With concerns over preventing global warming, the usage of diesel engines, which have excellent thermal efficiency properties and are expected to reduce CO₂ emissions is attracting people's attention. Furthermore, nitrogen oxide and particulate matter emissions have been greatly reduced due to the development of emission reduction and combustion control technologies in recent years. To apply the latest combustion control technologies, optimization of the control parameters is required to achieve both exhaust gas suppression and heat efficiency improvement under various operation conditions. In this paper, we describe a method that optimizes the control parameters in actual engines such that they can operate at high efficiency and accuracy.