Gas turbine combustion with methane: finding air-fuel ratio for 1200K

[simonre7]

Again another homework question, all help greatly appreciated


A gas turbine plant is fuelled by Methane,. After compresssion the air and fuel enter the combustion chamber at a temp of 600K and excess air is supplied in order to limit the temp of the combustion products to 1200K after steady flow, adiabatic combustion.

1) Illustrate the combustion process on a temp-enthalpy axes (have got this question right i believe but wouldn't hurt to double check my graph)

2) Find the volumetric air-fuel-ratio used

3) What air-fuel-ratio would be required to achieve the maximum temp of the combustion products?


thank you in advance

 

[member 553083]

!1) The graph would show a line that starts at 600K on the temperature axis and 0 on the enthalpy axis. Then, as combustion occurs, the temperature will rise and the enthalpy will increase until it reaches 1200K on the temperature axis and the maximum enthalpy for the process on the enthalpy axis. 2) To find the volumetric air-fuel-ratio, you need to calculate the ratio of the mass of air to the mass of fuel. This can be found using the ideal gas law (PV = nRT). 3) To achieve the maximum temperature of the combustion products, the air-fuel ratio must be at the stoichiometric ratio, which is the ratio of the mass of oxygen to the mass of fuel required for complete combustion.