Method for controlled DPF regeneration

Abstract

One of the inventors' concepts relates to controlling a temperature of a diesel engine exhaust aftertreatment device, such as a DPF or a fuel reformer, in which combustion is taking place. The concept is to inject reductant to combust in an upstream device, thereby removing oxygen in the exhaust and limiting combustion in the downstream device. The same total amount of heat may be generated, but the distribution is different and limits temperatures in the downstream device. The temperature limiting effect may be through one or more of the thermal storage capacity of the upstream device, the additional heat loss to the surroundings due to higher temperatures upstream in the exhaust system, or the benefit of a more uniform distribution of heat in the downstream device, which mitigates local hot spots. This concept may be used in a temperature control system.

1 . A method of controlling a temperature in an engine exhaust aftertreatment system, comprising:
 operating the engine to produce an exhaust containing at least about 4% oxygen;   passing the exhaust through a first exhaust system device and then a second exhaust system device, wherein oxygen remaining in the exhaust when it reaches the second exhaust system device takes part in reactions that produce a substantial amount of heat;   detecting a temperature of the second exhaust system device;   in response to the detected temperature, increasing an injection rate of reductant into the exhaust before it enters the first exhaust system device, whereby the rate of oxygen consumption in the first exhaust system device increases, less oxygen remains in the exhaust when it reaches second exhaust system device, significantly less heat is released by reactions with oxygen in the second exhaust system device, and the result is a decrease in a heating rate within the second exhaust system device.   
   
   
       2 . The method of  claim 1 , wherein the second exhaust system device is a DPF. 
   
   
       3 . The method of  claim 2 , wherein the first exhaust system device is a fuel reformer. 
   
   
       4 . The method of  claim 3 , wherein the exhaust is passed through a third exhaust system device between the fuel reformer and the DPF, and the third exhaust system device has a large thermal mass in comparison to that of the fuel reformer. 
   
   
       5 . The method of  claim 4 , wherein the third exhaust system device is a LNT. 
   
   
       6 . The method of  claim 1 , wherein the second exhaust system device is a fuel reformer. 
   
   
       7 . The method of  claim 6 , wherein the first exhaust system device is a DPF comprising an oxidation catalyst. 
   
   
       8 . The method of  claim 6 , wherein the first exhaust system device comprises an oxidation catalyst and the exhaust is passed through the first exhaust system device, a DPF, and then the fuel reformer. 
   
   
       9 . A vehicle comprising an exhaust aftertreatment system and a controller configured to operate the exhaust aftertreatment system using the method of  claim 1 . 
   
   
       10 . A method of operating a diesel engine-powered vehicle, comprising:
 operating the engine to produce an exhaust containing soot and at least about 4% oxygen;   trapping soot from the exhaust with the DPF; and   from time-to-time, regenerating the DPF by steps comprising:
 heating the DPF until soot combustion within the DPF attains a self-sustaining rate; and 
 limiting local rates of soot combustion within the DPF by injecting reductant into the exhaust upstream of a first exhaust system device upstream of the DPF, the device comprising an oxidation catalyst, whereby oxygen is consumed in the first exhaust system device and less oxygen remains in the exhaust when it reaches the DPF. 
   
   
   
       11 . The method of  claim 10 , wherein the first exhaust system device is a fuel reformer. 
   
   
       12 . The method of  claim 11 , wherein the exhaust is passed through a third exhaust system device between the fuel reformer and the second exhaust system device, and the third exhaust system device has a large thermal mass in comparison to that of the fuel reformer. 
   
   
       13 . The method of  claim 12 , wherein the third exhaust system device is a LNT. 
   
   
       14 . A vehicle comprising a controller that operates the vehicle using the method of  claim 10 . 
   
   
       15 . The method of  claim 10 , wherein the reductant is injected into the exhaust by the engine prior to the exhaust leaving the engine. 
   
   
       16 . The method of  claim 10 , wherein the reductant is injected into the exhaust as the exhaust travels through an engine manifold upstream of a turbocharger. 
   
   
       17 . The method of  claim 10 , wherein the reductant is injected into the exhaust downstream from the engine. 
   
   
       18 . The method of  claim 10 , wherein the reductant injection rate is used in a feedback control loop controlling a temperature of the DPF. 
   
   
       19 . The method of  claim 10 , wherein the reductant injection rate is varied as soot combusts in the DPF in order to control the soot combustion rate.