Theoretical studies of variable geometry : hot section of the miniature jet engine

The aim of this article is to present the results of theoretical studies regarding the use of variable geometry hot section of a miniature gas turbine. The variable geometry combustor and variable area nozzle concepts for GTM-120 miniature jet engine are presented in particular. Recent trends of propulsion system size reduction, low-emission combustion and improved fuel efficiency have been considered. A system of variable geometry combustor and variable area nozzle has been proposed as solution. The basic zero-dimensional analytical models for variable geometry combustor and variable area nozzle are developed. Chemkin based model shows significant NOX/CO emissions reduction and combustor outlet enthalpy increases with the use of variable geometry combustor chamber. The analytical model of the variable area nozzle has been proposed. It shows turbine effectiveness increase across its operating range by raising the compressor working line. As a result, noticeable turbine stage efficiency increase has been obtained. Finally, physical implications and future work plans regarding variable geometry hot section of miniature gas turbines are discussed.