From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Reprint from 'The Automobile Engineer' on the Cambridge Exhaust-Gas Analyser for determining mixture strengths.
| Identifier | ExFiles\Box 102\1\ scan0149 | |
| Date | 1st January 1934 | |
| Reprinted from THE AUTOMOBILE ENGINEER, January, 1934. THE CAMBRIDGE EXHAUST-GAS ANALYSER. Determining Mixture Strengths while Running on the Road. THE analysis of exhaust gases in internal-combustion engines may constitute an important part of research. Since complete combustion rarely takes place, the exhaust gas normally contains carbon monoxide and hydrogen, the proportion being approximately 40 per cent. of carbon monoxide content. The fact that both these gases have a different thermal conductivity from that of air has made it possible to apply the thermal conductivity method of analysis to exhaust gases and so determine the air-fuel ratio of the combustible mixture. This method has been employed for many years in connection with other gas analysis problems, notably in the determination of the percentages of CO2 and CO in boiler flue gases. The principle is as follows :— If a platinum wire, which is surrounded by a gas in a chamber, is connected to a source of constant electromotive force, the temperature of the wire will rise until a condition of equilibrium is reached when the continuous dissipation of thermal energy is equal to the electrical energy supplied to the wire. The thermal energy is dissipated by conduction, by radiation and end cooling losses, and by convection. By suitably arranging the conditions, the loss of heat by radiation and convection may be reduced to a negligible proportion of the whole, so that the temperature attained by the wire when equilibrium is reached depends on the thermal conductivity of the surrounding gas. The temperature of the wire may be determined by measuring its electrical resistance, the electric current which heats the wire being used for this purpose. As the temperature of the wire varies with the temperature of its surroundings, even if the excess temperature remains constant, it is found convenient in practice to introduce a second wire for comparison purposes which is exposed to a standard gas, and to measure the difference in the resistance of the two wires when the condition of equilibrium is reached. The diagram, Fig. 1, shows a simple form of Fig. 1. Wheatstone bridge diagram. Fig. 2. Cambridge exhaust-gas tester. | ||