Articles

What are combustion temperature, calorimetric combustion temperature, theoretical combustion temperature, and actual combustion temperature? What about combustion efficiency?

  1. Combustion temperature
    Temperature in the reaction zone or flame zone. In engineering, the peak flame temperature and the average furnace temperature are typically of interest.

  2. Calorimetric combustion temperature
    An equivalent combustion temperature inferred under calorimeter conditions (forced cooling, specific boundary conditions), mainly for standardized comparison and not directly equal to in-furnace flame temperature.

  3. Theoretical combustion temperature (adiabatic theoretical temperature)
    Assumptions:

  • Complete combustion
  • Adiabatic (no heat loss)
  • Products reach the same temperature
    Adiabatic flame temperature TadT_{ad} from energy conservation.
    Typical levels (air combustion, ambient feed, adiabatic, approximate):
  • Methane-air: Tad≈2200 KT_{ad} \approx 2200\ \text{K}
  • Hydrogen-air: Tad≈2400 KT_{ad} \approx 2400\ \text{K}
    Actual values are lower due to α>1\alpha>1, heat losses, and dissociation.
  1. Actual combustion temperature
    Significantly affected by:
  • Excess air: α\alpha increases -> more dilution -> lower temperature
  • Preheating: air/fuel preheat -> higher temperature
  • Heat losses and charge heat absorption -> lower temperature
  • High-temperature dissociation (CO2,H2OCO_2,H_2O partial dissociation) -> lower temperature
  1. Combustion thermal efficiency (fraction of chemical energy converted to useful heat)
    Common form: ηcomb=1−qlossQin\eta_{comb} = 1 - \dfrac{q_{loss}}{Q_{in}}, where qlossq_{loss} includes incomplete combustion loss (COCO, unburned carbon), flue-gas sensible heat loss, heat loss to surroundings, etc. Industrial kilns usually manage overall system efficiency or specific energy consumption.