Concept of Lean Combustion by Barrel-Stratification

• Main Authors: Kiyota, Yuhiko, Akishino, Katsuo, Ando, Hiromitsu
• Format: Report
• Language: English
• ISSN: 0148-7191; 2688-3627
• DOI: 10.4271/920678

A novel leanburn concept, ‘Barrel-Stratification’ is proposed. Fuel is introduced into the cylinder through one of the intake ports of a dual-intake-valve engine of which the tumbling air motion is intensified by the sophisticated intake port design. Because the velocity component in the direction parallel to the axis of tumble is small, charge stratification realized during the intake stroke is maintained until the end of the compression stroke. By the effects of charge stratification and the turbulence enhancement by tumble, stable combustion is realized even at extremely lean conditions. The concept was verified by flow field analysis applying a multi-color laser sheet technique and the flame structure analysis employing the blue-end image intensification realized by the interference mirror and the short delay phosphor. The combustion process in a spark ignition engine is generally characterized as a combination of the air entrainment process, in which the flame front propagates at a speed determined by the turbulence intensity, and an eddy burning process in which the burning rate is determined by the laminar burning velocity and the turbulence length scale. For the enhancement of air entrainment, an increase of turbulence intensity is required, while for the increase of the eddy burning rate, a reduction of turbulence scale is required. Small scale turbulence is subject to dissipation. Therefore, to conserve the intense turbulence with a small scale until the combustion process, it is necessary to increase the kinetic energy introduced into the cylinder during the intake process, thereby conserving the kinetic energy by maintaining a large scale vortices and convert it into turbulence immediately before the combustion. As the large scale vortex employed for this purpose, swirl, that is, the horizontally rotating air motion has been adopted. Recently it has been reported that tumble, a large scale vertical rotational air motion around the axis perpendicular to the cylinder axis, may be adopted as an alternative of the conventional swirl (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 and 21). Tumble is an air motion suitable for two-intake-valve engines with a pentroof-type combustion chamber. The authors have performed studies on the generation and distortion processes of tumble and its effects on combustion (22,23). During the study, it was found that when the charge is stratified during the intake process by introducing the fu