Nitrogen Oxide
Nitrogen Oxide and Combustion Catalysts*
Ocean going vessels are now facing increased pressure to reduce the air pollution emitted during both their voyages and while in port. Public attention to the fact that emissions are contributing to health, environmental and economic concerns around the glob has had a huge impact on the marine operator to bring levels of certain contaminants into line with the limits imposed by the International Maritime Organization (IMO) and, in particular, those outlined in MARPOL Annex VI, Regulation 13. Nitrogen oxides, specifically NO and NO2, known collectively as NOx are highly toxic and contribute to upper atmospheric pollution through the formation of ozone.
There are only two ways to reduce nitrogen oxide (NOx) in engine exhaust: 1) cool the flame and 2) convert NOx to N2. The most commonly used methods of cooling the flame are by adding water to the fuel, de-rating the engine or by utilizing some form of catalyst technology. Recently, much attention has been focused on exhaust gas scrubbing, a type of selective catalytic reduction technology and yet, in addition to the expenditure of the equipment purchase it brings with it the additional burden of ongoing maintenance which can become both costly and time consuming.
FuelSpec® combustion catalysts are a viable option and, with the further benefit of reducing fuel consumption, provide perhaps an even greater advantage to the user. The FuelSpec® line of combustion catalysts, containing iron and magnesium, increase combustion efficiency leading to reduced fuel consumption plus reduce particulate matter and NOx.
Mechanism of Action
The formation of nitrogen oxides is a high energy reaction occurring at combustion temperatures. The naturally occurring nitrogen dimer (N2) has a triple bond; the nitrogen atoms share three electrons in order to complete their octets. This is an unusually strong bond and takes considerable energy to break. It is interesting to note that at the accepted combustion temperature of 2,500º C., only a few hundred ppm of nitrogen oxides are formed.
Research confirms that several percent of the fuel burns incompletely (particulate matter and carbon monoxide) or exhausts as unburned hydrocarbon. The combustion process is continuing at the end of the power stroke indicated by higher exhaust temperatures as compared with catalyst use.
The combustion reaction is very high energy. Based on 2nd order reaction rates required for the fuel to complete combustion during the time of the power stroke, we estimate that the rate of reaction if 35,000 moles¯¹ second¯¹ at 2,500º C. with an estimate that the reaction rate has decreased to 5,000 at 2,450º, the Heat of Activation is 2.58 x 10^5 calories per mole.
We postulate that the mechanism for the combustion catalyst to reduce NOx formation is based on cooling, or more succinctly, the time the reaction mixture is at the combustion temperature. The combustion catalyst causes the reaction to take place at a faster rate, more energy is absorbed by the mechanical cycle of the piston moving, expanding the chamber and reducing the temperature, leading to less time at elevated temperatures. Laboratory and field observations have demonstrated that use of FuelSpec® results in a significant reduction of nitrogen oxides in reciprocating engine exhausts. We have observed this phenomenon in fuels ranging from low molecular weight aliphatic fuels to those containing high molecular weight condensed aromatic compounds.
The Advantages of Using FuelSpec® Are:
- Energy is not lost by reducing temperature by the addition of water.
- Expensive catalyst systems and injections systems for reducing NOx to N2 in the exhaust stream are not required.
- The fuel born combustion catalyst reduces fuel consumption resulting in savings to the operator and reduction of particulate matter while meeting NOx requirements.
*Based on ‘NOx Supression with Combustion Catalysts‘ by Dr. Walter R. May of SFA International.
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