Published papers

Homogeneous Charge Compression Ignition(HCCI) engine has the potential to achieve lower NOx and PM emissions with high thermal efficiency. Although it has these merits, operation region is still limited by knocking. Combustion phasing retard is one of the methods to avoid knocking. However, excessive retard of CA50 will lead to unstable combustion. In this study, we developed a combustion control system for HCCI engine fuelled with DME. The cyclic dispersion mechanism on the excessive retard of CA50 was analyzed. And the controlling road map for reducing combustion variations was obtained. Based on these results, reduction of cyclic dispersion is realized by combustion control.

反応論的に自己着火時期を遅延させる効果を持ち、また蒸発潜熱の大きいEthanolを予混合気に中に筒内直接噴射して温度不均一を寄与するとともに、局所の着火時期の分散効果による圧力上昇率低減効果について検証したので報告する。

Operating range of HCCI engines is limited by an excessive pressure rise rate (PRR) in high load region resulting in engine knock. Dispersing auto-ignition timing at each local area in the combustion chamber and retarding combustion phasing (CA50) are main methods of decreasing the excessive PRR. Changing mixing ratio of two fuels which have different auto-ignition characteristics leads to the change of combustion phasing. The objective of this study was to investigate the effect of making the variation of mixing ratio in the mixture to change the combustion phasing at each local area in the combustion chamber on reducing PRR. The test fuels were DME and n-Butane which both have LTHR and HTHR during HCCI combustion. In addition to in-cylinder gas pressure measurement, in order to assess the combustion at each local area, chemiluminescence imaging and numerical analysis with multi-zones modeling were used. Maximum PRR changes depending on mixing condition of DME and n-Butane. When DME is stratified and n-Butane is distributed uniformly in the combustion chamber (Case3), maximum PRR becomes lowest. In Case3, the appearance timing of chemiluminescence at each local area is dispersed and the duration of chemiluminescence is longer than in Case1 (DME and n-Butane are both distributed uniformly). By numerical analysis, it is found that the temperature distribution and difference of HTHR start temperature makes difference of HTHR start timing in each zone.

In recent years, higher thermal efficiency and lower emissions are required on a reciprocating engine development and therefore cycle-to-cycle combustion control is necessary. Especially it is a key factor to control HCCI combustion engine. In HCCI engine, one of the most promising combustion methods to achieve high thermal efficiency, the ignition timing strongly depends on the mass-averaged temperature of charged gas and residual gas and very precious combustion phase control is required. Therefore it is important to detect the changes of cycle-to-cycle intake air flow rate, EGR gas flow rate and as well as residual gas in each cycle. The traditional laminar flow meter has too low responsivity to measure cycle-to-cycle flow rate. In this study, the fast-response laminar flow meter was developed in order to measure cycle-to-cycle dynamical flow rate. The availability of the fast-response laminar flow meter for cycle-to-cycle intake air flow rate measurement of the HCCI engine is shown in this paper.

The purpose of this study is to investigate combustion robustness of HCCI engines at retarded combustion phasing operation by going through numerical analysis with multi-zone model. The reason of calculation with the multi-zone model is to examine the mechanism of combustion phasing retard to reduce an excessive pressure-rise rate and keep combustion robustness with thermal stratification. It is found that excessive combustion phasing retard causes cyclic dispersion and misfire. With thermal stratification, combustion robustness at retarded combustion phasing operation is analyzed. As a result, in case of same initial mass averaged gas temperature as larger thermal stratification was set, 50% heat release timing of high temperature heat release (HTHR) was advanced because higher initial gas temperature zone was auto-ignited in turn. It was confirmed to trade off between pressure-rise rate and 50% heat release timing in HTHR

The most important issue for diesel engines for the last decade is the emission reduction to improve urban enviroments. For this problem, the emission regulation were tightened four times from '98 to '09, and many of diesel technologies such as turbocharging, fuel injection system, EGR and aftertreatment devices are remarkably improved. This article refers the progress of these technologies for ten years briefly.

