The Promise of Greater Efficiency with Steam-cooling.
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THE need for cooling the cylinder heads and walls of an internal-combustion engine persists and must do so until pistons, piston rings and valves become altered in form or material so that they do not call for protection from the high temperature of the naming gases in the combustion chamber. There is no present prospect of the attainment of this ideal, so that water-jacketing of the cylinders and valve chests may be regarded as an essential feature of the internal-combustion motor suitable for heavy-vehicle propulsion, despite the obvious loss of energy resulting from the wasteful dissipation of heat through the medium of the radiator.
Water-cooling, as we show in a special article in this issue, presents other objections. Water is cold in the engine jacket after the vehicle has been idle for a given period ; it is also colder in the winter than in the summer, is always slow to reach a proper working temperature, and will vary between hot and cold according to the conditions of working, the periods of idleness, etc. This variation is quite undesirable, as it makes for sluggishness of the engine, difficulty of starting and wastage of fuel.
Users are being forced by reason of the evergrowing demand for volatile fuels to use heavier and heavier motor spirit. There is every advantage in using heavy fuels, because they can be produced in larger quantities than the light fractions and therefore must be cheaper, but they call for a closer approach to constancy in the heat conditions of the engine in which they are being used. As water-cooling will not give this constancy, modern thought has turned to steam-cooling, which is effected by making the skin of water extremely thin so that it quickly reaches boiling point, as in the common or household geyser, and the working parts are brought to the required temperature in a few moments, instead of minutes as occurs with water-cooling. The temperature can never rise above 212 degrees Fahr., or only 20 degrees to 30 degrees more than with water-cooling, this difference being unimportant. The steam formed in the jackets is recondensed and returned to the jackets by a pump., and both the pump and the quantity of water carried are smaller than in the case of the water-cooled engine. The saving in weight alone means a welcome economy of fuel. In many cases the commercial motor is subjected to a large proportion of stopping and restarting for loading or unloading, picking up and setting down. With steam-cooling, the loss of engine heat when the engine is stopped is much slower, because the water in the jackets is stagnant, and thus a nearer approach to a constant temperature is at tained. It certainly seems as if steam-cooling calls for very careful consideration on the part of designers and makers of commercial vehicle engines and is of interest to users of all types of vehicle.
From Tramcar to Trolley-bus and then to Motorbus.
IN our advocacy of the trolley-bus we have always maintained that it must be regarded, first, as the substitute of the tramcar and, secondly, as the stepping-stone from a tramway system to a bus service. It would be wasteful to jettison every tramway undertaking, even if one were agreed upon its inefficiency when compared with an adequate motorbus service. A tramway system can rarely be run in competition with a bus service and, with some exceptions (of which few remain in this country), only when traffic is in excessive volume is it profitable to run, as during the hours of peak loads. It is safe to assert that in the provision of a passenger-carrying service for, let us say, a newly formed community, no traffic manager would today propose a tramway; nor would be suggest a trolley-bus system. The untrammelled motorbus would be his choice ; but where a power station has been erected on the assurance of a load during the hours of daylight to operate a tramway system, it is not reasonable to suggest substitution of motorbuses for the tramcars. The trolley-bus is the correct implement in such a ease, where the tramcar and the permanent way cannot be renewed. In time, a full load will• usually be developed by the demand of new factories for • power or of old factories for increased supplies. Then comes the opportunity for the motorbus to displace the trolley-bus, as has already been proposed by the York Tramways Committee in respect of its Heworth service, with the projected extension to the Tang Hall Estate. It is a development we have always contemplated and shall always encourage.
Suiting the Chassis to Its Work.
MTE have often commented upon the need for so designing chassis that they can be more exactly suited to the particular class or classes of work which they are called upon to perform. We do not allude to the more obvious divergencies, such as are required between models built for goods.and for pussengers, but to differences desirable in chassis constructed to meet the requirements such as are found in the rapid transport of light fragile articles of large bulk, and those of the comparatively slow carriage of small but heavy materials. Similarly, it does not seem quite correct to supply one type of vehicle for use both in long-distance transport with but few stops and, say, door-to-door delivery. In this connection we draw attention to the policy of a famous French concern which is outlined in an article in this issue, and which shows that certain new ideas have been-incorporated in the production of a new range of chassis. In brief, the system consists of building three standard sizes of engine, and not employing these in the usual manner, which is to use a larger engine immediately, the pay load is increased, but to utilize the most efficient unit for the class of work to which the vehicle is to be allotted, providing suit able gear reductions therefor. For instance, a 14 h.p. engine is fitted to a medium-load chassis with a moderate top-speed performance; a 17.9 h.p. unit is used for a similar chassis with a rather better performance, and which is more suitable for high-speed work such as that required by light buses ; whilst a 24.8 h.p. engine is used in the coach chassis. In another type the pay load is increased slightly, but the smallest Unit is fitted, the ratio of the final-drive gearing being reduced considerably. Thus the buyer can pick out a chassis which should almost exactly meet his requirements, and yet the number of units necessary to permit this is but small.
Is the Solid Tyre Doomed ?
ECENT interviews which we have had with users show that in the majority of cases they are nearly all much in favour of the increased use of the pneumatic tyre, from which extraordinarily high mileage averages are now being obtained, and these, in conjunction with the higher speeds at which the vehicles can be operated, considerable reduction in damage to the road and thelowering in general maintenance charges which soon shows itself, have all tended to popularize this form of tyre equipment. In the lighter types of transport vehicle the employment of the pneumatic tyre is becoming almost universal, and it is obvious that it is gradually spreading upwards and absorbing heavier models of 4-ton load capacity or more. There was a reference in the article which appeared in our issue of last week to the demand of a transport user for tractor-trailer vehicles of 9ton load capacity to run on pneumatic tyres, and there is little -doubt that this will be met. • Very few troubles are now experienced with goodquality covers, and there is usually little to do beyond vulcanizing any serious cuts. Inflation is but seldom required; in fact, we know of cases where tyres have run for many thousands of miles without this being necessary. With the larger pneumatics it is quite reasonable to expect mileages of 20,000 or more. Thus, even on a mileage basis, the pneumatic compares very favourably with the solid. After this mileage, it is ofteu quite possible to retread such a tyre with safety. We think, however, that it will be a long time before the solid tyre is completely replaced, if this ever does occur, but that its use will be relegated to the slowest forms of transport where exceptionally heavy loads have to be carried or hauled.