Butane gas and air enter a furnace at a temperature of $25C$ and a pressure of $100$ kPa. The products of combustion exit at a temperature of $1000K$ and a pressure of $100$kPa. The heat transfer during this process is measured to be $1\mathrm{.}2$ million kJ$/$kmol of butane. Calculate the amount of excess air that enters into the furnace.