Published papers

In this research, the influence on natural gas combustion of H2 and CO was investigated by numerical calculations with elementary reactions. The investigation was carried out using the following procedures: 1. To research basic oxidation characteristics of CH4/H2/CO mixed fuel, parametric calculations for initial temperature were carried out. 2. For investigation of the effect of H2 and CO on CH4 combustion, the calculations with H2 and CO initial mole fraction variation was carried out. As a result, it was clarified that the oxidation temperature of CO was higher than that of CH4 and H2, the increase of H2 initial fraction has the effect to advance CH4 ignition timing, and increase of the CO fraction, under the condition that only CO was added, has the opposite effect of H2 addition.

For practical application on the HCCI engine, solution of subjects, such as control of auto-ignition timing and avoidance of knocking, is indispensable. This study focused on the technique of controlling HCCI combustion appropriately, changing the mixture ratio of two kinds of fuel. Methane and DME/n-Butane were selected as fuel. The influence, which the mixing ratio of two fuels does to ignition timing, ignition temperature, rate of heat release and oxidation reaction process, were investigated by experiment with 4-stroke HCCI engine and numerical calculation with elementary reactions.

Homogeneous Charge Compression Ignition (HCCI) engine is regarded as next generation engine in terms of high thermal efficiency and low emissions. However, it is difficult to control ignition timing in HCCI combustion because auto-ignition depends on oxidation reaction of fuel. It is desirable that ignition temperature can be changed freely to control ignition timing. Changing ignition temperature is impossible by one component fuel. To solve this problem, the fuel blended with Methane and DME was used in this study. The effects of Methane / DME mixing ratio on ignition temperature and ignition timing in HCCI combustion were researched by the numerical calculation with elementary reactions and the experiment.

HCCI燃焼エンジンにおいて，二種燃料を用いて予混合気中に混合割合の不均一性を導入し，着火温度の異なる混合気の分布を作成することによって着火時期を時間的に分散させ,最大圧力上昇率を低下する効果についてそのポテンシャルを検証する。二種の燃料としては着火温度が低い燃料としてジメチルエーテル（以下DME）を，着火温度が高い燃料としてn-Butaneを用いた．

予混合圧縮自己着火（Homogeneous Charge Compression Ignition：HCCI）機関は，空気と燃料の予混合気を燃焼室内に導入し，ピストンの圧縮により高温・高圧とすることで多点同時に自己着火させる機関である．HCCI 機関は，その燃焼方式から高効率・低公害を実現しうる機関として注目されており，地球環境問題や石油資源の枯渇問題を緩和しうる手法の一つとしてその実用化が求められている．しかし，HCCI機関には，着火が燃料固有の着火温度に依存するため着火時期の制御が困難である，またノッキングのために運転領域が低負荷に限られるといった課題が存在し，課題解決のために多くの研究がなされている．HCCI 機関は，着火に至るまでピストンの圧縮によってのみ温度が上昇するので，着火時期の制御には圧縮開始時の筒内ガス温度が重要となる．また，ノッキングは急峻な燃焼により生じるため，その回避には燃焼反応速度の抑制が不可欠となる．本報では，各大学の研究室で行なわれている HCCI 燃焼研究の一部を紹介する

A Homogeneous Charge Compression Ignition (HCCI) engine is supposed to achieve high thermal efficiency and low NO_x PM emissions at the same time. Though it is expected to come into practical use, it has some serious problems such as ignition timing control, knocking at high load and securing of high combustion efficiency. In this study, a four-stroke HCCI engine running on Di-Methyl Ether (DME) is developed to make it practicable as a generator engine. A new HCCI combustion control method, controlling the gas fraction of internal EGR gas at high temperature, external EGR gas at low temperature and premixture at stoichiometric ratio, is proposed. And effects of the gas fraction on HCCI combustion are researched by numerical calculation with elementally reactions and experiment. To conclude, HCCI combustion can be optimized with controlling the fraction of internal EGR gas, external EGR gas and premixture.

Emissions factors, which is described by mass emission per distance, are applied to the estimation of the amount of exhaust emissions from running vehicles. However the difference of the emissions factor by road infrastructure is not clear. Road infrastructure, traffic conditions, driver’s operations, vehicle running conditions and NOx, PM emissions were investigated in order to clarify the difference of NOx and PM emissions factors between a narrow and a wide street by on-board emissions measurement system installed in a light-duty freight vehicle. It was found that affectors influencing NOx and PM emissions factors were different wide and narrow streets. The frequencies of the accelerator operations in the narrow street were more than that in the wide street. Difference of frequencies of NOx emissions factor were observed in both streets.

