A diesel exhaust system which includes: (a) an exhaust pipe having a diesel oxidation catalyst and a downstream diesel particulate filter, (b) a dosing module which comprises: a housing having a diesel fuel inlet attached to a source of filtered fuel, an air inlet attached to a source of filtered air, and a dosing fuel/air outlet, a dosing line attached to the dosing fuel/air outlet and having a nozzle at a distal end of the dosing line, the nozzle positioned to spray diesel fuel into the exhaust pipe upstream of the diesel oxidation catalyst, a fuel shut-off valve and a fuel dosing valve positioned at least partially within the housing, and an air purge valve positioned at least partially within the housing, in which the fuel shut off valve and fuel dosing valve selectively provide diesel fuel to the nozzle, in which the air purge valve selectively purges diesel fuel from the dosing line and the nozzle, and (c) an electronic control unit positioned at least partially within the housing which (i) manages the provision of diesel fuel to the nozzle dependent on the temperature of the diesel oxidation catalyst and on the pressure drop between the inlet and the outlet of the diesel particulate filter, and (ii) manages the air purge valve state, supplying purge air to purge the dosing line of diesel fuel at the end of a dosing cycle. (a) an exhaust pipe having a diesel oxidation catalyst and a downstream diesel particulate filter, (b) a dosing module which comprises: a housing having a diesel fuel inlet attached to a source of filtered fuel, an air inlet attached to a source of filtered air, and a dosing fuel/air outlet, a dosing line attached to the dosing fuel/air outlet and having a nozzle at a distal end of the dosing line, the nozzle positioned to spray diesel fuel into the exhaust pipe upstream of the diesel oxidation catalyst, a fuel shut-off valve and a fuel dosing valve positioned at least partially within the housing, and an air purge valve positioned at least partially within the housing, in which the fuel shut off valve and fuel dosing valve selectively provide diesel fuel to the nozzle, in which the air purge valve selectively purges diesel fuel from the dosing line and the nozzle, and a housing having a diesel fuel inlet attached to a source of filtered fuel, an air inlet attached to a source of filtered air, and a dosing fuel/air outlet, a dosing line attached to the dosing fuel/air outlet and having a nozzle at a distal end of the dosing line, the nozzle positioned to spray diesel fuel into the exhaust pipe upstream of the diesel oxidation catalyst, a fuel shut-off valve and a fuel dosing valve positioned at least partially within the housing, and an air purge valve positioned at least partially within the housing, in which the fuel shut off valve and fuel dosing valve selectively provide diesel fuel to the nozzle, in which the air purge valve selectively purges diesel fuel from the dosing line and the nozzle, and (c) an electronic control unit positioned at least partially within the housing which (i) manages the provision of diesel fuel to the nozzle dependent on the temperature of the diesel oxidation catalyst and on the pressure drop between the inlet and the outlet of the diesel particulate filter, and (ii) manages the air purge valve state, supplying purge air to purge the dosing line of diesel fuel at the end of a dosing cycle.