Oxides of Nitrogen

Oxides of Nitrogen, why should we care?

The various oxides of nitrogen are considered as Greenhouse Gases, as they have impact on our climate arising from their (inter)action with ozone, O3, in the stratosphere, which is compounded in sensitivity by the length of time (approximately 110 years) that these compounds take to breakdown under influence of UV.

The source of nitrogen is from atmospheric fraction, being the most common gas in the atmosphere, and it is also found in fuel stock, and it is present in the combustion process as a consequence, where oxides will form. Nitrogen is otherwise quite an inactive gas in its N-N form, although the bonds between N atoms is very strong, and is one of the reasons that it can be normally found in explosive materials.  

NOx

For nitrous oxide byproducts exhausted by each jet engine, the actual effect or change is not quantified yet as nitrous oxide formation is complex. However, a couple of matters can be considered directly from the current information:

Thermal NOx

Requires high temperature to achieve the reaction.

N2 + O → NO + N N + O2 → NO + O N + OH → NO + H

Prompt NOx 

First proposed by Charles Fenimore in 1971. This comes from atmospheric nitrogen combining in the lower temperature parts of combustion. It becomes more important with control of the Thermal NOx mitigation. 

N2 + O → NO + N N + O2 → NO + O N + OH → NO + H' + N´ + O2 → NO + O´ HCN + O2 → NO + CO + H´

Fuel NOx

Release of NOx from the nitrogen in the fuel itself. 

All 3 of the formations of NOx are impacted by the STC, the lower fuel burn leads directly to lower NOx, and the lower combustion temperatures leads to lower Thermal NOx.

How much more? watch this space, but it is going to be a greater change than the CO2 percentage change, yet to be fully quantified. 

How  Much NOx do we produce?

A quick review of the NOx emissions from a turbofan engine design software, GasTurb14, indicates that for every metric ton of jet fuel consumed, somewhere between 0.5-1.0kg of NOx can be expected to be emitted. Thus:

• Reducing fuel burn reduces these emissions. 
• Reducing peak combustion temperatures reduces these emissions.