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New Light on Gas Fuel
Page 74
Page 75
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Experts Pool Knowledge at Swansea. Mechanical Engineers' Meeting on Coal Fuel for I.C. Engines
NO insurmountable technical difficulties are likely to be encountered in the development of producer-gas for transport, but development in this country in peace time would be slow unless gas vehicles were permitted to carry the same load and to travel at the same speed as petrol or oil machines of equal size and power.
This view was expressed by H. L. Pine, M.I.Mech.E., in one of the papers forming a basis for discussion at the Swansea meeting of the Institution of Mechanical Engineers, held this week. All the papers dealt with various phases of the use of coal as a fuel for internal-combustion engines.
The coal industry, said Mr. Pixie, had appointed a committee to investigate producer-gas problems representing the Mining Association of Great Britain, the Coal Utilisation Council and the British Coal Utilisation Research Association.
Comparing producer-gas with liquid fuel, he made the following points: the lower cost of the former; its desirability through being a home product, and the boost its use would give to mining employment. '
Regarding the question of the lower power developed with gas, he suggested that this would need compensating by increased engine capacity in all except smaller vehicles.
He thought the private car offered no scope for gas, but for goods, and passenger vehicles and tractors it was highly suitable. In December last .there were in use in this country 18 goods vehicles, 2 passenger vehicles, and 3 tractors operating on producer-gas.
The fuel-economy attraction, he thought, was not sufficient inducement so long as the unavoidable extra weight resulted in higher duty and lower speed limit for equal pay-load. The gas vehicle was heavier by 10 per cent.; moreover, solid fuel was twice as heavy as petrol and nearly four times as heavy as oil fuel in relation to distance travelled.
In the case of a popular type of vehicle, the pay-load would be reduced by 15-16 cwt., representing a loss of revenue of £5 a week.
PERSONAL experiences with a Gilford H.S.G. 31-seater were related by W. H. Fowke, of the Highland Transport Co., Ltd. This vehicle had covered 36,000 miles in the service of his company.
His observations had resulted in the conclusion that much importance was attached to the nature of the fuel used, and that filtering required further investigation. He held that a producer-gas engine must be at least 33 per cent. larger than a petrol engine to develop equal power. Output was much influenced by combustion-chamber design. Comparable fuel costs during 1938 were :—Gas, £90; petrol £253; and oil, £136.
A second gas-vehicle had been ordered by his company, six orders had been placed by other undertakings, whilst as many were contemplating doing so.
c20
QUITABILITY of fuel was more important on producer
gas vehicles than on stationary plants, because considerations of space and weight forbade the elaborate equipment common to the latter, to be incorporated in the former— equipment such as clinker-removing gear and scrubbing towers. This was one of the factors influencing design discussed by Bosworth Monck, of the Koela Producer-Gas Plant Co., Ltd.
Uniformity of quality was essential and difficult to obtain; reactivity, size and moisture, volatile and ash contents were main characteristics to control.
Fuel suppliers and plant makers would both be assisted by a tabulation of comparative reactivities of various fuels, or even by the establishment of a standard method of testing. Upon reactivity depended producer design. Grading and size primarily influenced performance. Rate of gasification was affected to a surprising degree. Volumetric efficiency also was obviously affected by the ratio of air-space to fuel in the fire bed. If the resistance to flow in the fuel bed were low, more elaborate cleaners were permissible. On thermal-efficiency grounds, Mr. Monck thought it preferable to supply the fuel bed with steam heated by outgoing gas, which was cooled in the process, rather than with water which extracted heat from the fire. Incoming air should similarly be heated.
Because it was impracticable to incorporate tar extractors in the system, the down-draught producer was to be preferred. In it, tarry matter underwent destructive distillation, This type, however, generated gas with a lower calorific value than that of the up-draught type, and was less flexible. Also the CO, content was higher, adversely affecting consumption rate. This was of little moment on grounds of cost, but of consequence because of bulk.
Ash content influenced grate design, and fusion characteristics governed operating temperature. According to the author, the valuable reactions predominated between 1,000 and 1,200 degrees C, and ash slagged above 1,200 degrees C. In a French producer, however, 1,600-2,000 degrees C. was aimed at. Close control of temperature was therefore desirable.
On the subject of power loss, Mr. Monck advocated designing cylinder heads for gas as well as raising compression, also the examination of other means such as supercharging or changing the cycle of operations. Having stressed the importance of saving weight and loading space, and of standardizing parts, he suggested directions for possible development, notably the use of new materials, and the employment of air-cooled engines, particularly in view of the cooler running afforded with gas fuel.
