Published papers

The purpose of this study is to propose an estimation method which can estimate NOx, PM, CO2 emission from vehicle to roadside. Driving tests were preformed on the road by a diesel freight vehicle with on-board measurement system, measuring actual emissions. Vehicle speed, acceleration, travel resistance were focused to clarify the influence on behavior of vehicle emission factors. Based on these results, vehicle emission factors model was composed and evaluated. As a consequence, it became possible that NOx, PM, CO2 emission factors are estimated with a high degree of accuracy.

A Rapid Compression Machine (RCM) has been used to study the effects of n-Heptane based equivalence ratio on Homogeneous Charge Compression Ignition (HCCI). The major intents were to characterize the combustion reaction time and its temperatures under various initial temperatures, different mixing ratio, stratified charge conditions and homogeneous charge conditions. To achieve this time resolved pressure and piston lift were taken. The fuels were used n-Heptane, iso-Octane and blending fuels, which are primary reference fuels in engine tests. The result showed that initial temperature increase low temperature reaction times are early. The effects of n-Heptane based on equivalence ratio are stronger at the case of lower initial temperature than higher of that. Moreover, stratified charge cases have less been the effects of n-Heptane based on equivalence ratio than homogeneous charge cases.

Homogeneous Charge Compression Ignition (HCCI) engine is supposed to achieve high thermal efficiency and low emissions. Meanwhile Di-Methyl Ether (DME) is expected as an alternative fuel for the internal combustion engines. In this study, four-stroke HCCI Engine running on DME, which include control system using EGR, is developed to make it practicable. Combustion characteristics are researched by numerical calculation with elementally reactions and experiment. Besides, developed engine performance is estimated. To conclude, DME is suitable fuel for the HCCI engines in terms of combustion characteristics but specific power of developed DME HCCI engine much is lower than conventional engines.

往復動機関のHCCI機関は回転速度に応じ予混合気の圧力および温度上昇速度が変化する．本研究では回転速度が着火時温度，燃焼期間および燃焼効率等のHCCI燃焼特性に与える影響を素反応数値計算により解析した． 燃料はNTC領域の有無が異なるメタンとDMEを用い，衝撃波管の着火遅れ特性との関係を考察した．

予混合気に温度および燃料濃度分布を与えることで予混合圧縮自己着火機関における急峻な圧力上昇を回避する手法を検証する．急速圧縮装置の燃焼室内に予混合気の温度ないし燃料濃度を層状に給気して，圧縮自己着火時の燃焼室内ガスの圧力履歴および化学発光像より，圧力上昇率の低減効果を解析した．

In HCCI combustion, sometimes there are two stage heat release; low temperature heat release (LTHR) and high temperature heat release (HTHR). Some experimental results clearly show pressure also is very important in determining whether we get LTHR or not. For instance, we found that if we ran the engine with boosted intake pressure and low temperature, we could see LTHR but LTHR disappears if the same fuel is run with low intake pressure and high intake temperature. Thus whether you see LTHR in HCCI tests depends very much on the operating conditions. The purpose of this study is to evaluate the elementary reaction path affected by an initial Pressure and Temperature. The influence of the fuels between high octane number and low octane number fuels are also considered. For this reason, n-Heptane (PRF0) that has large heat release in LTHR and iso-Ocatne (PRF100) that has small heat release in LTHR were used as test fuels. The method of calculate the contribution of each elementary reactions and chemical species are also considered.

２０世紀のエンジン開発は，高性能，高効率，低コストの追求でした．そして環境問題への対応から排気浄化技術の導入が図られました．さらには，地球温暖化の防止の視点からの環境性能が求められています．すなわち，「環境や資源に負担の少ないエンジンとは何か」ということを起点にして，社会のコンポーネントとしての次世代型エンジンが求められている．エンジンの効率および性能を左右するエンジン燃焼について，大学における燃焼:研究の最先端の取り組みを紹介する．

HCCI機関の実用化に向けて，高負荷時におけるロバスト性を確保した高効率運転が重要となる．本研究では単気筒エンジンを用い，量論比予混合気・高温EGRガス・低温EGRガスの供給比をスロットルで変化させ，圧縮開始時筒内ガス質量平均温度を変化させることにより燃焼制御を行うシステムを対象とした制御モデルを作成し提案する．

HCCI燃焼において、燃料に低温酸化反応での発熱量が多いn-Heptaneと少ないiso-Octaneを用いて、それぞれ単一の場合と混合した場合での供給する予混合気の温度及び圧力の違いが熱発生に及ぼす影響を、詳細な素反応数値解析により考察した。

HCCI機関において，吸気温度を変化させて燃焼位相を遅延化することにより，膨張行程で燃焼を行うことが圧力上昇率の低減および燃焼効率に及ぼす影響を解析した．燃料にはDME，Methaneおよびn-Butaneを使用し，詳細な素反応を考慮したマルチゾーンモデルを用いた素反応数値計算を行った．

HCCI機関において自着火特性の異なる二種の燃料を用い，圧縮前の燃焼室内局所における燃料の混合比に違いを与えることによる圧力上昇率の低減効果を検証した．実験には4ストローク単気筒可視化エンジンを用い，圧力計測に加えて燃焼室内の化学発光像を撮影し，燃焼室内局所におけるHCCI燃焼の様子を評価した．

本研究では、予混合気の温度および濃度の不均一性によって燃焼時の筒内ガス圧力上昇率が低減する機構を解明し、併せて排気特性への影響を調べることを目的として素反応数値解析を行った。

In HCCI engines, IMEP is limited by knocking in high load operation. Knocking occurs when pressure rise rate reaches 5MPa/ms. To investigate the factors which dominate pressure rise rate during HCCI combustion, this study investigates the effect of fuels and thermal stratification on pressure rise rate using optically accessible engine and rapid compression machine. By optically accessible engine, the effects of fuels stratification of DME which has large heat release in LTR and n-Butane which has smaller heat release in LTR than DME are investigated using pressure measurement and chemiluminescence imaging. On the other hand, by rapid compression machine, the effects of thermal stratification fueled with DME are analyzed using pressure measurement.

Homogeneous charge compression ignition (HCCI) engines are drawing attention as the next-generation internal combustion engine, but have not been put to practical use because of several issues. One of the issues is that increasing the fuel charge causes rapid combustion in the combustion chamber, which results in knocking that limits its operation region. In this study, the focus was put on a method to increase the operation region of HCCI engines by mixing two fuels with different reactivities. First, dimethyl ether (DME), n-butane, or hydrogen was mixed with methane to investigate how the changes in mixing ratios affected the oxidation reaction of the pre-mixture based on numerical calculations with elementary reactions. From the calculation results, applicable types of double componential fuels for HCCI engines were considered. Based on the results of the consideration, DME or n-butane was mixed with methane to conduct combustion experiments and to clarify mixing conditions of the double componential fuels that realize high output and high thermal efficiency simultaneously.