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).
Promotional brochure for the Cambridge Exhaust Gas Tester, explaining the necessity of road tests for accurate carburettor adjustment.
| Identifier | ExFiles\Box 155\3\ scan0015 | |
| Date | 12th April 1935 guessed | |
| PANEL 1 (LEFT): THE NECESSITY FOR ROAD TESTS INCORRECT carburettor settings are almost certain to result if the adjustments are made on the garage floor with an unloaded engine, because the conditions of operation of the carburettor with an unloaded engine at 1,000 to 2,500 r.p.m. are greatly different from those of a motor under normal or heavy loads. The proportions of air and petrol supplied by the carburettor (air-fuel ratio) under the two sets of conditions will be seen from the curves in Figure 12 to be very different. Operating an unloaded engine on the floor at high speeds in an endeavour to simulate road conditions while tests and adjustments are being made may result in damage to the engine. Motor engineers have therefore recognised the value of making carburettor adjustments on the road under normal loads, but a suitable instrument has not hitherto been available that will give continuous and satisfactory results under such conditions. The Cambridge Exhaust Gas Tester has been especially designed to enable continuous exhaust gas analysis to be made on the road with the vehicles carrying their usual load; tests can rapidly be made whilst the cars are in everyday service, such practice being economical since it avoids vehicles being laid up for testing, and it also makes the installation of expensive equipment to simulate road conditions unnecessary. Readings which enable carburettors to be set for maximum engine power and fuel economy may be obtained on the roughest roads. FIG. 8. In use on a Vauxhall Saloon Car. By courtesy of the Vauxhall Motor Co. Ltd., Luton. Figures 5, 8 and 9 show respectively the Exhaust Gas Tester being used by the Ford Motor Co. Ltd. on a Fordson 2-ton truck, by the Vauxhall Motor Co. Ltd. on a car of their manufacture and on a Dennis “Ace” 20-seater bus by Dennis Brothers Ltd., and are published by the courtesy of the three Companies. FIG. 9. In use on a Dennis “Ace” 20-seater bus. By courtesy of Messrs. Dennis Bros. Ltd., Guildford. PANEL 2 (MIDDLE): TYPICAL CURVES PLOTTED FROM INSTRUMENT READINGS FIGURES 10 and 11 show the results of tests made with the Cambridge Exhaust Gas Tester, before and after adjusting the carburettor on a passenger car. The car was considered by competent mechanics to be in good adjustment; but Figure 10 indicates an over-rich mixture in the low and intermediate speed ranges. Through various steps of test and adjustment this condition was corrected until the result shown in Figure 11 was obtained. It will be noted that under level road conditions, at speeds from 10 to 40 miles per hour, the average air-fuel ratio was increased by over 20 per cent.—representing a saving in fuel of a similar amount. With full throttle at car speeds from 10 to 30 miles per hour the average air-fuel ratio was increased by nearly 10 per cent. Greater full-load economy could have been effected if desired, but acceleration and power are the prime considerations under this condition of load. Figure 12 shows air-fuel ratios at various speeds obtained during operation of a lorry on the road, compared with those on the garage floor settings and road settings. There is no relation whatever between the full throttle curve with the engine running light on the floor and the same curves at level road and full throttle. This carburettor could not, therefore, have been properly set to give economical performance except by road or dynamometer tests. This is the usual experience with lorries and high-powered vehicles. Figure 13 shows the effect of air valve adjustments on the mixture supplied by a carburettor. It indicates that the air valve controls the low-speed mixtures over a wide range. It has less effect as the speed increases and ceases to make any difference at all above 50 miles per hour. This information is of prime importance in making carburettor adjustments. Graph Captions: FIG. 10.—Air-fuel ratio vs.{J. Vickers} Speed curves on test car before carburettor adjustment. FIG. 11.—Same car as in Figure 10 after adjustment. FIG. 12.—Comparative floor and road tests on lorry. FIG. 13.—Effect of air valve adjustments on carburettor characteristics. SOME USERS' OPINIONS "We have tested the Cambridge Exhaust Tester at our laboratory, and have a number of them in use on road testing cars, during which time they have proved very satisfactory.”—(From the research department of a large oil company.) “Its use eliminates all guesswork as to adjustment of carburettors, effects of restrictions such as air cleaners, adaptors, etc.”—(From a lorry manufacturer's engineering department.) “One of the most useful instruments that has ever been developed for the determination of the operating conditions of a petrol engine.”—(From a motor testing engineer.) “After several years' experience with various devices for analysing mixtures of gases, I have found that the thermal conductivity method is the simplest and most reliable.”—(From a motor testing engineer.) “Without question this type of instrument places the service station in a position to perform work with laboratory exactness.”—(From a motor lorry manufacturer.) “We are finding this instrument of considerable use in checking distribution.”—(From a motor car manufacturer.) “It is a pleasure to recommend the Cambridge Exhaust Gas Tester. It is used in our car-testing laboratory with dynamo brake, flowmeter, etc., and is giving excellent results, enabling us to give customers the best possible service.”—(From a car-testing laboratory.) PANEL 3 (RIGHT/COVER): CAMBRIDGE EXHAUST GAS TESTER FOLDER No. FILE A TOOL FOR MOTOR ENGINEERS MANY petrol-driven vehicles waste from 15 per cent. to 30 per cent. of the fuel supplied, due to incorrect setting of the carburettors. Much of it can be saved by the adjustments of skilled engineers provided that they have instruments available to enable them to take full advantage of their experience. Analysis of the exhaust gas is generally recognised as a reliable way to determine combustion efficiency and the extent of avoidable fuel losses. This folder describes the Cambridge Exhaust Gas Tester, which enables tests to be rapidly made on the road under working conditions, is of material help to those who wish to render a high quality of service or maintain economy of operation. [Stamp] TEL: WAVERTREE 1695. RESIDENT ENGINEER, W. J.{Mr Johnson W.M.} COLE, 19 TOWERS ROAD, LIVERPOOL, 16. “Adjust carburettors scientifically and reduce your fuel bill” WORKS : LONDON and CAMBRIDGE CAMBRIDGE INSTRUMENT CO. LTD. 45, GROSVENOR PLACE, LONDON, S.W.1 | ||