MOTORING

Hawera Star, Volume XLIX, 15 February 1930, Page 15

MOTORING

CARBURATION NEED OF IMPROVEMENT. To anyone who lias motored for a | number of years it is obvious that thei e is still a great field for improvement in ear bur at ion. The modern carburettor is a very perreet instrument of its [ Kind,, but there is still much to be done to get the fast ounce ot elficiencj out of the fuel. An interesting invention has recently been tested by tlie American army, authorities which, according to their report, gives excellent results. It is known as the God ward cias Generator, and is designed to utilise petrol, parartin, gas oil, or fuei oil. In the normal • carburettor tlie tuel is vaporised by passing air through or over it at a High speed, and in tne induction system much of this fuel recondenses on the walls of the pipes. The Godward system provides for the slowing up of the charge, takihg advantage of the dropping out of the wet particles, which are delayed until they gasify. ’ , , • , This is done by a chamber the capacity of which equals one cylinder in area. The chamber is so constructed that the incoming charge is subjected to centrifugal action, which throws outward all wet particles contained in the charge rather on the principle of a cream separator. There are, however, no moving parts, as the speed of the vapour itself supplies the energy. The unvaporised fuel spreads itself oh a curved vertical plate surface heated from the bottom of the chamber. Ihe heat ascending the plates by conduction furnishes a varying temperature from a maximum at the bottom to a minimum at the top. The wet fuel spread in a thin film upon the plates by the action of the air gravitates towards the heat. In cold weather the whole range of wet fuel gravitates further towards the heat than in summer, and the less volatile the fuel the further it has to descend the plates to find for itself the necessary heat and other factors for evaporation. The device can be attached to the intake manifold of any internal combustion engine and it is also provided with a flange for the usual type of carburettor. In the report it is stated that the addition of the Godward apparatus to an internal combustion engine does provide for the alternate use of a number of fuels, such as petrol, kerosene, fuel oil, or alcohol, and that additional power, with the added advantage of greater fuel economy, results.'

THE HOUSE THAT JACK BUILT This is the malt, and hops, and corn, That lay in the House That Jack Built. This, is the car with the crumpled horn That jumped the ditch to afield of corn. This is the man all tattered and torn Who drove the car with the crumpled

horn. This is the bunch to folly sworn, Who warbled, “We won’t go home till

morn.” This is the maiden all forlorn Who was dead when they found her

’mid the corn. This is the priest all shaven and shorn Who buried the maiden all forlorn. Who was one of the bunch to folly

sworn, Singing, “We won’t go home till morn; 5 ’ Who rode in the car with the crumpled

horn That hurdled the fence to a field of

corn, Because the man all tattered and torn Was full of the malt and hops and

corn That lay in the House That Jack Built

THE VITAL SPARK CHOOSING BEST PLUGS. Why are there so many different types- of sparking plugs ? And why should one type perform better in a given engine than another ? These and similar questions are interestingly answered in the current issue of the “Light Car and Oyclecar.” In the case of normal touring types of engine no special kind of plug is necessary —that is to say, it need not be designed exclusively to resist high temperatures or excessive oiL. Before going further, however, it will be instructive to consider what is required of an efficient sparking plug. In the first place, the insulation between the central electrode and the body must be perfect under all temperature changes; furthermore, it must be mechanically robust, so as to withstand a certain amount of rough usage. It is essential also that part of the 'insulation of the central electrode which comes into contact with the hot gases should resist the formation of carbon deposit as much as possible. The electrode must be secured in a perfectly gas-tight manner through the insulation, and if the plug be of the detachable type the sealing arrangements must also be proof against high pressure.

ELECTRODE METAL. it is usual to employ nickel as the metal of which to make the electrodes, lor this resists high temepratures m a very satisfactory manner and is also to a great extent proof against corrosion. by acids formed during the process of combustion. The electrode on the body of the plug must be securely fixed so that there is no possibility of its becoming loose and lulling into the cylinder. This essential is, of counse, amply provided for in modern plugs, where the electrode either forms part of the body or is welded to it. The plugs of British and Continental engines are almost invariably provided with a metric thread, the diameter being 18 mm. and the pitch 1.5 mm., whilst the reach of a| standard plug, that is, the distance from the shoulder to the points, is jj-inch, the dimensions of the long-; reach plugs being 2-inch. The location of a plug in the cylinder is not a question which need he considered here, as it may be taken that the makers have ascertained the exact paint at which the best results can be obtained. As -a rule, on normal sidevalve engines the plug is placed directly over the inlet valve, or closely adjacent to it, whilst in overhead valve engines it is usual to fit the plug either in the exact centre of the head between the valves or eles horizontally through one side, so that the points are near the inlet valves. - . ... The question of single or multi-point plugs also need not be discussed. Each type has its advantages and its adherents. but it may be accepted, in general, that no advantage is gained by using more than three points, although that"type of plug which has a central

electrode projecting into an annular gap, 'which, in effect, has an infinite number of points, has certain advantages

