Adaptive control of reformer inlet oxygen concentration

Abstract

A vehicle on-board computer method for controlling a diesel engine intake air throttle valve during LNT regeneration. The method comprises setting a software limit on the throttle valve position. The limit is a dynamic value affected by the engine operating state. A variable relating to the exhaust oxygen concentration is controlled to approach a setpoint by adjusting the intake air throttle valve position subject to the limit. In one embodiment, the valve position limit is based in part on an exhaust oxygen content measured while the throttle valve is fully open. In another embodiment, the valve position limit is adjusted based on the setpoint, whereby greater throttling is allowed when exhaust oxygen content is targeted to a higher value. In a further embodiment, the setpoint is adjusted based on the engine load. The method allows extensive intake air throttling without causing instability in the engine.

1 . A method of operating a power generation system, comprising:
 operating a diesel engine to produce an exhaust containing NOx;   passing the exhaust through an exhaust line containing a fuel reformer;   passing the exhaust through a LNT that adsorbs and stores NOx from the exhaust under lean conditions;   generating a control signal to regenerate the LNT to remove stored NOx;   in a sequence of events trigged by the control signal, in a rich phase, providing fuel to the exhaust at a rate that leaves the exhaust rich, whereby the fuel reformer produces reformate-containing exhaust;   passing the reformate-containing exhaust through a LNT to regenerate the LNT and reduce the adsorbed NOx;   in the sequence of events trigged by the control signal, setting a throttle valve position limit based on a state of the diesel engine; and   controlling an engine intake air throttle valve position to reduce the exhaust oxygen concentration;   wherein the engine intake air throttle valve position is controlled to approach a setpoint while not exceeding the throttle valve position limit.   
   
   
       2 . The method of  claim 1 , further comprising:
 in the sequence of events trigged by the control signal, in a lean phase prior to the rich phase, warming the fuel reformer by providing fuel to the exhaust at a rate that leaves the exhaust lean, whereby fuel combustion in the exhaust line heats the reformer;   wherein the reformer catalyzes steam reforming reactions during the rich phase.   
   
   
       3 . The method of  claim 1 , wherein the throttle valve position limit is set based at least in part on an exhaust oxygen concentration measured while the valve position is fully open. 
   
   
       4 . The method of  claim 1 , wherein the setpoint is determined based at least in part on an engine load. 
   
   
       5 . The method of  claim 1 , wherein the throttle valve position limit depends on the setpoint. 
   
   
       6 . The method of  claim 5 , wherein the limit depends on the setpoint in a manner that allows the throttle valve to close to a greater degree when the setpoint is higher as compared to when the setpoint is lower. 
   
   
       7 . The method of  claim 1 , wherein controlling the engine intake air throttle valve position comprises integrating an error and the integration ceases when the valve position reaches the limit. 
   
   
       8 . The method of  claim 1 , wherein controlling the engine intake air throttle valve position is accomplished with feedback based on a delay free estimate developed from a measured exhaust condition. 
   
   
       9 . A vehicle on-board computer method for controlling a position of a diesel engine intake air throttle valve, comprising:
 setting a software limit on the throttle valve position, wherein the limit is a value that is variable in a manner relating to one or more of engine speed and engine load;   controlling a variable selected from the group consisting of exhaust oxygen concentration, exhaust oxygen flow rate, and exhaust air-fuel ratio to approach a setpoint value by adjusting the intake air throttle valve position without passing the limit.   
   
   
       10 . The method of  claim 9 , wherein the limit is set based at least in part on an exhaust oxygen concentration measured while the valve position is fully open. 
   
   
       11 . The method of  claim 9 , wherein the setpoint is determined based at least in part on the engine load. 
   
   
       12 . The method of  claim 9 , wherein the limit is made to depend on the setpoint. 
   
   
       13 . The method of  claim 12 , wherein the limit is made to depend on the setpoint in a manner that allows the throttle valve to close to a greater degree when the setpoint is higher as compared to when the setpoint is lower. 
   
   
       14 . The method of  claim 9 , wherein the control comprises integrating an error and the integration ceases when the valve position reaches the limit. 
   
   
       15 . The method of  claim 9 , wherein the control comprises feedback based on a delay free estimate developed from a measured exhaust condition. 
   
   
       16 . The method of  claim 9 , wherein the software limit is set as part of a sequence of steps carried out to regenerate a LNT. 
   
   
       17 . The method of  claim 9 , wherein the software limit is set as part of a sequence of steps carried out to regenerate a DPF. 
   
   
       18 . A power generation system comprising:
 a diesel engine operative to take in fuel from a fuel supply and air from an air supply and to produce an exhaust containing NOx;   an engine intake air throttle valve configured to throttle the air supply;   an exhaust line configured to receive the exhaust;   a LNT configured in the exhaust line and operative to adsorb and store NOx from lean exhaust and to reduce the stored NOx and be regenerated when provided with rich reductant-containing exhaust; and   a controller configured to control a position of the engine intake air throttle valve and to control a provision of reductant to the exhaust;   wherein the controller is operative to regenerate the LNT by controlling the position of the engine intake air throttle valve and a rate of provision or reductant to the exhaust;   the controller is configured to control the engine intake air throttle valve position during LNT regeneration to approach an exhaust oxygen content to a setpoint; and   the controller is also configured not to adjust the valve position beyond a limit that is set dynamically by the controller at each regeneration.   
   
   
       19 . The system of  claim 18 , further comprising:
 a fuel reformer operative to produce reformate and configured to provide the reformate to the exhaust;   wherein the reductant is reformate;   
   
   
       20 . The system of  claim 19 , wherein the fuel reformer is configured in the exhaust line upstream of the LNT. 
   
   
       21 . The system of  claim 20 , wherein the fuel reformer is adapted to catalyze steam reforming. 
   
   
       22 . The system of  claim 21 , wherein the controller is configured to regenerate the LNT by heating the fuel reformer under lean exhaust conditions prior to making the exhaust rich. 
   
   
       23 . The system of  claim 18 , wherein the controller is configured to set the throttle valve position limit based at least in part on a measured exhaust oxygen concentration. 
   
   
       24 . The system of  claim 23 , wherein the controller is configured to set the throttle valve position limit based at least in part on an exhaust oxygen concentration measured while the throttle valve is fully open. 
   
   
       25 . The system of  claim 18 , wherein the controller is configured to adjust the setpoint based on an engine load. 
   
   
       26 . The system of  claim 18 , wherein the controller is configured to set the throttle valve position limit based in part on the setpoint. 
   
   
       27 . The system of  claim 26 , wherein the controller sets the limit in a manner that allows the throttle valve to close to a greater degree when the setpoint is higher as compared to when the setpoint is lower. 
   
   
       28 . The system of  claim 18 , wherein the controller is configured to integrate an error between the setpoint and a feedback quantity and is configured to cease the integration when the valve position reaches the limit. 
   
   
       29 . The system of  claim 18 , wherein the controller is configured to control the valve position based on a delay-free estimate of the current exhaust oxygen concentration. 
   
   
       30 . The system of  claim 18 , wherein the controller is part of a set of controls in which the engine is controlled independently of the intake air throttle control. 
   
   
       31 . The system of  claim 18 , wherein the system is the product of combining an engine designed and manufactured without an intake air throttle valve with an exhaust aftertreatment system and an intake air throttle valve.