An exhaust system for an internal combustion engine which burns a hydrocarbon fuel mixture and which produces a carbonaceous particle carrying exhaust gas stream that passes through a filter of the system that retains at least part of the particles therein, the system having a burn-off unit for periodically burning the retained particles in the filter to tend to periodically clean the filter of the retained particles thereof. The burn-off unit is adapted to raise the temperature of the exhaust gas stream intermediate the engine and the filter to raise the temperature of the filter to particle burning temperature thereof, the burn-off unit injecting and burning a certain amount of the hydrocarbon fuel mixture in the exhaust gas stream intermediate the engine and the filter to raise the temperature of the exhaust gas stream intermediate the engine and the filter. The fuel mixture is injected into the exhaust gas stream by an aspirating unit of the burn-off unit, and the temperature of the exhaust gas stream is raised by an electrical heater and a catalyst bed in which the injected fuel mixture is to burn.