Propane Revolution

The 53 new green and cream-colored buses that went into service in Chicago last week looked like any other buseson the outside. But their mechanical innards were different. Instead of running on gasoline, they ran on propane gas, a petroleum distillate. They were the first of a new fleet of 500 ordered by Chicago's Transit Authority from Twin Coach Co. of Kent, Ohio. The fleet, largest of its kind in the U.S., marked the fast progress of the propane-propelled revolution in engine fuels.

Truckers and other bus companies have used propane on & off for more than 15 years, but only recently has propane begun to eat into the gasoline market in a sizable way. About 20 cities, including San Antonio, Orlando, Fla. and Winnipeg, Canada, have recently added propane buses to their transit systems. Three months ago Milwaukee's Boynton Cab Co. began converting its 279-cab fleet to propane, the first cab company to do so. With its new fleet Chicago hopes to save up to 2-c- a mile in operating expenses.

In the Chicago busesas in otherspropane gas, liquefied under pressure, is carried in thick-skinned steel tanks. The gas moves through seamless copper tubing, in liquid form under its own pressure (eliminating the need for a fuel pump), and is converted into a gas as it enters the carburetor. Chief advantages: the gas sells for one-half the price of gasoline, burns completely, leaving no carbon, is odorless, and runs the motor more smoothly and quietly, requiring fewer changes of oil and less maintenance. Insurance companies consider propane engines as safe as diesel or gasoline.

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