Sensor carburetor system

Three-Way Conversion (TWC) Catalyst. The dual-bed method requires net fuel-rich operation of the engine and therefore lower fuel economy. Interest has heightened recently in a technique to control all three pollutants—carbon monoxide, hydrocarbon, and nitrogen oxides— by maintaining the air/fuel (A/F) at near-stoichiometric ratios and by converting all pollutants over a single catalyst. A sensor is used to control the partial pressure of oxygen in the exhaust stream by feedback to a carburetion or fuel injection system (13). The increased cost of the sensor-carburetor system will be compensated for by better fuel economy,... 

Such tight mixture control is beyond the capability of the traditional carburetor. Consequently, after sorting through a number of alternatives, industry has settled on closed-loop-controlled port-fuel injection. Typically, an electronically controlled fuel injector is mounted in the intake port to each cylinder. A sensor in the air intake system tells an onboard computer what the airdow rate is, and the computer tells the fuel injectors how much fuel to inject for a stoichiometric ratio. An oxygen sensor checks the oxygen content in the exliaust stream and tells the computer to make a correction if the air/fuel ratio has drifted outside the desired range. This closed-loop control avoids unnecessary use ot an inefficient rich mixture during vehicle cruise. 

Figure 6 is a schematic of a closed loop system. It consists basically of an oxygen sensor to monitor the exhaust air-fuel ratio, a "black box" electronic control system, a carburetor or fuel injector which is controlled and adjusted by the "black box" and, finally, a three-way or dual bed converter. The signal from the oxygen sensor is monitored continuously by the electronics package which then adjusts the carburetor or fuel injector to control the air-fuel ratio at stoichiometric. 

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