A light source to emit light, an optical structure constituting an optical system to modulate or combine emission light of the light source, a projection element to project exit light of from the optical structure, a flow passage to flow a cooling fluid to cool the light source, and a housing structuring an exterior are provided. The method may include adjusting timing of subsequent desulfation based upon a delay between initiating the desulfation process and a temperature increase in the NOx trap. The conveyor unit conveys a transfer medium onto which the image is to be transferred.