Reagent dosing system and method of dosing reagent

1. A reagent dosing system for dosing a reagent into the exhaust gas stream of an internal combustion engine, the system comprising:

a reagent tank for storing a supply of reagent;

an injector module comprising an atomising dispenser and a positive-displacement metering pump which draws reagent from the reagent tank and delivers it to the dispenser;

a supply line coupling the reagent tank to the injector module;

a dosing control unit operable to control the injector module to inject reagent into the exhaust gas stream;

an additional priming pump arranged, in use, to urge reagent along the supply line toward the injector module under selected conditions; and

a tank module mountable within the reagent tank, said tank module comprising:

a reservoir comprising a tubular member with a first open end and a second closed end, the second end having an opening therein to enable the inflow of reagent from the reagent tank;

a closure member for closing the first end of the tubular member to prevent the flow of reagent therefrom; and

a reagent pickup tube having a first end disposed within said reservoir and a second end in fluid communication with said supply line;

wherein the priming pump is disposed within the tank module.

2. A system according to claim 1 , wherein the dispenser and the metering pump are integrated within the same unit.

3. A system according to claim 1 , wherein the priming pump is operable at or during a start-up mode.

4. A system according to claim 1 , wherein the priming pump is operable continuously or intermittently during running of the engine.

5. An exhaust system for an internal combustion engine comprising:

a common exhaust portion comprising a particulate filter and having a first end coupled to the engine for receiving an exhaust gas stream emitted therefrom and a second end which divides into first and second branches;

wherein the first branch comprises an SCR catalyst and an SCR doser for injecting reagent into said first branch at a location disposed upstream of said SCR catalyst; and

the second branch comprises a Lean NOx Trap and a hydrocarbon doser for injecting hydrocarbons into said second branch at a location disposed upstream of said Lean NOx Trap.

6. An exhaust system according to claim 5 , comprising a 3-way valve disposed at said second end of said common exhaust portion, said valve being operable to direct said exhaust gas stream along at least one of said first and said second branch.