A gas turbine (Brayton cycle) at a natural gas pipeline pumping station uses natural gas (methane) as its fuel. Air is drawn into the turbine at 101 kPa and 25°C; and the pressure ratio of the turbine is 8. The natural gas fuel is injected into the combustor such that the excess air is 40 percent. Determine the net specific work produced by this engine and the engine’s overall thermal efficiency.