Nariyoshi Kobayashi

Combustion Oscillation Analysis of Premixed Flames at Elevated Pressures

A new analytical time lag flame model based on Bloxidge’s flame model was introduced for calculating combustion oscillation of premixed flame to take into account the distribution of heat release rate and flame speed which was calculated by analytical formulas dependent on pressure, temperature, fuel-to-air ratio and velocity. The transfer matrix technique using the new flame model was applied to the calculation of acoustic resonance. To verify the model, combustion oscillation experiments were performed for methane-air premixed flames stabilized by a swirl burner at elevated pressures between 0.6–0.9MPa. Fluctuating pressure had the maximum peak at the specific value of fτf. Here f is the frequency of resonance and τf is the passing time of premixed gas through flame length. The analysis could simulate the dependency of fuel-to-air ratio and static pressure for dynamic pressure local peak.© 1998 ASME

Performance Demonstration of the Full-Size Multi-Cluster Combustor for DME Under Real Engine Conditions

DME (dimethyl ether: CH3 OCH3 ) is currently attracting worldwide attention because it is a clean fuel which can be synthesized from various materials such as natural gas, coal, biomass, etc. But DME has the possibility of spontaneous ignition in gas turbine use because of its low auto-ignition temperature. To avoid spontaneous ignition or flash-back, a coaxial jet cluster nozzle burner configuration was proposed previously which can mix air and fuel effectively within a short time. In this work, demonstration tests were carried out for the developed full size combustor, called the multi cluster combustor for 25MW class gas turbine. The combustor, which is composed of cluster nozzle burners, was tested under practical gas turbine operating conditions from start up to base load using a full pressure combustion test rig. In the tests, LNG was also used as the test fuel because it is expected to be used as a back up fuel when DME is first introduced for wide commercial use. Test results showed good combustion performances for the developed multi cluster combustor. NOx emission level was below 24ppmv (15%O2 ) and combustion efficiency was over 99.9% for the base load condition of the 25MW class gas turbine when fueled with DME or LNG. Dynamic pressure level and liner metal temperature were low. No flash-back phenomena occurred throughout the demonstration tests.Copyright

Robust Design of the Coaxial Jet Cluster Nozzle Burner for DME (Dimethyl Ether) Fuel

DME (dimethyl ether) is currently attracting worldwide attention due to its potential as a clean fuel. But, DME has a low auto-ignition temperature and a higher combustion velocity compared with other power generation gas fuels (LNG, LPG). Therefore, in the case of lean-premixed design to limit the formation of NOx in the burning zone, a shorter premixing length than that for natural gas is required. In this research, the main objective is the development of a low NOx emission and high efficiency combustion system that is suited to quick and uniform mixing between the air and gaseous DME. A coaxial jet cluster nozzle burner configuration is proposed as the low NOx combustion system, and 18 different configuration burners are designed and tested by the robust design. Based on the analysis of test results, the optimized configuration of a coaxial jet nozzle burner is selected.Copyright

Development of Multi Cluster Burner for Fuel Grade DME

Recently, DME (dimethyl ether: CH3 OCH3 ) has attracted attention as a clean next-generation fuel, but it has the possibility of spontaneous ignition in gas turbine use. To avoid spontaneous ignition or flash-back, a coaxial jet cluster nozzle burner configuration was proposed previously, which can mix air and fuel effectively within a short distance. In this research, the full size multi cluster burner composed of coaxial jet cluster nozzle burners was designed, and combustion tests for gaseous fuel grade DME were carried out. (Fuel grade DME includes minor amounts of methanol and water as impurities.) In making the configuration tests of the multi cluster burner, the robust design method was applied. Characteristics of NOx emission, combustion efficiency, combustion stability, etc. were evaluated, and the optimal configuration of the combustor was determined. Also, the influences of impurities of fuel grade DME on the combustion performance were evaluated. With the optimal combustor, the prospects were good for achieving the targets, NOx 99.9%, and pressure oscillation < 3.5 kPa. Regarding the influences of impurities of fuel grade DME, there was no great difference in combustion efficiency and pressure oscillation with addition of impurities in this test range.Copyright

The Effect of Impurities in Fuel Grade Dimethyl-Ether on Combustion Characteristics

In order to investigate the effect of impurities contained in fuel grade dimethyl-ether on combustion characteristics, laminar burning velocity tests and diffusion flame combustor tests were carried out with various contents of impurities in fuel grade dimethyl-ether (with about 0–9wt% methanol and 0–10wt% moisture). From the laminar burning velocity tests, it was found that the burning velocity of fuel grade dimethyl-ether was slightly slower than that of high purity dimethyl-ether and it was faster than that of methane. This indicates that fuel grade dimethyl-ether has a high potential of flash back, like high purity dimethyl-ether. Moreover, the diffusion flame combustor tests showed that NOx emission decreased when the impurities contained in fuel grade dimethyl-ether were increased, however CO emissions were almost constant, irrespective of the content of impurities. Further, by comparing NOx emissions with various contents of impurities in fuel grade dimethyl-ether, it was clear that NOx emissions could be estimated from the adiabatic flame temperature. From these results, a lot of valuable data regarding impurities content has been obtained, which will assist in the development of a gas turbine combustor for fuel grade dimethyl-ether.Copyright

Estimation of the Operating Characteristics of the Adjustable Speed Gas Turbine Power Generation System During Partial Load Operation

This paper proposes an application of the simple cycle adjustable speed gas turbine power generation system for use as an independent power producer combined with a heavy duty gas turbine (output power 25MW, turbine inlet temperature 1400K class) having adjustable speed generators. Comparison results for a method to improve the thermal efficiency of this system using low NOx combustors are obtained.The results of a performance study of the static characteristics for the system using forced IGV (Inlet Guide Vane) opening control during partial load adjustable speed operation, show an effect on thermal efficiency improvement. Comparison of the dynamic characteristics for the system using existing controllers and the system using the proposed controllers shows, the latter is able to restrain fluctuation of the fuel to air mass ratio during a transient changing the target rotational speed, under restricted operating conditions.Copyright

流れ場中の粒子による配管表面摩耗モデルの提案とその評価〔流体工学, 流体機械〕

A new erosion model and rebound coefficient was proposed by a modification of Finnies theoretical approach. The present erosion model includes the effects of impingement velocity, impingement angle, particle density. Main features of the model are as follows : (1) The erosion rate is proposed to the particle velocity cubed. (2) The relationship of the impingement angle and the erosion rate is in good agreement with authors experimental data.