More About Coal-gas.
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Interest in the possibilities which attach to the use of coal-gas for road-traction purposes is undoubtedly growing. The bulkof the Press comments are favourable : those which are the reverse are 'usually based upon inaccurate information ; those which condemn the potential value of coal-gas on the score of its failure 18 years ago are unworthy of any contemporary. We are merely concerned to keep putting forward the points, both for and against, which have a bearing upon the factors as they exist to-day.
Tests at Guildford.
One of many important pieces of information which have been communicated to us during the past week comes from Dennis Bros. (1913), Ltd., of Onslow Works, Guildford. This company, on our suggestion; made a series of bench tests with W.D. subsidy engines, running them successively on coal-gas and petrol. The following tests are comparable :—(1) r.p.m., 1190; h.p. on coal-gas, 43.5, with a consumption of 1200 cubic ft. of gas per hour ; h.p. on petrol, 49.5 (at same r.p.m.) ; consumption of coal-gas per h.p. hour, 27.6 cubic ft. ; ratio of power on coal-gas to power on petrol, 87.9 per cent. (2) r.p.m., 1160; h.p. on coal-gas, 40.5, with a consumption of 1011 cubic ft. of gas per hour ; h.p. on petrol, -48 (at same r.p.m.); consumption on coal-gas per h.p. hour, 25.0 cubic ft. ; ratio of power on coal-gas to power on petrol, 84.4 per cent.
The foregoing comparative tests are of the greatest significance for everybody who is interested in commercial motoring—manufacturers, -users, and intending users alike. We have authority for the statement that anything from 70 per cent, upwards, of relative efficiency, expressed in the percentage of h.p. on coalgas to the maximum h.p. on petrol, can be expected from any modern petrol engine, without alteration, as a minimum. The percentages will be higher as the compression is higher, and it is, of course, known that the Dennis engine has a very good compression.
We quote the example of the experiments at the Dennis works, by reason of the fact that the relative percentages of maximum power, to which we have referred, are the highest which have yet been brought to our notice as the results of recorded tests. It is settled internal-combustion-engine practice to use a compression for coal-gas which is from 20 to 25 per cent. higher than the usual compression pressures when petrol is the fuel. Apparently, the ordinary petrol engine uses ordinary coal-gas quite well enough for there to be no real occasion to increase the compression.
Widespread Use of Coal-gas for "Running-in."
Our correspondence with several of the leading makers of commercial motorcars, all of whom, we are pleased to be able to report, are showing a mostresponsive attitude towards our suggestions that they should look more closely into the possibilities with coal-gas, indicates that practically none of them has hitherto been concerned to ascertain the ratio of maximum h.p. on coal-gas to maximum h.p. on petrol, for the same engine. They have been only interested in the use of coal-gas in their test shops for the purpose of partly running the engines in, prior to the fullload test on petrol. They have not studied the correct diameters of gas orifices, or the requisite crosssections of the gas-supply pipes leading from the gas mains, so as to allow a sufficient number of cubie ft. of gas to pass to the engine to obtain its full power. They have not, in short, wanted the full la.h.p. on coal-gas. We may remark, incidentally, that we scarcely think that any existing choke-tube on a petrol engine is too small for the purposes of working on coal-gas. The usual diameters of gas orifice, to pass enough gas for the stated powers, will indicate our meaning : 10 h.p., 20-64ths in. ; 15 h.p., 24-64ths in. ; 20 h.p., 28-64ths in. These diameters are furnished to us by an experienced gas engineer, who points out that, in practice, when consumption concerns an internal-combustion engine, the sizes can be substantially lower, by reason of the suction of the piston. The same informant, who is an authority on matters concerning the flow of gas, tells us that it is important to drill any jet truly circular, and not to reduce the diameter of a larger bore by closing the tube.
Unaltered Petrol Engines: Storage the Problem.
It may be accepted as a definite fact, that coal-gas can be economically and commercially used in any modern petrol engine without alteration of the engine. Not even the carburetter need be removed. A typical connection, as adopted by Messrs. Andrew. Barton Bros., of Beeston, Nottingham, on at least one of their chars-h-banes which are running on coalgas, is reproduced herewith in the shape of a sketch. The ordinary air inlets hold good, and it will be observed that a single link, connected to the accelerator, jointly controls the movement of the gas cock and the throttle. If the gas, gives out on the road, the imminence of which is indicated by the usual "popping," the petrol is immediately turned on and allowed to run to the carburetter, without its being necessary for the driver to leave his seat. The engine need not be stopped for the change-over. It is thus possible, by reason of the fact that no interference with the ordinary functioning of a petrol engine occurs when coal-gas is introduced as an alternative fuel, to use coal-gas for part of a long journey, having recourse to petrol for the balance. This important factor is one which adds to the potentialities which lie before coal-gas in the directions that we are advocating. The storage problem is tot a simple one. Later on, no doubt, as undertakings in different parts of the country will install storage for coal-gas at reasonable pressures, say, anything between 150 lb. and 300 lb. on the ,sq. in., at their depots. The directors of the Gas Light and Coke Co., Ltd.' are about to do this, and we have had pleasure in talking over the details with one of the company's experts at its Horseferry Road works, S.W. We may mention, incidentally, thatthe company is converting two of its heavy commercial vehicles to run on coalgas, and is having the necessary storage cylinders on the vehicle, in part relying upon an improvization which includes the adaptation of certain gas cylinders from the Gt. Western Railway Co., and in part anon new gas-holders from the 8teeel Barrel. Co., Ltd., of Uxbridge.
