Steam as a Motive Power for Public Service Vehicles.
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Mr. Thomas Clarkson's Reply to the Discussion on his Paper.
One had to wait until the last of the three meetings of the Institution of Mechanical Engineers, at which Mr. Clarkson's paper has been discussed, to hear any serious criticism of the Chelmsford system for application to the steam omnibus. Curiously enough, the hostile criticism, when it did come, emanated, not from the advocates of the petrol vehicle, or indeed from any quarter whence criticism was, perhaps, expected. The severest critic of the system of steam generation described in the paper came from Chief Inspector Bassons, of Scotland Yard, who, as he said, has no prejudice in favour of any particular system of mechanical traction so long as it meets the many requirements of public service. Bassom was asked to contribute to the debate at an earlier period, but was, apparently, satisfied to lie low until the engineers, and others, had had their innings. It must be admitted, however, that the contribution to the debate of this critic from Scotland Yard was by no means the least important from among a long list of speakers. The engineers, probably because they realised to the full the difficulties of the problem to be solved in connection with the application of steam as a motive power for public service vehicles, had practically nothing but praise to bestow for what has been accomplished in the Chelmsford system, and, from this source, Mr. Clarkson has little or nothing to answer, when the time came for him to reply upon the whole question. We are glad to be able to say that Mr. Clarkson has overcome the difficulties quoted by Mr. Bassom.
Mr. CLARKSON, who was warmly received on rising, said, in a lengthy reply, that the primary object of the paper he had read was to bring before the Institution some of the results of the work he had been engaged on during the past 12 years, and to promote a general discussion of a subject of very great interest and importance. Colonel Crompton, who opened the debate, was one of those who realised the possibilities of steam in this connection. One of the most important points as regards the steam omnibus was the experience that had been gained at Torquay, and the figures presented for the three years' operation were undoubtedly a unique record. He did not know at the time he had drawn. up the table the number of omnibuses kept in reserve in order to effect the very fine records in respect of lo-t mileage, but, during the summer service, he understood, from information supplied by the officials of the company, that they had seven buses running and one in reserve. That seemed to yield the best results. In the winter, two were laid by, five were running, and one was in hand.
He might, perhaps, make one or two remarks on the experiences in Torquay with regard to side-slipping troubles. Owing to the hills in that district, the roads had rather an excessive camber, and the material being a type of oolitic limestone, which was very greasy in certain states of the atmosphere, the risks of side-slipping were considerably accentuated. Originally a Parsons chain had been used, but latterly they had not required to use chains, owing to the employment of a harder and somewhat inferior rubber for the tires, although the same price had to be paid for it. With the finer sorts of rubber employed originally there seemed to be a tendency for the rubber to conform to the inequalities of the road service, but with a harder tire this did not happen, and the side-slipping trouble had practically been overcome. There was one other result, however : the tire which was better in respect of skidding was not so good from the point of view of durability, some of the earlier, purer rubber tires having run 27,000 miles, whilst the harder rubber averaged only from 8,000 to 10,000 miles. In spite of this fact, the allowance of lid. per car mile for tire renewals appeared to be ample.
Mr. Hans Renold had referred to the use of chains, and he (Mr. ('larkson) had employed chains in his system for the reason that they had a high mechanical efficiency, and were very flexible.
Professor Spooner had referred to the Perkins flash generator, but he thought that Perkins had failed to appreciate sufficiently the importance of thermostat control. It was a fact that with that type no deposit was found in the tubes. Perkins had got over the lubrication question by the employment of anti-friction metal. He personally had tried some of this anti-friction metal
some years ago, and, whilst admitting it was an excellent metal for working under high temperatures, he must point out that it was extremely brittle—so brittle, indeed, as to be, in his opinion, outside the pale of ordinary engineering. Professor Spooner had suggested that the regenerating principle might be extended so as to recover more of the waste heat of the gases, but he could not do more than bring the coolest water in contact with the coolest gases, and that had already been done.
The Question of Fuel.
