Daisuke Kawano

混合燃料の気液平衡や物性値を推定する多成分燃料噴霧モデルは、多成分燃料噴霧の燃料濃度分布特性を表現できる。本論文では、WAVE-MTABモデルを分裂モデルに適用し、高圧噴射条件下における二成分燃料噴霧の噴霧特性を解析した。その結果、二成分燃料噴霧の先端挙動及び各燃料の濃度分布を再現することができた。

© 2020 SAE International. All rights reserved. Fuel design concept has been proposed for low emission and combustion control in engine systems. In this concept, the multicomponent fuels, which are mixed with a high volatility fuel (gasoline or gaseous fuel components) and a low volatility fuel (gas oil or fuel oil components), are used for artificial control of fuel properties. In addition, these multicomponent fuels can easily lead to flash boiling which promote atomization and vaporization in the spray process. In order to understand atomization and vaporization process of multicomponent fuels in detail, the model for flash boiling spray of multicomponent fuel have been constructed and implemented into KIVA3V rel.2. This model considers the detailed physical properties and evaporation process of multicomponent fuel and the bubble nucleation, growth and disruption in a nozzle orifice and injected fuel droplets. In this study, the results from numerical simulation using this model were compared with experimental data (liquid and vapor distribution and spray tip penetration) which were obtained using a constant volume vessel. It was confirmed that high volatility fuel vaporized earlier than low volatility fuel and high vapor concentration region of high volatility fuel was located in the upstream of the spray, as well as the numerical results. The spray tip penetration obtained from numerical simulation also showed good agreement with the experimental results. In addition, the effect of flash-boiling on the spray characteristics of multicomponent fuel was verified by changing the initial fuel temperature using numerical simulation. As a result, flash-boiling rapidly vaporized both fuel components due to the appearance of bubbles in nozzle orifice and injected fuel droplets.

以前の研究では、多成分燃料の瞬間沸騰噴霧のモデルを構築し、KIVAコードに実装した。最新のディーゼルエンジンに多成分燃料を適用するためには、高い噴射圧力での噴霧特性を調査する必要がある。本研究では、高噴射圧力での噴射特性に及ぼす初期燃料温度の影響を調査した。

局所的排出ガス汚染の把握には実路における実走行車両の排出ガス量の評価が必要だが，全ての車両に対する計測は不可能である。既報において，エンジン試験，車両試験の結果を基にしたNOx排出量計算式を提案した。本報では，実路走行時のNOx排出量予測に必要となるドライバモデルの構築を行った結果を報告する。

局所的排出ガス汚染の把握には、リアルワールドにおける実走行車両の排出ガス量の評価が必要だが、全ての車両に対する計測は不可能である。本研究では実走行車両の排出ガス性能の評価のために、エンジン試験、車両試験の結果をベースとしたシミュレーションモデルを構築し、その精度について検討を行った。

著者らが提案している従来の航続距離延長自動運転は何れも直線走行のみを考慮しているが、旋回時にはタイヤの横滑りによる抵抗や左右輪の回転速度差等が生じるので、旋回を含んだコースに適用することはできない。本稿では、車両の旋回運動、その際にタイヤの横滑りによって生じるコーナリング抵抗をモデル化することで、航続距離延長自動運転を旋回を含んだコースで適用できるように拡張すした。また、シミュレーション及び実験によって提案法の有効性を示した。

エンジンの暖機過程を予測することは、冷機始動時における燃費・排出ガス性能等のシミュレーションや、エンジン水温センサ異常時の制御機能の維持に有効である。本研究では、簡易的なモデルと実験的に定量化したエンジンシステムの総熱容量を用いて、暖機過程におけるエンジン水温の変化を予測する手法を構築した。

Electric vehicles (EVs) have been intensively studied in the last decade due to their environment-friendly characteristics. However, the miles-per-charge of EVs is less than that of internal combustion engine vehicles. To improve the miles-per-charge, the authors' group proposed a Range Extension Autonomous Driving (READ) system that minimizes consumption energy by optimizing the velocity profile. However, conventional systems can be applied to driving on only straight roads. Therefore, this study extends READ system to be applied to driving not only on straight roads but also on curved roads by modeling the vehicle rotation motion and the cornering resistance. The effectiveness of the proposed method is verified by simulations and experiments.

