During World War I in the UK and Europe gasoline supplies were tight to non-existent in many areas for passenger cars, taxis, and trucks. All available gasoline was diverted to power military motor vehicles, boats and airplanes during the war efforts, leaving little for private passenger cars and commercial vehicles.
Earlier in the 1800s during the development of the internal combustion engine a number of non-petroleum base fuels including: coal dust, coal gas, city gas (natural gas), methane and others were used in addition to oil-based fuels. By the time Karl Benz, the pioneer German engine designer had perfected his 1885 Benz Patent Motorwagen, he had settled on the use of gasoline as the fuel to power his early automobiles and others soon followed.
As fuel supplies became scarce, necessity became the mother of invention and those in the know looked back in time to other fuels that had powered engines in the previous century. Coal gas, which is produced by heating coal in enclosed ovens with an oxygen-poor atmosphere became available commercially as early as the 1820s. After ninety-plus years of development and the establishment of a distribution network, it was the fuel of choice during World War I as an alternative for motor vehicles.
Containing the gas was the next issue, references were found to using steel tanks filled with compressed coal gas as early as 1910 for vehicles in France; during wartime the manufacture of the containers was not an option. Lighter than air flying craft had been in use since the late-1700s, and it was reported that the general construction methods and materials for air ship balloons were used to make the gas bags for vehicles at the time.
Other than the gas bag and an appropriate roof rack to hold it, little more than a flexible hose and some minor carburetor modifications were needed to run a vehicle on coal gas. Although specially manufactured coal gas fuel and air mixers were available in England for use on commercial trucks and buses, a modified Model T Ford Holley three-screw unit can be seen below.
The illustration (above) from an article in the Automotive Trade Journal, October 1, 1917 issue, shows the minor changes used at the time on a Ford Holley carburetor. The gas inlet tube was inserted into a hole drilled just before the throttle valve with a fixed-sized jet used in it for admitting the gas. It was found at the time through general experience that a jet orifice of about seven-thousandths of an inch per engine h.p. was about the correct size. As an added benefit the car could also be operated on gasoline.
According to the The Gas Age magazine, a Model T Ford Touring car with an 11-foot long by 4-foot diameter gas bag that held about 130 cubic feet of gas, was able to run about 17-miles on a filling.
Below you can watch a short thirty-second long British Pathe video titled Gas Bag Motor Cars showing several vehicles equipped with gas bags and a Model T Ford fitted with a tank of compressed coal gas. For further information view European Progress in The Gas Age (1918) and Use of Gas as Automobile Fuel (1920).