Effects of Ambient Air Temperature on Gaseous Emissions of Turbofan Engines

Abstract

This study presents the results of analyses related to the effects of ambient air temperature (ranging from 5.2 to 23.9 degrees C) on certain engine performance parameters and gaseous emissions, carbon monoxide and nitrogen oxides. The data set used in the analyses was developed from gaseous-emission measurements of aircraft turbofan engines, during routine test-cell operations after overhauls. The engine focused on is the CFM56-7B26. Because the data were recorded in a continuous manner, all of the parameters have been characterized throughout the operations between idle to takeoff power. Two important parameters, combustion efficiency and specific fuel consumption, are also identified for all of the power settings, and are used to evaluate the effects of ambient air temperature on emissions. The results suggest that ambient air temperature is negatively correlated with thrust and pressure ratios, whereas it is positively correlated with exhaust-gas and combustor-inlet temperatures. In addition, the effects of ambient air temperature on thrust, combustor-inlet pressure, and overall and high-pressure compressor pressure ratios are higher at higher power settings than at lower power settings. Furthermore, the higher the ambient air temperature is, the higher are the combustion efficiency and specific fuel consumption, particularly at low power settings. At ground-idle power settings, the specific fuel consumption is found to be 41 and 24 g/kNs for above and below 14.0 degrees C of ambient air temperature. The nitrogen oxides results are generally found to be lower than the International Civil Aviation Organization nitrogen oxides values, and the results point out, as anticipated, a tendency toward higher nitrogen oxides at higher ambient air temperatures. Carbon monoxide emissions at low power settings are found to be highly variable compared to those for the International Civil Aviation Organization values, due to the fact that the carbon monoxide emissions are strong functions of engine power at low power settings, and any difference in engine power leads to substantial differences in carbon monoxide emissions. Therefore, this difference is addressed to the difference in idle power assumption of the International Civil Aviation Organization. The effects of ambient air temperature on carbon monoxide emissions also suggest a negative correlation, particularly at low power settings, whereas it is not as discernible as with the nitrogen oxides emissions.