System to reduce engine exhaust oxygen using exhaust hydrocarbons and a catalyst positioned upstream of a fuel reformer-LNT system

Abstract

One of the inventors' concepts relates to a power generation system, comprising a diesel engine and an exhaust system. The exhaust system comprises a first oxidation catalyst, a fuel reformer, and a LNT. A fuel injector is configured to inject fuel downstream of the oxidation catalyst, but upstream of the reformer. Preferably, the first oxidation catalyst is located near the engine. The first oxidation catalyst can extend the range of exhaust temperatures at which the aftertreatment devices operate by raising the temperature through reactions with residual hydrocarbons in the exhaust. The first oxidation catalyst also stabilizes the reformer operation by reducing the exhaust oxygen concentration. In a preferred embodiment, the engine operation is changed for LNT regenerations to increase the hydrocarbon content of the exhaust.

1 . A power generation system, comprising:
 a diesel engine operative to produce an exhaust containing NOx, hydrocarbon, and at least about 4% oxygen;   an exhaust system configured to receive the exhaust   a first oxidation catalyst configured in the exhaust system and operative to oxidize the hydrocarbons and thereby remove some of the oxygen from the exhaust;   a fuel reformer configured in the exhaust system downstream of the first oxidation catalyst and operative to produce reformate from rich exhaust when heated;   a LNT configured in the exhaust system downstream of the fuel reformer and operative to adsorb and store NOx from lean exhaust and to reduce the stored NOx and regenerate when provided with rich reformate-containing exhaust;   a fuel injector configured to inject fuel into the exhaust between the first oxidation catalyst and the fuel reformer.   
   
   
       2 . The power generation system of  claim 1 , wherein the engine is configured to change operation in order to increase the hydrocarbon content of the exhaust in response to a signal to regenerate the LNT. 
   
   
       3 . The power generation system of  claim 1 , wherein the power generation system comprises a turbo-charger and the first oxidation catalyst is in close proximity to the turbocharger. 
   
   
       4 . The power generation system of  claim 1 , further comprising a SCR catalyst in the exhaust system downstream of the LNT. 
   
   
       5 . The power generation system of  claim 1 , wherein the exhaust system comprises a branch allowing a portion of the exhaust to bypass the fuel reformer as the exhaust travels to the LNT. 
   
   
       6 . The power generation system of  claim 1 , wherein the engine is configured to inject fuel into the exhaust during operation of the reformer in order to reduce the oxygen concentration in the exhaust by combustion in the oxidation catalyst. 
   
   
       7 . The power generation system of  claim 1 , wherein the engine comprises an intake air throttle and is configured to increase a degree of intake air throttling in order to facilitate operation of the fuel reformer to produce reformate. 
   
   
       8 . The power generation system of  claim 1 , further comprising a second fuel injector configured to inject fuel into the exhaust system upstream of the oxidation catalyst. 
   
   
       9 . The power generation system of  8 , wherein the exhaust system comprises a turbocharger and the second fuel injector is configured to inject the fuel upstream of the turbocharger. 
   
   
       10 . The power generation system of  claim 1 , wherein the oxidation catalyst is operative to catalyze the conversion of a significant amount of NO in the exhaust to NO 2 . 
   
   
       11 . The power generation system of  claim 1 , further comprising a DPF downstream of the fuel reformer. 
   
   
       12 . A vehicle comprising the power generation system of  claim 1 . 
   
   
       13 . The power generation system of  claim 1 , wherein the oxidation catalyst is not effective for catalyzing conversion of NO to NO 2  in the exhaust. 
   
   
       14 . A method of operating a power generation system, comprising:
 operating a diesel engine to produce an exhaust containing NOx and hydrocarbon;   passing the exhaust through a first oxidation catalyst to oxidize the hydrocarbons and thereby remove some of the oxygen from the exhaust;   passing the exhaust through a fuel reformer;   passing the exhaust through a LNT that adsorbs and store NOx from the exhaust;   generating a control signal to regenerate the LNT;   in response to the control signal, injecting fuel into the exhaust downstream of the oxidation catalyst to form a lean mixture that combusts in the fuel reformer to generate heat and warm the reformer;   increasing the injection rate of fuel into the exhaust to form a rich mixture from which the fuel reformer forms reformate-containing exhaust; and   passing the reformate-containing exhaust through LNT to regenerate the LNT and reduce the adsorbed NOx.   
   
   
       15 . The method of  claim 14 , further comprising changing the operation of the engine in response to the control signal in order to cause the engine to produce an exhaust containing more hydrocarbon. 
   
   
       16 . The method of  claim 14 , wherein the regeneration takes place at an exhaust temperature that would be too low to warm the reformer effectively with the lean fuel injection were it not for the effect of the oxidation catalyst. 
   
   
       17 . The method of  claim 14 , wherein the NOx in the exhaust comprises NO and wherein the method further comprises converting a significant portion of the NO in the exhaust to NO 2  using the oxidation catalyst. 
   
   
       18 . The method of  claim 14 , wherein the oxidation catalyst is not effective for catalyzing conversion of NO to NO 2  in the exhaust. 
   
   
       19 . The method of  claim 14 , further comprising passing the exhaust through a DPF after the exhaust passes through the LNT.