What Was The Blown Diffuser In F1?

F1 is full of technological innovations that were once a hot topic but were just as quickly written out of regulations. Understanding the concept of these innovations is still relevant to how the teams maximize their performance. One of these innovations includes the blown diffuser.

The blown diffuser in F1 generates downforce by expanding the air leaving from below the car, creating a low pressure under the car. A blown diffuser had the engine exhaust blowing over the diffuser, increasing the volume and velocity of the air through the diffuser, which generated more downforce.

This downforce was a significant performance factor of the cars at the time. Blown diffusers were a major technology development race and had many nuances. Below, we discuss more of the details around how it worked, why it was so powerful, and why F1 got rid of it in the end.

What Does A Diffuser Do In F1?

A diffuser in F1 influences the way air flows under the car to maximize aerodynamics and generate additional downforce. It is the rear part of the bodywork underneath the car, a diverging duct that directs the air out from underneath, therefore changing the airflow.

The main purpose of the diffuser is to expand the air exiting from underneath the car in such a way that it maximizes the velocity of the air. In this way, it generates a lower pressure underneath the car that sucks the car down onto the road. This low pressure provides significant downforce without adding drag. This is different from a wing that creates drag while creating downforce.

A diffuser also tries to keep different types of air separate, such as the air coming off the rear brakes or the rear wheels. Compared to the air flowing directly underneath the car, each airflow has different temperatures, flow patterns, and velocities. Generally, if these mix, the aerodynamics lose efficiency. It is easier to extract maximum efficiency if they are kept separate.

A diffuser on an F1 car generally, as defined by the rules, starts behind the rear axle. Several changes to the regulations around diffusers over the years have led to various versions, notwithstanding the return of ground effect aerodynamics in the 2022 regulations.

When Was The Blown Diffuser Used In F1?

The blown diffuser was used in F1 during the 2010 and 2011 seasons. It continued in a less potent form through the 2012 and 2013 seasons as the Coanda effect exhaust. Blown diffusers were used extensively through the ‘80s and ‘90s, after ground effect aerodynamics had been understood to an extent.

This development in diffusers began in the 2009 regulation changes that aimed to reduce overall downforce and allow F1 cars to follow each other more closely without losing major amounts of downforce. The diffuser was an area that was overhauled in this regulation change.

The 2009 season was subsequently dominated by Brawn GP and their “double diffuser.” That won’t be dealt with in detail here, but it took advantage of an unusual interpretation of the new rules. The double diffuser provided significant downforce and was instrumental in Brawn’s success. However, the legality of the double diffuser was contentious, and the regulations were adjusted for 2010.

With F1 being the sport that it is, and the engineers in the sport always looking for different interpretations of the rules to find that extra lap time, the revised regulations still allowed Adrian Newey from Red Bull to find the application of the blown diffuser. Even after some tweaks to the regulations for the 2011 season, the teams were able to use blown diffusers for benefit.

Coanda Effect Exhausts

The regulations were again adjusted for the 2012 season in order to outlaw the blown diffuser. A defined box position and exit angle for the exhausts were enforced to attempt to make exhaust blowing impossible. However, the engineers at Red Bull and McLaren were still able to carry through the blown diffuser concept to 2012/13, although in a less effective manner, by Coanda effect exhausts.

The Coanda effect is that a jet of air, once attached to (flowing along) a surface, will tend to follow that surface, even as it curves away from the initial direction of flow. With this, being careful about the way the gases exit the exhaust, the jets of air could be made to follow the car’s bodywork and downwards into the diffuser.

Therefore, even though the regulations had been changed to try to avoid blown diffusers, the engineers had managed once again to get around them in order to extract benefits. F1 did not act again to try to prevent the use of the Coanda effect to achieve a blown diffuser.

From 2014, the new hybrid regulations came into force. Part of these regulations was that the exhaust needed to discharge along the centerline of the car. This immediately did away with any possibility of using the high-velocity gases from the exhaust to improve the efficiency of the diffuser. As a result, blown diffusers have not featured in F1 cars since 2014.

How Did The Blown Diffuser Work?

The blown diffuser worked by using the exhaust gases of the car’s engine to maximize the effect of the diffuser, thus increasing downforce. The combustion gases leave the engine, flow through the exhausts, and are directed in such a way that maximizes the air flowing through the diffuser.

In the 1980s and ‘90s, the blown diffusers literally had the exhaust outlets directed into the diffuser, blowing hot exhaust gases through the diffuser. In 2010, the blown diffuser was implemented more subtly by running the exhaust pipe outlets down low on the body of the car, not directly exiting through the diffuser but rather blowing over it.

This was over the rear axle, in the space between the wheels and the main body of the car. There were some variations to how this was done, but one version had holes to allow some air to enter the diffuser with the rest blowing over it. The effect, in either case, is to ‘energize’ the airflow (speed it up) and entrain air to induce a greater volume of air running underneath the car.

The major effect though was the stream of exhaust gases providing a ‘seal’ alongside the diffuser. This shielded it from lateral airflow off the rear wheels that would typically interfere with the air leaving the diffuser. This chaotic and turbulent air off the tires is caused by the compression of the tire under load, as well as the air bouncing off the rotating tire.

Using the stream of exhaust gas on either side of the diffuser allowed the air under the car to exit the diffuser cleanly, thereby improving the efficiency of the diffuser significantly. Combined with energizing the air leaving the diffuser, the overall downforce generated was increased.

Challenges With Blown Diffusers

The major problem with a blown diffuser historically was that the downforce would come and go. When the driver was on the throttle, the large volume of exhaust gases would generate good downforce. However, once the driver lifted, for instance when entering a corner, no combustion would be taking place in the engine, and the low volume of exhaust gas would see that downforce disappear.