ポスト新長期規制適合車に搭載されているディーゼルエンジンを用いて、従来の重量車燃費試験法による燃費計算値とエンジンベンチにおける燃費計測値を比較した。さらに、個々のエンジンの過渡特性に基づいた補正方法を考案し、その効果を検証した結果、本補正方法により高精度に試験エンジンの過渡特性を表現できることがわかった。

重量車の型式認証試験における燃料消費率試験法では、エンジンの定常状態で計測した燃費マップから参照した瞬時燃料消費量を積算しモード走行燃費を計算しているため、過渡的なエンジン性能は考慮されない。本研究では、エンジン個々の過度特性に基づいて補正を行う高精度に重量車の燃料消費率を算出する方法を考案し、ポスト新長期規制適合した重量車用エンジンを用いてその妥当性を検証した。

Electric vehicles (EVs) have been intensively studied over the past decade, owing to their environmentally-friendly characteristics. However, the miles-per-charge of typical EVs is lower than the cruising range of typical internal combustion engine vehicles. To increase miles-per-charge, the authors' research group has proposed a series of control systems, including Range Extension Control Systems (RECS) and Range Extension Autonomous Driving (READ) systems. In this paper, by considering the load transfer, slip ratio, motor losses, a READ system is proposed that optimizes the velocity trajectory and the front and rear driving-braking force distribution ratio; these techniques help reduce the consumption energy of the autonomous vehicle. The effectiveness of the proposed method is verified by simulations and experiments.

Electric Vehicles (EVs) are deemed as an appealing and practical solution for environmental and energy problems. The mileage per charge of EVs, however, is shorter than the mileage of Internal Combustion Engine Vehicles (ICEVs). In this paper, Range Extension Autonomous Driving (READ) system considering road gradient information is proposed. The proposed system optimizes the velocity trajectory and the driving-braking force distribution ratio for autonomous driving. The authors carried out simulations and bench tests that prove the effectiveness of the proposal in terms of mileage per charge.

Recently, Intelligent Transport Systems (ITS) technology have been intensively studied to solve environmental and energy problems by improving traffic flow. Along with the development of ITS and autonomous driving technologies, vehicle velocity control has to be considered for energy efficiency. In this paper, a minimum time autonomous driving (MTAD) system, which minimizes the traveling time considering energy constraint for an electric vehicle (EV), is proposed. The proposed method minimizes the traveling time by optimizing the velocity profile and front and rear driving-braking force distribution. The effectiveness of the proposed method is verified by simulations and bench tests.

Widespread use of biofuels for automobiles would greatly reduce CO&lt inf&gt 2&lt /inf&gt emissions and increase resource recycling, contributing to global environmental conservation. In fact, activities for expanding the production and utilization of biofuels are already proceeding throughout the world. For diesel vehicles, generally, fatty acid methyl ester (FAME) made from vegetable oils is used as a biodiesel. In recent years, hydrotreated vegetable oil (HVO) has also become increasingly popular. In addition, biomass to liquid (BTL) fuel, which can be made from any kinds of biomass by gasification and Fischer-Tropsch process, is expected to be commercialized in the future. On the other hand, emission regulations in each country have been tightened year by year. In accordance with this, diesel engines have complied with the regulations with advanced technologies such as common-rail fuel injection system, high pressure turbocharger, EGR and aftertreatment system. Unfortunately, the engine control system with these advanced technologies is adapted to conventional diesel fuels. Therefore, the use of new fuels to the latest diesel vehicles has a possibility to increase exhaust emissions. From the above background, many researches evaluated emission characteristics of diesel engine fueled with biodiesel such as FAME and HVO in test cells, and indicated the increase in NOx emission by the use of FAME. As for HVO, it was revealed that the NOx emission level was almost the same as that of conventional diesel fuel. In order to evaluate the real value of emission characteristic from a diesel engine fueled with biodiesel and disseminate information about environmental impact of biodiesel, it will be necessary to conduct not only evaluation in a test cell but also measurement by on-road driving tests. In this research, real-world emissions from a heavy-duty diesel vehicle fueled with biodiesel such as FAME, HVO and BTL were evaluated by the on-road emission measurement using a portable emission measurement system (PEMS). As a result of statistical analysis of real-world emission data, it was indicated that hydrocarbon biofuels such as HVO and BTL have an advantage of emission characteristics compared with FAME.

