| 摘要 |
A diesel or other compression ignition engine exhaust gas purification system comprises: (a) a catalytic filter (16), connected to the exhaust outlet duct (7); and (b) a recycling duct (10) leading from duct (7) at a point upstream or downstream of filter (16) and back to the engine intake manifold (8). Duct (10) includes a second filter (18) designed to absorb nitrogen oxides, and flow from duct (7) into duct (10) is automatically controlled by a valve (11) in response to the exhaust gas temp. monitored by probe (19). Filter (16) is ineffective at low temps., so valve (11) opens to recycle up to 50% of the gas through filter (18) which absorbs the NOx. At higher temps. (e.g. > 200 deg C) filter (16) becomes effective to remove all impurities and valve (11) partly closes, to allow only a small flow of gas to be recycled, this flow of relatively hot gas desorbing the filter (18). |
