Self-recovering soot detector, particularly to monitor carbon content in diesel engine exhaust gases

System to determine smoking of a Diesel engine comprising

• a self-recovering soot detector to monitor the presence and absence of soot in the exhaust gases from the diesel engine, said soot detector including
• a support body (11, 21, 31) of electrically insulating material;
• two electrodes (14, 15;
• 24, 25;
• 33, 34) secured to the electrically insulating support body having end portions directly exposed to in contact with the exhaust gases spaced from each other by an open gap (16, 35) therebetween to provide for a resistance between said electrodes of essentially an open circuit and to detect the presence of soot upon smoking of the engine by the deposition of soot forming an electrically conductive bridge across said open gap and between the spaced, exposed end portions;
• a layer (13, 26, 32) of an electrically essentially non-conductive catalytically active material located on said support body in the region of said gap and directly exposed to said gases, said essentially non-conductive catalytically active material catalyzing, in the presence of oxygen, in the exhaust gases, upon non-smoking operation of the engine, the oxidation of soot present and deposited on the surface thereof and hence in the gap between said electrodes to remove soot precipated from the exhaust gases under smoking condition by catalytically activated oxidation of the soot to thereby restore essentially open circuit state between the electrodes and of the sensor for subsequent detection of accumulation of soot in said gap;
• means (A, B) determining change of resistance of the electrical path between said electrodes in operation of said engine as a measure of the deposit of carbon particles or soot in the gap between the electrodes and forming a conductive bridge therebetween upon the presence of soot;
• and means (A1, A2) deriving an output signal from said electrodes representative of and responsive to said change in resistance of the path between the electrodes between conduction and essentially non-conduction to permit control of the air-fuel supply to the engine in a direction to maintain the resistance between the electrodes at a high level.