Hierarchical scatter-bands were constructed to determine engine specifications in the early stages of development, and development efficiency was enhanced. The four elements of thermal efficiency and combustion stability, oil dilution, and soot, which conflict with thermal efficiency, were defined and the requirements of intermediate parameters were analyzed in order to link them to parts step by step. Using engine data, it was confirmed that the parameter linkages are generally correct. The issues of turbocharged direct injection engines and their causes were analyzed based on system characteristic analysis and requirement analysis using scatter-bands, thereby enabling efficient implement countermeasures. The in-cylinder flow was enhanced by changing the piston top to a shallow dish shape, which decreased the combustion period by 0.5 deg. and reduced the brake specific fuel consumption by approximately 0.6%. Countermeasures were also implemented for conflicting events, and the injection control was changed. This reduced the oil dilution rate by 2.6 wt% and allowed balancing of the performance demanded of the engine.
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