Why General Electric put an airplane engine on a truck and drove it to the top of Pikes Peak.
- By Donald Sherman
- Air & Space magazine, May 2001
(Page 2 of 4)
But the pursuit of efficiency prompted engineers to give turbochargers another chance. The typical piston engine converts only one-third of the energy from its fuel to useful work. Another third is squandered to friction and cooling-system losses, and the remainder is spit out the exhaust pipe as waste heat. A turbocharger could recover some of that exhaust energy.
In the United States, Sanford Moss, a 22-year-old mechanical engineering student at the University of California at Berkeley, had an inspiration during a class on thermodynamics and hydrodynamics: Why not combine the best aspects of internal combustion and steam turbines? A British scientist had patented the same brainstorm a century earlier, but that didn’t diminish Moss’ enthusiasm for spinning heat into horsepower. In his master’s thesis, Moss proposed replacing a locomotive’s thumping piston engine with a smoothly humming gas turbine. (He simply picked the wrong vehicle; today many warships are powered by turbines.)
In 1901, he began studies and research at Cornell Uni-
versity, and after working for a year, persuaded a spherical combustion chamber to deliver a continuous source of flaming hot energy. Gas-
es from the chamber were directed against a five-inch-diameter turbine wheel; Moss wrote that it was probably the first time a turbine had ever been driven by combustion gases in the United States—or perhaps anywhere.
Moss’ 1903 doctoral thesis, “The Gas Turbine, an Internal Combustion Prime Mover,” caught the eye of General Electric executives. Formed in 1892 as the amalgamation of the leading AC and DC power companies, GE was responding to mounting consumer demand by constructing ever larger electricity generating and distribution systems. Moss came to GE at the very time when reciprocating engines for power generation were being replaced by more efficient steam turbines.
He worked for four years at GE on gas-turbine reliability, but he couldn’t crack the efficiency nut. His best turbine consumed four gallons of kerosene per hour for every horsepower produced, versus only one gallon per horsepower-hour for the day’s best reciprocating engines. The materials available in 1907 could not withstand the high temperatures needed to achieve better efficiency in a turbine, so GE shelved its research. But back in Europe, the war was heating things up nicely.
The advent of the Great War focused intense interest on packing more air into engines to gain altitude performance. In Germany, Mercedes, Maybach, and BMW took a brute-force approach, building bigger engines that also squeezed the air-fuel mixture to a greater degree during the piston’s compression stroke. Power had to be limited at sea level or the engines would fail structurally, so BMW’s 19.1-liter engine, with a compression ratio of 6.4 to one (4 or 5 to one was more typical), had three throttle levers. If all three were opened at sea level, the engine would destroy itself, so the throttles were opened progressively as the airplane climbed. The first-stage throttle delivered 185 horsepower for take-off at a modest 1,400 rpm. The other two throttles were opened in succession above 6,500 feet, permitting higher engine speeds without the usual loss of power because the engine’s high-compression design squeezed more energy out of the thinner air. Rumpler C.IVs equipped with 260-horsepower “over-dimensioned” Mercedes engines and oxygen for their crews flew reconnaissance missions above 20,000 feet, well beyond anyone’s reach. The Germans were slower than the British and French at sea level, but at altitude they ruled.