Metering Module and Mixer: Notes

The metering module is responsible for injecting the urea-water solution into the exhaust pipe. It features a valve that is similar to the fuel injector in a petrol engine with intake manifold injection.

Fig 1: Identifying Metering Module Metering Line Connection And Metering Valve Connection

Courtesy of BMW OF NORTH AMERICA, INC.

Although the metering module does not have a heater, it is still heated by the exhaust system to such an extent that it even requires cooling fins.

The metering module is actuated by a pulse-width modulated (PWM) signal from the DDE such that the pulse duty factor determines the opening duration of the valve.

The metering module is equipped with a tapered insert (6) that prevents urea-water solution residue drying up and clogging the valve. Its shape creates a flow that prevents urea-water solution from collecting on the walls of the exhaust system. Urea deposits on the insert are burnt off as it is heated to very high temperatures by the flow of exhaust gas.

Fig 2: Metering Module Flow Diagram

Courtesy of BMW OF NORTH AMERICA, INC.