Arrangement for injecting a reductant into an exhaust line of an internal combustion engine

1. An arrangement for injecting a reducing agent into an exhaust line of a combustion engine, the arrangement comprising:

an exhaust line connected with the engine for leading exhaust gases out from the engine;

a first turbine situated in the exhaust line;

a second turbine situated in the exhaust line at a location downstream of the first turbine with respect to the direction of flow in the exhaust line;

an injector connected for injecting the reducing agent into the exhaust line where the reducing agent is warmed and vaporized by warm exhaust gases in the exhaust line so that ammonia is formed by the exhaust gases and the reducing agent; the injector situated in the exhaust line at a location downstream of the first turbine and upstream of the second turbine with respect to the direction of flow in the exhaust line;

an SCR catalyst situated downstream of the second turbine in which nitrogen oxides in the exhaust gases is reduced by the ammonia formed in the exhaust line;

a hydrolysis catalyst situated at a location downstream of the injector and upstream of the second turbine in the exhaust line;

a temperature sensor situated in the exhaust line at a location downstream of the second turbine configured for monitoring the temperature of the exhaust gases of the second turbine;

a bypass line extending from upstream to downstream of the second turbine having a valve configured to lead exhaust gases past the second turbine; and

a control unit configured and operable to receive information from the temperature sensor and to open the valve of the bypass line extending from upstream to downstream of the second turbine so that exhaust gases are led past the second turbine at times when they are at too low a temperature for advantageous reduction of nitrogen oxides to take place in the SCR catalyst.

2. An arrangement according to claim 1 , wherein reducing agent is a urea solution.

3. An arrangement according to claim 1 , wherein the control unit is configured for controlling the amount of reducing agent injected into the exhaust line.

4. An arrangement according to claim 3 , wherein the control unit receives information about the temperature of the exhaust gases from the temperature sensor downstream of the first turbine and upstream of the second turbine and selectively opens the valve of bypass line extending from upstream to downstream of the first turbine to lead exhaust gases past the first turbine when the exhaust gases are at too low a temperature in the exhaust line to vaporize the reducing agent.

5. An arrangement according to claim 1 , further comprising another temperature sensor situated in the exhaust line at a location downstream of the first turbine and upstream of the second turbine configured for monitoring the temperature of the exhaust gases downstream of the first turbine and upstream of the second turbine and for communicating with the control unit for affecting the amount of reducing agent injected into the exhaust line before the second turbine.

6. An arrangement according to claim 1 , wherein the exhaust line further comprises another bypass line extending from upstream to downstream of the first turbine having a valve for selectively leading exhaust gases past the first turbine or for leading exhaust gases through the first turbine.

7. An arrangement according to claim 1 , wherein the first turbine is connected to a compressor configured to compress air which is then led to the engine.

8. An arrangement according to claim 1 , further comprising a shaft of the engine and a transmission connecting the second turbine to the shaft of the engine.