PLUG COMPARISONS. It lias already been mentioned that normal engines require only normal plugs, but it plug which works .satisfactorily in a - potterer’s touring car would be very little use in a_ sports engine and absolutely useless for racing work. The reason for this is that a normal touring engine has a comparatively low compression ratio, and is seldom driven hard, at least icr ally length of time, therefore the plug points remain cool \\ itli the liigher compression ox a sports engine, however, the internal temperature of the, cylinders is very niucn greater tmm that in the touring engine, therefore there will ue a tendency for the plug points to burn away, thus increasing the gap between the points until it reaches a dimension across which the spark can no longer jump, in this connection it must be remembered that the resistance to the passage or the spark ottered by the highly compressed gas is much greater than that of a gas at normal atmospheric pressure. Carrying the comparison of engine requirements a step further, it will be obvious that a touring plug could not stand up to the strain imposed upon it in a purely racing engine using a supercompression, probably a special form of fuel, and running at a continuous high speed. In the same way a plug suitable for use in a racing engine would not work satisfactorily in tlie power unit of a touring car because the specially thick electrodes would remain too cool, so that if the engine were at all inclined to be over-lubricated oil would collect on the points and cause a short circuit. Quite often the central electrode of a racing plug is made of copper and is about Jin. in diameter, whilst the upper end, where the high tension lead is attached, is provided with cooling fins to carry away the excess heat conducted from the lower end. It is a question of temperatures as they affect sparking plugs that in large measure makes it necessary for racing car engines to be kept revolving fast even when the car is stationary, because should they be allowed to idle the temperature would fall and oil would be quickly deposited upon the rapidly cooling plug points. It will be interesting now to pay a little attention to the question of sparking plug maintenance. In a cleanrunning touring engine it should be necessary to remove tlie plugs for cleaning or gap adjustments only at very infrequent intervals; to ensure easy starting and regular idling, however, the gaps must be maintained at the correct setting, ' generally about .02in. . . ~ In the course of time it is probable that the central electrode will become burnt away at a point immediately opposite the side electrode or electrodes. This, of course, increases the gap. If the point is of the. single-point type, the defect can be overcome .in the ease of a detachable plug by rotating the central electrode slightly, so as to bring an unburnt portion into line with the side electrode. With threepoint plugs the central electrode can be filed gently, and the gaps corrected by closing over the three side electrodes.

THE SPARKING GAP. It is very seldom that any improvement in speed can be obtained by running ivitli a gap wider than that recommended by tlie manufacturers; furthermore. no" attempt should be made to alter the shape of the electrodes. Especially it is inadvisable to arrange them so that the opposed ends are sharply pointed, because a discharge from a magneto or a coil takes place much more rapidly between rounded surfaces than between points. In any case tlie electrodes must be reasonably heavy, not only to prevent overheating, but also to dispose of the surplus energy generated by a good modern magneto or by a coil. In this connection it is appropriate to mention that all present-day coils and a larger number of magnetos are of the jump-spark type—that is to say, the current generated in the armature instead of being led to the sparkingplug via a wire-contact distributor, is caused to jump a gap before entering the high-tension leads; thus the actual spark at the plug points is. intensified by reason of the building-up effect ol the first gap. For this reason those motorists who imagine that they can improve the performance of their engines by fitting auxiliary spark gaps on tlie plug terminals should go warily and discover, first of all, what type oi distributor is fitted to their magnetos. If it be of the wire-contact type, well and good, but it will be useless to fit an auxiliary gap to a jump-spark magneto or to any modern coil unit. The persistent oiling-up of plugs in dirty engines can be extremely annoying. The only real cure is, of course, to prevent excess oil from getting into the combustion chamber. This, however, is apt to be an expensive process, as it may mean reboring the cylinders or fitting new piston rings. In certain cases, however, a cure may be available in the use of plugs having fairly thin electrodes which become sufficiently hot to burn off the oil; but ' tlie combination of excess oil and a rich mixture may cause heavy deposits of carbon to be formed within the body of the plug, so that in course of time the central, electrode becomes shortcircuited.

The first indication of this will be severe misfiring, or, perhaps, explosions in the silencer or through the carburettor, the cause of which is that the spark, instead of taking place at the plugs, is jumping the carbon inside the plugs, where, being pocketed considerably, it causes very late firing of the charge in the same manner as a wrongly timed magneto.

COMBATING CARBON DEPOSIT. The formation of carbon on tiie insulation of the central electrode, it it cannot be prevented altogether, can at least be delayed by using special forms of plug having steps formed in the insulation, which has the effect of increasing the surface area. A central electrode insulated in this way can also oe of considerable benefit in an engine of considerable beneiit in an engine which tends to throw liquid oil on to the plug. With regard to plug cleaning, it is as well to utter a word of warning to the effect that the insulation of the central electrodes should never be filed or scraped with a knife, as by doing so the surface may be spoiled. Cleaning can be quite effectively,carried, out by wiping with a petrol-soaked rag, t,iie insulation material being finally ipolislied by the use of an ordinary liquid metal polish fairly vigorously applied. ft is very important always to make certain that the plugs are properly screwed home in the cylinders and also that, the glands of the central electrodes on detachable types of plugs be fully tightened, because leakage at any point will mean not only less of compression, and therefore power, but it may also cause the plugs to become overheated and oiled up.