国内のスギ廃材から製造される水素、メタノール、ジメチルエーテル（DME）、および合成軽油（FTD）を対象とし、実データを用いたWell to WheelにわたるLCA分析を行い、各バイオ燃料のCO2排出量削減効果を検証した。その結果、バイオ燃料の種類によりそれぞれ異なる長所・短所を有するものの、国内のバイオマス資源を利用する場合は、共通して製造時の所内動力の削減と車両燃費の向上が今後の課題であることが示唆された。

各種BDFやHVO・BTLを想定した炭化水素燃料をディーゼル機関に使用した際のNOx排出特性を解析した。その結果、既存のディーゼル機関にバイオマス由来の燃料を適用する場合、低位発熱量が軽油と変わらず、かつ高H/C比により火炎温度が低下するHVOやBTLが有望であることが示唆された。

本報ではKIVA3Vをベースに筆者らが構築した多成分燃料噴霧モデルにShellモデルを導入し、定容容器における実験値との比較からその妥当性を検証するとともに、種々の二成分混合燃料噴霧の着火機構を調べた。さらに、このモデルを用いて、沸点ならびに着火性の異なる二成分からなる混合燃料による燃焼制御法の実現可能性を調べた。

Utilization of biofuels to vehicles is attracting attention globally from viewpoints of preventing global warming, effectively utilizing the resources, and achieving the local invigoration. Representative examples are bioethanol and biodiesel. This study highlights biodiesel and hydrotreated vegetable oil (HVO) in view of reducing greenhouse gas emission from heavy-duty diesel vehicles. Biodiesel is FAME obtained through ester exchange reaction by adding methanol to oil, such as rapeseed oil, soybean oil, palm oil, etc. As already reported, FAME has fuel properties different from conventional diesel fuel, resulting in about 10% increase in NOx emission [1],[2],[3]. Suppression of such increase in the NOx emission during operating with biodiesel requires adjustment of the combustion control technology, such as fuel injection control and EGR, to the use of biodiesel. However, designing of vehicles and engines for dedicated use of biodiesel cannot be expected much because of the development cost. Besides, biodiesel suffers deterioration in low-temperature fluidity in cold climate, so that certain users use diesel fuel only in such cold climate. In this way, many issues must be solved before the vehicles and engines use only biodiesel. On the other hand, HVO is fuel produced by the hydrotreating reaction used in the oil refining process. It is possible for any fatty oil to be raw oil of this fuel. In addition, HVO is able to be used in substitution for conventional diesel fuel since it mainly consists of paraffinic hydrocarbon. In this study, NOx emission was investigated when FAME and HVO were used for heavy-duty diesel engine under steady-state condition and JE05 driving cycle. From the results of this study, it was confirmed that the fuel injection volume had increased compared to the hydrocarbon fuels such as HVO and diesel fuel because the FAME had small lower heating value (LHV) per unit volume. It was thus confirmed that the combustion control state such as the EGR ratio and the fuel injection pressure had changed. This was presumed to be one of the factors causing the increase in NOx. It was revealed that FAME and the hydrocarbon fuel could suppress the increase in the NOx emission because the higher the H/C ratio of a fuel was, the more the flame temperature decreased. The above results showed that HVO having the LHV per unit volume equivalent to diesel fuel with the high H/C ratio was the biomass-derived diesel alternative fuel which could suppress the increase in NOx emission. Copyright © 2012 SAE International.

