A high CO2 reading in the gases of combustion is a sign of what?

A high CO2 reading in the gases of combustion is indeed a sign of high combustion efficiency. When combustion is efficient, more of the fuel's carbon is converted into carbon dioxide rather than into other products like carbon monoxide or unburned hydrocarbons. This indicates that the fuel is being burned completely under ideal conditions, maximizing energy output and minimizing waste. In efficient combustion, the reaction between fuel and oxygen is optimized, resulting in a higher concentration of CO2 in the exhaust, which is generally viewed as an indicator that the fuel is being fully consumed.

In lower combustion efficiency scenarios, one would typically see higher levels of pollutants like carbon monoxide and unburned fuel due to incomplete combustion. This reflects that not all carbon from the fuel was converted into CO2, which is not the case when high CO2 levels are present.