Controlling exhaust gas emissions

An exhaust gas separator is described for inclusion in the exhaust gas path from an internal combustion engine to separate solid particles from the gas. The separator comprises a generally elongate pipe (14), means (16) for causing the exhaust gases flowing along the pipe (14) to perform a helical swirling motion about an axis parallel to the longitudinal extent of the pipe (14), a radially enlarged cylindrical collection chamber (22) immediately downstream of the swirl producing means (16), an exit pipe (24) downstream of the chamber, the diameter of the exit pipe (24) being smaller than that of the chamber (22), and a tangential offtake from the collection chamber (22) by which trapped particles can be removed from the chamber (22).