多成分燃料噴霧モデルに着火・燃焼モデルを組み込むことにより、二成分燃料の噴霧燃焼モデルを構築した。本モデルによる計算結果と定容容器による二成分燃料の噴霧燃焼実験の結果を比較した結果、計算結果と実験結果は良い一致を示し、構築したモデル、ひいては混合燃料を用いた燃焼制御手法の妥当性が示された。

単気筒エンジンを用いたBDFの基礎燃焼実験、および0次元サイクルシミュレーションによる数値解析により、NOx増大を引き起こす要因を詳細に解析した。その結果、軽油運転時に対する顕著な熱発生率の変化や、燃焼ガスの比熱変化に伴う燃焼温度上昇は見られず、噴霧中への空気導入量の変化等がNOx排出量増大の主要因であることがわかった。

The use of biofuel is essential for the reduction of greenhouse gas emission. This paper highlights the use of biodiesel as a means of reducing greenhouse gas emission from the diesel engine of heavy-duty vehicles. Biodiesel is fatty acid methyl ester (FAME) obtained through ester exchange reaction by adding methanol to oil, such as rapeseed oil, soybean oil, palm oil, etc. The CO2 emission from combustion of biodiesel is defined to be equivalent to the CO2 volume absorbed by its raw materials or plants in their course of growth. On the other hand, however, biodiesel is known to increase the NOx emission when compared with operating with conventional diesel fuel [1], then suppressing this increase is regarded as a critical issue. This study is intended to identify the fuel properties of biodiesel free from increase in the NOx emission. For this purpose, multiple kinds of biodiesel differing in fuel properties were used with the single-cylinder diesel engine, so that the effects of the difference in fuel properties on combustion and exhaust gas characteristics were clarified. © Copyright 2011 Society of Automotive Engineers of Japan, Inc. and SAE International.

軽油に対するBDFの混合割合が尿素SCR触媒を装着したディーゼル機関のNOx排出特性に与える影響を解析した。JE05モード試験を行った結果、BDFの混合割合増加によりエンジンアウトのNOx排出量は増加するとともに、尿素SCR触媒のNOx浄化率が大きく低下した。これは、BDF使用時に尿素SCR触媒入り口でのNO2/NOx比が低下したことが主な原因であった。

The application of biodiesel as an alternative fuel for petroleum diesel fuel is very effective for the reduction of CO 2 emission, because biodiesel is produced from renewable biomass resources. In Japan, neat biodiesel derived from waste cooking oil has often been applied to commercial vehicles. However, it is possible that the difference of fuel properties between conventional diesel fuel and biodiesel causes the problems on exhaust emission characteristics of diesel engine. Therefore, it is necessary to clarify the effect of biodiesel fuelling on exhaust emissions from commercial vehicles. Light-duty garbage trucks and heavy-duty diesel buses which were actually fueled with biodiesel in Kyoto, Japan were used for test vehicles in this study. The exhaust emissions from these vehicles during JE05 mode tests were compared between biodiesel derived from waste cooking oil and conventional diesel fuel. As a result, the application of biodiesel to older vehicles did not cause a negative effect on the exhaust emissions. On the other hand, biodiesel blending deteriorated NOx emission from new vehicles. In addition, other problems related to the use of biodiesel have been reported (e.g. oil dilution in vehicles equipped with DPF, etc.). Therefore, it will be necessary to modify engine components for the improvements of safe and environmental performances when using biodiesel. Copyright © 2010 SAE International.

