At all the directions of impingement here the spray flame diminished at almost same time with the CCD jet and earlier than without the CCD jet. However, the mechanism of flame extinction appeared to be different at different directions. In Cases 4 and 5 the flame reaching the wall was limited by the opposing CCD jet, and oxidation of soot was achieved at the high temperature zone with strong turbulence by the jet. In Cases 6 and 7, the luminous flame reached the wall at high velocity due to the CCD jet, and turbulence was generated by the impingement of flame to wall. This secondary turbulence at the wall together with the direct turbulence by the jet collision enhanced the oxidation of soot even in the low temperature region in the vicinity of the wall.
Analysis of local turbulent flows with PIV showed that when the vortex size is equivalent to the flame cloud and when they overlap the flame, the flame only rotates without enhancing mixing with air. At this scale the relative locations of vortices and flame are important in the distortion of the flame. By optimizing the microscopic mixing process of fuel and air together with the macroscopic jet momentum and time, the residence tune for NOx formation and available oxygen for soot oxidation may be controlled to give the minimum emissions.
7. CONCLUSIONS
1) Strong turbulence generated late in the combustion period effectively reduces smoke and particulate without increasing NOx. Thermal efficiency is improved at high loads because of a shortening of the combustion period.
2) The results for two-stage combustion showed that NOx was reduced to one third of the base engine while maintaining fuel consumption and particulate emissions. However the favorable result was limited to the range other than the full load clue to increased smoke.
3) NO reaction kinetic considerations suggest that key factors to maximize the effect of the two-stage combustion are to maintain an uniform fuel-rich mixture until the late expansion stroke and reducing the mixing time scale.
4) Smoke reduction extent due to the turbulent jet can be correlated to the mixing parameter determined from the integrated jet momentum over the effective crank angle degrees relative to the mass of the gas in the cylinder. This result indicates that the macroscopic design of combustion-system is to achieve the largest value of the mixing parameter.
5) It was observed that the soot cloud in a spray flame oxidized and disappeared quickly by the impingement of a turbulent jet. When the distance between the main spray and the turbulent jet was too short, the turbulent jet penetrated the soot cloud without causing effective mixing. To maximize the local mixing of fuel and air, microscopic mixing process is important together with the macroscopic jet momentum and period of the jet.
ACKNOWLEDGMENT
This research is partially supported by the Scientific Research Program of Japan Ministry of Education and by a research pro- gram of the Japan Society of Mechanical Engineers. The author express appreciation to Professors T. Murayama, M. Konno, Y. Hishinuma, and K. Kikuta for their advice and contribution to the research. The author also wish to express his appreciation to many students involved in the research; among them Drs. K. Yamane and T Araki made great contribution in their doctoral research.
REFERENCES
[1] M. Kamimoto, et al., "Smoke Emission Characteristics of DI Diesel Engine with Air Cell", Trans. of JSME, 50-453 (1984), p1363-1371 (in Japanese)
[2] Murayama, T., Chikahisa, T., and Ymamane, K., "Simultaneous Reduction of Smoke and NOx by Active Turbulence Generated in the Late Combustion Stage in D.I. Diesel Engines", 7th Int. Combust. Eng. Symp. Japan, 107 (1988), p37-42 (in Japanese)
[3] Murayama, T., Chikahisa, T., Ymamane, K., and Xu, M., "Reduction of Smoke and NOx Emissions by Active Turbulence Generated in the Late Combustion Stage in D.I. Diesel Engines", Proc. 18th Syrup. Int. Con. Combust Eng. (CIMAC), D132 (1989), p1129-1141
[4] Konno, M., Chikahisa, T., and Murayama, T., "Reduction of Smoke and NOx by Strong Turbulence Generated During the Combustion Process in D.I. Diesel Engines", SAE Trans, 920467, (1992).
[5] Yamaura, K., Kakegawa, T., Furuhama, S., Suzuki, T., Kim, Y., and Sibuya, H., "A Study for Reducing Diesel Exhaust Emissions by Gas Injection (1st Report; Reduction of Black Smoke by Combustible Gas Injection)", 8th. Int. Combust. Eng. Symp. Japan, 123 (1990), p129-134 (in Japanese)
[6] Kawazoe, H., Nagano, S., and Osawa, K., "Reduction of Soot Emission by Air-Jet Turbulence Generator with Cam in a Diesel Engine", JSAE paper, 902116, (1990) (in Japanese)
[7] Nagano, S., Kawazoe, H., and Osawa, K., "Reduction of Soot Emission by Spring Accumulatored Air-Jet Generator in DI Diesel Engine", 9th lnt. Combust. Eng. Symp. Japan, 231 (1991), p439-444 (in Japanese)
[8] Konno, M., Chikahisa, T., and Murayama, T., "An Investigation on the Simultaneous Reduction of Particulate and NOx by Controlling Both the Turbulence and the Mixture Formation in DI Diesel Engines", SAE paper, 932797 (1993), p1-9
[9] Chikahisa, T., Murayama, T., and Konno, M., "Two- stage Combustion with a Turbulence Generation System for Reducing NOx and Smoke Emitted from DI Diesel Engines", Proc. of IPC-8 (Int. Pacific Conference on Automotive Engineering), 9531066 (1995), p93-98
[10] Chikahisa, T., and Araki, T., "In-Cylinder Control of Smoke and NOx by High Turbulent Two-Stage Combustion in Diesel Engines", SAE 962113 (SP-1206) (1996), p173-180
[11] Araki, T., Chikahisa, T., and Hishinuma, Y., "Experimental Study on Smoke and NOx Reduction by High- Turbulent Two-Stage Combustion in Diesel Engines (Trials of Variety Types of Piston Configurations, EGR Combination, and Fumigation), Trans. of JSME, 65-632 (1999), p1491-1497 (in Japanese)
[12] Chikahisa, T., Konno, M., and Murayama., T., "Analysis of NO Formation Characteristics and Control Concepts in Diesel Engines from NO Reaction-Kinetic Considerations", SAE paper, 950215 (1995), p1-8
[13] Araki, T., Kikuta, K., Chikahisa, T., and Hishinuma, Y., "Analysis of Major Parameters in Smoke Reduction with Turbulent Jets Aimed at Spray Flame in DI Diesel Engines", Proc. of 4th COMODIA 98 (1998), p69-74
[14] Kondo, T., Chikahisa, T., and Hishinuma, Y., "Turbulent Mixing for Effective Soot Reduction During Combustion Process", Proc. of 15th Internal Combustion Engine Symp., JSAE and JSME (1999), p321-326
[15] Ushida, H., Chikahisa, T., and Hishinuma, Y., "Mixing Conditions with Spray-Jet Interaction for Effective Soot Reduction in Diesel Combustion", Proc. of FISITA 2000, F2000A099 (2000) (in print)
[16] Amsden, A., et al., "KIVA - A Comprehensive Model for 2-D and 3-D Engine Simulations", SAE Trans., Vol. 94, Section 4, 850554 (1985), p1-15
[17] Park, C., Appleton, J.P., "Shock-Tube Measurements of Soot Oxidation Rates", Combust. Flame, 20 (1973), p369
[18] I. Wiebe, "Halbempirische Formel fur die Verbrennungsgeschwindigkeit", Verlag der Akademie der Wissenschaften der UdSSR, Moscow, 1956; as cited by G. Sitkei, Kraftstoffaufbereitung und Verbrennung bei Dieselmoteren, (1964), p156-159, Springer Verlag
