What is a blown diffuser?
On road cars, the engine exhaust exits are normally located at the rear of the car. On a Formula One car they are deliberately located in front of the rear wheels so that the hot, fast flowing exhaust gases can be channelled towards the car’s rear diffuser. This increases airflow through the diffuser and in turn increases the amount of downforce the diffuser produces. This is perfectly legal under current F1 regulations.
What is an off-throttle blown diffuser?
Normally the engine will only produce exhaust gases when the driver is on the throttle. This means when the driver lifts off, the blown diffuser is suddenly robbed of the additional airflow. To get around this, some teams have modified their engine mapping so that when the driver lifts off, although fuel supply and ignition are cut, airflow through the exhaust - and hence to the diffuser -continues. This technique has become known as ‘cold blowing’ - the exhaust is still ‘blowing’ into the diffuser, but that airflow is now ‘cold’ since no fuel or ignition is involved.
What is ‘hot blowing’?
Some teams have taken things a step further. To make the off-throttle ‘blowing’ as similar - ie as hot and fast flowing - to the on-throttle ‘blowing’ as possible, they cut the ignition when the driver lifts off the throttle, but continue to inject some fuel through the engine’s valves into the exhaust. This fuel ignites on the hot exhaust, increasing the amount, speed and temperature of the airflow exiting towards the diffuser.
