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.