Emissions Reduction Technologies for Military Gas Turbine Engines

Future military gas turbine engines will have higher performance than current engines, resulting in increased compressor and combustor exit temperatures, combustor pressures, and fuel-air ratios with wider operating limits. These combustor characteristics suggest undesirable exhaust emission levels of nitrogen oxides and smoke at maximum power and higher carbon monoxide and unburned hydrocarbons at low power. To control emission levels while improving performance, durability and cost, requires major advances in combustor technology. Current emissions control approaches as applied to conventional swirl-stabilized combustors include rich- and lean-burn strategies, together with staged combustion. These approaches, even in fully developed form, may not be sufficient to satisfy the projected design requirements. Unconventional combustor configurations may become necessary. Different engine cycles other than the standard Brayton cycle may also be used for special applications in order to avoid the use of excessive combustion temperatures. The paper presents an overview of the currently utilized emissions control approaches, comparing their performances and likely potential for meeting future requirements. Experimental results are presented for two non-conventional combustor configurations that have shown promise for advanced engine applications. A brief discussion is offered on cycle changes that could result in lower peak temperatures while maintaining advanced performance.