http://www.agsem.com/Ger-1914 Chgo-Pneu Compressor.html

1914 Chicago-Pneumatic air compressor. 1 cylinder horizontal two cycle semi diesel oil engine. 70HP -- 52.2kW at 150 rpm. 11 inch bore, 12 inch stroke, 3396 cubic inch displacement. 279.4mm bore, 304.8mm stroke, 55.65 liters displacement. Flywheel 5 feet, 2 inches -- 1.575m -- diameter, manufactured by Chicago Pneumatic Tool Company. This engine is a combination engine and air compressor. The forward cylinder with the large exhaust pipe is the power cylinder. The rear cylinder i s the air-compressing cylinder, which is a double-acting cylinder. Every time the piston moves either forward or back, one side of the piston is compressing air. It is a 2-cycle Hot-Bulb engine. There is a metal bulb which protrudes from the cylinder head, and it is heated to red-hot by a flame. Normal air is compressed in the cylinder. Once the piston reaches top-dead-center, a heavy fuel, such as Diesel fuel or heating oil is injected into the cylinder. The fuel enters the bulb, vaporizes, mixes with the air, and because of the extreme heat inside the bulb, ignites. This causes the piston to be forced down, and the power is generated. Compressors of this size were often used in mining applications, either to drive steam engines within the mine to provide power for moving carts around, or to provide compressed air for jackhammers and pneumatic drills. This engine was used at a mine in Quartzite Arizona. It was donated to our Museum in 1983, and restored to operating condition by Volunteers.