled process to avoid the cracking and distortion of the exhaust system.It’s a common misconception that the exhaust system is solely there to transport hot gases from the engine. In modern F1, there is more to exhausts than just leaving the engine. In F1, exhausts are built to assist with energy recovery from the turbocharger and the heat MGU (Motor Generator Unit – Heat). The turbocharger uses a turbine that is powered by exhaust gases to boost an engine and in doing so, can charge the battery or mitigate turbo lag to some extent. The design of the exhaust system can enhance or hinder the efficiency of these functions, in addition to the above F1 requirements.
To maximize the efficiency of, and to fuel, an F1 engine, modern exhaust systems have optimally sized piping with regards to length, diameter, and shape of bends. Because F1 is so design constrained, engineers must resort to computer modeling to get a feel for how gases will behave in the system. Because of the physical properties of exhaust system materials, there are unavoidable design constrictions that engineers must factor into their models. Even if airflow and weight sacrifices aerodynamically, a pipe cannot be designed to be thinner than what the mechanic and thermal properties of the materials used allow. The properties of design materials impose severe restrictions on design flexibility.
Another challenge is thermal expansion. As Inconel heats up from cold to operating temperature, it expands. The entire exhaust system, including Inconel, can grow several millimeters in length. If both ends are tightly bolted to the car, the exhaust system has nowhere to expand, and the pipes will buckle or crack. Engineers have to design an expansion system, typically with bellow sections or flexible joints, and still be flexible enough to keep the exhaust from vibrating itself to pieces.
Vibration is a real problem. The engine itself generates thousands of combustion events per minute, and with every event goes a pressure pulse through the exhaust system. These pressure pulses create a vibration at a certain frequency, and if the exhaust system has a natural frequency that corresponds to one of those vibrations, the exhaust will be guaranteed to experience destructive vibrations that will quickly lead to a fatigue failure. Engineers have to balance material choice with temperature resistance, weight, and the desired resonant frequency of the exhaust system, to achieve the desired level of vibration.
The weight of the exhaust system (10 kg) is also located at the top rear of the car. Removing some exhaust weight improves weight distribution and lower the center of gravity, which helps handling. You also can’t just make the pipes thinner, because they have to withstand the thermal and mechanical loads. It’s a constant balancing act between weight, strength, and durability.
The system also has to survive full race distances. It hasn’t been common for other components to survive practice, qualifying, and the race (300 + km). Most components need to be replaced. Other components also cycle between hot and cold at peak temp and stress levels, but not for nearly the same distance as the exhaust. Inconel’s fatigue resistance is what allows it to be used for this purpose without developing cracks.
Coating technology is creating another layer. For example, some F1 exhausts employ ceramic coatings on the outside for the purpose of reducing heat radiation that affects nearby components. These coatings reflect heat back into the exhaust flow, minimizing the heat radiation into nearby bodywork or suspension items. The coatings are usually applied with thermal spray techniques, and need to be adequately bonded with the Inconel substrate and be thin enough to avoid significant weight increases.
Creating an F1 exhaust requires specialized skill. The complex shapes and tight bends are not achievable with simple tube bending. Some sections are shaped with mandrel bending to prevent the pipe from collapsing or wrinkling. Other sections may be constructed from numerous pieces that have been welded together. Each weld is a possible weak spot that needs to be perfect: a weld that is not done well will fail quickly due to thermal and mechanical stresses.
Exhaust sections tend to go through X-ray or ultrasonic testing for weld validation and to check for any defects or voids in the materials. Small voids in materials can lead to a failure during a race that would retire the car and cost the team valuable points in the championship. These inspection methods are essential for reliability, but add cost and time to the production.
F1 team are constantly focusing on exhaust sytems due to complicated set of legal guidelines surrounding them. Teams must check what the newest legal guidelines are and redesign their exhaust systems accordingly. Teams must focus on exhaust systems not only to improve previous designs, but also to comply with new regulations.
The different systems that make up F1 exhaust systems are extremely complicated and must use modern engineering every time. F1 exhaust systems must utilize lightweight materials to deal with the extremes of heat and pressure. When watching a night F1 race, looking at the glowing exhaust, know that the engineering surrounding the exhaust systems are of the highest quality.