On-board ammonia generation and exhaust after treatment system using same
Often NOx selective catalysts that use ammonia to reduce NOx within exhaust to a harmless gas require on-board storage of ammonia which can be hazardous and inconvenient. In order to generate ammonia in exhaust, the present disclosure increases a NOx concentration in exhaust from at least one combustion chamber, at least in part, by injecting fuel in a predetermined increased NOx generation sequence that includes a first injection during non-auto ignition conditions and a second injection during auto ignition conditions. At least a portion of the NOx is converted to ammonia by passing at least a portion of the exhaust with the increased NOx concentration over an ammonia-producing catalyst.
1. A method of generating ammonia in exhaust comprising the steps of:
increasing a NOx concentration in exhaust from at least one combustion chamber, at least in part, by injecting fuel in a predetermined increased NOx generation sequence including at least a first injection during non-auto ignition conditions and a second injection during auto-ignition conditions, and igniting the fuel in the combustion chamber; and
converting at least a portion of the NOx to ammonia, at least in part, by passing at least a portion of the exhaust with the increased NOx concentration in proximity of an ammonia-producing catalyst.
2. The method of claim 1 wherein the step of increasing NOx includes a step of injecting the first injection in a first spray pattern with a small average angle relative to a centerline of the combustion chamber and injecting the second injection in a second spray pattern with a large average angle relative to the centerline of the combustion chamber.
3. The method of claim 1 including a step of adding unburnt fuel into the exhaust, at least in part, by injecting an additional amount of fuel into a non-combustible environment of the combustion chamber during at least one member selected from the group consisting of an expansion stroke and exhaust stroke.
4. The method of claim 1 including a step of adding unburnt fuel into the exhaust, at least in part, by injecting fuel into the exhaust passage downstream from the combustion chamber.
5. The method of claim 1 including the steps of:
mixing the ammonia with other exhaust; and
passing the ammonia and other exhaust over a NOx selective catalyst.
6. The method of claim 5 including a step of setting an ammonia production amount to reduce an expected NOx concentration from the other exhaust.
7. The method of claim 6 wherein the step of increasing NOx includes a step of injecting the first injection in a first spray pattern including a small average angle relative to a centerline of the combustion chamber and injecting the second injection in a second spray patter includes a large average angle relative to the centerline of the combustion chamber; and
adding unburnt fuel into the exhaust, at least in part, by injecting fuel into the exhaust passage upstream from the ammonia-producing catalyst or injecting an additional amount of fuel into a non-combustible environment of the combustion chamber during at least one member selected from the group consisting of an expansion stroke and exhaust stroke.