Published papers

本研究ではDMEを燃料とした素反応数値計算により，HCCIエンジンの燃焼シミュレーションを行うことを念頭に置き，μｓオーダーで高温・高圧場が形成されるショックチューブを想定した計算を行ない， １．ショックチューブによる着火遅れの実験結果と計算結果を比較し，素反応モデルの妥当性を調査する。 ２．ステップ状に与えた温度，当量比といったパラメーター変化が低温酸化反応および高温酸化反応の発現時期，発現期間，熱発生率といった着火・燃焼特性に与える影響を調査する。 ３．高温酸化反応および低温酸化反応期間の熱発生に関わる素反応を調査する。

東京都　定置型内燃機関に関する窒素酸化物排出低減技術検討会

An investigation was carried out which the aim of making clear the effect of fuel properties, such as aromatics contents and 90% distillation temperature, on NOx and soot formation in diesel exhaust. Fuel spray was injected into the combustion chamber through a nozzle hole. The ignition and combustion processes of diesel spray were observed with high-speed direct photography. Flame temperature and KL factor which indicates the soot concentration were analyzed with the two-color method and the rate of heat release from indicated diagrams.

To make clear the effects of diesel fuel properties, nozzle hole diameter and EGR ratio on flame temperature and soot formation (in diesel spray combustion), an investigation was made into free spray formed by a single-hole nozzle in high-pressure and high-temperature atmosphere produced by a rapid-compression machine. Diesel fuel properties were changing with aromatic ring number and T90. EGR ratio was reproduced by changing surrounding gas temperature and CO2 density. The behavior of diesel spray combustion was observed with high-speed direct photography and in-cylinder pressure measurement. KL value and flame temperature were analyzed with the two-color method.

ガソリンエンジンよりもクリーンで，ディーゼル並みの燃焼効率を実現できる「異種交配」エンジンが，直接噴射ガソリンエンジン（ＧＤＩ）に続く「第４のエンジン」として期待を集めている。

The amount of environmental load emissions in each stage of each vehicle, from raw materials mining and material production to disposal and recycle, is estimated on an alternative vehicle, a hybrid vehicle and a fuel cell vehicle as next-generation vehicles. So their environmental impact in their total life cycle is assessed using the concept of Life Cycle Assessment (LCA). In this study specially noticing their fuel production processes, from raw materials mining to consumption, the cutting down potential of environmental load of each next-generation vehicle

In this study, effects of internal EGR ratio on the ignition and the combustion of homogeneous charge compression ignition (HCCI) engine are investigated experimentally. At first, using single cylinder test engine, relation between exhaust valve close timing and internal EGR (Exhaust Gas Re-circulation) ratio is clarified. Effects of an internal EGR gas on autoignition timing, combustion duration and knocking limits are discussed. As a result of an experiment, it became clear the following facts ; with advancing exhaust valve close timing, ⅰ) internal EGR ratio is increasing, ⅱ) both knocking limits at high load and misfiring limits at low load are　expanding, ⅲ) ignition timing is advancing, ⅳ) combustion duration is decreasing and ⅴ) combustion efficiency is increasing.

本研究では，DME着火の過程を詳細な素反応で記述した反応モデルをDME空気予混合気HCCIエンジンの圧縮自己着火のプロセスに適用し，DME空気予混合気の素反応数値計算を行う。 １．ショックチューブによる着火遅れの実験結果と計算結果を比較し，素反応モデルの妥当性を調査する。 ２．当量比，圧縮開始温度，初期組成（EGR率），機関回転速度などの因子が低温酸化反応および高温酸化反応の発現時期，発現温度といった着火特性，熱発生率履歴，化学種モル分率履歴といった燃焼特性に与える影響を調査するとともに，HCCIエンジンの実験結果と比較検討する。

This study was aimed at reducing Soot and NOx by uniform and lean distribution of fuel in diesel spray using high-pressure fuel injection and a micro-hole nozzle. But this injection system made ignition delay shorter. So that, it couldn't completely make uniform and lean distribution of fuel in diesel spray. Then, in addition to this injection system, using low cetane number of fuel, which can not easily ignited, we made ignition delay longer, and attempted to make complete uniform and lean distribution of fuel in diesel spray. The combustion event was observed by high-speed direct photography, ignition and combustion was analyzed by the combustion chamber pressure history, and KL values and a flame temperature was analyzed by the two-color method from the two-dimensional flame image.

