Control and Reduction of Aircraft Turbine Engine Exhaust Emissions

Abstract

The aircraft turbine engine exhaust emissions in the category of air pollutants, that are generated to some degree, consist of carbon monoxide (CO), unburned or partially oxidized hydrocarbons (H/C’s), carbon particulates as soot or smoke, oxides of nitrogen (NO_x) and sulfur oxides (SO_x). The primary concern associated with these emissions is their possible impact on the environments of major airport localities, where the exhaust emissions resulting from high volumes of localized aircraft operations may tend to be concentrated.

To minimize any adverse effects on the environments of airport localities, significant development efforts have been conducted and are underway within the industry and government to provide technology for the control and reduction of the levels of any objectionable emissions. To date, extensive engine evaluations have been conducted to determine the exhaust emissions characteristics of both production and development aircraft turbine engines. Significant progress has also been made in the development of technology for the design of engine combustors with reduced smoke emission levels. As a result of these latter efforts, combustors with virtually non-visible smoke emission levels have been developed and are being placed into service.

More recently, some promising results have been obtained in efforts to develop improved fuel atomization and primary zone stoichiometry control methods for reducing CO and H/C’s emissions levels. Essentially, these investigations involve the development of methods for improving combustion efficiency performance at the low power operating conditions. It is anticipated that, with sufficient development, these efforts will result in the definition of combustor designs with improved low power combustion efficiency performance and, therefore, that future engines will have significantly lower CO and H/C’s emissions levels than those of current technology engines.

Because the NO_x emissions characteristics of any given engine are directly and strongly related to its combustor inlet air temperature levels, obtaining significant reductions in the levels of these emissions by combustor design techniques appears to be a more difficult task. Recent investigations have shown that some degree of suppression is attainable by design approaches which involve improved control of the primary combustion zone stoichiometry and gas residence time. Also, these investigations have shown that reductions in the levels of these emissions are attainable with the use of water injection into the combustor. However, extensive additional research and development efforts to provide NO_x emissions abatement technology for use in turbine engines appear to be needed.