Published papers

On-board measurement system that can simultaneously obtain such information as road infrastructure，traffic conditions，driver’s operations，vehicle running conditions and exhaust mass emissions， was installed into a light duty freight vehicle and one box vehicle. Mechanism of roadside pollution caused by test vehicles with and without EGR emission reduction system was analyzed by conducting actual road tests. Different types of intensive NOx pollution were observed in two test vehicles. The vehicle with EGR system showed intensive NOx pollution at vehicle acceleration, where EGR ratio is low, but it was effective to reduce NOx mass emissions at low speed running in traffic jams where EGR ratio is rather high. On the other hand, the vehicle without EGR system showed intensive NOx pollution in low speed running such as in traffic jams

Homogeneous charge compression ignition (HCCI) engine is expected as next generation engine. However, it is difficult to control auto-ignition timing and combustion duration. In this study, numerical calculations with elementary reactions were carried out in order to investigate auto-ignition and combustion completion of DME/Air mixtures in HCCI engine. As a result, it was clarified the relation of maximum temperature and combustion efficiency, and emissions. It was also clarified the factor to determinate combustion speed was mol number of fuel throwed into the combustion chamber. In addition, increase of internal EGR rate makes combustion speed be slow, but it is impossible to rise IMEP by increase of this rate.

The present study focuses on clarifying the auto-ignition and combustion mechanism in HCCI engine, and acquiring the comparable results in numerical calculations with elementary reactions. Chemical luminescences from radicals were measured in single cylinder 4-stroke optical access engine with DME fuel. DME shows multistage heat release with low temperature reaction (LTR) and high temperature reaction (HTR) at compressed rapidly as same as alkanes that have over 4 carbon. DME is expected to be alternative fuel, because of low flame temperature and no soot in a reciprocating engine. First, two dimensional chemical luminescence images were obtained by framing camera, and influences of distribution of fuel in combustion chamber was clarified. Next, by using photo multiplier, chemical luminescence intensity profiles all over the combustion chamber were measured. These data were compared with calculated mole concentration profiles and luminescence intensity profiles, and relationship between chemical luminescence and mole concentration was investigated

An investigation was made into the influences of the blend ratios of n-butane with low temperature reaction on ignition and combustion in methane/n-butane/air mixtures using elementary reactions calculation and experimental study. As a result of elementary reactions and experimental study, the following facts are made clear ; ⅰ) As the blend ratio of n-butane increases, the autoignition temperature becomes lower, the autoignition advances. These are most sensitive to the small blend ratio of n-butane, further amounts of n-butane have a comparatively smaller effect. ⅱ) The generation of O, H, OH, HO2 radicals advances with increasing the blend ratio of n-butane. This effect becomes smaller with increasing the blend ratio of n-butane. ⅲ) As the blend ratio of n-butane increases, the CO emission decreases, and the maximum cycle temperature and combustion efficiency become higher.

Actual exhaust emissions from running vehicle considerably depend on driver’s operation based on traffic conditions and road structure etc. It can result in local air pollution at roadside. It is necessary to clarify the influence on exhaust emissions by driver’s operation for analyzing of air pollution mechanism at roadside. Simultaneous on-board measurement system for vehicle running condition and actual exhaust emissions was developed to evaluate vehicle running condition and NOx emissions based on distance and time. The measurement system was installed in a freight vehicle whose payload is two tons, and actual driving test was conducted to evaluate the effectiveness of the system.

予混合圧縮自己着火機関の着火および燃焼は燃料の化学反応過程に大きく依存しており，その制御には化学反応機構の把握が必要である．従来の予混合圧縮自己着火機関に関する研究では当量比，吸気温度，機関回転速度，EGR率，圧縮比，加給圧力が着火・燃焼に与える影響が明らかにされている．これらの研究で主に解析される，燃焼室内圧力履歴，温度履歴，熱発生率履歴等は，各素反応過程で生じる熱発生を積算したものであり，詳細な化学反応過程を解析，評価するには不十分である．化学反応過程の解析には素反応過程を考慮した数値計算が行われているが，計算結果の検証には実機内での化学反応過程に立ち入った結果が必要となり，素反応計算での化学種濃度履歴とLIFによる化学種濃度履歴の比較・検証等の試みも行われている． 着火および燃焼時の化学反応の進行状況を実験的に理解する上で，化学発光を計測することは重要である．そこで，本研究では予混合圧縮自己着火機関の着火・燃焼過程の化学反応機構の解明，素反応数値計算結果との比較検証を行える結果の取得を目的に，まず素反応数値計算に発光モデルを組み込み発光強度履歴の予測を試みた．次に４ストローク単機筒可視化エンジンにジメチルエーテル（DME）空気予混合気を投入し，圧縮自己着火燃焼過程での化学発光の強度履歴を計測し，計算結果との比較を行った．また予混合気中の燃料濃度の不均質性が圧縮自己着火燃焼に及ぼす影響を二次元発光画像の計測により調査した．