Iputting the case for the dry air blast In road-vehicle producers, Mr. A. R. Griggs, of British Gazogenes, Ltd., pointed out that, with the cross-draught type, which had many attractions for vehicle work, there was no need to
use water to keep down •,temperature, nor did water materially enhance the quality of the gas.
Furthermore, water or steam affected the thermal efficiency of the producer, and the quantity was difficult to control precisely, to do which was important Whilst the addition of water or steam produced hydrogen and carbon monoxide, it also resulted in the formation of carbon dioxide which countered the gain: With the highvelocity dry cross blast, the minimum of CO, was produced, whilst the CO content approached its maximum theoretical value.
FOR present purposes, said Major J. A. Macdonald, D.S.O., M.C., of the Sentinel and H.S.G. companies, there was justification for regarding temperature as the measure of the rate of the release of heat. • It was accepted theory that increased temperature gave more and better gas in a given time. He questioned, indeed, whether theory had reached the limit to which this principle had been carried in practice.
At 1,300 degrees C. the conversion of CO, into CO was complete in 3 secs., whilst at 1,000 degrees C., in the same time it was only 6 per cent. complete. At the same respective temperatures steam decomposition in 3 secs. was 99.5 per cent. and 15 per cent. complete.
Turning to the matter of fuel, Major Macdonald said that to get passable results from charcoal was child's play compared with obtaining even mediocre results from coal. The future of producer gas rested more on the supply of suitable fuels than on suitable plant.
His paper contained an interesting contribution to the information placed before the meeting in his analysis of the factors making up the quality of reactivity.
ABRIEF history of the development of the town-gas vehicle was included in the paper by C. M. Walter, D.Sc., engineer in charge of Birmingham Gas Department Industrial Research Laboratories. Ile also considered the vehicle equipment, notably the storage cylinders, and dwelt at some length on compressing plant.
As a previous authority had done in the case of producer gas, Mr. Walter stressed the need for government help in respect of the handicap constituted by the greater weight of the equipment necessary on the vehicles, From the economic point of view, he concluded that with gas at 4d. per therm this form of transport could successfully compete with petrol under certain conditions. If the fuel were employed in high-compression engines with fuel• injection, the cost would compare with that of the oil-fuel vehicle.
SUCH a scheme was referred to in the paper by R. A. Erren, who outlined a system in which a full charge of air was taken in at every suction stroke and the gas injected after the closing of the inlet valve.
He described briefly tests made with a converted A.E.C.
I N the course of speeches and discussions, a number of
interesting comments was made by prominent persons.
Mr. le'styn Williams said transport was now consuming 8 per cent. of the coal produced in the United Kingdom.
Mr. W. C. Whalley said an approach to the Ministry of Transport on the subject of producer-gas propulsion was to be made. The M.T.T.A. was in touch with the I.A.E. and the S.M.M.T. in this connection and the I.M.E. might join them. They wanted the extra half-ton, as al/owed for trolleybus emergency batteries, to be 'extended to other home-produced-fuel vehicles.
Mr. S. E. Crooke said it °tight to be made clear that no taxation would be imposed until the companies using solid fuel had had time to establish themselves.
Mr. Bosworth Monck disagreed with Mr. Pine's figure of 15 lb. of fuel equalling a gallon of petrol and suggested that 12 lb. would be nearer.
A cross-draught producer could be operated with success even if a bucket of water was poured into the hopper, stated Mr. H. MacGillivray. It was desirable to use fuels as near as possible in their natural form. Rather than have recourse to supercharging, an engine of capacity greater than normal was required.
After a day's work of 150 miles, drivers came off the producer-gas vehicle fitter than if they had been using oil or petrol, stated Mr. Fowke. The system had special utility for country services and goods vehicles. The " Highland " bus ran 150 miles on one filling.
Tests were being made with superchargers, said Mr. Mouck. He had tried the centrifugal type and was now trying the Rootes and Zoller types.
A strong case could be made out for giving the coal-using vehicle preferential treatment said Sir Evan Williams (President of the Mining Association of Great Britain).
Among the coal vehicles at the rally were two Sentinel H.S.G. machines—a coach and a 5-ton model—a SentinelFordson conversion, two British Gazogene Bedfords, and a Latil tractor. R.tuming on town gas was a Birmingham Corporation Austin Six van, whilst an East Midland Leyland Tiger coach was using oil fuel from coal by the Coalite process. A Fordson van and a Rolls-Royce car represented the petrol from coal section. A Morris van was present. that used gas or petrol on the Erren system.