Abstract: This invention relates to a method and a device for optimizing purification of diesel exhaust gases, the purification being carried out by using a catalyst.It is the object of the present invention to avoid the development of NO.sub.2 in the catalyst at the same time as the contents of carbon monoxide (CO) and hydrocarbons are maintained at a low level.This object is accomplished by adjusting the temperature of the exhaust gases when they pass the catalyst. The adjustment is carried out by finely divided injection of some cooling medium into the exhaust gases.

Abstract: An exhaust cleaner containing a catalyst material and intended for temporary use on a motor car is arranged as a portable or transportable unit. It is provided with means for suspension on the car and with means for passing the exhaust gas from the exhaust pipe of the car through the catalyst material. The catalyst material has a large heat capacity and there are provided means for electrically preheating the catalyst material.