When there is storage under pressure at a depot, it is only a matter of a couple of minutes to refill the storage vessels, which are on the vehicle. For example; at Neath, the gas tramcars' are recharged in a maximum period of two minutes, to a pressure on the vehicle of 190 Ib. on the sq. in., from the depot storage tanks, which are filled, by a two-stage compressor, to a pressure of 200 lb. on the sq. in. Less than 5 per cent, of the total gas bill is due to the consumption to drive the compressor.
Certain factors which arise in 'connection with the fitting of a compressor on the vehicle, such a, compressor to be driven by the engine on the vehicle, are given on the next page. We would particularly point out. that auxiliary eooling is seen to be necessary, if any considerable volume of coal-gas, for example 1000 cubic ft. at atmospheric pressure, is to be compressed into the gas-holders on the vehicle in a reasonable period of time. With slower compression, of course, the heat might be dissipated without such watercooling, although this could not be the case at pressures materially higher than a few atmospheres. Any net rise in. temperature reduces the net volume compressed into the tontainer. We recommend the provision of water-cooling, in order that valuable time may be saved, and for the other reasons. There now remains the flexible gas-holder, and we publish herewith the latest example of the arrangement which has been adopted by Messrs. Andrew Barton Bros. During the recent gales, they found that the lashings of their gas-holders were not strong enough to keep the bags. in place, and they have accordingly added eyeletted tabs,, sewn on to the lower edges of the gas-holders, and secured to the tops of the vehicles, as well as surrounding each gas-holder with what they term a "fence," as is shown in the illustration, on this page.
This Beeston firm is now supplying waterproof and gas-proof two-ply or three-ply gas-holders, to various sizes, the price for one to hold 450 cubic ft. being £15. At the present time, these suppliers have to ask as much as £8 for a flexible gas-holder of 100 cubic ft. capacity, although no doubt the prices for the smaller holders will be reduced as the demand for them increases. It is found, as the, result of experience to date, that it is unwise to use a lot of netting to restrain the gas-holder, due to the feet that the addition to the points of frictional contact increases the wear.
Proved Equivalents.
We are in a position to summarize the following proved, equivalents for coal-gas, as compared with petrol :—Maximum of 330 pubic ft. of coal-gas equals one gallon of petrol, and this may fall to 2'70 cubic ft. if the gas is not stripped-of benzole; a consumption varying between 28 and 22 cubic ft. per h.p. hour, according to strength of the gas, compared with, say, 0.75 to 0.65 of a pint of petrol, according to load on the engine; coal-gas at 3s. per 1000 cubic ft. is equal to petrol at not more than is. per gallon ; a petrol
vehicle, if loaded with three tons of goods and if running on coal-gas, will, require anything between 45 cubic ft, and 22 cubic ft. peemile run', according to state of roads, gradients, and wind resistance. It should also be mentioned that coal-gas is a wonderfully clean fuel,' that, there is no trouble from carbon deposit when using it.
The Editor, THE COMMERCIAL MOTOR.
[1300] Sir,—As president of the Institution of Gas Engineers, I feel that I must disavow on behalf of that body of professional gentlemen the suggestion that they, ass a body, have scoffed. at the idea of it being possible to use coal-gas in petrol engines. Of course, they all know that coal-gas is a most suitable fuel for the engine. The only difficulty is the matter of carrying a sufficient 'quantity on a vehicle to enable it to run a considerable distance.
When it was first suggested that compressed coalgas might be used on motorcars, including the touring type, they did scoff at the idea of loading a touring car with nearly a ton weight of cylinders to enable it to run 40 or 50 miles. Not only was there the disadvantage of the extra weight, but the bulk also was difficult to accommodate on an ordinary touring car.
The weight and bulk difficulty are certainly very much less when considered, in connection with the commercial type of 'vehicle, but still, at 150 lb. pressure, which you suggest, the bulk for 1000 cubie ft, of )compressed gas is fairly considerable, although the difficulty is not insurmountable.
This company at the present time is arranging to carry out some experiments in connection with the British Commercial Gas Association, and at a later date the results will be available for your publication.
When the principle of gas-driven vehicles is applied to a tramway, the matter becomes very simple, as charging stations can be arranged at each end of the track, or, if necessary, at convenient intervals, so that the cylinders need not be at-all large for containing the necessary gas to run from point to point. —Yours faithfully, A. E. Bnommennv, M.Inst.C.E. Chief Engineer and General Manager. Tottenham District Bight, Heal and Power Co,
[We are pleased to observe that the President of. the,Institntion of
Gas Engineers and his colleagues dissociate themselves frommose who scoff at the idea of the commercial use of coal-gas for road-traction purposes.—En.]