One of the most important questions in connection with the omnibus problem was the fuel question, which had become so acute in relation to the supply of petroleum spirit that the Motor Union had appointed a Fuels Committee to investigate the matter with references to the possible control of the supply of petrol and the employment of a substitute. The Society of Motor Manufacturers and Traders had also taken action in a similar direction, and had employed an experienced chemist to investigate the question of a possible substitute for petrol. The report of that chemist had now been published, and it amounted practically to this : that the only available substitute was denatured alcohol, which, it was stated, could be produced at 2s. per gallon from potatoes at £2 per, ton. Mr. Clarkson took occasion to point out, however, that this calculation made no provision in respect of excise. The calorific value of denatured alcohol was inferior to petrol, and, if 2s, per gallon represented the price of the petrol substitute, compared with 2s. 6d. per gallon for petrol, it might be taken that this price represented the possible limitations in the rise of the cost of petrol. Another point in connection with the employment of alcohol was that it was not an interchangeable fuel, and could not be used indiscriminately in internal-combustion motors. The same motors would not use both petrol and alcohol, alcohol, in order to obtain proper combustion, requiring a specially-constructed engine, otherwise there would be trouble from corrosion of the internal parts of the cylinders, due to the formation of organic acids. Moreover, it had to be borne in mind that any considerable enlargement of the supply of petrol was somewhat improbable, as it would be necessary to find a market for the other products : it would, clearly, not pay to pump oils for the production of petrol only. The steam omnibus was using paraffin, either Russian, Borneo, or American, and recent improvements that had been made in the omnibus had brought within measurable distance the employment of crude oil, which would reduce the working costs very much below the present figure. He could see greater possibilities in the way of using cheap fuel than was the practice at the present time. Another point was that in the alcohol engine the motors would have to start with 120 lb. compression, which was not altogether an encouraging feature.
Degrees of Superheat.
Referring to the observations made by Mr. D. J. Smith, M. Serpollet's representative, it had been said that in the Clarkson system an insufficient degree of superheat was employed-800 degrees Fahrenheit against the 1,200 degrees Fahrenheit employed by Serpollet. Mr. Clarkson, who was very emphatic on this point, said he did not consider that greater economy could be secured by the use of a higher degree of superheat than that employed by himself, for the reason that at the present time there were no materials available of which to construct the generator suitable for temperatures over 800 degrees Fahrenheit: in that matter they were waiting on the steel maker. It was quite possible to produce steam at higher temperatures, but you did it at the cost of destroying the generator, and, although one might be prepared to do it for racing purposes. these were not the conditions for public service. The present steels available began to scale at temperatures above 800 degrees, and that fixed the practical working limits of superheat. Reference had also been made to the temperature of exhaust, but he could see no greater economy in exhausting from an original superheat temperature of 1,200 degrees at 800 degrees than in employing an original superheat temperature of 800 degrees and exhausting at about 300 degrees. The steel used for the coil was a mild, low-carbon steel, with about 0.23 per cent. of carbon, and, for certain parts of the generator, they were using steels which had superior fire-resisting qualities, but were not able to get them made in the form of tubes. Mr. Georges De Prelle, the chief engineer of the Road Car Coin
pany, had referred to experiments he was making in connection with the gear problem, and, while listening to what was said on that subject, he thought that Mr. De Prelle's explanation of the troubles to be overcome in that direction was the best possible argument in favour of doing away with change-speed gears altogether.
In connection with the working of the motor omnibuses at Torquay, some explanation ought to be offered as to the reason for the adoption of a tramway scheme, in face of the fact that the motor omnibuses had given such satisfaction. The explanation was that, some four years ago, pressure was put upon the Corporation by a tramway construction company, and a postcard ballot was taken, when an overwhelming majority was recorded in favour of improved traffic facilities. At that time the tramway scheme was the only one proposed, but some of the inhabitants, who were not in favour of the introduction of tramways, decided upon the introduction of motor omnibuses. The total capital expenditure had been the small sum of £3,000, the company had carried ale:lilt 11; millions of passengers, had paid 7.1 per cent, dividends, and had a reserve of about £2,800. The position of the tramway company was this : a sum of over £80,000 had been expended in track and equipment, and the Torquay Corporation had expended nearly £20,000 in extension of its power station to provide current for the tramways, whilst not a single passenger had so far been carried.
Difficulties with Scotland Yard.
