Technology review of aeroengine pollutant emissions

Constant volume combustion (CVC) in gas turbines is a promising way to achieve a step change in the efficiency of such systems. The most widely investigated technique to implement CVC in gas turbine systems is pulsed detonation combustion (PDC). Unfortunately, the PDC is associated with several disadvantages, such as sharp pressure transitions, entropy generation due to shock waves, and exergy losses due to kinetic energy. This work proposes a new way to implement CVC in a gas turbine combustion system: shockless explosion combustion (SEC). This technique utilizes acoustic waves inside the combustor to fill and purge the combustion tube. The combustion itself is controlled via the ignition delay time of the fuel/air mixture. By adjusting the ignition delay in a way such that the entire fuel/air volume undergoes homogeneous auto-ignition, no shock waves occur. Accordingly, the losses associated with a detonation wave are not present in the proposed system. Instead, a smooth pressure rise is created due to the heat release of the homogeneous combustion. The current article explains the SEC process in detail, and presents the identified challenges. Solutions to these challenges and the numerical and experimental approach are presented subsequently alongside with first preliminary results of the numerical studies.

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Shockless Explosion Combustion: An Innovative Way of Efficient Constant Volume Combustion in Gas Turbines

Combustion and evaporation processes occurring in a closed chamber can result in signie cant pressurerise and direct work transfer. The pressure and volumetric changes that accompany such processes allow substantial work potential to be achieved in cyclic nonsteady devices, such as internal combustion engines and pulsed combustion or detonation engines. The ideal pressure gain or work production is a function of the prescribed ine ow and oute ow conditions, volumetric cone nement, e uid properties, and other parameters. The generalized thermodynamic limits of pressure gain and work production in such devices are investigated. Analytic and iterative methods are provided to evaluate cyclic combustion and evaporation processes for enhancing airbreathing combustion engine performance.

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Thermodynamic limits of work and pressure gain in combustion and evaporation processes

Combustion within the channels of a wave rotor is examined as a means of obtaining pressure gain during heat addition in a gas turbine engine. Three modes of combustion are assessed: premixed autoignition (detonation), premixed deflagration, and non-premixed autoignition. The last two will require strong turbulence for completion of combustion in a reasonable time in the wave rotor. The autoignition modes will require inlet temperatures in excess of 800 K for reliable ignition with most hydrocarbon fuels. Examples of combustion mode selection are presented for two engine applications.

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Assessment of combustion modes for internal combustion wave rotors

Combustion within the channels of a wave rotor is examined as a means of obtaining pressure gain during heat addition in a gas turbine engine. Three modes of combustion are assessed, premixed autoignition (detonation), premixed deflagration, and non-premixed autoignition. The last two will require strong turbulence for completion of combustion in a reasonable time in the wave rotor The autoignition modes will require inlet temperatures in excess of 800 K for reliable ignition with most hydrocarbon fuels. Examples of combustion mode selectio are presented for two engine applications.

Assessment of Combustion Modes for Internal Combustion Wave Rotors

The objective of the work was to compare on both an ideal and, where possible, an actual basis the approximate performances of four types of pressure-gain combustor. Such combustors are potentially suitable for use in gas turbines in place of conventional steady-flow combustors. The ideal theoretical performance comparison was based on a specially conceived, universal, analytical model capable of representing, in a fundamental manner, the dominant features of each of the systems studied. The comparisons of nonideal performance were based on actual test results and, where these were not available, on ideal performance characteristics suitably modified to take irreversibilities, etc., into account. It was found that in general the pressure-gain potential of the concepts studied increased with increasing system complexity. It was also found that with most concepts the combustor pressure ratio achievable increases with combustor temperature ratio.

Methods for Achieving a Combustion-Driven Pressure Gain in Gas Turbines

A description is given of a simple, prototype, pulse, pressure-gain combustor for a gas turbine. The work reported was targeted at alleviating problems previously observed with the prototype combustor. These were related to irreversibilities, causing a performance deficiency, in the secondary flow passage. The work consisted of investigating experimentally the effect of tuning the secondary-flow path length, adding a flow restrictor at the combining-cone entry station, and redesigning the combining cone itself. The overall result was to eradicate the previously noted performance deficiency, thereby increasing the maximum pressure gain obtained in the gas turbine from 1.6 to 4.0 percent of the compressor absolute delivery pressure.

J. A. C. Kentfield

Papers

Methods for Achieving a Combustion-Driven Pressure Gain in Gas Turbines

Improvements to the Performance of a Prototype Pulse, Pressure-Gain, Gas Turbine Combustor