METHANE is available from natural and artificial' sources in enormous quantities. It can be assumed that approximately 50,000 million cubic metres of gas containing at least 85% of methane are obtained annually from petroleum wells. The distillation and cracking of petroleum and the destructive distillation of coal produce a further quantity of methane which may amount to a quarter of that given above. If translated into calories this quantity would be as important as the total quantity of petrol produced by distillation or cracking of petroleum. In Italy the total sum of " gaseous calories" that are evolved from petroleum wells, from water wells or natural wild sources is probably much greater than the " liquid calories " that up till to-day have been won. from the soil.
The ability to use methane from natural or artificial sources as a motor fuel would be a definite contribution to the world requirements. of fuel and it would have a special importance for Italy.
The problem is, however, not so simple. Methane considered from a thermodynamical point of view is an excellent motor fuel. Tests with Italian natural gas in petrol engines confirm the good results obtained by others. A motor running on methane is easy to start, is very flexible, and has a good thermal efficiency; moreover it gives a power output about equal to that obtained with petrol. One cubic metre of natural gas containing 9,000–10,000 calories is equivalent to 1 kilo gram of petrol. Engines constructed for petrol do not require special modifications to run on gas if we only substitute for the carburettor a simple air-gas mixer, but to make full use of the gas it is advisable to increase the compression ratio to 5–7 to 1.
A disadvantage of a gaseous fuel is small heat content per unit volume. Its gaseous state takes away from methane those characteristics that justify the supremacy of the petrol, viz. great concentration of heat both in volume and weight, the freedom of the vehicle to travel anywhere, easy refuelling, distribution and storage.
To overcome these inherent defects in adapting methane to motor propulsion one can follow two ways physical concentration by compression or liquefaction_ or chemical transformation into liquid fuels.
COMPRESSION OR LIQUEFACTION.
The compression of methane at pressures of at least 180–200 atmospheres in steel cylinders adapted for fitting to heavy motor vehicles reduces the volume of the gas and facilitates refuelling, but it increases the price of the gas and causes further problems in the adaptation of cylinders for motors. In particular the construction of a compact and robust reducing valve that will continually reduce the varying pressure in the cylinders to a constant pressure near to that of the atmosphere and which quickly responds to the variations in the engine requirements, presents not inconsiderable difficulties. Above all, the compression system adds to t