Homogeneous charge compression ignition (HCCI) combustion engine is bulk combustion, so it is easy to arise knocking that operation region is confined low load region. We have investigated　HCCI engine combustion tests using Methane/DME at high load operation region. DME has low ignition and combustion temperature compare to Methane. Temperature elevation and intermediate product are made by low temperature reaction of DME and they accelerate oxidization of Methane. So, the mixing ratios of Methane/DME could control ignition timing. This paper is written about improvement of IMEP in HCCI engine as control combustion timing put expansion stroke.

天然ガスを燃料とするＨＣＣＩ機関に排気タービン過給を適用することを想定して，過給機効率を模擬した場合の性能および排気特性を詳細に調査した．これに基づき過給による平均有効圧力の向上，熱効率の向上の可能性を明らかにした．また無過給と過給の性能を比較することで過給による性能改善の原因についても検討した．

本研究ではDMEを燃料とするHCCI機関を汎用小型発電機用の機関として実用化することを目的とし，高温の内部EGRと低温の外部EGRを用いたHCCI機関の制御システムを構築し，機関の開発を行う．本報では，素反応数値計算及び燃焼実験によって，DMEの燃焼特性を調査すると共に，開発したHCCI機関の性能の評価を行う．

The purpose of the research is to investigate of diesel spray combustion for simultaneously reduce way NOx and PM．The pressure diesel injection were done into intermediates that are generated by very lean DME HCCI combustion using a rapid compression machine (RCM)．The concentration of intermediate could not be directly measured; we estimated it by CHEMKIN calculation．Homogeneous charge compression ignition characteristic of DME-air mixture is surveyed． Validations of the CHEMKIN calculation were confirmed pressure rise of an experiment and pressure rise of a calculation． Using a framing streak camera captured two dimensional spontaneous luminescence images from chemical species at low temperature reaction(LTR) and high temperature reaction (HTR)． Also， the combustion events were observed by high-speed direct photography， the ignition and combustion were analyzed by the combustion chamber pressure profiles and the KL values and flame temperatures were analyzed by the two-color method from the two dimensional flame image．

本研究では，このエンジンシステムにおいて実現される，天然ガスとその改質ガスである水素と一酸化炭素の圧縮自己着火燃焼を対象として，素反応数値計算により燃焼解析を行った．天然ガスの主成分であるMethaneと空気の予混合気に対し，改質により生成される水素（H2）と一酸化炭素（CO）を添加して計算を行い，Methaneの酸化反応に及ぼす影響について調査した．

In HCCI Engine, inhomogeneity of fuel distribution and temperature in pre-mixture microscopically exists and has possibility to affect the ignition and combustion process. In this study, the effect of charge inhomogeneity of fuel distribution on the HCCI combustion process was investigated. Pressure profiles were measured and two dimensional chemiluminescence images were captured by using a framing camera with a 4-stroke optical access engine. DME was used as the test fuel. Changing the way of mixing air and fuel in the intake manifold, inhomogeneity of fuel distribution in the pre-mixture was varied.

Numerical calculation with elementary reaction model is very available to analyze ignition and combustion process. On the other hand, the Livengood-Wu integral model is the simplified model to predict ignition timing or knocking timing. In this study, in order to verify the Livengood-Wu model, numerical calculation with elementary reactions was carried out. At first, ignition delays at each equivalence ratio, initial pressure and temperature with shock-tube condition was calculated. And then, in two steps temperature condition, the ignition delay acquired from numerical calculation and that calculated from the Livengood-Wu Integral were compared. As a result, in case of Methane, if any temperatures were selected, the ignition delays from these two ways were almost accorded. In case of DME and n-Butane, if the temperatures higher than NTC (Negative Temperature Coefficient) Region were selected, the ignition delays from these two ways were almost accorded.

The past researches clarify the advantages and the disadvantages of HCCI Engine. In this paper, the conditions such as the amount of intake fuel and EGR gas, that can realize the operation, are investigated by using the past experimental data and the numerical analysis. On the basis of this, actually the engine is designed and tested. In addition, EGR gas is controlled by two ways, one is changing the exhaust tappet clearance and another is using the new cam that has two ledges in exhaust. The effect of the difference of the residual ways is investigated.

In the HCCI Engine, inhomogeneity of fuel distribution and temperature in pre-mixture microscopically exists and has possibility to affect the ignition and the combustion process. In this study, the effect of charge inhomogeneity of fuel distribution and temperature on the HCCI combustion process was experimentally investigated by the two dimensional chemiluminescence images. First, the effect of inhomogeneity of fuel distribution in the pre-mixture was investigated in the 4-stroke optical access engine. Second, comparing the combustion of the homogeneous mixture in a rapid compression machine, which has no residual gas, and the combustion in the 4-stroke engine, the effect of the residual gas was analyzed. DME was used as the test fuel. The result showed that a time rag appears spatially in combustion on the inhomogeneous condition in the 4-stroke engine. The luminescence intensity of the combustion in the rapid compression machine has less spatial variation than that in the 4-stroke engine.