化学反応論的見地からHCCIエンジンの燃焼制御の可能性について検討を行った。ｎ－ブタンの空気予混合気は圧縮自己着火過程で典型的な低温酸化反応，高温酸化反応過程を示すアルカン系で最も炭素数の少ない単体で，過去の研究により，確度の高い素反応スキームが得られている。予混合圧縮自己着火過程を代表する燃料としてｎ－ブタンを選択し，炭化水素混合気の詳細な酸化反応機構を考慮した反応速度計算を行った。 　まず，衝撃波管を想定した解析を行い，実測の着火遅れデータと比較検証し，素反応スキームの有効性，再現性について検討した。続いて，往復動型予混合圧縮自己着火機関での圧縮自己着火過程の詳細なシミュレーションを行った。その結果，小島のスキームにより，HCCI機関の予混合気の着火過程における二段の熱発生過程が表現された。低温酸化反応は当量比によらず予混合気がある一定の温度に達した時点で発生すること，低温酸化反応に伴う熱発生は主にホルムアルデヒドの酸化過程に伴うもので，その発熱量は，低温酸化時の予混合気の圧力が大きいほど大きくなることを明らかにしている。高温酸化反応の発生は，その主体により２段階に分類され，最初は低温酸化反応で生成されたホルムアルデヒド等の中間反応生成物の酸化（青炎），続いてＣＯの酸化によるＣＯ2生成およびＨＯ2とＯＨからＯ2とＨ2Ｏとの生成反応（熱炎）である。また，ＨＣＣＩエンジンにおいて，自己着火（熱炎の発生）は必ずしも燃焼反応の終結を意味しない。高温酸化反応過程において，燃焼の中間生成物の大半を最終燃焼生成物であるＨ2ＯおよびＣＯ2まで進行させるには，バルク温度を１５００Ｋ以上まで到達させることが必須である。バルクのサイクル履歴最高温度として１５００Ｋを確保することができないと，ＨＣおよびＣＯの排出が多くなり，高い燃焼効率を確保できない。

In this study, the numerical calculation of the Homogeneous Charge Compression Ignition (hereafter HCCI) process is carried out by using Curran et al.’s DME elementary reaction model for DME fueled HCCI engine. On condition simulating shock tube, the validity of the DME elementary reaction model is investigated. And main elementary reactions releasing heat are investigated in case of multi-stage ignition. As a result, numerical calculation using Curran et al.’s elementary reaction model can qualitatively predict the influence of equivalence ratio, temperature and pressure on the appearance timings of low temperature reaction and high temperature reaction under the pressure and the temperature in HCCI engine.

Homogeneous Charge Compression Ignition (hereafter HCCI) engine can realize low emission and high thermal efficiency. However, its ignition and combustion processes are difficult to control and thus the reaction mechanisms of auto-ignition and combustion are needed to be clarified. In this study, the numerical calculation of auto-ignition and combustion processes in HCCI engine is carried out. Curran et al.’s DME (Dimethyl Ether) elementary reaction model is used. The results of the calculations are compared with the experimental results and the validity of the elementary reaction model is investigated. And followings are investigated: the influence of equivalence ratio, intake temperature, EGR ratio and engine speed on rate of heat release, ignition timing, ignition temperature and histories of species’ mole fractions. As a result, Curran et al.’s model can qualitatively predict the influence of equivalence ratio, intake temperature on the ignition timings and the peeks of the rate of heat release.