A silencer for a combustion engine, which silencer comprises a casing with a substantially circular cylindrical shell surface, a first end element and a second end element, at least one inlet for leading an exhaust flow into the casing and at least one outlet for leading the exhaust flow out from the casing, a selective catalytic reduction purification system which comprises an SCR substrate, a vaporisation pipe and an arrangement for adding a reducing agent to the exhaust flow in order to reduce NO x contents of the exhaust flow, characterised in that - the silencer comprises a first cylindrical space close to the inlet, a particle filter close to the first space, and a first cylindrical duct close to the particle filter, which particle filter is circular cylindrical and surrounds the SCR substrate in the radial direction, such that the exhaust gases are caused to flow from the first space to the first cylindrical duct through the particle filter in a substantially radial direction relative to the silencer's centreline, in which duct the exhaust gases are caused to flow in a first direction towards the first end element of the casing; - the first cylindrical duct surrounds the SCR substrate; - the vaporisation pipe is situated substantially concentrically with the SCR substrate, and the SCR substrate surrounds the vaporisation pipe, such that the vaporisation pipe is connected to the first duct via a passage and the exhaust gases in the vaporisation pipe are caused to flow towards the second end element of the casing in a second direction which is opposite to the first direction; - a second duct is provided between the vaporisation pipe and the SCR substrate, such that the exhaust gases flow to the SCR substrate through the second duct on the outside of the vaporisation pipe and the exhaust gases in the second duct are caused to flow in the first direction; - the outlet is situated close to the SCR substrate such that the exhaust gases are caused to flow out from the silencer via the outlet when the exhaust gases have passed the SCR substrate. - the silencer comprises a first cylindrical space close to the inlet, a particle filter close to the first space, and a first cylindrical duct close to the particle filter, which particle filter is circular cylindrical and surrounds the SCR substrate in the radial direction, such that the exhaust gases are caused to flow from the first space to the first cylindrical duct through the particle filter in a substantially radial direction relative to the silencer's centreline, in which duct the exhaust gases are caused to flow in a first direction towards the first end element of the casing; - the first cylindrical duct surrounds the SCR substrate; - the vaporisation pipe is situated substantially concentrically with the SCR substrate, and the SCR substrate surrounds the vaporisation pipe, such that the vaporisation pipe is connected to the first duct via a passage and the exhaust gases in the vaporisation pipe are caused to flow towards the second end element of the casing in a second direction which is opposite to the first direction; - a second duct is provided between the vaporisation pipe and the SCR substrate, such that the exhaust gases flow to the SCR substrate through the second duct on the outside of the vaporisation pipe and the exhaust gases in the second duct are caused to flow in the first direction; - the outlet is situated close to the SCR substrate such that the exhaust gases are caused to flow out from the silencer via the outlet when the exhaust gases have passed the SCR substrate.