Opinions from Others.
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To Keep Down Following Dust.
The Editor, THE COMMERCIAL MOTOR.
 Sir,—We have experienced considerable trouble with the dust nuisance on buses with rear entrances, more particularly with the dust being drawn into the interior, settling on the cushions and also on passengers. This not only applies to fast vehicles out on country roads, but also to a comparatively-slow vehicle, such as an electric, running at 12-14 m.p.h. for purely town work.
We have been able considerably to reduce the nuisance by fitting ventilators in the front of the body and keeping them open so as to give a draught through, but this, whilst being fairly satisfactory. during the summer time, makes the body very cold in winter time, and even then does not overcome the trouble sufficiently.
We have experimented with a ventilator, fitted in the roof of the bus close to the rear entrance, so as to get an air current at the entrance opposing the direction of the flow caused by the movement of the bus, but this makes very little difference. We strongly object to doors and curtains, which are a nuisance in every way. We shall be glad to know if any of your readers have experienced this difficulty, and whether they hays been able successfully to deal with it—Yours faithfully,
Tnr. Lou-oHsoRoitort ROAD CAR CO., LTD.
W. H. ALLEN, Director. 2nd October.
[We hope that some of our friends who are concerned with country motorbus service will write to us. We may also, with advantage, refer our correspondent to an article on this subject, entitled Ventilation v. Draughts, which was published on pages 296 and 237 of our issue of the 15th May, 1913._ED.]
The Claims of Coke.
The Editor, THE COMMERCIAL MOTOR.
115531 Sir,—Yeur article of the 23rd ult. ought to
esting a profitable discussion, and it will be to hear what has already been done. We may safely assume that wagon owners are only eeneernecl in the " Fuel cost per mile." It is a matter of complete indifference to them what they burn. With a few exceptions, all the steam wagons in use at present are designed to use bituminous or semibituminous fuel (small grate area, large heating surface). The use of semi-bituminous fuel (Welsh coal) has been proved by experience to give the best results hitherto, because from the products of combustion of the volatile carbons a higher conductive quality is obtained than from the products of combustion from fixed carbons. In other words, with flaming coal the heat is distributed at a more-uniform rate through the firebox and tubes. Bituminous coal, on the other hand, is too rich in volatile carbons, and is not suitable for road-wagon work on account of smoke. The smoke is caused by the cooling effect of the firebox and tubes on the volatile gases, and it is difficult to keep a bed of fire of sufficient thickness of fixed carbon to ignite and to retain the temperature of the products of combustion.
With coke there is intense local heat, depending on conduction for its utility, and nearly all the heat must be taken up in the firebox. Coke is similar in chemical composition to anthracite, and on American railways it was proved long ago that this particular fuel could only be efficiently burned by having a large grate area with low firebox to get the full advantage of radiation.
I have recently been carrying cei seine extensive experiments with coke breeze ,tr_der Lancashire boilers : these throw an interestin. --rht on the difference between heat passed by rathation and heat
passed by conductivity. The results were as follow :— Same boiler, Lancashire 30 ft. by 8 ft,
IL will be noted that, by mixing one part of highlyvolatile coal with three parts of coke breeze, the products of combustion were able to evaporate more lb. of water per lb. of fuel fired than with either of the fuels used separately ; in fact, taking 3 lb. of coke breeze giving -IS lb. steam, and 1 .lb. of coal giving 7.2 lb. of steam, adding these and dividing by fonr, the result one would expect to obtain by using the mixture would be 6.2 lb. of water per lb. of fuel.
It would thus appear that the volatile gases in the coal mix with the hot gases from the coke, producing far better results than can be obtained by burnitg either separately. In fact, the mixture burned is in chemical constitution and in calorific value very similar to Welsh coal, but it can be obtained practically anywhere at about one-half or one-third the cost of the latter.
With reference to the suggestion of placing a ferrule in the blast pipe, this would have the effect of reducing the efficiency of the engine by increasing the back pressure on the pistons, besides placing more strain on the engine generally. It is a well-known fact that the practice is to get as large a blast-pipe orifice as possible. " Sharpening the blast" is, after all, only tinkering with " effects." Why not tackle the " cause" ?
Take an average firebox and consider the passag.? of air through the fire. It is safe to assume that air will pass through the line of least resistance, and the
natural line of least resistance is the shortest distance from the blast pipe to the damper. If the fire Is thinner in one part than another (and it is impossible to prevent this), there will be a rush of air, with correspondingly-increased combustion in this area than through the rest of the fire, with the result that about 2i) per cent. of the grate area is doing about 70 per cent. of the work.
To overcome this, I have designed a furnace in sections, and, for a small wagon, use four separate and distinct furnaces, with firebars so placed that the air for combustion is mechanically passed evenly between these, resulting in an equal rate of combustion over the grate area. The steam jets only take 18 lb. of steam per hour, and they keep the bars cool, preventing the adhesion of clinker and enabling the furnace to be run for 12 hours without cleaning out. This grate is working on a traction engine very successfully with coke and coal ; another advantage is that this furnace can be used for burning any class of fuel.--Yours faithfully, V. R. CHADWICK, Technical Director. The Turbine Furnace Co., Ltd., Caxton House, S.W.
[Mr. Chadwick will agree that it is not a matter of "complete indifference" to wagon owners "what they burn." Cost is only one consideration of several. Ease of corabusiion,eleanliners, weight of fuel per cubic ft., and steam.raising qualities must be considered. :We 118..ve known of this system for some time. It promises to overcome difficulties with coke, and to iniffrove the economy of fuel consumption in steam wagons and tractors._En.] The Editor, THE COMMERC/AL MOTOR.
 Sir,—I was interested in the article On "The Claims of Coke," in your issue of 23rd September, also the articles by Mr. E. W. L. Nicols in previous issues of your journal.
Whilst holding the opinion that coke is an ideal fuel for steam motor wagons, on account of its cheapness and smokelessness, 1 do not think it can be successfully used on motors with loco-type boilers. The fact that its use is unpopular in Lancs. and Yorks., as mentioned in. your article, proves this, as there is a plentiful supply of cheap coke in those districts.
The absence of volatile matter in coke renders the greater part of the tube beating surface ineffective ; consequently a larger firebox is necessary and greater draught through the tubes. It is not sufficient merely to alter the firebars and give more air space ; it is also necessary to reduce the exhaust nozzle to give a stronger draught and so to increase the fuel consumption per sq. ft. of grate area. This reduction of the exhaust nozzle increases the back pressure on the pistons and therefore decreases the horse-power developed by the engine, which is a fatal drawback. The attention the fire requires with respect to clinkering is also another great drawback to the use of this fuel.
Successfully to use coke, would require a motor with a boiler specially designed for the purpose and this could very easily be done.—Yours faithfully.