How can the formation of NOx be controlled?

The formation of nitrogen oxides (NOx) is a significant concern in combustion processes because these compounds contribute to air pollution and smog. To effectively control NOx emissions, one of the most critical factors is the temperature at which combustion occurs. NOx is primarily formed during combustion at high temperatures, where nitrogen from the air reacts with oxygen.

When excess air is restricted, it reduces the oxygen available for combustion, which can lower the combustion temperature. A lower combustion temperature not only helps in reducing the formation of NOx but also improves combustion efficiency. By managing the air-fuel mixture and striving for optimal combustion conditions, the production of nitrogen oxides can be significantly mitigated.

The other options would not effectively control NOx emissions. Increasing fuel quantity generally raises the combustion temperature and can lead to more NOx formation, while enhancing combustion pressure may also elevate temperatures. Lowering chamber humidity could potentially change combustion characteristics, but it is not as directly significant in controlling NOx emissions as managing air and temperature is.