| Budget Amount *help |
¥3,900,000 (Direct Cost: ¥3,900,000)
Fiscal Year 1997: ¥1,600,000 (Direct Cost: ¥1,600,000)
Fiscal Year 1996: ¥2,300,000 (Direct Cost: ¥2,300,000)
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| Research Abstract |
This research was aimed to conduct precise observations of the flame structure, to elucidate the relationship between ambient pressure and turbulence scale and intensities, and to explore the effects of ambient pressure on turbulent burning velocities. Turbulent premixed flames for CH_4-air, C_2H_4-air, and C_3H_8-air mixtures were stabilized by a nozzle burner installed in a high-pressure. The following results were obtained.
1) Measured turbulence characteristics showed that turbulence intensities increatsed with increasing mean velocities. Nevertheless, at ordinary pressure, the increase was small in the region of small mean velocities because of an extensive dumping of turbulence. At high-pressures, turbulence intensity linearly increased with the mean velocities in the entire range of the mean velocities.
2) At high-pressures, flame structure becomes fine and complicated. S_T/S_L increased rapidly with increasing u'/S_L particularly for weak turbulence regions (u'/S_L<l), indicating
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effects the hydrodynamic instability becomes extensive in a high-pressure environment. For CH_4-air flames, S_T/S_L increases with u'/S_L, up to 30 at 3. OMPa for the experimental conditions achieved.
3) The rate of the increase in S_T/S_L for C_3H_8-air flames was smaller than that for C_2H_4-air flames. This is because the flame area increase due to the hydrodynamic instability at high pressures was restrained by diffusive-thermal effects because the larger Lewis number of C_3H_8-air mixtures.
4) The data for awide range of turbulence intensities showed that the u'/S_L dependence of S_T/S_L for C_2H_4-air flames is almost the same as that for CH_4-air flames. Nevertheless, S_T/S_L for C_3H_8-air flame showed smaller S_T/S_L than in the cases of C_2H_4-air and CH_4-air flames.
5) The applicability of existent correlation between S_T/S_L, u'/S_L, aud turbulence Reynolds number, R_L, to high-pressure flames were examined, and it was found that the data of our experiments had a similar tendency to the correlation by Abde1-Gayd but had larger S_T/S_L than their correlation. 1/4 power law of R_L was seen for S_T/S_L in the strong turbulence region (u'/SL>l.0), consistent with the fractal flamelet model of turbulent burning velocity proposed by Gouldin.
6) The best general correlation which can express the experimental data for a whole range of u'/SL and pressure was in the for of S_T/S_L* [ (P/P_O) (u'/S_<1L>) ]^n and the exponent n was close to 0.4. Less
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