Exhaust system for an internal combustion engine, burn-off unit and methods therefor

In a burn-off means for an exhaust system of 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 means of said system that retains at least part of said particles therein, said burn-off means being adapted for periodically burning said retained particles in said filter means to tend to periodically clean said filter means of said retained particles thereof, said burn-off means comprising means for raising the temperature of said exhaust gas stream intermediate said engine and said filter means to raise the temperature of said filter means to particle burning temperature thereof, said means for raising the temperature of said exhaust gas stream comprising means for injecting and burning a certain amount of said fuel mixture in said exhaust gas stream intermediate said engine and said filter means, the improvement wherein said means for injecting and burning comprises means for aspirating said certain amount of said fuel mixture into said exhaust gas stream intermediate said engine and said filter means and said means raising the temperature of said exhaust gas stream comprises an electrical heater means and a catalyst bed in which said injected fuel mixture is to burn, said electrical heater means being disposed upstream from said catalyst bed, said means for aspirating said fuel mixture being disposed upstream of said catalyst bed, said heater means being disposed intermediate said means for aspirating said fuel mixture and said catalyst bed, said means for raising the temperature of said exhaust gas stream also comprising passage defining means having an inlet for receiving said exhaust gas stream from said engine and an outlet for directing said received exhaust gas stream to said filter means, said passage defining means having first and second passages respectively between said inlet and said outlet, said catalyst bed and said heater means being disposed in said second passage, said means for aspirating said fuel mixture being disposed to feed said fuel mixture to said second passage upstream of said heater means therein, said passage defining means having valve means for directing said exhaust gas stream to said filter means only through said first passage during the time said filter means is not being cleaned and for directing said exhaust gas stream to said filter means through said second passage during the time said filter means is to be cleaned, said valve means comprising a first valve disposed in said second passage between said means for aspirating said fuel mixture and said heater means for closing said second passage between said inlet and said outlet and a second valve disposed in said passage defining means for closing said first passage between said inlet and said outlet.

In a method of operating 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 means of said system that retains at least part of said particles therein, said method comprising the steps of periodically burning said retained particles in said filter means with burn-off means to tend to periodically clean said filter means of said retained particles thereof, said step of burning comprising the step of raising the temperature of said exhaust gas stream intermediate said engine and said filter means to raise the temperature of said filter means to particle burning temperature thereof, said step of raising the temperature of said exhaust gas stream comprising the step of injecting and burning a certain amount of said fuel mixture in said exhaust gas stream intermediate said engine and said filter means, the improvement wherein said step for injecting and burning comprises the step of aspirating said certain amount of said fuel mixture into said exhaust gas stream intermediate said engine and said filter means with an aspirating means and said step of raising the temperature of said exhaust gas stream comprising the steps of operating an electrical heater means and burning said injected fuel mixture in a catalyst bed, said step of raising the temperature of said exhaust gas stream also comprises the step of operating said electrical heater means upstream from said catalyst bed, said step of aspirating said fuel mixture comprising the step of aspirating said fuel mixture into said exhaust stream upstream of said catalyst bed, said heater means being disposed intermediate said aspirating means and said catalyst bed, said step of raising the temperature of said exhaust gas stream also comprising the steps of directing said exhaust gas stream from said engine into an inlet of a passage defining means, directing said received exhaust gas stream out of an outlet of said passage defining means to said filter means, said passage defining means having first and second passages respectively between said inlet and said outlet, said catalyst bed and said heater means being disposed in said second passage, said aspirating means being disposed to aspirate said fuel mixture into said second passage upstream of said heater means therein, and operating valve means of said passage defining means to direct said exhaust gas stream to said filter means only through said first passage during the time said filter means is not being cleaned and to direct said exhaust gas stream to said filter means through said second passage during the time said filter means is to be cleaned, said valve means comprising a first valve disposed in said second passage between said aspirating means and said heater means for closing said second passage between said inlet and said outlet and a second valve disposed in said passage defining means for closing said first passage between said inlet and said outlet.