This meant that a car with a blown diffuser was very difficult to drive and needed the driver to adapt their driving style significantly to accommodate for it. At times a driver would need to be on the throttle at a counterintuitive point in order to gain the downforce.

The key to solving this problem in 2010 was for the engine supplier (in this case, Renault) to make far-reaching changes to their engine operation. These changes would aim to keep a meaningful volume of exhaust gas moving through the system regardless of whether the driver was pushing the engine or not.

Cold Blown vs Hot Blown Diffuser

In order to provide the downforce of a blown diffuser at the most critical times, such as through a corner, it is important to keep the volume of exhaust gases high regardless of how heavily the driver is using the throttle. Cold blowing was an approach where the driver lifting off the throttle pedal would cut the fuel and ignition to the engine but would open the air intake to 100%.

This way, the engine would be pushing as much air as possible through it, without producing power as no fuel was being burned. Essentially, the engine was being used as an air pump to push air through the diffuser. This was called cold blowing as there is no burning or ignition happening during this operation.

Hot blowing was a further enhancement, designed to increase the volume of gas through the exhausts even when the driver was not on the throttle. Fuel was injected into the exhaust, but this fuel was not ignited in the cylinder of the engine but rather allowed to ignite on the hot surface of the exhaust piping.

This generated a large volume of combustion gases, but with some obvious issues. Firstly, the fuel consumption was higher. Secondly, the exhaust temperatures were higher, which risked overheating or damage to some components. As a result, hot blowing could only be carried out for short periods, such as during a qualifying lap, or when aggressively chasing lap time.

Each of these approaches needed the engine mapping to be prepared specifically for this mode of operation. To extract the maximum benefit of the blown diffuser, and to keep the car driving in a predictable manner, a minimum airflow needed to be available to the edge of the diffuser under all conditions. This was only possible through clever and specific engine responses.

Which Teams Used The Blown Diffuser?

The teams that used the blown diffuser included Red Bull, Ferrari, Mercedes, and Renault. Other teams created their own versions over time. The blown diffuser originated with Red Bull, first developed by Adrian Newey. The blown diffuser was copied and developed by many other teams.

The team that pioneered the blown diffuser was Red Bull, specifically their Chief Technical Engineer Adrian Newey. Newey explained that while he had been at McLaren in the early 2000s, they had done a lot of work on blown diffusers, although at the time it had suffered from the issue of losing downforce in the corners when the driver lifted off the throttle.

Newey was convinced of the success that could be had on Red Bull’s 2010 car and spent significant effort developing it. It was necessary to have support and development from their engine supplier Renault. However, knowing that it would trigger other teams to copy the concept, Red Bull waited as long as possible before running their car with the blown diffuser.

On the third and last day of pre-season testing in 2010, Red Bull ran their car with the revised exhaust positions. They even included a sticker on the bodywork showing the exhaust outlets in their normal place, to try to avoid drawing attention to the new exhaust layout. However, as expected, the innovation was noticed immediately, and the other teams set about to understand and replicate it.

The Development Race

The Spanish Grand Prix usually signals the first major upgrades to be brought to the F1 cars, as it is generally the first Grand Prix of the year in Europe. By the 2010 Spanish Grand Prix, Ferrari, Mercedes, and Renault (the constructor team) had developed their own versions of the blown diffuser.

The remaining teams followed suit to develop their own designs. Particularly in 2011, there were several different concepts from other teams. Lotus tried a forward-facing exhaust exit at the front of the sidepods that blew exhaust gases under a greater length of the car. McLaren tried exits at the edge of the sidepods, blowing down through slots to try to form a skirt seal.

However, Red Bull had a development advantage being the first team with the solution, and they continued to maintain that advantage as the blown diffuser solutions were further developed. 2010 to 2013 is the period that Red Bull was dominant, winning both the drivers’ and constructors’ championships every year in that period.

Why Did F1 Ban The Blown Diffuser?

F1 banned the blown diffuser primarily because it went against their fundamental approaches. F1 did not approve of how the blown diffuser used the engine to heavily influence the aerodynamics of the car or how it required automated control that was done without driver involvement.

At a fundamental concept level, one of the problems with a blown diffuser is that the engine was being used to heavily influence the aerodynamics of the car. This goes against F1’s long-standing approach to avoiding moveable devices that influence the car’s aerodynamics.

In some sense, it is inevitable that the exhaust gases from the car will have some influence on the aerodynamics, but before the ‘80s, that had been assumed to be a negative effect, or neutral at best. Blown diffusers took the engine and made it a fundamental part of the downforce generation of the car, which F1 frowned upon.

Further to this, the way that the engine maintained this downforce was not directly controlled by the driver. The engine maps, and the cold and hot blowing techniques all required automated control of the engine that was done without driver involvement. This was against another fundamental approach of F1 to the rules, to limit electronic driver aids, forcing the driver to remain in control.

Finally, blown diffusers worsened the car’s fuel efficiency, particularly when using hot blowing. Bear in mind that this was at a time when F1 was discussing the overhaul of the engine regulations to bring in the expensive and complex hybrid power units. That risk was taken with the aim of staying relevant to the road car industry by pursuing fuel efficiency.

Allowing a practice that was willfully burning more fuel for the sake of an aerodynamic advantage did not sit well with F1. As a result, for the 2012 season, the regulations were changed to attempt to prevent blown diffusers. This was done by forcing the positions of the exhaust outlets to be higher and further away from the diffuser.

Final Thoughts

The blown diffuser was a key element in performance in F1, particularly in 2010/2011. It directed exhaust gases to flow over the diffuser, creating more efficient downforce. However, F1 tried to regulate blown diffusers out of the sport for having a major influence on aerodynamics.