Adiabatic flame temperature dependence: The adiabatic flame temperature of a fuel–air system depends on the initial temperature of which streams?

Introduction / Context:
Adiabatic flame temperature (AFT) is the theoretical maximum temperature achieved by complete combustion without heat loss to surroundings and without dissociation (or including dissociation in a refined model). AFT sets upper bounds for thermal efficiencies and materials selection.

Given Data / Assumptions:

• Closed adiabatic control volume; no heat loss or shaft work.
• Complete combustion to equilibrium products.
• Specified initial temperatures of reactants (fuel and oxidizer).

Concept / Approach:
Energy conservation gives: sensible enthalpy of products at AFT equals chemical heat release plus sensible enthalpies of reactants at their inlet temperatures. Preheating either fuel or air increases the reactant sensible enthalpy term, raising the AFT; preheating both amplifies the effect. Thus AFT depends on the initial temperature of both streams.

Step-by-Step Solution:
Write balance: Σ h_products(T_ad) = Q_release + Σ h_reactants(T_in).Increase T_in,fuel → larger Σ h_reactants → higher T_ad.Increase T_in,air → same effect; both together give the largest increase.Therefore, AFT depends on both fuel and air initial temperatures.

Verification / Alternative check:
Calculated flame temperatures for gas turbines and furnaces rise with air preheat (regenerators/recuperators) and with fuel preheat, consistent with practice.

Why Other Options Are Wrong:
Options limiting dependence to one stream ignore symmetry of the energy balance. Claiming 'neither' contradicts conservation of energy.

Common Pitfalls:

• Neglecting dissociation at very high temperatures, which moderates the increase.
• Confusing adiabatic temperature with actual flame temperature under heat losses.

Final Answer:
both (a) & (b)