Combustion Testing

Overview

Engineering reference data for Combustion Testing in combustion engineering.

Key Formulas

Heat Release

$Q = \dot{m} \cdot HV$

Fuel energy release rate.

Air-Fuel Ratio

$AF = \frac{m_{air}}{m_{fuel}}$

Mass of air per mass of fuel.

Excess Air

$EA = \frac{O_2}{21 - O_2} \times 100\%$

From flue gas oxygen measurement.

Variables

Carbon Dioxide (CO2) in Flue Gas

The CO2 content in flue gas is a primary indicator of combustion efficiency and burner performance.

• Low CO2 Content (less than 8%): Indicates inefficient operation where heat is lost up the chimney. Possible causes include:

  • Burner nozzle too small
  • Air leakage into the furnace or boiler
  • Underfiring in the combustion chamber

• High CO2 Content: Typically accompanied by excess smoke. Possible causes include:

  • Insufficient draft
  • Over-fired burner

Smoke Measurement (Fuel Oil Burners Only)

Smoke in the flue gas is a direct indicator of poor burner performance. The amount of smoke is measured using a smoke tester, where particles collected on filter paper are interpreted according to the Bacharach scale.

Common Causes of Smoky Combustion:

• Soot formation on heating surfaces
• Insufficient draft or incorrectly adjusted draft regulator
• Improper fan delivery
• Poor fuel supply, malfunctioning fuel pump, or defective oil-burner nozzle
• Excessive air leaks in the boiler or furnace
• Incorrect fuel-air ratio

Stack Temperature Analysis

The net stack temperature is the difference between the flue gas temperature inside the chimney and the room temperature outside the burner.

• Typical Range: 330 - 500 °F (160 - 260 °C)
• High Temperature Threshold: Net stack temperatures consistently above 700 °F (370 °C) are generally considered too high, indicating significant energy loss.

Common Causes of High Stack Temperature:

• Undersized or incorrectly sized combustion chamber
• Excessive draft
• Over-fired burner or improperly adjusted draft regulator
• Soot formation on heating surfaces

References

• Original Source