Which gas is considered the best lean indicator for an engine during combustion?

Oxygen is considered the best lean indicator for an engine during combustion due to its pivotal role in the combustion process. When an engine is operating in a lean condition, which means there is more air (and hence more oxygen) in the combustion chamber relative to the amount of fuel, the unburned oxygen will be present in the exhaust gases. Measuring the concentration of oxygen allows for an accurate assessment of how effectively the combustion process is occurring and provides insight into whether the engine is receiving too much air compared to fuel.

This oxygen measurement is crucial as it helps in tuning the engine for optimal performance, fuel efficiency, and reduction in harmful emissions. If the oxygen levels are too high, it can indicate a lean mixture, which may lead to incomplete combustion and can cause engine knocking or damage over time. Therefore, monitoring oxygen levels is a reliable way to gauge the combustion efficiency and overall engine health.

While the other gases mentioned play roles in combustion and emissions, they do not serve as direct indicators of lean combustion in the same way oxygen does. Nitrogen typically indicates engine performance but does not directly affect combustion optimization, hydrogen is mainly produced during certain fuel processes, and carbon dioxide is a product of combustion rather than an indicator of the air-fuel mixture