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the tomfsoraturo roquirod for aflorburning Dual-bod catalyst (re OWC). Oxlditil+an mid roduction reactions take place The thermal reactor, which is made of sheet in succession with two dif>foronl catalysts: In ISei and is flange-mountod to the cylinder, is the first bed the oxides of nitrogen are reduced Cnally heated by the exhaust gases. After with an air deficiency after reaction cl), then, the reaction the exhaust gases flow through an after secondary air has been added, reactions a outer jacket, providing external thermal insu- and b are effected in a second bed with excess lation. air to oxidize the incompletely burnt CO and The hot tube is a normal exhaust manifold C„Hm components. encased with insulating material. (Less ef- fective since the hot exhaust gases remain in Singie-bed catalyst the hot tube for a far shorter period of time.) Reduction and oxidation (reactions a ... c) take If the residual oxygen in the exhaust gas place simultaneously with a single catalyst. is not sufficient for afterburning. additional air Accurate adjustment of the stoichiometric air- Is blown in at the exhaust valves.The secondary fuel ratio (A = 1) is thus necessary the lambda air pump must be driven by the engine, so sensor being used for closed-loop control power losses are incurred. purposes. Catalytic exhaust-gas aftertreatment The catalysers (catalytic converters) consist of a sheet-steel housing filled with granular Lambda-sensor material or a honeycomb element. The surface of this material or element is covered with a Construction catalytic compound (precious metals or metal One part of the ceramic body is located in the oxidos). It does not change during afterburning path of the exhaust. the other being in contact but promotes combustion merely by Its pre- with the ambient air.The surface of the ceramic Ab nce. The use of catalysts for afterburning body (zirconium dioxide) is provided with elec- uires the use of unleaded fuel. trodes composing a thin, gas-permeable plati- num layer. In addition, a porous ceramic layer CO NOx CH is provided at the end exposed to the exhaust 3 NOR t gases to guard against contamination caused 1. 12 E•. by combustion residues. CA m l �1. t300t t. t I ` t. :38 t 1 / 1 t t 6 cc 200- O t 1 t a 200 E ' o t I = rn 4 Special Contairt Contact Terminal ;, I _ i i+inmii glerve cjiilntj 4 -1 -- L- L I u � 0 1 f - • • • U CH �N�� I O 0 0 - — -- --- 0 0,6 0,8 1 1,2 Excess-air factor i Exhaust gas Ambient air Wf ion of toxic substances using catalysers Cross-section of lambda sensor before cataiysor - - - - after cataiysor `} See table on previous page.