Process for reducing nitrogen oxides on SCR catalyst
AssigneeHJS Fahrzeugtechnik GmbH & Co.
InventorWerner Weisweiler
Life of this patent
Estimating the term…
Abstract
A process for reducing nitrogen oxides on a SCR catalyst disposed in an exhaust gas system of an internal combustion engine is performed by a device adapted to introduce ammonia (NH3) into the exhaust gas flow of the exhaust gas system before it reaches the SCR catalyst. The device includes a heatable pressure-tight converter, an NH3 store and a control unit with control signals processing engine operating characteristics and determining therefrom the NOx output for controlling a timed valve for injection of an NH3 dose.
Claims9
Process for reducing nitrogen oxides (NOx)on a SCR catalyst, disposed in an exhaust gas system of an internal combustion engine, with ammonia (NH3) which is introduced before the catalyst into the exhaust gas flow, characterized in that the process comprises the following steps:
- heating in a converter implemented as a pressure-tight receptacle an NH3-containing substance, of which NH3 can be thermolytically split off, to a temperature within a range at which the splitting-off of NH3 takes place, the NH3-containing substance being able to come to a state of equilibrium with the split-off NH3 at a predetermined pressure within the converter, the converter being heated from heat generated during operation of the internal combustion engine;
- maintaining the splitting-off temperature within the range for building an internal pressure in the converter up to a known internal pressure at which, without removal of the gas, the state of equilibrium is established between the temperature-conditioned NH3 splitting substance and the split-off NH3 so that the pressure in the converter does not rise while the splitting-off temperature is maintained;
- intermediately storing within the converter a specific quantity of the split-off NH3;
- acquiring engine operating characteristics according to which the NOx content in the exhaust gas flow can be calculated and, based on the acquired engine operating characteristics, carrying out a determination of the NH3 dosing necessary for reducing the calculated NOx content in the exhaust gas flow;
- drawing off and injecting a predetermined dose of the intermediately stored NH3 into the exhaust gas flow of the internal combustion engine with the last two process steps repeating at optional frequency during the operation of the engine such that due drawing off of the dose from the converter needed for the injecting into the exhaust gas flow the pressure in the converter drops and the state of equilibrium between the temperature-conditioned NH3 and the split-off NH3 in the converter is destabilized such that additional split-off NH3 will thermolytically be produced from the NH3-carrying substance contained in the converter.
Dependencies are inferred from the claim text.