論文

The purpose of this study was to compare the spray characteristics, the combustion characteristics and the emissions (nitrogen oxides, carbon monoxide, hydrocarbon and smoke) of typical fuels (100% diesel and 100% dimethyl ether) and diesel–dimethyl ether fuel blends in a constant-volume chamber and a single-cylinder direct-injection diesel engine. The spray characteristics were investigated by varying the ambient pressure and the fuel injection pressure using a commonrail fuel injection system with various fuel mixture ratios. The spray characteristic research parameters were the spray shape, the penetration length and the spray angle at the seven-hole injector. Common types of injector were used (Bosch). Two types of fuel blended by mass fraction were employed. Typical fuels (100% diesel and 100% dimethyl ether) and fuel blends with diesel:dimethyl ether mixture ratios of 95:5 and 90:10 were used. The injection pressure was fixed at 70 MPa while the ambient pressure was varied (0 MPa, 2.5 MPa and 5 MPa). The combustion experiments were conducted in a single-cylinder engine equipped with a common rail. The injection pressure was 700 bar at 1200 r/min. The amount of injected fuel was adjusted to obtain a fixed input calorific value of 972.2 J/cycle in order to make a comparison between the fuel types. The results showed that the injection quantity was greater with diesel fuel but not for dimethyl ether fuel and for the fuel blend with the higher mixing ratio. The spray penetration length increased with increasing ambient pressure for diesel but decreased for dimethyl ether with a larger spray angle. The ignition delay and the heat release rate decreased with increasing dimethyl ether which led to a higher indicated mean effective pressure and higher thermal efficiency because there was less negative work in the expansion. The total hydrocarbon emissions and the carbon monoxide emissions decreased with increasing dimethyl ether, but the nitrogen oxide emissions generated were greater owing to the increased combustion temperature.

Object of this study is to realize improving thermal efficiency and emission reduction with low temperature combustion. EGR is a solution to low temperature combustion, however it occurs burning velocity decrease. To prevent this phenomenon, Dedicated EGR was adjusted to SI engine run by natural gas. The entire exhaust gas of a single cylinder operated by the equivalence ratio varied from lean to rich was recirculated to the other cylinders. Due to H2 and CO included in EGR, slowed burning velocity problem was overcome with increasing degree of constant volume, thus thermal efficiency could be improved.

This study experimentally investigates the effects of the combustion phasing on the homogeneous charge compression ignition (HCCI) combustion, and implements a closed-loop control of HCCI combustion to reduce pressure-rise rate (PRR) with combustion-phasing retard. The experiments were conducted using dimethyl ether (DME) in a single-cylinder HCCI research engine equipped with an exhaust gas recirculation (EGR) loop for external EGR and a two-stage exhaust cam for rebreathed EGR. The results show that a maximum PRR (PRRmax) and a maximum in-cylinder charge temperature decreases with combustionphasing retard. However, excessive combustion-phasing retard leads to unacceptable coefficient of variation (COV) of CA50 and IMEP with partial-burn and/or misfire cycles. To dampen increasing cycleto- cycle variations around the limit of combustion-phasing retard, the closed-loop control of HCCI combustion was implemented using three feedback variables. Finally, stable stoichiometric HCCI operation could be achieved with extensive combustion-phasing retard while maintaining acceptable PRRmax with the higher level of IMEP.

An investigation was conducted to examine the effects of key parameters such as intake temperature, equivalence ratio, engine load, intake pressure, spark timing and spring stiffness on the transition from SI combustion to HCCI combustion in a two-stroke free piston linear engine. Operation of the free piston engine was simulated based on the combination of three mathematical models including a dynamic model, a linear alternator model and a thermodynamic model. These mathematical models were combined and solved by a program written in Fortran. To validate the mathematical models, the simulation results were compared with experimental data in the SI mode. For the transition from SI combustion to HCCI combustion, the simulation results show that if the equivalence ratio is decreased, the intake temperature and engine load should be increased to get a successful SI-HCCI transition. However, the simulation results also show that the in-cylinder pressure is decreased, while the peak in-cylinder temperature in HCCI mode is increased significantly if the intake temperature is increased so much. Beside the successful SI-HCCI transition, the increase of intake pressure from Pin = 1.1 bar to Pin = 1.6 bar is one of solutions to reduce peak in-cylinder temperature in HCCI mode. However, the simulation results also indicate that if the intake pressure is increased so much (Pin = 1.6 bar), the engine knocking problem is occurred. Adjusting spring stiffness from k = 2.9 N/mm to k = 14.7 N/mm is also considered one of useful solutions for reducing the peak in-cylinder temperature in HCCI mode as well as avoiding engine knock. Besides, the change of spark timing is suggested as a benefic method to help the control of the SI-HCCI transition to be more convenient. To get a successful SI-HCCI transition with reducing of peak temperature in HCCI mode as well as avoiding engine knock, the simulation results show that the engine should be operated with following conditions: equivalence ratio / = 0.7, engine load RL = 180 X, intake temperature Tin = 400 K, intake pressure Pin = 1.2 bar, spark timing in SI mode xig = 3 mm and spring stiffness k = 14.7 N/mm.

