Which two methods are effective in decreasing NOx emissions?

The most effective methods in decreasing NOx emissions involve utilizing specially designed burners and adjusting the fuel to air ratio. Special burners are designed to optimize combustion efficiency and reduce peak flame temperatures, which is essential because NOx emissions are primarily formed at the high temperatures typically found in the combustion process. These burners may incorporate features like flue gas recirculation or other technologies to lower flame temperatures.

Decreasing the fuel to air ratio is also crucial because a leaner fuel mixture (more air relative to fuel) generally results in lower combustion temperatures. This reduction in temperature contributes significantly to lowering NOx production, as the formation of NOx is significantly influenced by the high temperatures reached during combustion. The combination of these two methods—using special burners and adjusting the fuel to air ratio—creates an environment that effectively mitigates NOx emissions while maintaining combustion performance.

The other options, while they may include components that can affect emissions, do not directly combine the most effective strategies for specifically addressing NOx reduction in the same way as the selected answer.