Exhaust
Art in making
Masterpice done
Red hot
Blown away
Masterpice at display
Ferrari F60 engine at Chinese F1 Grand Prix, Shanghai, 17th-19th, April 2009
Designing a F1 exhaust system is an extremely complex business that calls for an intimate knowledge of the laws of acoustics if the engineers are to tease the last reserves of power out of the engine.
That's because, like in a trumpet, the exhaust gases vibrate at a specific frequency depending on the speed of the engine. As the valves open and close, they generate a pulsating column of exhaust, with regular peaks and troughs of pressure. To ensure that the 4 cylinders per bank don't interfere with one another in this respect, all the exhaust pipes must be the same length. And at the end of the collector, the exhaust gasses from each bank exit the car from a single tailpipe.
Early last century, as piston engines came under the scrutiny of academics, it was noticed that if an engine was run at an RPM such that the firing frequency coincided with the natural frequency of the exhaust system, i.e. the "note" of the exhaust pipe, a resonance was set up in the pipe. However, it was not until MIT published a paper on how this phenomenon could be exploited to increase the performance of an engine, that the tuning of exhaust systems really took off. Among the first to experiment with exhaust tuning were the motorcycle engine tuners. In the late 1940s and early 50s, they tried different length exhaust pipes on their single-cylinder Nortons etc to obtain maximum power and to shape the torque curve. There is some evidence that Mercedes-Benz were experimenting with exhaust systems on their pre-War GP cars, but there is no mention of this in any of the books on these cars and the technique was probably not fully understood. It was not until the 2.5 liter GP cars of the 1950's that we really see exhaust system tuning applied to Formula1 racing engines.
The objective of the engine designer is to create a negative pressure at the exhaust valve during the overlap period when both exhaust and intake valves are open. To do this he designs an exhaust system that resonates at a particular RPM, and uses the pressure waves reflected by the ends of the pipes to modify the time history of the pressure at the exhaust valve. By coupling two or more of the cylinders' exhaust primary pipes together, interaction between the pulses created by each cylinder modify the pressure characteristics at any given RPM. The ends of each primary pipe are brought together in a collector, such that their ends are close enough together to interact, and the tail pipe(s) form a secondary resonant system. At the same time, the designer will chose intake lengths to form another resonant system, which also interacts with the exhaust system.When two or more cylinder's exhaust pipes are coupled, the firing order of the engine becomes significant, and the firing order of V-8's are chosen as a compromise between exhaust tuning and the torsional dynamics of the crankshaft.
Exhaust and intake geometry, valve timing, exhaust gas temperature and velocity, and RPM all affect that characteristics, and any system is only optimised at one RPM. Torque curve shape is very sensitive to these effects, and is inevitable a compromise between maximum power and driveability. The natural frequency of a pipe is set by its length, everything else being equal; the shorter the pipe, the higher the frequency. As engine RPM has risen over the years, the length of the exhaust pipes for a given engine configuration has shortened
To accomplish an "as much as possible" ideal exhaust, some very different factors have to be compared and calculated. Some of these all very important factors are the exhaust and intake geometry, valve timing, exhaust gas temperature, velocity, and RPM all affect the characteristics. Reminding these characteristics, an exhaust system can only be optimised for one certain RPM. The lenght of the exhaust pipe affects as well the maximum RPM and suppleness of the engine in lower RPM. At peak revs, a formula engine will blast out exhaust gases 95,000 times a minute. To scavenge maximum power the exhaust pipes need to be as short as possible. Unfortunately , to help generate maximum torque and responsiveness at lower revs, longer splender pipes are called for. As F1 regulations don't permit variable-geometry exhausts, the answer lies in the best possible compromise.
The exhaust is therefore a compromise between engine power in lower of higher RPM. That brings us to the aerodynamic part of the car. As soon as aerodynamicists knew that a diffuser speeded up the air passing under the car and generated downforce, they discovered that blowing exhaust gasses into the diffuser would affect the downforce significantly. However, another problem rised with diffuser blowing: as soon as the driver lifted the throttle, it would affect the flow of air in, after and immediatly before the diffuser and thus also the downforce which was in conflict with the general FIA reglutions.
Although, as it is proven that any exhaust affects the aerodynamics, forbidding the diffuser blowing in area around diffuser would make all exhausts illegal. This effect on the aerodynamics will probably have been a reason for Ferrari to abandon the regular type of exhausts, and start blowing the exhaust air over the rear top of the car, before the air has passed the rear wing. Raising the exhaust pipes needed heat shielding of the aerodynamic parts of the car. Due to the hot air passing by the rear wing, it would become very fragile if it wasn't protected against such high air temperatures.
However, further trend have led to Ferrari considering and then adopting an alternative exhaust arrangement. In the quest to move weight forward that has resulted from the width limitation on the rear tyres and the grooves in the treads which led to Bridgestone introducing a wider front tyre in 1998, the engine has moved forward relative to the rear of the bodywork, defined in the regulations by the rear axle centre line. At the same time the peak RPM of engines climbed relentlessly upward, now 18,000 rpm. Thus, while exhaust pipes needed to become shorter to stay in tune with the higher RPM, the exhaust pipes had to be longer to reach the trailing edge of the underbody. For Ferrari, the arrangement that provides for nearer optimum length exhaust pipes, by leading them the short distance from the engine to an exit port set into the top surface of the bodywork, is better than one that still blows into the base region around the trailing edge of the diffuser. For McLaren and their, in this time, engine partner, Mercedes-Illmor, the latter layout provides them with the best compromise.
The two arrangements have other implications, for instance the Ferrari exhausts raise the mass of the tailpipe and part of the primary pipes above the lower position possible with the McLaren exhausts, and require heat shielding for the bodywork and top suspension links, particularly when they are manufactured in CFRP. The heat from the exhausts also plays upon parts of the rear wing structure that are normally spared, and must be protected or reinforced.
Nevertheless, F1 exhausts rarely completes more than 1200km since the need to save weight means they have to be designed close to the limit. The thickness of the heat-resistant steel adopted from the aerospace industry varies but is never more than 1 millimeter. But what eventually kills these waste-gas works of art is not vibration or temperatures of 1000 degrees and more, but stress, The different radii of the various pipes ultimately produce fatigue which leads to cracks where the stress is greatest. Not surprisingly, at this high level of performance even the best exhaust are soon exhausted.
Heat-resistant steel adopted from the aerospace industry it's called inconel also called Alloy 718 (approximately 60% Nickel and 22% Chromium + trace Molybdenum and Niobium). Inconel is a registered trademark of Special Metals Corporation that refers to a family of austenitic nickel-based superalloys. Inconel alloys are typically used in high temperature applications. It is often referred to in English as "Inco" (or occasionally "Iconel"). Inconel alloys are oxidation and corrosion resistant materials well suited for service in extreme environments. When heated, Inconel forms a thick, stable, passivating oxide layer protecting the surface from further attack. Inconel retains strength over a wide temperature range, over 1000C. Inconel is a difficult metal to shape and machine using traditional techniques due to rapid work hardening
Cutting of plate is often done with a waterjet cutter
