Laserfiche WebLink
IV. REACTIONS OF CATALYST <br /> Typical chemical reactions of the exhaust gas are as follows: <br /> A. Removal of NOx with CO as a reducing agent <br /> 1) NO2 + CO—►NO + CO2 <br /> ,y£ <br /> 2) 2N0 + 2C0-"►2CO2 + N2 <br /> Both NOx (NO2 and NO) and CO are reduced to CO2 and N2. <br /> xi S. Removal of NOx with HC (CH4) as a reducing agent. <br /> 1) 4NO2 + CH4--►4NO + CO2 + 2H2 <br /> 2) 4NO + CH4_►CO2 + 2H2O + 2N2 <br /> C. Removal of CO in the presence of a catalyst (oxidizing reaction) <br /> 02 + 2C0--►2CO2 <br /> D. Removal of CH4 in the presence of a catalyst (oxidizing reaction) <br /> r 202 t CH 4�►2H2O + CO2 <br /> See Diagram 1. <br /> By controlling the A/F ratio a "window" or area of favorable operating condi- <br /> tions exist which allow for the optimization of all the reactions. This occurs <br /> at or near the stoichiometric point of the exhaust system. (See Figure 2 and <br /> Diagram 2) <br /> t <br /> This "window" is optimized by using one of three methods: (1) controlling <br /> the CO level, (2) use of an oxygen sensor in conjunction with a high impedance <br /> voltmeter, (3) use of an automatic air-to-fuel ratio control system provided <br /> by the engine manufacturer. <br /> Misfiring and operation above 1200OF should be avoided when using the <br /> catalytic silencer. Misfiring causes an increase of hydrocarbons to be <br /> forced through the catalytic silencer where combustion occurs, temporarily <br /> raising the exhaust operating temperature. <br /> C/22 <br />