Calculate modified combustion efficiency from excess CO2 and CO, or solve for the missing concentration from any two values in ppmv.
Note: MCE is a combustion completeness metric based on CO and CO2. It is not the same as the thermal combustion efficiency used for boilers/furnaces (which is based on useful heat output versus fuel energy input).
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Modified Combustion Efficiency (MCE) Formula
The calculator uses excess carbon dioxide and excess carbon monoxide to calculate modified combustion efficiency. “Excess” means the measured concentration above the background concentration.
MCE = \frac{\Delta CO_2}{\Delta CO_2 + \Delta CO} * 100- MCE = modified combustion efficiency, as a percent
- ΔCO2 = excess carbon dioxide concentration, in ppmv
- ΔCO = excess carbon monoxide concentration, in ppmv
If you enter ΔCO2 and ΔCO, the calculator solves directly for MCE.
\Delta CO_2 = \frac{e * \Delta CO}{1 - e}- e = MCE divided by 100
- ΔCO2 = excess carbon dioxide concentration, in ppmv
- ΔCO = excess carbon monoxide concentration, in ppmv
If you enter MCE and ΔCO, the calculator rearranges the MCE equation to solve for ΔCO2. MCE must be greater than 0% and less than 100% for this calculation.
\Delta CO = \frac{\Delta CO_2 * (1 - e)}{e}- e = MCE divided by 100
- ΔCO = excess carbon monoxide concentration, in ppmv
- ΔCO2 = excess carbon dioxide concentration, in ppmv
If you enter MCE and ΔCO2, the calculator rearranges the MCE equation to solve for ΔCO. MCE must be greater than 0% and less than 100% for this calculation.
Typical MCE Ranges and Interpretation
MCE is often used to describe how completely carbon in fuel is converted to CO2 instead of CO. Higher values usually indicate more efficient flaming combustion. Lower values indicate more incomplete combustion.
| MCE range | General interpretation | Common combustion condition |
|---|---|---|
| 98% to 100% | Very complete combustion | Clean, well-ventilated flaming combustion |
| 95% to 98% | High combustion efficiency | Mostly flaming combustion with some incomplete oxidation |
| 90% to 95% | Moderate combustion efficiency | Mixed flaming and smoldering combustion |
| Below 90% | Lower combustion efficiency | More smoldering or oxygen-limited combustion |
Input Checks for MCE Calculations
| Value | Allowed input | Reason |
|---|---|---|
| ΔCO2 | 0 or greater | Excess concentration should not be negative. |
| ΔCO | 0 or greater | Excess concentration should not be negative. |
| MCE | 0% to 100% | MCE is a percentage of carbon emitted as CO2 relative to CO2 plus CO. |
| Solving for ΔCO or ΔCO2 | MCE must be between 0% and 100%, not equal to either endpoint | The rearranged formulas require division by e or by 1 – e. |
Example Calculations
Example 1: Calculate MCE from ΔCO2 and ΔCO
Suppose you measured:
- ΔCO2 = 1800 ppmv
- ΔCO = 90 ppmv
MCE = \frac{1800}{1800 + 90} * 100MCE = 95.24\%
The modified combustion efficiency is 95.24%.
Example 2: Calculate ΔCO from MCE and ΔCO2
Suppose you know:
- MCE = 96%
- ΔCO2 = 2400 ppmv
First convert MCE to a decimal:
e = 96/100 = 0.96
Then solve for ΔCO:
\Delta CO = \frac{2400 * (1 - 0.96)}{0.96}\Delta CO = 100\ \text{ppmv}The excess carbon monoxide concentration is 100 ppmv.
FAQ
What does modified combustion efficiency mean?
Modified combustion efficiency is the percentage of emitted carbon, counted as CO2 and CO, that appears as CO2. A higher MCE means more of the carbon was oxidized to CO2, which usually indicates more complete combustion. A lower MCE means a larger share of carbon was emitted as CO, which usually indicates more incomplete combustion.
Why does the formula use excess CO2 and excess CO?
The formula uses excess concentrations so background air does not distort the result. To get excess concentration, subtract the background concentration from the measured plume concentration. For example, if plume CO is 125 ppmv and background CO is 2 ppmv, then ΔCO is 123 ppmv.
Can MCE be exactly 100%?
MCE can equal 100% only when ΔCO is 0 and ΔCO2 is greater than 0. In real combustion measurements, a value near 100% may occur for very efficient combustion, but exact 100% is uncommon because some CO is usually present. If you are solving backward for ΔCO2 or ΔCO, MCE cannot be exactly 0% or 100% because the rearranged formulas would require division by zero.
