Designing small gas turbine engines for low noise and clean exhaust

Abstract

Preliminary results of design studies involving the use of small gas turbine engines to reduce noise and exhaust emissions from aircraft are reviewed. Comparisons of reciprocating engines with small turboprop engines indicate lower carbon monoxide and hydrocarbon emissions for the latter engine type at all power settings. The piston engines show somewhat lower nitrogen oxide production above 20 percent power, consistent with the fuel-rich operation of such engines. Small gas turbine engines have higher CO and unburned hydrocarbon emissions at low power and lower NO/sub x/ levels at higher power than large gas turbines. The comparatively poor performance of the small engines at low power is due primarily to operation at low combustor pressure and temperature as well as to a high ratio of combustor surface area to volume and to the use of relatively simple and low-cost combustor and fuel systems. The good NO/sub x/ performance at high power is due principally to lower levels of combustor inlet pressure and temperature. Early development data indicate that major reductions in CO and unburned hydrocarbons can be achieved with only small increases in NO/sub x/ by means that do not imply appreciable changes in the size, weight, or complexity of themore » gas turbine engines.« less