a compressed air regulating valve 34 the control unit 20 contains a first functional block 41 to ascertain the exhaust gas speed vabg a second functional block 42 to ascertain the exhaust gas pressure pabg a third functional block 43 to ascertain a calculated exhaust gas temperature tabgr and a fourth functional block 44 to ascertain a torque md the control unit 20 additionally contains a reagent substance pressure set point setting 50 which emits a reagent substance pressure set point preasw to a reagent substance pump trigger activation 51 which supplies the reagent substance pump activation signal 31 and also contains a compressed air pressure set point setting 52 which emits a compressed air set point pdlsw to a compressed air regulating valve trigger activation 53 which supplies the compressed air regulating valve activation signal 33 the reagent substance temperature sensor 23 records the temperature of a reagent substance stored in a reagent substance container 60 the compressed air regulating valve 34 adjusts the compressed air set point pdlsw of a compressed air which is available in a compressed air container 61 the compressed air passes through a super critical choke 62 and a check valve 63 and moves thereafter into a mixer 64 which mixes the compressed air with the reagent substance introduced by the metering valve 30 the mixer 64 is connected to the spray device 13 the catalytic converter 15 which is disposed in the exhaust area of the internal combustion engine 10 is preferably a scr catalytic converter which reduced the nitrogen oxides no and no 2 contained in the exhaust gas to nitrogen the scr catalytic converter 15 needs ammonia for the reduction reaction the ammonia can be obtained from a urea water solution.