Mr. Clarkson then came to grips with Inspector Bassom. No one, he hinted, could accuse that critic. of having displayed partiality. however, Mr. Clarkson claimed to have had no difficulty with Scotland Yard, and had no doubt that some of his petrol friends would be very glad if they could say the same. As to the slow development of the use of steam for public service, Mr. Clarksoa advanced what is doubtless the true reason—that the ordinary methods of steam generation were not suitable, and the invention of a new system had taken time. With regard to the fact that out of SOO mechanically-propelled omnibuses in 'London only 40 were steam buses, it had to be remembered that the omnibus companies found themselves forced to put buses on the road, and the petrol bus was at that time the only type available, and, indeed, up to the present time, the only steam omnibuses running in London were the Chelmsfords. And here Mr. Clarkson issued an invitation to others to take up the problems connected with the development of steam for road vehicles, as there is plenty of room in the industry for other people.
It was not an easy job that had to be undertaken : there were critics of the type of Dr. Hele-Shaw who recognised the difficulties and many disappointments that had to he faced. Still, they had some results to point to as the outcome of the work done. Mr. Clarkson joined issue with Inspector Bassom on
the fuel question. One important point in connection with fuel was that of safety in handling and storage, and the use of paraffin obviated risk, and, although a number of petrol buses had been completely burned in London by accidental ignition. there had not been a single serious fire on a steam bus.
Dealing with some of the other points raised, Mr. Clarkson re• ferred to the fallacy of placing a complicated machine such as the steam bus in the }lauds of men who were frequently without mechanical training, and expecting everything to run smoothly. However, a better class of driver was being gracho
ally developed, and he was glad that Scotland Yard was taking such pains to see that only properly-qualified men were put in charge of omnibuses. He could not understand the official attitude with regard to a canopy, seeing that it was allowed on a tramcar, although it was to be noted that the Board vf Trade was the controlling authority for tramways and Scotland Yard for omnibuses. The question of any increased power required rather concerned the proprietors of the omnibus than the authorities at Scotland Yard, and, at all events, against any increased cost of operation arising front the provision of a canopy, there was to be set the chance of additional earnings in wet weather. Referring to the effects of wind pressure on a canopy, Mr. Clarkson thought that this might really be regarded as a negligible quantity, as a canopy need not weigh more than a couple of outside passengers. The P. and 0. Company, Litt years ago, was afraid of wind pressure upon canopies, and would only fit canvas ones to the decks. This idea of wind pressure had been exploded, and he was informed that fixed wooden canopies were now used.
Smell and Smoke.
The smell and smoke questions were important, and a chimney was the most natural remedy. The slow steering of the omnibus, he considered, was rather an advantage than otherwise, imposing caution on the driver, whilst, at the same time, giving him so great a mechanical purchase that he could control the bus with one hand. Compared with the mechanical force which had to be exerted by the driver of a petrol bus, and who had to change gears over 2,000 times per day, there was far less strain on the driver—a most important point. Many other matters were ieferred to by Mr. Clarkson ; he said that, with the greater accuracy of modern machine-cut gears, the hunting cog was not called for ; he expressed the opinion that, with higher temperatures of superheat, the use of tappet valves would be extended, and, with regard to the fan, condemned by Mr. Druitt Halpin, he stated that, after many experiments, he had come to the conclusion that the four-bladed fan now fitted was the best for the wok. Mr. Druitt Halpin had suggested the use of wind guards to trap the air, but Mr. Clarkson pointed out that the speed of the motorbus is too slow for such a device to prove effective. At the same time, they were utilising the motion of the vehicle to the fullest extent possible. Nor did he agree with the suggestion of driving in front and steering behind.
Automatic Control.
On the question of automatic control, Mr. Clarkson was brief but forcible. If it was said that automatic control was not reliable, it was the business of the engineer to make it so ; certainly it was not argument against its use. The question of thermal control was a most vital one, and it could only be done effee• lively by automatic devices. In this connection, Mr. Clarkson made an effective analogy of the horse, with its automatic lubrication, automatic circulation of the vital fluid, automatic thermal control, the whole of the mechanism contained in a dust-proof covering, and a most striking illustration of rear driving and front steering. He believed success in machinery working was to be best attained by a close approximation to the living organism.
Finally, Mr. Clarkson claimed that there was ample evidence of the suitability of steam as a motive power for public service vehicles.