Homogeneous charge compression ignition (HCCI) combustion is regarded as next generation combustion method in terms of high thermal efficiency and low emissions. Natural gas is regarded as the most promising alternative fuel due to its clean burning and abundant supply. In this study, it was investigated characteristics of autoignition and combustion of natural gas in an HCCI engine by using chemical reactions calculation and experimental study. And also, the operation conditions to realize combustion completion in an HCCI engine were suggested. The influences of n-butane blend ratio on autioignition and combustion was clarified in methane / n-butane / air mixtures. As a results of experiment and chemical reactions calculation, it becomes clear the following facts; ⅰ) Autoignition temperature of natural gas is in a range of 1000 ±100K without relations of equivalence ratios, intake temperatures and intake pressures. ⅱ) To realize high thermal efficiency and low CO emissions, it is necessary to prepare operation conditions that maximum cycle temperature is over 1500K. ⅲ) As blend ratios of n-butane are increased in Methane / n-Butane / air mixtures, autoignition temperature and autoignition pressure become lower.

本研究では代替燃料として注目されているジメチルエーテル（DME）を燃料として用い，HCCIエンジンを想定した素反応数値計算を行い，また予混合気中の燃料濃度の不均質性がHCCIエンジンの着火および燃焼に及ぼす影響を実験的に調査する．実験においては，４ストロークの可視化エンジンを用いて筒内圧力を計測すると同時に，二次元自発光画像の計測を行う．

Homogeneous charge compression ignition (HCCI) is regarded as the next generation combustion regime in terms of high thermal efficiency and low emissions. It is difficult to control autoignition timing and combustion duration because they are controlled primarily by the chemical kinetics of fuel-air mixture. In this study, it was investigated the characteristics of autoignition and combustion of natural gas in a 4 stroke HCCI engine. And also, to clarify the influence of n-butane on autoignition and combustion of natural gas, it was changed the blend ratio of n-butane from 0 mole-% to 10 mole-% in methane / n-butane / air mixtures. Autoignition strongly depends on in-cylinder gas temperature. Autoignition of natural gas occurs when in–cylinder gas temperature reaches in a range of 1000±100K under this experimental condition. To realize high thermal efficiency and low CO emissions, it is necessary to prepare operation conditions that maximum cycle temperature is over 1500K. Autoignition temperature is 25K lower by increasing n-butane blend ratio of 10%. As the blend ratio of n-butane increases, the maximum cycle temperature increases, and THC, CO emissions reduce.

The present study focuses on clarifying the combustion mechanism of the homogeneous-charge compression-ignition (HCCI) engine in order to control ignition and combustion as well as to reduce HC and CO emissions and to maintain high combustion efficiency by calculating the chemical kinetics of elementary reactions. For the calculations, n-butane was selected as fuel since it is a fuel with the smallest carbon number in the alkane family that shows two-stage autoignition (heat release with low- temperature reaction (LTR) and with high-temperature reaction (HTR)) similarly to higher hydrocarbons such as gasoline. The CHEMKIN code was used for the calculations assuming zero dimensions in the combustion chamber and adiabatic change. The results reveal the heat release mechanism of the LTR and HTR, the control factor of ignition timing and combustion speed, and the condition need to reduce HC and CO emissions and to maintain high combustion efficiency.

