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Heat Capacity Changes Predict Nitrogen Oxides Reduction by Exhaust Gas Recirculation
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Abstract
Earlier work has demonstrated that exhaust gas recirculation (EGR) decreases peak combustion temperature and thus reduces the concentration of nitrogen oxides (NOx) in spark ignition engine exhaust. The present authors hypothesized that NOx formation is primarily affected by the heat capacity of the combustion gases and recycled exhaust. The hypothesis was tested in an experimental program involving the admission of inert gases such as He, Ar, H2, and CO2, and water in place of EGR.
In addition to confirming the validity of the original hypothesis, the test data also indicated that engine output and efficiency were significantly affected by the heat capacity of the combustion gases. The authors conclude that EGR functions by increasing the heat capacity of the working fluid, and demonstrates that the correlative changes in NOx and engine performance can be predicted from heat capacity considerations. These studies, together with further work on combustion pressures, should be useful in evaluating various NOx control techniques.
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Ohigashi, S., Kuroda, H., Nakajima, Y., Hayashi, Y. et al., "Heat Capacity Changes Predict Nitrogen Oxides Reduction by Exhaust Gas Recirculation," SAE Technical Paper 710010, 1971, https://doi.org/10.4271/710010.Also In
References
- Newhall H. K. “Control of Nitrogen Oxides by Exhaust Recirculation-A Preliminary Theoretical Study.” SAE Transaction 76 1967 paper 670495
- Benson J. D. “Reduction of Nitrogen Oxides in Automobile Exhaust.” Paper 690019 presented at SAE Automotive Engineering Congress Detroit January 1969
- Wimmer D. B. McReynolds L. A. “Nitrogen Oxides and Engine Combustion.” SAE Transactions 70 1962 paper 380 E
- Huls T. A. Nickol H. A. “Influence of Engine Variables on Exhaust Oxides of Nitrogen Concentrations from a Multi-Cylinder Engine.” Paper 670482 presented at SAE Mid-Year Meeting Chicago May 1967
- Starkman E. S. Stewart H. E. “An Investigation into the Formation and Modification of Emission Precursors.” Paper 690020 presented at SAE Automotive Engineering Congress Detroit January 1969
- Eyzat P. Guibet J. C. “New Look at Nitrogen Oxides Formation in Internal Combustion Engines.” SAE Transactions 77 1968 paper 680124