Apparatus and Method for NOx Reduction

Abstract

Apparatus and method for NOx reduction. A reducing catalyst is provided on a monolith or other suitable catalytic converter element. A multi-mode fuel processor of liquid hydrocarbon fuel is capable of delivering a required quantity and composition of a reducing agent while operating in a desired sequence of the following modes: partial oxidation, incomplete pyrolysis, evaporation, combustion, and atomization. Temperature sensors detect the catalyst temperature and means are provided to introduce the reducing agent into the exhaust stream at a rate correlated to the measured temperature. Means also provided to implement a predetermined control algorithm.

1 . A system for reducing oxides of nitrogen (NOx) in the exhaust stream produced by an internal combustion engine operating at lean air/fuel ratios into non polluting emissions comprising:
 (a) a reducing catalyst on a monolith or other suitable catalytic converter;   (b) a multi-mode fuel processor of liquid hydrocarbon fuel such as diesel capable of delivering a required quantity and composition of a reducing agent while operating in a desired sequence of at least the following modes: partial oxidation, incomplete pyrolysis, evaporation, combustion, atomization;   (c) means to introduce said reducing agent into said exhaust stream; and   (d) means to implement a predetermined control algorithm.   
   
   
       2 . A system according to  claim 1 , further comprising means to introduce atomized liquid hydrocarbon fuel into said exhaust stream in addition to the amount of reducing agent already delivered by said fuel processor. 
   
   
       3 . A system according to  claim 2  wherein the atomized liquid hydrocarbon fuel is introduced into the hot stream of reducing agent generated by the fuel processor. 
   
   
       4 . A system according to  claim 1 , further comprising temperature sensors. 
   
   
       5 . A system according to  claim 1  wherein a multi-mode fuel processor of liquid hydrocarbon fuel is a plasma fuel reformer. 
   
   
       6 . A system according to  claim 1 , further comprising an on-board source of hydrogen. 
   
   
       7 . A system according to  claim 1 , further comprising a diesel particulate filter (DPF). 
   
   
       8 . A system according to  claim 1 , further comprising means to cool gases upstream of the said catalyst. 
   
   
       9 . A system according to  claim 1 , further comprising means to cool gases upstream of the said catalyst if the temperature of said catalyst is above a predetermined level. 
   
   
       10 . A system according to  claim 9 , further comprising control means such that said means to cool gases are activated only when a high catalyst temperature is detected or conditions are determined that are expected to lead to high catalyst temperatures. 
   
   
       11 . The method of reducing oxides of nitrogen (NOx) in the exhaust stream by controlling the system described in  claim 1  via the following steps:
 (a) Determining temperature of the catalyst and/or temperature of exhaust stream;   (b) Changing the control parameters and/or operating mode of said fuel processor on the basis of said measurements in accordance with a predetermined control algorithm.   
   
   
       12 . The method according to  claim 11 , wherein the fuel processor is specifically operating in the combustion mode to provide for fast light off of the catalyst. 
   
   
       13 . The method according to  claim 11 , wherein a setpoint value for a reducing agent feed is based on the engine's parameters. 
   
   
       14 . The method according to  claim 11 , wherein the output of said fuel processor is also delivered upstream of DPF. 
   
   
       15 . The method according to  claim 11 , wherein a diesel internal combustion engine is equipped with exhaust gas recirculation, and wherein the exhaust gas is partially directed to said fuel processor. 
   
   
       16 . The method of  claim 11  wherein in order to decrease a response time only one control parameter (namely fuel flow rate) is changed when switching from one operation mode to another whilst other control parameters (primarily air flow rate) remains constant. 
   
   
       17 . A system according to  claim 11  wherein the fuel processor's mode of operation is changing from complete combustion to partial oxidation to incomplete pyrolisys to vaporization inversely proportional to catalyst temperature increase. 
   
   
       18 . A method according to  claim 11 , wherein at least one of the control parameters is processed by a dedicated signal processor. 
   
   
       19 . A method according to  claim 11 , wherein at least one of the control parameters is processed by a main engine control unit or EMS. 
   
   
       20 . The method of reducing oxides of nitrogen (NOx) in the exhaust stream by controlling the system described in  claim 1  using a predetermined control algorithm based on an engine map. 
   
   
       21 . A system according to  claim 1 , wherein the reducing catalyst is an SCR catalyst comprising silver on alumina. 
   
   
       22 . A system according to  claim 1 , wherein the reducing catalyst is an SCR catalyst comprising a combination of silver and one or more other metals on a metal oxide (e.g. Al 2 O 3  or SiO 2 ) or on a zeolite (MFI, MOR, BEA or Y). 
   
   
       23 . A system according to  claim 1 , wherein the catalyst is an SCR catalyst comprising silver or any other catalyst showing increased low temperature reduction activity in the presence of hydrogen and hydrocarbons. 
   
   
       24 . A system according to  claim 1 , wherein such fuels as bio-diesel, ethanol, gasoline, propane, methane and biofuels or their mixtures are used as a source of hydrocarbons in the reducing agent.