NOx Abatement

• NOx are the various possible oxides of nitrogen, NO, NO2, NO3 and NO4, of which NO2 is the main emission of concern.
• There are two general approaches to NOx abatement: prevent NOx forming; and post combustion conversion back to N2 and O2. Most abatement technologies have some aspects of both.
• For more details about NOx causes and formation see INDEPTH

INDEPTH
NOx are formed from elements present in all air, the nitrogen N2 that makes up about 79% of our atmosphere, and the O2, which makes up the bulk of the rest. It arises when these two elements are made hot together, so all combustion processes create NOx. The longer and the hotter the combustion processes the more NOx that are formed. Since higher combustion temperatures can lead to greater thermal efficiencies some trade-offs between high efficiencies or low NOx are possible.

Some fuels have nitrogen embodied within their molecules – Nitrogen is an essential constituent of all life, including that which formed the oil – but has not been a significant contributor to the NOx. As engines get better at avoiding NOx formation, the contribution of NOx from fuel will become more evident.