[66 



NATURE 



[November i, 19 17 



COAL-QAS FOR MOTOR TRACTION. 



ONE of the results of the scarcity of petrol 

 has been that inquiry has been stimulated 

 into other possible fuels for power purposes on 

 motor vehicles. Benzol, being a home-produced 

 fuel, would have been an admirable alternative, 

 but the entire output is already required for other 

 more urgent purposes. Alcohol, too, could have 

 been used, had it been available, but too little is 

 produced in this country to meet the demand, even 

 if other difficulties had not stood in the way. The 

 only available alternatives are paraffin and illu- 

 minating gas. Paraffin can be used quite well on 

 slow-moving vehicles, provided that the load is 

 reasonably steady, and that a small quantity of 

 petrol is available for starting the engine with 

 reasonable dispatch ; but this, again, is not home- 

 produced. 



The problem is essentially a war one, and it 

 arises from the present limitation of ocean trans- 

 port. The alternative fuel must, therefore, be 

 one which not only can be, but actually is now 



iptL-d for coal-gas proiiulsion 



being, produced in these islands. Coal or its 

 derivatives is clearly indicated. Benzol is not 

 available for the reason already given ; coal could 

 be used in some form of "suction producer," 

 thus affording a supply of " suction gas " ; but a 

 satisfactory producer capable of attachment to a 

 car has yet to be developed. Coke has been 

 satisfactorily employed on heavy vehicles, but the 

 process, being one of external combustion, is not 

 adaptable to the great majority of vehicles. Hence, 

 by a process of exhaustion, illuminating gas is 

 arrived at as the only possible present alternative. 

 It has, however, to be remembered that any such 

 alternative fuel must be used in a way that does 

 not require additional equipment making any 

 substantial demand on raw materials. For this 

 reason it is scarcely worth while to adopt any 

 plan which requires the gas to be stored at pres- 

 sure, since this would need storage cylinders of 

 steel. The scheme must be one for carrying the 

 gas at atmospheric pressure, or at best at pres- 

 sures but little higher. 



NO. 2505, VOL. 100] 



Such a scheme is practicable, and has already 

 been applied to some hundreds of vehicles. The 

 main drawback is the bulk of the storage bags. 

 A gallon of petrol has a net calorific value of 

 79,000 pound-calories, and the mean calorific 

 value per cubic foot of petrol vapour with enough 

 air for complete combustion is 56 pound-calories. 

 Coal-gas has a calorific value of about 350 per 

 cubic foot, and the mean calorific value per 

 cubic foot of gas and air for complete 

 combustion is 58. - It will be seen from 

 these figures that an engine of given dimen- 

 sions should yield the same power on either fuel, 

 assuming the thermal efficiencies to be the same 

 (as they probably would be) ; and that 1000 cub. ft. 

 of coal-gas would contain the same calorific 

 value as about 4^ gallons of petrol. If, therefore, 

 the gas costs, say, 35. per 1000 cub. ft., the equi- 

 valent cost of petrol would be 8d. per gallon. This 

 serves to show that a very large financial economy 

 arises from the substitution. 



The remaining consideration is the bulk of the 

 storage chamber. Now, 1000 cub. ft. are seen 

 to be equivalent to 4|- gallons of 

 petrol, and although the road 

 tests so far made give a rather 

 larger gas consumption, there is 

 no reason why an equivalence to 

 4 gallons of petrol should not be 

 attained. On this basis a car run- 

 ning twelve miles to the gallon of 

 petrol would run forty-eight miles 

 to 1000 cub. ft. of gas. A Ford 

 car can carry about 250 cub. ft. 

 of gas on the roof, and as this is 

 equal to exactly i gallon of petrol, 

 the distance run between fillings 

 would be about twenty miles. If 

 the gas could be contained in 

 strong bags capable of withstand- 

 ing 15 lb. per square inch (gauge 

 pressure), this distance would be 

 doubled. 

 The method is seen to be useful only for running 

 short distances out and home, or for use on road- 

 ways having supply stations about every ten 

 miles. Repairs to the engine would be minimised 

 rather than increased by the use of gas instead 

 of petrol ; the sparking plugs would need less 

 attention, and the cylinders would not require to 

 be cleaned out so frequently. Moreover, the 

 change over from the one fuel to the other is of 

 the simplest ; a pipe is taken from the holder to 

 a tap near the driver, and from that point direct 

 to the engine side of the existing carburettor. 



As is well known, it is now customary at some 

 engineering works for automobile and aircraft 

 engines to be "run in" with coal-gas as fuel; 

 moreover, it is within the writer's recollection that 

 on the breakdown of a power station in the very 

 early days of petrol-engine construction the whole 

 machinery of a workshop was run by a petrol 

 engine fed from the gas mains. This instance 

 afforded an insight into not only the adaptability 

 of the engine, but also, on comparing the size 



