Recent advances in the use of frequency analysis of high-speed diode-laser-absorption measurements of temperature to combustion control are discussed in the context of the sensing and suppression of thermoacoustic instabilities and lean blowout (LBO) in a model-gas-turbine combustor. The tunable diode laser (TDL) sensor for gas temperature is based on wavelength-scanned absorption of two neighboring water vapor transitions near 1.4 μm. Although the gas composition and temperature are not uniform along the sensor line-of-sight, temperature oscillations and fluctuations are clearly identified in the power spectra determined from the Fourier transform of the time-resolved data. The power spectrum intensity of the temperature fluctuations is used to suppress the thermoacoustic oscillations in a phase-delay feedback control system. The intensity of the low-frequency temperature fluctuations is used to identify the proximity to LBO and provides a control variable for active LBO suppression without knowing the LBO fuel/air ratio limit.
Laser Induced Plasma Spectroscopy (LIPS) is a technique aiming at obtaining mixture fraction inside practical combustor. The fundamental bases of the technique are first exposed and effects of pressure or blended fuels are discussed. A typical experimental setup is discussed as far as the application of LIPS to high-pressure is concerned. Some results obtained in combining LIPS and laser ignition are presented and discussed. Finally, strategies for global control are presented, in which plasma spectroscopy is becoming a sensor-actuator, quite unique and with several interesting possibilities.
The experimental study of hydrocarbon fuel droplets burning in the electro-magnetic environments has been carried out to examine the effect of electro-magnetic wave on the combustion of fuel droplets. The characteristics of electro-magnetic wave developed for the study are around 1200 cm-1 in wave number, which corresponds to the absorption band of methane molecule. The combustion process of hydrocarbon fuels ultimately includes the reaction of methane and methyl with oxygen as a result of thermal decomposition. So it is very important to examine whether the combustion of hydrocarbon fuel droplets is promoted by electro-magnetic wave or not. The fuels used for the study are n-heptane, n-hexadecane, methanol, benzene, kerosene and heavy oil A. The initial droplet diameter is approximately 1.70 to 1.85mm. The acquisitions obtained here show that such electro-magnetic wave may be very effective to accelerate the combustion rate of hydrocarbon fuel droplets by utilization of resonance frequency to methane molecule.
The methane-air counterflow twin-premixed flame of fuel lean mixture is investigated with chemical kinetics model. For the confirmation of the effect of equivalence ratio and flame stretch rate, the steady counterflow flames, in which the Lewis numbers of each species are fixed from 0.5 to 1.5, in addition to the case of using actual Lewis numbers, are calculated. As a result, when the Lewis number is fixed, the maximum heat release rate is influenced by Lewis number effect and the summation of heat release rate is influenced by the Lewis number and the incomplete combustion. The influences of flame stretch rate on flame structures of the counterflow premixed flame using actual Lewis number are changed in each equivalence ratio. Moreover, the determination of the burning velocity in counterflow premixed flame is investigated.
This paper proposes a unified model that can be applied to the premixed and diffusion flames based on the author's premixed combustion model [1-4]. The proposed model has the following features. 1) It includes the laminar flame speed and the gradient of the mixture fraction as parameters. When the gradient of the mixture fraction is close to zero, the model is also close to the previous premixed combustion model as an asymptotic form. 2) It considers the effects of pressure in the combustor, unburned gas temperature, and flame stretch on combustion based on the laminar flame speed. 3) The effect of turbulence is considered through the turbulent eddy viscosity of all turbulence models. To verify the accuracy of the model, the counterflow diffusion flame presented by Tsuji and Yamaoka  was numerically simulated, as an example of a laminar diffusion flame. Further, a turbulent diffusion flame, which was assisted by the burning of a pilot jet , was demonstrated using the united combustion model as an example of the turbulent diffusion flame discussed by Barlow and Frank. The flame is well known as Sandia Flame D. Both results were in good agreement with the experimental data. These comparisons with the experimental data and this agreement confirmed the proposed unified model was able to accurately simulate diffusion flame.