In the HCCI Engine, inhomogeneity in fuel distribution and temperature in the pre-mixture exists microscopically, and has the possibility of affecting the ignition and combustion process. In this study, the effect of charge inhomogeneity in fuel distribution on the HCCI combustion process was investigated. Two-dimensional images of the chemiluminescence were captured by using a framing camera with an optically accessible engine in order to understand the spatial distribution of the combustion. DME was used as a test fuel. By changing a device for mixing air and fuel in the intake manifold, inhomogeneity in fuel distribution in the pre-mixture was varied. The result shows that luminescence is observed in a very short time in a large part of the combustion chamber under the homogeneous condition, while luminescence appears locally with considerable time differences under the inhomogeneous condition. It is also shown that the local luminescence durations are almost the same in both conditions.

In this study, we have investigated the operation conditions to achieve high combustion efficiency and low CO emission in a four stroke HCCI engine using experimental analysis and elementary reactions calculation. It is shown that the combustion efficiency reaches higher than 90%, the CO emission can be reduced considerably when the mass averaged maximum temperature is over 1600K.

着火および燃焼の解析では，素反応過程を考慮した数値計算は，着火燃焼過程の詳細な化学反応の進行を評価できる手法として有効である。一方，実験則を用いたLivengood-Wu Model，化学反応過程を簡略化したShell ModelやSchreiber Modelといった簡略化モデルでも着火時期の予測は可能である。簡略化モデルをマルチディメンショナルの流体モデルに結合することで，確度の高い燃焼予測計算を行うことが期待される。 そこで本研究では，まず燃料種（DME，CNG，n-Butane），当量比，圧力をパラメータとして，詳細モデルによって各温度での着火遅れを算出し，データベース化する。その上でLivengood-Wu Modelに基づく推算値と詳細モデルの予測値が一致するか否かを，次の３つのケース，１）温度がＴ１からＴ２へステップ状に変化する場合，２）温度が連続的に上昇する場合，３）温度，圧力が共に断熱的に上昇する場合について順に比較する。最終的には確度の高いLivengood-Wu Modelに基づく推算式およびデータベースを提供する。

In the HCCI (Homogeneous Charge Compression Ignition) engine, a mixture of fuel and air is supplied to the cylinder and auto-ignition occurs resulting from compression. This method can expand the lean flammability limit, realizing smokeless combustion and also having the potential for realizing low NOx and high efficiency. The optimal ignition timing is necessary in order to keep high thermal efficiency. The Ignition in the HCCI engine largely depends on the chemical reaction between the fuel and the oxidizer. Physical methods in conventional engines cannot control it, so a chemical method is demanded. Combustion duration is maintained properly to avoid knocking. In addition, the amount of HC and CO emissions must be reduced. The objective of this study is to clarify the following through calculations with detailed chemical reactions and through experiment with the 2-stroke HCCI engine: the chemical reaction mechanism, and HC and CO emission mechanisms. Ignition and combustion mechanisms and the effect of pre-mixture heterogeneity on ignition and combustion are also clarified. This is done by using an optically accessible engine and measuring the luminescence at auto-ignition and during the combustion process.

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.

The purpose of this research is to get fundamental knowledge and to experimentally understand about combustion characteristics of the fuel mixture. This paper shows the Homogeneous Charge Compression Ignition (HCCI) characteristics of a mixture of n-Heptane and iso-Octane in a rapid compression machine. The experimental matrixes cover the n-Heptane mixing ratios, r (n- Heptane) , ranging from 0 to 100vol% and the equivalence ratios ranging from 0.1 to 0.6. The experimental study on the effect of mixing fuels focuses on the low temperature oxidation reaction temperatures, T(L) , the high temperature oxidation reaction temperatures, T(H) , the low temperature oxidation reaction starting times, t(L) , the high temperature oxidation reaction starting times, t(H) , and the degeneration period. The results show that as r (n -Heptane) decreases, t(L) and t(H) become longer and T(L) and T(H) increase by 30K. As the equivalence ratio increases, t(L) becomes longer but t(H) is not a function of equivalence ratio. Moreover, for the partial equivalence ratio of n-Heptane lower than 0.2, t(L) , t(H) , T(L) and T(H) are a function of partial equivalence ratio of n-Heptane, while for the partial equivalence ratio of n-Heptane higher than 0.2, there are no effects on any oxidation reaction.