Japanese industrial research on lean combustion: A case study: International Research Monitoring Program

Abstract

In recent years, Japanese automakers have introduced a number of successful lean-combustion engines. These engines, in addition to the general expertise in building small cars, have made the Japanese automobiles into the gas mileage champions of the U.S. market. The lean-combustion engines also provide very satisfactory performance and acceptable emissions. United States automakers and research managers, who were probably better informed about leancombustion than the Japanese were, actively investigated lean-combustion but did not develop an engine. This report examines the basis for the Japanese innovations, the research that took the Japanese past the U.S. state of the art to permit engine development. A preliminary review of recent {1980s) Japanese literature did not turn up strong evidence of new research activity in the lean-combustion area, but did provide background on new engines developed by several major manufacturers. Developments by the most important automaker in Japan, the Toyota Motor Company, were then chosen for a case study. The study was conducted solely through the Japanese and U.S. published literature, with emphasis on early research conducted in the 1970s. Particular attention was paid to combustion chamber research, notably work which addressed the effects of turbulence and swirl and of prechamber combustion. All these techniques are used in Toyota's lean-combustion engines. References to early research conducted by Toyota engineers show a heavy reliance on information provided by previous work in the United States. This reliance appears to be characteristic of all Japanese work at the time of lean combustion in automobile engines. Rather than begin with the concept of lean combustion and proceed through stages of research that eventually led to engine designs, Japanese researchers apparently evaluated the more promising options reported in the international literature and then began developmental work on the selected options. By tracing subsequent publications from particular research and development (R&D) groups, it is possible to view the development of various leancombustion engine components. In the case of Toyota's prechamber combustion i i i design, the turbulence generator pot (TGP), the evolution of the design and changes to optimize performance and emissions levels can be seen in the Japanese literature. Even more clearly traceable are the stages that led to Toyota's development and selection of a helical intake port and a swirl control valve (SCV) for swirl generation. This arrangement was used in both the central injection engine and the Toyota lean-combustion system that were described in engine announcements published in 1984 (Shiozawa et al. 1984, Matsushita et al. 1984, Takeda et al. 1984). Despite the successful results, Toyota's research typically involved little more than standard engine tests, Schlieren photography, and some hotwire anemometry. More fundamental research, resembling that supported by the U.S. Department of Energy, did not begin to occur systematically un...