HEED THE VEED

While many variances existed between the companies building Brons or Hvid engines, the operating principles were the same. Shown here is a Hercules/Thermoil. The Hvid was a four-stroke engine and at 500-600 psi maximum firing pressure, it was right in there with diesels of the day. The actual firing pressure varied according to the fuel used. When built for kerosene, the firing pressure was in the 350-400 psi realm because kerosene ignited more easily and hit hard when it did. With heavier fuel oils that burned more slowly, firing pressure was up there near the maximum. The compression ratio was altered in some engines by shimming the connecting rod and change the position of the piston to increase or decrease combustion chamber volume. Also, the size of the orifices in the fuel cup (9) had a similar effect, with larger orifices better for heavy fuel and smaller orifices better for lighter fuel, such as Kerosene. The “injection” system used little more than gravity and intake suction on the intake stroke to feed fuel. The fuel was gravity fed from a tank to the fuel reservoir (1). The amount of fuel delivered was regulated by the fuel metering pin (2), the position of which was regulated by the governor via the governor rod (3). Fine adjustment of rpm could be made using the speed control wheel (5) which adjusted the highest position of the metering rod. The metered fuel and a little air filled in behind the fuel inlet valve (6) and that valve was synchronized to open during the intake stroke. The fuel valve was operated by the fuel valve rod (7). The fuel valve opened into the fuel cup (8) and was timed to close partway into the compression stroke, leaving fuel in the fuel cup. Heat in the combustion chamber and the rising heat of compression would vaporize the lighter elements in the fuel in the fuel cup and they expanded to blow the heavier parts of the fuel out several orifices in the fuel cup (9) and heat of compression ignite the rest of the charge in the main combustion chamber (10). The intake (11) and exhaust (12) valves operated as most other engines, though some Hvids used atmospheric intake valves.