In this study, for the development of a lightweight and small-sized generator HCCI engine fuelled with Dimethyl Ether (DME) which is low-emission and easy to autoignite, a simple HCCI combustion control system is suggested, and the control system is evaluated experimentally. In the control system, the means of controlling gas temperature at inlet valve closure (IVC) is focused on to control CA50 as the specific autoignition temperature of a fuel is constant in HCCI combustion. The amount of premixture of air and fuel at stoichiometric ratio necessary to achieve load is fixed, and gas temperature at IVC is controlled by changing the mixing ratio of hot (internal) EGR gas and cold (external) EGR gas. And also cold EGR gas plays a role in the avoidance of a very rapid combustion reaction speed. The exhaust cam has two stages to use hot EGR gas, and exhaust gas is cooled through the heat exchanger to use cold EGR gas. The mixing ratio of three gases, stoichiometric premixture, hot EGR gas and cold EGR gas, is controlled by four throttles placed in the flow path of these gases.

"予混合圧縮自己着火燃焼は高負荷域において急峻な圧力上昇によって生じるノッキングが実用化への課題となっている．ノッキングの回避には最大圧力上昇率を抑制することが重要となり,その方法として予混合気内に温度分布を生じさせる方法が注目されている． 本研究では温度分布を生じさせる手法として燃料濃度不均質性に着目し，燃料としてDMEを用い，HCCI燃焼に及ぼす影響を調査した.化学発光によって燃焼室内局所の燃焼特性を評価した. 不均質混合気においては当量比の分布により燃焼室内局所ごとに発光強度ピーク時期が分散したことから,熱発生率ピーク時期もまた分散したと考えられ,均質混合気に比べ最大圧力上昇率が低下した. 予混合圧縮自己着火燃焼は，高効率・低公害の燃焼方式として注目されている．しかし，高負荷域において急峻な圧力上昇によって生じるノッキングが実用化への課題となっている．ノッキングの回避には最大圧力上昇率を抑制することが重要となり，本研究では予混合気中の燃料濃度不均質性の，最大圧力上昇率などへの影響ラジカル発光像を用いて燃焼室局所ごとの燃焼特性を評価することで，燃料濃度の不均質性がHCCI燃焼に与える影響を調査する． 予混合圧縮自己着火（以下HCCI）燃焼は，高効率・低公害が可能となることから次世代の燃焼方式として注目されている(1)．しかし，高負荷域において急峻な圧力上昇によってノッキングが発生してしまい，運転領域が低負荷に限られることが実用化への課題となっている．ノッキングの回避には最大圧力上昇率を抑制することが重要となり,その方法として予混合気内に温度分布を生じさせる方法が注目されている(2)．本研究では温度分布を生じさせる手法として予混合気中の燃料濃度不均質性に着目する．そしてラジカル発光像を用いて燃焼室局所ごとの燃焼特性を評価することで，燃料濃度の不均質性がHCCI燃焼に与える影響を調査する． "

ノッキングにより運転領域が制限されるというHCCI機関の課題に対し，本研究では二成分混合燃料を用いて運転領域の拡大を試みた。本報では，Methaneに対しDME，n-Butane，水素あるいは一酸化炭素を混合した場合に，その混合割合の変化が予混合気の酸化反応過程に及ぼす影響を素反応数値計算によって調査した。

ノッキングにより運転領域が制限されるというHCCI機関の課題に対し，本研究では二成分混合燃料を用いて運転領域の拡大を試みた。本報では，前報の素反応数値計算結果を受け，メタンに対しDMEあるいはn-Butaneを混合して燃焼実験を行い，高出力，高熱小効率を同時に実現可能な燃料の混合条件を明らかにした。

