Patent ID: 8899021

Claim:
A method of dosing a reagent into an exhaust gas stream of an internal combustion engine having an SCR catalyst, the method comprising: injecting reagent from a reagent tank into the exhaust gas stream at a position upstream of the SCR catalyst using a reagent injector in accordance with a first dosing schedule in order to remediate a predetermined proportion of NOx in the exhaust gas stream, the first dosing schedule being associated with a first range of engine operating conditions; injecting reagent from the reagent tank into the exhaust gas stream at a position upstream of the SCR catalyst using a reagent injector in accordance with a second dosing schedule in order to enable heat transfer between the reagent injector and said injected reagent, the second dosing schedule being associated with a second range of engine operating conditions; and dosing in accordance with said first or said second dosing schedule in dependence on whether engine operating conditions lie within said first or said second range of engine operating conditions; wherein the proportion of NOx in the exhaust gas stream which is remediated by dosing using said second dosing schedule is less than said predetermined proportion, and wherein said second range of engine operating conditions is characteristic of at least one of higher engine load and higher engine speed than said first range of engine operating conditions.