GB614633A - Exhaust gas analysis apparatus - Google Patents

Abstract

<PICT:0614633/III/1> <PICT:0614633/III/2> <An apparatus for analysing exhaust gas resulting from combustion of hydrocarbon fuel and air by measuring changes in thermal conductivity of a gas in a thermal conductivity cell as determined by variations in the resistance of the filament of the cell, comprises a bridge circuit having in one arm a first thermal conductivity cell and in an opposite arm a second cell of twice the sensitivity of the first cell, means for supplying the exhaust gas which contains water of combustion in the vapour phase to the first cell and means for supplying dried exhaust gas to the second cell, whereby the second cell cancels the effect on the bridge of carbon dioxide in the first cell and in addition produces an equal effect in additive relation to the effect of water vapour in the first cell. According to Fig. 1, exhaust gas is supplied by exhaust pump 27 to cells having filaments 10, 11 and 12, 13 and arranged in series in opposite arms of a Wheatstone bridge circuit; the gas enters the circuit through a conduit 19, constriction 29 and cell 20 containing heated copper oxide or other oxidizing agent, then contacts filament 10, passes through a drier 22, contacts filaments 12 and 13, and finally contacts filament 11 after passing through a carbon dioxide absorber 24. Instead of a single stream, the gas supplied may be divided into parallel streams and treated separately. The circuit shown in Fig. 2 compensates for atmospheric humidity and employs the same bridge arrangement as that of Fig. 1, but has two filaments 30 and 32 of equal sensitivity and two filaments 31 and 33 of double the sensitivity. Exhaust gas supplied through conduit 43 &c. is divided into a main stream which contacts filament 31 and a minor stream which is drawn through a constriction 46 to contact filament 32, the gas in this section being maintained at a low pressure by valve 49 and pump 54 which also maintain a flow of air at the same pressure in contact with filament 30. Filament 33 is in contact with air saturated with water vapour. The walls of the cells are preferably kept at the same temperature for respective pairs or for all the cells by forming them in a metal block.