All commercial small-scale turbogenerator systems use the positive Brayton gas turbine cycle, where
the inlet air is compressed to a higher pressure, ignited and used to drive the turbine. A less common way
of operating a gas turbine is illustrated in Fig. 11. Combustion gases enter a turbine at atmospheric
pressure. A partial vacuum is created at the turbine exit by a compressor, which draws the gases through
the turbine. On leaving the turbine, the gases are cooled by a heat exchanger before being drawn into the
compressor. Although the compressor pulls the gases through the system, enough power is developed by
the turbine to drive the compressor and an alternator. T m his mode of gas turbine operation is known as the
inverted Brayton cycle