VINTAGE SMOKE
BEATING DR. DIESEL
A 6 HP HORNSBY OIL ENGINE
BY JIM ALLEN
SPECIAL THANKS TO RAY HOOLEY AND MIKE MURPHY
Dave Tomblson’s engine is a Hornsby 1912-style, Type L, and has a 3.9 x 5.5-inch bore and stroke. It was rated at 6 horsepower at a whopping 260 rpm. That calculates to about 121 lbs-ft of torque. Production began in 1912 and they were a third evolution of the original Hornsby-Akroyd design with a number of improvements and updates. They were built into 1934, from 1918 with a Ruston & Hornsby tag. This one is mounted on a cast iron base that doubles as a fuel tank. The rusty part is the vaporizing chamber and it has a cover with a removable cap. The intake valve is on this side of the engine and the shaft that comes from the crankshaft drives the open roller cam that operate both valves and the injection pump. The injection pump is the part that hangs down and you can see the priming lever.
Dr. Diesel’s 1898 patent on the compression ignition engine is the well-charted beginning of the engine type we now call a diesel. Missed in all that historical hoopla… when the first production diesels entered the market, they weren’t the only engines running on fuel oil. The Hornsby-Akroyd vaporizing oil engine had been in production six years at that point and tens of thousands had been sold all over the world.
Herbert Akroyd-Stuart (1864-1927) started work on his vaporizing oil engine in 1885 after accidentally setting a fire with paraffin (kerosene). Lamp-grade kerosene is not volatile, which is why it was used indoors as lamp oil, but when he spilled some into a pot of molten tin, it vaporized and was ignited by a nearby open flame. At the time, internal combustion engineers were trying to resolve fuel volatility issues, with gasoline being considered too dangerous for many applications. Fuel oil satisfied the safety aspects (which is why oil engines were often marketed as “safety engines”) but was difficult to ignite. Akroyd-Stuart’s accident had given him a simple idea for igniting fuel oil, kerosene and other less volatile petroleum products.