ディーゼル機関においてHPL及びLPL-EGRを組み合わせたシステムについて調査を行った結果、低負荷では両EGRシステムを併用することで燃費の悪化を招かずに排出ガスを低減することが可能となった。一方高負荷では、LPL-EGRの増量と高過給の組み合わせによりNOxとsootの同時低減が可能となった。

The investigation of vehicle performances under on-road conditions has been required for emission reduction and energy saving in the real world. In this study, Real Car Simulation Bench (RC-S) was developed as an instrument for actual vehicle bench tests under on-road driving conditions, which could not be performed by using conventional chassis dynamometer (CH-DY). The experimental results obtained by RC-S were compared with the on-road driving data on the same car as used in RC-S tests. As a result, it was confirmed that RC-S could accurately reproduce the behavior of fuel consumption and exhaust emissions under on-road driving conditions. © 2009 SAE International.

A variable valve timing mechanism has been applied in a high-speed direct injection diesel engine. The effective compression ratio (eat) is lowered by means of late intake valve closing, while keeping the expansion ratio constant. Premixed charge compression ignition (PCCI) combustion, adopting the Miller cycle, was experimentally realized and numerically analysed. Significant improvements in NO (nitrogen oxides) and soot emissions were achieved for a wide range of engine speeds and loads frequently used in a transient mode test. The operating range of the Miller-PCCI combustion has been expanded up to an indicated mean effective pressure of 1.3 MPa.

LPL-EGRシステムを導入した多気筒ディーゼル機関を用い、従来のHPL-EGRシステムとの併用による高効率･低エミッション化の可能性を検証した。その結果、低負荷ではHPL-EGRを主体としたLPL-EGRの併用、高負荷ではLPL-EGRと高過給の組み合わせにより、燃費の悪化を抑制しつつ低エミッション化が可能となった。

NSR触媒を装着した最新型ディーゼル機関の燃焼・排出ガス特性に対する軽油へのBDFの混合割合の影響を解析した。その結果、混合割合により触媒前後の排出ガス特性が大幅に変化した。特に、BDFの混合割合の増加に伴い、NSR触媒によるNOx浄化率が大幅に低下することがわかった。

菜種油メチルエステル（RME）およびRME5%混合軽油をディーゼルエンジンで用いたときのノズルチップ上のカーボンデポジット堆積過程を定量的に把握するとともにSEM観察により微細構造を明らかにした。蒸留特性、粘度、微粒子生成傾向がカーボンデポジット生成に与える影響について検討し、蒸留特性の影響が最も大きいことを明らかにした。

従来よりも低温度かつ多量のEGRガスが得られる低圧ループEGR（LPL-EGR）システムを商用車用の多気筒ディーゼル機関に導入し、それらが機関性能に与える影響を明らかにした。従来の高圧ループEGR（HPL-EGR）システムと比べてLPL-EGRシステムでは吸気温度が低下するため、NOxとsootを同時に低減することができた。

LPL-EGRシステムを導入した商用車用の多気筒ディーゼル機関を用い、液化合成燃料（GTL）を用いた場合の排出ガス特性について軽油を用いた場合との比較検討を行った。GTLの高セタン価、低soot・THC等の特性を生かし、低負荷域では従来のHPL-EGRを、中・高負荷域でLPL-EGRを使用することにより、広い負荷域で燃費の悪化を招くことなく大幅なNOx低減効果が得られた。

