59983 - Air-Steam Dual Loop Gas Turbine Engine With Pulse Detonation Combustion 

The incorporation of Pulse Detonation Combustor (PDC) into a gas turbine engine provides significant advantages in terms of specific work output and thermal efficiency. A pulse- detonation-based gas turbine engine could show performance gains in both propulsion and stationery power generation applications. The operation of a pure pulse detonation engine (PDE) used in propulsion applications includes: (i) admission of air into the Detonation Chamber (DC) followed by fuel injection, detonation initiation and mixture burnout in a propagation detonation wave; (ii) quasi-steady expansion of detonation products through a supersonic nozzle; and (iii) steady expansion of the remaining detonation products through the nozzle during filling of DC with fresh air.

But, if the same principle is applied to conventional gas turbines, a quasi-steady expansion of detonation products through the turbine results in unsteady operation of turbine. This requires a modification in the design and construction of a turbine unit. Further, the detonation products during quasi-steady expansion are initially at a very high temperature (over 2500 K) and hence, they cannot be expanded in the turbine as it is.

                In the present work, to overcome the difficulties surfaced in replacing the Steady Flow Combustor (SFC) of conventional gas turbine engine with Pulse Detonation Combustor (PDC), and also use the existing steady flow gas turbine as it is, the following design modifications are made: (i) quasi-steady expansion of detonation products through a supersonic nozzle into the shell of Exhaust-to-Water Heat Exchanger (EWHE) and (ii) steady expansion of the remaining detonation products directly through low pressure (LP) turbine. The quasi-steady expansion of detonation products into the shell causes a significant pressure gain in the shell and then the they are expanded in high pressure (HP) turbine initially and later on in the LP turbine along with steady expansion of detonation products. Preheated water is also injected into the shell so as to control the temperature of detonation products and thereby keeping the temperature of gases below 1500 K before entering the gas turbine unit.

            Air-Steam Dual Loop Gas Turbine (ASDLGT) engine consists of a gas turbine engine, (operating by the Brayton cycle) with air as the working fluid and a steam turbine engine (operating by the Rankine cycle) with steam as the working fluid. The steam circuit comprises feed pump, EWHE, steam turbine and condenser. The feed water (condensate) is heated, boiled and superheated in the EWHE and then expanded in the steam turbine to produce work. After expansion in the steam turbine, the steam is condensed in the condenser and recycled through the system.

            The thermodynamic cycle of operation of ASDLGT engine is analyzed based on quasi-steady state one dimensional formulation, and a computer code is developed in MATLAB to simulate the engine performance. The power output and thermal efficiency of ASDLGT engine are estimated at different operating conditions. It is found that ASDLGT engine achieves 54-64% overall thermal efficiency depending on the cycle pressure ratios and operating temperatures.

Key words:  Dual loop gas turbine engine, pulse detonation combustion, Brayton cycle, Rankine cycle.