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Thermal barrier coatings

We have discussed a number of applications for thermal barrier coatings in RET-Monitor, and also in RET magazine. Most of these are concerned either with maintaining the heat within the exhaust gas flow for improving turbocharger transient response or minimising the transfer of heat through radiation or convection to other components close to the exhaust system. Where coating the exhaust isn't possible, then coating heat-sensitive components or the heat shields protecting them is another option.

In recent years, aerodynamicists have tried hard in Formula One to take advantage of the energy contained in the exhaust flow. In 2011, there was a lot of controversy over the use of blown diffusers and blown floors, which gave extra downforce. For 2012, such devices were banned, and the regulations stated that the exhaust exits had to be on the top surface of the bodywork, with the direction of the exhaust pointing slightly upwards at an angle of 10º from the horizontal. There is, of course, the option of simply using the thrust coming from the momentum of the exhaust gas to increase the motive force. The flow could be directed toward the rear wing of the car; increased mass flow over the rear wing should increase downforce.

The solution chosen by a number of the teams is to use a 'Coanda Effect' exhaust system. There is a lot of material published in the press about which teams are using this technique, but the basic idea behind such systems is to cause the exhaust flow to attach itself to the top of the bodywork, from where it sweeps down toward the rear of the car. Experts surmise that the exhaust flow is directed toward the gap between the diffuser at the rear of the car and the rear tyre.

As clever as all of this undoubtedly is, it makes life very difficult for a number of components. These new exhausts, adopted by an increasing number of teams as the season wears on, rely on the interaction between the relatively solid bodywork and the hot, fast-flowing exhaust plume. Therefore the bodywork is the first to suffer from the effects of heat. Further downstream, other items of bodywork and suspension components may be affected.

Thermal barrier coatings are used to protect sensitive areas of the car from the damaging effects of heat transferred from the hot exhaust flow. While there are composite materials which are resistant to the effects of extreme heat, teams often prefer to use materials that they have a lot of experience with and to protect these from damage from hot gases. Sprayed ceramic thermal barrier coatings can be applied directly to both metallic and carbon composite components. This gives the race teams the chance to coat bodywork, floor and suspension components where protection from exhaust heat is required. The last thing engineers want to do with their clever exhaust systems is to torch some bodywork!

For 2014, and the change to turbocharged Formula One engines with low mass flow through the exhaust, and with much of the exhaust energy removed by the combined turbo-generator, there will be less that can be usefully done in terms of aerodynamics with the exhaust flow.

Written by Wayne Ward

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