Air Injection: Description and Operation

Secondary-Air Injection

The new 911 Turbo has secondary-air injection for quick heating of the catalytic converters after a cold start. This technology, which is not used in the 911 DFI Carrera models, is required to cover the higher heat requirement due to the additional heating of the turbochargers situated upstream of the catalytic converters. The new 911 Turbo features an electrically driven secondary-air pump.

The use of direct fuel injection (DFI) reduces the additional need for secondary air when the engine is warm, allowing the use of a smaller pump with a weight advantage of approx. 25 %.

In the catalytic converter heating phase, the combination of multiple injection strategy and secondary air helps to bring the catalytic converter to the temperature required for optimal conversion of pollutants as quickly as possible. The objective here is to achieve the latest possible ignition of the fuel-air mixture in order to obtain high exhaust-gas temperatures in the exhaust port. Intensive post-oxidation of uncombusted hydrocarbons and a further rise in the exhaust-gas temperature on its route to the turbocharger are achieved in combination with the secondary air supplied here.

The switch-on conditions of secondary-air injection are as follows:

Altitude up to 3000 m, engine temperature from -10 to 34 °C, duration approx. 50 s. Secondary-air injection is switched off in the event of an accelerator pedal position of >50 % during the secondary-air phase.







If secondary-air injection is active (up to approx. 50 s after cold start), the ambient air is blown from the SP-secondary air pump via the RV - check valves (banks 1 and 2) downstream of the exhaust valves. This results in post-oxidation of the combustion gases in the exhaust tract and therefore drastically reduces pollutant emissions.