HCCI機関などの次世代のエンジン開発では，燃焼のサイクル毎の安定性の確保が効率および出力の向上，排出ガスの低減の観点から求められている．さらに往復動機関は間欠燃焼を行うため，サイクル毎にシリンダ内に供給されるガスの流量を把握することが重要である．本研究ではサイクル毎のシリンダへの吸気流量を計測するため高い応答性を持つ層流形流量計測システムを試作し，単気筒HCCI機関に適用し，その性能を確認した．その結果，構築したシステムが高い応答性で正確に動的な流量計測を行えることが明らかになり今後のエンジン開発に有用あると考えられる．

Operating range of HCCI engines is limited by an excessive pressure rise rate (PRR) in high load region resulting in engine knock. Dispersing auto-ignition timing at each local area in the combustion chamber and retarding combustion phasing (CA50) are main methods of decreasing the excessive PRR. Changing mixing ratio of two fuels which have different auto-ignition characteristics leads to the change of combustion phasing. The objective of this study was to investigate the effect of making the variation of mixing ratio in the mixture to change the combustion phasing at each local area in the combustion chamber on reducing PRR. The test fuels were DME and n-Butane which both have LTHR and HTHR during HCCI combustion. In addition to in-cylinder gas pressure measurement, in order to assess the combustion at each local area, chemiluminescence imaging and numerical analysis with multi-zones modeling were used. Maximum PRR changes depending on mixing condition of DME and n-Butane. When DME is stratified and n-Butane is distributed uniformly in the combustion chamber (Case3), maximum PRR becomes lowest. In Case3, the appearance timing of chemiluminescence at each local area is dispersed and the duration of chemiluminescence is longer than in Case1 (DME and n-Butane are both distributed uniformly). By numerical analysis, it is found that the temperature distribution and difference of HTHR start temperature makes difference of HTHR start timing in each zone.

Recently, a potentiality of Dedicated EGR (D-EGR) concept SI engine has been studied. This concept engine had four cylinders and operated with exhaust gas supplied from the single cylinder to the intake manifold. Compared with conventional SI engines, it was able to increase thermal efficiency and decrease CO, HC, and NOx emission by the high D-EGR ratio 0.25. In this study, numerical analysis of a SI engine with D-EGR system with various D-EGR ratios was conducted for detailed understanding the potentiality of this concept in terms of thermal efficiency and NOx emission. #1 cylinder of assumed engine was used as D-EGR cylinder that equivalence ratio varied from 0.6 to 3.4. Entire exhaust gas from #1 cylinder was recirculated to the other cylinders. The other cylinders run with this exhaust gas and new premixed air and fuel with various equivalence ratios from 0.6-1.0. To study the effect of D-EGR ratio, the number of engine cylinders was considered from 3 to 6, same meaning with D-EGR ratio 0.5-0.2. A Laminar burning velocity and a flame temperature were considered to analyze thermal efficiency and NOx emission. The results show that D-EGR system is able to make a similar level of thermal efficiency to that of conventional SI engines. NOx emission were reduced by decreasing flame temperature while the laminar burning velocity was increased without flame temperature rising due to the influence of H2 and CO that were included in EGR gas as intermediates.

High thermal efficiency with low emission can be realized by low-temperature combustion using EGR. Alger,T in SwRI proposed "Dedicated EGR" (a single sylinder run under rich condition and 100% of exhaust gas from this cylinder recirculated into the other cylinders.) to improve burning velocity by CO and H2 that included in EGR gas under high EGR ratio. This study investigates the dependence of burning velocity and flame temperature on equivalence ratio and EGR ratio by the combustion of premixed methane-air. Finally, it confirmed that "Dedicated EGR" had a potentiality of improving both thermal efficiency and NO emission.

A combustion method called Noise Cancelling Spike (NC-Spike) Combustion has been reported in the co-author’s previous paper, which reduces combustion noise in pre-mixed charge compression ignition with split injection. The overall combustion noise was reduced by lowering the maximum frequency component of the noise spectrum. In this paper, we investigates feasibility and controllability of the two-peak heat release rate during high temperature heat release by adding fuel in the adiabatic compression process of pre-mixed gas. The results show that the certain fuel addition timing generates the second heat release, and the interval of peak heat release rate could be controlled.

