Learn & Understand

The Unavoidable Product: Carbon Dioxide and Climate

Carbon dioxide in flue gas was long seen merely as a marker of good combustion — but it is also the central molecule of the climate crisis. Every time a carbon-based fuel burns, it inevitably produces carbon dioxide, and understanding this unbreakable link between combustion and CO2 is essential to grasping both efficiency and the warming of the planet.

Burning Carbon Makes CO2

The energy in fossil and biomass fuels comes largely from carbon, and releasing that energy by burning combines the carbon with oxygen to form carbon dioxide. This is not a side effect to be engineered away — it is the reaction itself. As long as we burn carbon-based fuels for energy, CO2 is the unavoidable product, produced in direct proportion to the fuel consumed.

A Marker of Good Combustion

Historically, engineers watched CO2 as a sign of efficient burning: a high CO2 percentage in the flue meant the fuel was combusting fully with little wasteful excess air. Rising CO2 and falling oxygen both signal a well-tuned fire. For combustion control, more CO2 in the exhaust was traditionally a good thing — a sign the fuel's energy was being released completely.

The Climate Dimension

The same molecule that marks a good fire is the leading driver of climate change. Carbon dioxide traps heat in the atmosphere, and the vast quantities released by burning fossil fuels have raised its concentration and warmed the planet. The link between combustion and CO2, once a mere efficiency indicator, is now the crux of humanity's energy and climate dilemma.

Capturing the Carbon

Because CO2 cannot be eliminated from burning carbon, one response is to capture it from the flue gas before it reaches the atmosphere and store it underground — carbon capture and storage. Knowing how much CO2 an exhaust contains is the starting point for such efforts. The molecule that once merely tuned a flame is now something we increasingly try to catch.

Estimating Flue CO2

To relate excess air to flue CO2, use the Flue Gas CO2 Calculator. Check the oxygen side with the Flue Gas Oxygen Calculator, and the total exhaust with the Flue Gas Volume Calculator.