Method for controlling a dosage device and/or an engine , said engine producing an exhaust stream being treated by an exhaust treatment system by use of an additive being injected into said exhaust stream by said dosage device , wherein said additive is intended to be evaporated in an evaporation chamber when being injected into said exhaust stream ; the method comprising: - determining a time dependent condition C i of a position P i at an internal wall of said evaporation chamber , said time dependent condition C i being determined based on a representation of an internal temperature T i related to said position P i , said representation of said internal temperature T i being determined based on a temperature model for said evaporation chamber and: a measurement of an exhaust temperature T exh for said exhaust stream upstream said evaporation chamber in said exhaust treatment system , and/or a prediction of an exhaust temperature T exh for said exhaust stream upstream said evaporation chamber in said exhaust treatment system ; - determining a risk for a critical condition C i_critical related to said position P i based on said determined time dependent condition C i such that said risk for the critical condition C i_critical has a spatial resolution along said internal wall of said evaporation chamber ; and - controlling said dosage device and/or said engine based on said determined risk for the critical condition C i_critical . - determining a time dependent condition C i of a position P i at an internal wall of said evaporation chamber , said time dependent condition C i being determined based on a representation of an internal temperature T i related to said position P i , said representation of said internal temperature T i being determined based on a temperature model for said evaporation chamber and: a measurement of an exhaust temperature T exh for said exhaust stream upstream said evaporation chamber in said exhaust treatment system , and/or a prediction of an exhaust temperature T exh for said exhaust stream upstream said evaporation chamber in said exhaust treatment system ; said time dependent condition C i being determined based on a representation of an internal temperature T i related to said position P i , said representation of said internal temperature T i being determined based on a temperature model for said evaporation chamber and: a measurement of an exhaust temperature T exh for said exhaust stream upstream said evaporation chamber in said exhaust treatment system , and/or a prediction of an exhaust temperature T exh for said exhaust stream upstream said evaporation chamber in said exhaust treatment system ; a measurement of an exhaust temperature T exh for said exhaust stream upstream said evaporation chamber in said exhaust treatment system , and/or a prediction of an exhaust temperature T exh for said exhaust stream upstream said evaporation chamber in said exhaust treatment system ; - determining a risk for a critical condition C i_critical related to said position P i based on said determined time dependent condition C i such that said risk for the critical condition C i_critical has a spatial resolution along said internal wall of said evaporation chamber ; and - controlling said dosage device and/or said engine based on said determined risk for the critical condition C i_critical . <EOS>