今回の「ガソリンベーパーを考えるシンポジウム」 では，「自動車に起因する環境問題」というタイトルで話題提供をいたします。自動車の普及とそれに伴い発生した環境問題の歴史をレビューし，その中から問題点の把握し，課題解決のために私たちがなすべきことについて考えたいと思います。

1990年代から高まってきた地球環境問題への関心は、3・11以降新たなステージを迎えています。世界中で喫緊となっている代替エネルギーの問題、ＰＭ2.5に代表される越境汚染の問題など、その解決のために専門分野を横断する知の集結が求められています。慶應義塾では2011年から大学院博士課程でのグローバル環境システムリーダープログラムによる教育・研究を始めていますが、さらなる学部横断的な教育の取り組みの必要性が高まる中、環境問題の現在を考えていく特集です。

コーニング社のイノベーションの：歴史を紹介して，21世紀がサプライヤにとって明るい未来を拓く世紀であることを解説した

This work investigates the potential of in-cylinder exhaust gas recirculation stratification for reducing the rate of pressure rise in dimethyl ether homogeneous charge compression ignition engines and its coupling with both thermal stratification and fuel stratification. Numerical analyses were performed using a five-zone version of the CHEMKIN-II kinetics rate code and the kinetic mechanics of dimethyl ether. The effects of inert components were used to represent the presence of exhaust gas recirculation in calculations. Three cases of exhaust gas recirculation stratification were tested in terms of both thermal stratification and fuel stratification at a fixed initial temperature, fixed initial pressure and fixed fuelling rate at bottom dead centre. In order to explore the appropriate stratification of exhaust gas recirculation, the exhaust gas recirculation width (defined as the difference between the exhaust gas recirculation ratios in zone 1 and zone 5 in the five-zone model) which we employed was from 0% to 30%. The case of exhaust gas recirculation homogeneity (called case 1), in which the exhaust gas recirculation width is 0%, was examined. In case 2, exhaust gas recirculation is located densely in a hot zone for combination with thermal stratification or in a fuel-rich zone for combination with fuel stratification. The last case (case 3) was the inverse of case 2. Ringing was reduced to an acceptable level in the case of fuel stratification with an appropriate exhaust gas recirculation distribution, which slowed the rapid burning during the compression stroke.

This study aimed at revealing the characteristics of burning velocity of fuel-air mixtures under the ambient temperature and pressure changing condition which was made by using rapid compression machine. The burning velocity was measured by a double kernel method applied to the schlieren photographs. At first, the applicability of the double kernel method was examined and verified by utilizing a proper technique to analyze the schlieren photographs. At the next stage, under a standard condition (298K, 0.10MPa), the dependence of burning velocity on the fuel type was obtained and compared with those of the other studies. Finally, the dependence of burning velocity on the ambient temperature and pressure was obtained and discussed under the condition that the ambient state was varying with time according to the flame propagation.

As a technique of the combustion improvement, we used high-pressure fuel injection and micro-hole nozzle which has orifices with a diameter smaller than 0.10mm to promote the atomization of fuel and the mixing of fuel and air. We researched the combustion and the emission of an illustrated single cylinder diesel engine with micro-hole nozzle (the minimization under the term of same injection rate) and various combustion chambers (toroidal type, shallow dish type) at a fuel injection pressure of 100MPa. And we investigated the effect of nozzle orifice diameter, stage spray injection angle, and wall impinging.

ディーゼル噴霧の着火機構の解明を目的に，着火反応中に生成されるホルムアルデヒドをレーザー誘起蛍光法により２次元可視化している．光源にはNd:YAGレーザーの第３高調波を用いている．噴霧内のホルムアルデヒドは着火反応による総発熱量が燃料の吸熱，蒸発による総吸熱量に等しくなる時期に検出され始め，高温酸化反応が始まる前までは噴霧先端領域全体に分布する．この事はディーゼル噴霧の着火過程初期においては，燃料は低温酸化機構により酸化される事を示している．高温酸化反応によるホルムアルデヒドの消失は噴霧先端領域で開始する．雰囲気温度の上昇は，ホルムアルデヒドの出現と消失時期をともに早める．