, UK) Early versions of the Me 163 had been powered by an earlier design running on a "cold engine" fueled with
Z-Stoff. This fuel tended to clog the jets in the combustion chamber, causing fluctuations in power and potentially explosions. Worse, however, was that the engine could not be throttled, and when the aircraft leveled off after its climb to altitude it quickly accelerated to speeds that caused serious
compressibility issues. The
RLM demanded that a version be developed with a throttle. Virginia, USA. During this period Walter had also been working with a new fuel known as
C-Stoff that gave off significant heat and was thus known as the "hot engine". C-Stoff was a mix of 30%
hydrazine hydrate, 57%
methanol, and 13% water, with a small amount of potassium-copper-cyanide. The oxidizer, known as
T-Stoff, consisted of an 80%-concentration
hydrogen peroxide-based formulation. The two
reacted violently on contact. The violent combustion process resulted in the formation of water, carbon dioxide and nitrogen, and a huge amount of heat sending out a superheated stream of steam, nitrogen and air that was drawn in through the hole in the mantle of the engine, thus providing a forward thrust of approximately 17 kN (3,820 lbf). To address the throttling issue, the new engine included
turbopumps with two settings. The pumps were driven by a single turbine, powered by steam created by decomposing the T-Stoff with a wire mesh
catalyst. Combined with a mechanical throttle, this provided four power settings from idle to full power for climbing. In practice it was found that throttling the engine dramatically decreased its
fuel economy to the point that it did not extend the endurance of the aircraft as expected. This version was put into the Me 163B in spite of this problem. The ultimate solution to the throttling problem was the B and C series of the engine. These engines used two combustion chambers, the original one (retroactively given
the name Hauptofen), and a second, smaller
Marschofen chamber directly beneath the main
Hauptofen chamber, tuned to provide the cruise power needed for high-speed level flight, about . This chamber provided that power at peak efficiency, so it did not suffer from the problems found while throttling on the original models. The throttle on the original combustion chamber was removed, and throttling was instead provided by turning the main engine on and off. This new version dramatically improved cruise endurance, with overall flight times improving from eight to twelve minutes, a 50% improvement. It was also mechanically simpler as the turbopumps were no longer throttled. The engine was an integral design with all components of the drive, with the exception of fuel tanks, locked in a cubical frame — this frame was discarded for the 109-509C dual-chamber design. ==Variants==