THE MOTOR WORLD

New Zealand Times, Volume XLII, Issue 9717, 20 July 1917, Page 8

THE MOTOR WORLD

PETROL SHORTAGE PROBLEMS 01' MORE EFFICIENT CARBUEATION. One result of thc> present shoi't-ago and high price of petrol should bo to focus mom and more attention upon the problems of carburalion. The carburettor as at present designed certainly gives good results when using the fuels to which motorists have been accustomed in x>ast years, but the number of motor vehicles put into use is being increased at an enormous rate each year, and the inroads which are being made into the limited stores of motor spirit—as known at present—suggest that it is vital that every effort should be 'made to ensure that none of it is wasted. In America, where the fuel problem is becoming acute, it baa been borne in upon those who have been investigating the subject that the carburettor of to-day has ceased to be more than a measuring device, and that the true vaporisation takes place in the intake manifold. This suggests that ideas regarding carburettors are in great need of revision in the direction of the fitting being considered not merely as a unit by itself, but as part of a complete vaporising device. This view is borne out by experiments which were carried out some time ago in Chicago. Various carburettors were tested, and in order to observe the action of the spirit a glass bell was arranged over the carburettor outlet, so that the suction of the engine fell on the jet in the usual manner, but the resulting mixture was thrown into the glass bell before being drawn into the engine. It was observed that at low throttle openings the vaporisation was practically complete, the mixture entering the engine in the form of a fog. But as the throttle was opened and the vacuum began to drop, instead of a fog the resulting mixture became a spray carrying large globules of raw gasoline to the engine. This raw gasoline was caught by the bends and elbows in the inlet pipe, and, collecting into pools, gradually ran down into the cylinders. It was found that the temperature to give a good mixture was 109 degrees Fahr. To attain this it was necessary for the entering air to have a temperature of about 153 degrees Fahr. in order to compensate for the 43 degrees drop in temperature which took place during vaporisation. As is well known, when using petrol in a cold engine, it is necessary to open the full jet to get a big supply of fuel, in order that the lighter elements may make up for the non-vaporisation of the heavier elements. The latter remains in liquid form and travels along to the engine, being unevenly distributed to the various cylinders and burnt incompletely with a deposit of carbon. This indicates the necessity for the installation of an arrangement for pre-heating the intake manifold, in, order to secure thorough vaporisation of the whole of the fuel. If this were done it would be possible to use smaller engines, for it has been calculated that engines are usually so large for their work that 98 per cent, of their operation takes place while the charge is greatly reduced by throttling. This decreases the amount of vapour charge necessary, and thus .lowers the temperature necessary to run. For instance, when the throttle is closed so that there is only 36 per cent, of a full air charge, a complete vapour charge could exist at 68 degrees Fahr., and the temperature of the incoming air need bo only 111 degrees Fahr. As the tendency is for the utilisation of the heavier grades of motor spirit, and at considerably increased prices over the old spirits, which easily vaporised a t ordinary atmospheric pressures. It is isurely opportune for the production of carburettors, or rather vaporising devices, which shall permit of the utmost power being obtained from the fuel used. BIVAL POEMS OF IGNITION.

Since the opening of the war the battery system of ignition has made considerable headway in America, so much so thlTt some people predict that it will supersede the magneto. The relative merits of the magneto and the dynamo battery is a very debatable question in America to-day. There remain plenty of people who are firmly convinced that there is something about the quality of a magneto spark which cannot be exactly _ imitated by me ana of an induction coil, and possesses value for ignition purposes. With a magneto the first spark which jumps from point, to point of the plug is followed by a fame, which is maintained for an appreciable period. The question ie whether this flame does any good or not, and directly wo try to settle this question by discussion we are involved in ail sorts of complications as regards the turbulence of the mixture in the cylinder and a number of other considerations. Probably .it is safer to argue from practice than from theory, tin'll from • experience on the road backed bya fair number of workshop tests. The writer believes that the magneto is the most efficient known form of ignition, assuming that the timing of the spark by the driver is not always perfect, haying regard to the engine speed. With perfect timing there does not appear to bo anything to choose between the two systems, but perfection is seldom obtainable, and the magneto limits appear to have the faculty of correcting imperfections or, at any rate, rendering their results less noticeable than with coil ignition. WAR TAX OX MOTOR TyRE"

On top of the recent rise in the price of motor tyres in America is to be added a further dual war tax by the American iOovornment. . A 5 per cent, tax on covers and tubes is to bo paid by the manufacturer on the selling price to dealers. and in addition a 10 per cent, duty is to bo levied on all crude rubber entering the States. Heretofore, crude rubber has been on the free list. During last year 115,000 tons of rubber was imported into America, of which some 90,000 tons (worth about .£3,500,000) would probably be absorbed in tyre manufacturing. The American tyre houses are making every effort to have the new taxes remover or modified, particularly the duty on crude rubber.