The use of biodiesel fuels as an alternative fuel for petroleum diesel fuel is very effective for the reduction of CO2 emission, because biodiesel is produced from renewable biomass resources. Biodiesel is usually blended to conventional diesel fuel in various proportions. It is possible that this biodiesel blending causes the problems on emission characteristics of modern diesel engine, because it could be confirmed that the application of neat biodiesel to modern diesel engines whose control parameters were optimized for conventional diesel fuel deteriorated the emission performances. It is necessary to clarify the effect of biodiesel blending on exhaust emissions of modern diesel engine. Rapeseed oil methyl ester (RME) was selected as a biodiesel used in this study. Biodiesel blended fuels were applied to the multi-cylinder light-duty diesel engine which included the various latest technologies for low emission (e.g. common-rail injection system, cooled-EGR system, variable geometry turbocharger (VGT), and aftertreatment systems). RME blending increased in engine-out NOx emission, as mentioned by many researchers. The main reason for that is a decrease in EGR rate with blending RME. In addition, an increase in NOx emission by RME blending was clarified more at tail-pipe, because the rich spike blended with RME for lean NOx trap (LNT) degraded the NOx reduction performance of LNT. An increase in oxygen content in the fuel with blending RME caused the drastic reduction of engine-out smoke emission, but high blending rate of RME increased tail-pipe PM emission. This is caused by an increase in soluble organic fraction (SOF) emission derived from poor volatility of rich spike which contains the large amount of RME. The results of JE05 transient mode test showed the same tendency of tail-pipe emissions at steady-state operation as mentioned above. These test results denoted that biodiesel blending led to a simultaneous increase in NOx and PM emissions of modern diesel engine without engine modifications. However, the optimizations of intake air and rich spike injection conditions according to blending rate of biodiesel will make it possible to meet the future emission regulations. © 2008 SAE International.

A novel approach to reduce diesel engine emissions at relatively low injection pressures is proposed. This approach is based on the use of a mixed fuel where an additive or a low boiling point fuel such as CO2, gas fuel, or gasoline is mixed with a higher boiling point fuel such as diesel gas oil. When producing such a fuel, the vapour-liquid equilibrium in the twophase region where the liquid and vapour phases of both components coexist is taken into account. In designing a mixed fuel, the authors intend to control both the physical process in the spray such as fuel evaporation and vapour air mixing and the chemical processes including spontaneous ignition and with reactions with regard to NOx, particulate matter (PM), and hydrocarbon (HC) formation. In this study flash boiling of mixed fuel is particularly focused on enhancing the mixing process in the spray because it has the potential to achieve fast evaporation and relatively lean and homogeneous mixtures. Experiments were carried out using two types of mixed fuel, both of which can generate flash boiling during injection events. In an experiment using a rapid compression machine (RCM) and an optical engine, mixed fuels consisting of liquefied CO2 as an additive and n-tridecane representing gas oil were employed with the aim of simultaneously reducting soot and NOx emissions. The high-speed images acquired for sprays reacting in the RCM and the engine clearly showed a significant reduction of soot formation in the spray. Reductions of soot and NOx emissions as well as the fuel consumption were also confirmed by emission measurements and a combustion analysis respectively. In other experiments, different types of mixed fuel consisting of gas or gasoline and gas oil were tested to see the effects on both the evaporation and ignition processes. The result of an engine experiment showed marked reductions of soot and HC emissions and fuel consumption. © IMechE 2008.

A variable valve timing (VVT) mechanism has been applied in a high-speed direct injection (HSDI) diesel engine. The effective compression ratio (εeff) was lowered by means of late intake valve closing (LIVC), while keeping the expansion ratio constant. Premixed charge compression ignition (PCCI) combustion, adopting the Miller-cycle, was experimentally realized and numerically analyzed. Significant improvements of NOx and soot emissions were achieved for a wide range of engine speeds and loads, frequently used in a transient mode test. The operating range of the Miller-PCCI combustion has been expanded up to an IMEP of 1.30 MPa. Copyright © 2008 SAE International.

前報では、既存のディーゼル機関にBDFを適用した際、軽油使用時と比べて排出ガス特性が悪化する傾向を示した。そこで本報では、BDF適用時における排出ガス特性の改善を目的とし、機関の改良を行った。その結果、高EGR化によりPMとNOxのトレードオフが回避され、排出ガス性能が大幅に向上した。

