研究発表

内燃機関のより高度な燃焼制御，ガス交換解析のためEGR流量に着目し，サイクル毎の流量を計測し，評価する．

サイクル毎のシリンダへの吸気量を計測するため，最適化した層流エレメント，差圧センサ，圧力導管からなる高速応答型層流式流量計を提案しその有効性を検証した．

従来ディーゼルエンジン制御は，実験的に作成されたエンジンの運転制御マップに従って行われていた．しかし，制御自由度増加によるマップ作成のための実験工数の増加，過渡運転での規制対応も考えると，マップに基づくエンジン制御は限界に近づいている．このような背景のもと，事前の実験回数を削減し，かつ過渡運転や様々な環境変化に対して柔軟に対応できるよう，モデルを利用したエンジン制御システムの検討が活発に行われている．モデルは現在までに様々な用途，種類のものが構築されてきた．しかしながら，計算速度の観点から，これらのモデルをECUに実装し，種々のエンジンの状態量から筒内の着火および燃焼をオンボード予測することや，制御則構築に有用な情報を提供するには至っていない．本研究では，ECUへの実装を見据え，エンジンの1サイクルを離散的に扱うことで，計算の高速化を図ったオンボード用ディーゼル燃焼モデルの構築を行う．

S I エンジンにおけるノッキング要因を調査するためにL i v e n g o o d － W u 積分および素反応数 値計算を用いた解析を行った．1 5 0 0 r p m ではL i v e n g o o d － W u 積分とノッキング強度の相関係数は0 . 1 2 1 となり， 3 0 0 0 r p mでは0 . 5 2 0 となった． 1 5 0 0 r p m のサイクルについて素反応数値計算を用いて自着火タイミングとノッキング強度の相関を取ると， 相関係数は- 0 . 3 6 6 となり， 実験から得た相関係数よりも向上したものの， 3 0 0 0 r p m の実験における相関係数よりも低い結果となり， ノッキ ングの要因解析を行うには十分ではない．

A combustion method called Noise Cancelling Spike (NC-Spike) Combustion is able to reduce combustion noise in pre-mixed charge compression ignition (PCCI) with split injection. This NC-Spike Combustion uses interference of the following “spike” of pressure rise (heat release) on the preceding peak of pressure rise. The overall combustion noise was reduced by lowering the maximum frequency component of the noise spectrum. The period of this frequency is two times of the time interval between the two peaks of the pressure rise rate. This maximum load range of conventional PCCI combustion is limited by the combustion noise, since the maximum pressure rise rate increases as the amount of injected fuel increases. In this paper, we investigates feasibility and controllability of the two-peak heat release rate during high temperature heat release by adding fuel in the adiabatic compression process of pre-mixed gas. The results show that the certain fuel addition timing generates the second heat release, and the interval of peak heat release rate could be controlled.

In spark ignition (SI) engines, exhaust gas recirculation (EGR) can realize reducing NOx emissions and heat loss by the low temperature combustion. However, adjusting the high level of EGR is limited because it incurs decrease of degree of constant volume and cut off flame propagation by the low laminar burning velocity. To improve laminar burning velocity with low flame temperature, numerical analysis of dedicated EGR concept SI engine with various EGR rates was carried out for detail understanding the potential of this concept engine in terms of thermal efficiency and amount of NOx emissions. The results show that Dedicated EGR concept SI engine was able to make higher thermal efficiency than the SI engine without EGR and conventional EGR. NOx emissions was reduced by decrease of the flame temperature while the laminar burning velocity was increased without flame temperature rising due to the influence of H2 and CO that were included in EGR gas as intermediates.

Homogeneous Charge Compression Ignition (HCCI) engine has advantages of high thermal efficiency and low emission over the conventional spark ignition engine and compression ignition engine. Although one way to achieve higher loads without knocking in HCCI engine is the combustion phasing retard, it is difficult to control a combustion-phasing since there is no external combustion trigger for controlling ignition like spark ignition and diesel fuel injection. In addition, recent researches show that too much combustion-phasing retard leads to unacceptable cycle-to-cycle variation of pressure rise rate and Indicated Mean Effective Pressure (IMEP). Thus, it is necessary to develop a HCCI combustion control system to control a combustion-phasing at constant phasing in the expansion stroke accurately to get the high load without knocking. This study investigates the HCCI combustion control system and the algorithm as a means of extending the limit of IMEP of HCCI combustion at high load for realize HCCI engine fuelled with Dimethyl Ether. The result from the model in this study nearly matches with that of experiments for all points and shows accurate traces for each input parameters.

Recent researchers point out that the fuel and the oil are mixed on the cylinder liner and then released from it. During the compression stroke the released droplets reach the auto ignition temperature before flame induced by spark ignition propagate to the spots of droplets, and it is called Pre-ignition. When pre-ignition is occurred, sometimes severe pressure happens and damages the engine severely. This work investigates effects of gas inhomogeneity induced by droplets of fuels and oils on the auto ignition timing and temperature in the direct-injection spark ignition (DISI) engine by means of detailed numerical calculation using multi zone model of CHEMKIN-PRO by changing initial temperature and initial equivalence ratio. In order to assume inhomogeneity in the combustion chamber, 16 zones by multiplying 4 types of equivalence ratio and 4 patterns of temperature is used for detailed numerical calculation. In this study used n-heptane that has to low-temperature oxidation (LTO). Consequently, we found that initial in-cylinder gas pressure affects the auto-ignition of air-fuel mixture and there is possibility to lead to cause Pre-ignition.