一柳 満久

Overall efficiency of internal combustion engines are heavily depended on intake air temperature which is directly related to the heat transfer inside an intake system. Previously, authors developed an equation by using port model setup to calculate Nusselt number with introduction of Graetz and Strouhal numbers. This study modified the port model equation to improve its accuracy in a real engine experimental setup. Predicted intake air temperature was compared to the measured data with a maximum error of 5.6%. Additionally, 100 K of temperature difference was found between the boost pressure values of 944hPa and 678hPa from 1-D engine simulation results.

An empirical equation was developed for modeling the heat transfer phenomena taking place in an intake manifold which included the backflow gas effect. In literature, heat transfer phenomenon at intake system is modeled based on steady flow assumptions by Colburn analogy. Previously, authors developed an equation with the introduction of Graetz and Strouhal numbers, using a port model experimental setup. In this study, to further improve the empirical equation, real engine experiments were conducted where pressure ratio between the intake manifold and engine cylinder were added along with Reynolds number to characterize the backflow gas effect on intake air temperature. Compared to the experimental data, maximum and average errors of intake air temperature estimated from the new empirical equation were found to be 2.9% and 0.9%, respectively. Furthermore, Colburn analogy and suggested empirical equation were consecutively implemented to 1-D engine simulation software on gasoline and diesel engine setups. Naturally aspirated gasoline engine simulations revealed the importance of the backflow gas effect in line with the real engine experiments. Maximum and average temperature differences between the Colburn analogy and suggested equation showed 36.0 K and 28.7 K, respectively. In turbocharged diesel engine simulations, intake air temperature's effect on auto ignition timing was analyzed. At engine speed of 2250 rpm, in-cylinder air temperature difference at IVC was found to be 5.8 K. This difference corresponded to an advanced auto-ignition timing by 1.15 deg. CA, which could be interpreted an estimated reduction of CO2 gas by 0.28%.

ディーゼル機関の過渡性能向上にはオンボード・モデルベースト制御による着火時期の予測が重要である．著者らは，筒内ガス温度をサイクルごとに予測するため，低計算負荷の圧縮ポリトロープ指数予測モデルを開発した．過渡運転条件に適用し，１Ｄ数値計算と比較した結果，構築したモデルの有用性が認められたので報告する．

本論文は，実機エンジンの吸気管にて温度測定を行い，吸気システムでの伝熱現象を検討した．その際，流れの非定常性および温度境界層の発達を考慮し，Nu数をRe数，Gz数，St数で表した実験式を導出した．また，熱力学モデルに基づきシリンダに吸入される空気温度を推定したところ，5.6%の誤差で推定可能であることがわかった．