低温反応での発熱量が違う，n-Heptane およびiso-Octaneを燃料として使って温度・濃度不均質が予混合圧縮自着火に及ぼす影響を調査した．急速圧縮装置を用いて予混合気を圧縮自己着火させ,筒内圧力、筒内平均温度，二次元発光画像の取得，解析を行い、不均質性を持つ燃焼ガスの着火・燃焼機構を調査した

In this paper the diesel in-cylinder control of nitrogen oxide(NOx) and soot formation was tested. Carbon dioxide(CO2) was used as a dilutuent to simulate the exhasut-gas recirculation(EGR) process at ratios of 4.3%, 9.5% and 14.3%, thus making oxygen(O2) concentrations of 20%, 19% and 18% respectively. In addition, three diesel fuels with different T90 distillation temperatures were used, The fuel parameters were isolated from the influence of the aromatics content, sulfer content, and cetane number. A single-cylinder rapid compression machine(RCM) was used to simulate the diesel-tye combustion. The igniton and combustion process of diesel-fuel spray were observed using high-speed direct photography. The flame temperature (an indication of NO formatio) and KL factor (an indication off soot concentration inside the diesel-fuel spray) were analyzed using two-color method. The study demonstrated that with an increase of the CO2 concentration in the intake charge, the maximum flame temperature and the soot formation decrease. Also, when therewas a CO2=4.3% concentration in the intake charge, the results showed no significant influence of the diesl-ffuel T90 distillation temperature on the maximum flame temperature and the soot formation.

HCCI機関の燃料としてメタンとDMEあるいはメタンとn-ブタンを用い，二種混合燃料の燃料組成の違いが運転領域に及ぼす影響を実験により調査する．また，その運転領域変化の要因について，素反応数値計算を用いた詳細な素反応過程を検証することで燃料組成がHCCI燃焼機構に及ぼす影響を調査する．

ジメチルエーテル（Dimethyl Ether : DME）は，低公害な燃料で，さらに低温酸化反応（Low Temperature Reaction : LTR）と高温酸化反応（High Temperature Reaction : HTR）の二段の熱発生を持ち，着火性に優れているため，ディーゼル機関やHCCI機関への適応が広く研究されている．本研究では，DMEを燃料とする軽量・小型発電機用HCCI機関の開発を目指し，スロットルを用いた量論比予混合気，高温内部EGRガス，低温外部EGRガスの三者のガス混合割合調節により，上記の課題を解決するシンプルな機構を持つHCCI燃焼制御システムを構築する．さらに，燃焼実験により構築した制御システムの評価を行う．

RC220では急速圧縮装置と可視化エンジンを用いて，ラジカル発光計測を行い，予混合気空間濃度の不均一性がHCCI燃焼機構に及ぼす影響を調査する．期待される成果としては，HCCI機関実用化の最重要技術として位置付けられる「着火時期および燃焼期間の制御」に関する知見を得ることに加え，knockingを回避して高IMEP化を達成するための知見を提供することができる．

Although HCCI engine attracts attention as a next-generation internal combustion engine, it must clear subjects, such as control of suitable auto-auto-ignition timing, and reservation of high IMEP avoiding knocking, for the utilization. Moreover, it is also an important factor to design the fuel that is ignited at the suitable crank angle. From the viewpoint of chemical reaction theory, it is necessary to investigate the fundamental combustion characteristic of the fuel in HCCI combustion. In this study, using two kinds of fuels, its attention was paid to the technique of controlling auto-ignition timing of HCCI combustion appropriately by changing the mixed rate of them, and fundamental investigation about the ignition and combustion characteristic was conducted. DME and n-Butane with low temperature reaction, and Hydrogen, which is easy to be ignited, are mixed to Methane without the reaction, respectively. The mixed rate of two kinds of fuel investigated the influence affect auto-ignition timing, and the influence affect IMEP by a combustion experiment and numerical computation with elementary reactions. When the rate of DME, n-Butane, and Hydrogen was made to increase from the result of a combustion experiment, it turns out that auto-ignition temperature became lower and auto-ignition timing became early. On the contrary, it became clear for it to be able to operate, while delaying auto-ignition timing to expansion stroke and securing high IMEP by making the rate of Methane increase. From the result of numerical calculation, it became clear that the promotion effect of DME, n-Butane, and Hydrogen shows up by accelerating oxidization of intermediate species, such as H2O2 and HCHO, and supplies of OH radical.

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.