A fuel delivery system for a combustion turbine engine, comprising: a fuel line having a fuel compressor and parallel branches downstream of the fuel compressor: a cold branch that includes an after-cooler; and a hot branch that bypasses the after-cooler; a rapid heating value meter configured to measure the heating value of the fuel from the fuel source and transmit heating value data relating to the measurements; means for controlling the amount of fuel being directed through the cold branch and the amount of fuel being directed through the hot branch; and a fuel-mixing junction at which the cold branch and the hot branch converge; wherein the fuel-mixing junction resides in close proximity to a combustor gas control valve.