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More on Vapipe
Page 47
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• The new development in pollution :ontrol known as Vapipe, announced by the Jepartment of Trade and Industry last veek (CM June 8), uses waste heat from the :xhaust to evaporate petrol to form an ntimate air-fuel mixture.
This thorough mixing permits uniform listribution of fuel between the engine ylinders and allows the engine to be run at
very weak mixtures which in turn lead to substantial reductions in the emission of CO and NOx. The design of the vaporizer is based on an application of the heat pipe, a small compact heat exchange unit consisting of a sealed vertical metal tube containing liquid and its vapour.
In use, waste heat from the exhaust gases heats the lower part of the tube causing the liquid to boil and recondense in the upper cooler part of the heat pipe. The heat given out by the condensing liquid is thus available to evaporate fuel added to the air upstream.
The condensed liquid returns by gravity to the base of the heat pipe, this cycle being continuously repeated and maintaining a steady evaporation of the fuel. Temperature is controlled by a servo-mechanism operating a valve in the exhaust gas.
The Vaporizer uses a divided air inlet system taking about 20 per cent of the total air requirement to carry the fuel from a carburetter or any other type of fuel injection system to the heat pipe vaporizer section. The unique application of a venturi nozzle to recombine the air streams considerably reduces the overall pressure loss through the Vapipe. Alternatively in a simplified version, the whole of the air and fuel can be passed through the evaporating section.