Closed-loop lambda control

The first concept is the closed-loop-controlled three-way catalyst. In this, one type of catalyst, which is placed in the exhaust gas stream, is able to promote all the main reactions that lead to the simultaneous removal of carbon monoxide, hydrocarbons and nitrogen oxides. To balance the extent of the oxidation and the reduction reactions, the composition of the engine-out exhaust gas is maintained at or around stoichiometry. This is achieved by a closed-loop engine operation control, in which the oxygen content of the engine-out exhaust gas is measured up-stream of the catalyst with an electrochemical oxygen sensor, also called lambda sensor. 

Closed loop control used to maintain the fuel/air ratio within narrow limits is well known. A lambda sensor delivers a very sensitive signal to oxygen concentration around the stoechiometric ratio. This signal is used to pilot the injection in order to correct observed deviations. 

---