How The Caloric Engine Worked
Ericsson’s caloric engine had four 2-part cylinders. The upper, or supply, cylinder drew in air from the outside and compressed it; in the lower, or working, cylinder the air was heated to provide power. The pistons in these two cylinders were connected with rigid rods; they moved in tandem. During a downstroke ambient air entered the supply cylinder while “used” air was exhausted from the working cylinder. During an upstroke air in the supply cylinder was compressed and then pushed into a receiver, while air in the working cylinder expanded under the influence of a flame.
The diagram above follows a cylinderful of air as it makes its way through the engine. In illustration 1 the air is taken into the supply cylinder during a downstroke. In illustration 2, after the air has been compressed during the first part of the upstroke, a valve opens, and it is sent into the receiver. In illustration 3 another downstroke occurs; more air is taken into the supply cylinder while the first batch remains in the receiver. In illustration 4, as the upstroke begins, the air is sent through the regenerator into the working cylinder. In illustration 5 the upstroke continues; the air is heated and it expands, powering the cycle. In illustration 6 a downstroke pushes the heated air through the regenerator and out of the engine.
The regenerator was Ericsson’s key gimmick. It was basically an insulated box, about the size of a mattress, filled with a tangle of tiny wires. The regenerator was supposed to absorb “caloric” from heated air being exhausted and then give it back to air that was about to enter the working cylinder. Ericsson claimed the device allowed caloric, which powered the engine, to be reused; only a small flame was necessary to replace losses from radiation and “heat lost by the expansion of the acting medium,” in Ericsson’s words. This phrase is as close as Ericsson came to recognizing what we now know as the mechanical equivalent of heat, but elsewhere in his writing he gives ample evidence that he greatly underestimated the amount of heat such expansion would use up.
Some caloric enthusiasts of the day went even further, asserting that “a common spirit-lamp” could “drive an engine of a hundred horsepower” or that “one ounce of coal per day” could “pump out the Niagara River.” Today every high school physics student can see that Ericsson’s scheme is thermodynamically impossible, but with the unsettled state of scientific knowledge in the 1850s , it seemed plausible to many educated observers.
The Ericsson ’s engine was enormous—the biggest of any kind built up to that point. It had four working cylinders, each with a piston 14 feet in diameter that moved through a stroke of 6 feet. Total displacement for the four working cylinders was 3,700 cubic feet (6.4 million cubic inches). The supply cylinders were 11.5 feet in diameter, giving the engine an additional 2,500 cubic feet (4.3 million cubic inches) of displacement. The working pistons were connected by walking beams and connecting rods to a central crankshaft that drove twin 32-foot paddle wheels, one on each side of the ship. The engine’s normal operating speed was 9 to 12 revolutions per minute. There is no record of the engine’s external dimensions, but it must have been at least 60 feet in length. Estimated width was 16 feet; its height was about 20 feet.