A variable valve timing (VVT) mechanism is applied to achieve premixed diesel combustion at higher load for low emissions and high thermal efficiency in a light-duty diesel engine. By means of late intake valve closing (LIVC), compressed gas temperatures near the top dead centre are lowered, thereby preventing too early ignition and increasing ignition delay to enhance fuel-air mixing. The variability of an effective compression ratio has significant potential for ignition timing control of conventional diesel fuel mixtures. At the same time, the expansion ratio is kept constant to ensure thermal efficiency. Combining the control of LIVC, exhaust gas recirculation (EGR), supercharging systems, and high-pressure fuel injection equipment can simultaneously reduce NO(x) and smoke. The NO(x) and smoke suppression mechanism in the premixed diesel combustion is analysed using a three-dimensional computational fluid dynamics (3D-CFD) code combined with detailed chemistry. LIVC can achieve a significant NO(x) and smoke reduction due to lowering combustion temperatures and avoiding local over-rich regions in the mixtures respectively.

EGR下で局所リッチ領域を低減する方策として、可変バルブタイミング機構を用いた低圧縮比高膨張比サイクルによる予混合ディーゼル燃焼の制御手法を提案した。これにより、NOx、煤（soot）、燃焼騒音の大幅な同時低減が可能であり、かつ排気温度が通常燃焼と比べて上昇するため、後処理装置の浄化率向上にも寄与することを確認した。

Application of biodiesel fuel (BDF) to diesel engine is very effective to reduce CO2 emission, because bio-diesel is carbon neutral in principle. However, when biodiesel was applied to conventional diesel engines without modification for biodiesel, NOx emission was increased by the change in fuel characteristics. It is necessary to introduce some strategies into diesel engines fuelled with biodiesel for lower NOx emission than conventional diesel fuel case. The purpose of this study is to reveal that exhaust gas recirculation (EGR) is one of the solutions for the reduction of NOx emission and meeting the future emission regulations when using biodiesel. Neat Rapeseed oil methyl ester (RME) as a biodiesel (B100) was applied to diesel engines equipped with high pressure loop (HPL) EGR system and low pressure loop (LPL) EGR system. Cooled HPL EGR was increased during steady-state operations and JE05 transient mode tests. An increase in HPL EGR rate drastically reduced NOx emission, and did not increase PM emission, because soot formation was suppressed by the oxygen in RME. It could be confirmed that an increase in EGR rate made it possible to achieve low emission meeting 2009 regulation in Japan. Engine-out emissions measurements were made to develop a comparison between HPL and LPL EGR in steady-state operation test. LPL EGR improved CO and NOx emissions, compared with the case of HPL EGR. An increase in the rate of LPL EGR caused simultaneous reduction of NOx and smoke emissions. Copyright © 2007 SAE International.

可変バルブ機構を備えたディーゼル機関を用い、高負荷において排出ガスを低減するための燃焼制御の方向性について実験的に検討した。EGRによりNOxの生成を抑制した上で、吸気バルブの遅閉じを用いた噴射時期遅角側での低温予混合ディーゼル燃焼を行うことにより、NOxとsmokeの同時低減が可能となることを示した。

Application of biodiesel fuel (BDF) to diesel engine is very effective to reduce CO2 emission, because biodiesel is carbon neutral in principle. However, biodiesels yield an increase in NOx emission from conventional diesel engine, compared with diesel fuel case. Therefore, some strategies are needed for meeting the future emission regulations when using biodiesel. In this study, rapeseed oil methyl ester (RME) was applied to diesel engine equipped with exhaust gas recirculation (EGR) system and NOx storage reduction (NSR) catalyst. NOx reduction rate of NSR catalyst was drastically decreased by using RME, even if injection quantity of RME for rich spike was enhanced. However, an increase in EGR rate could reduce NOx emission without the deterioration in smoke and PM emissions. Copyright © 2007 Society of Automotive Engineers of Japan, Inc.

BDFを既存のディーゼル機関に適用し、燃焼・排出ガス特性の解析を行い、軽油と比較した。定常試験とJE05モード試験双方で、BDFの方が軽油と比べてNOx、PM排出量が増加し、これらを改善するためには高EGR化やリッチスパイクの最適化が必要であることがわかった。

可変バルブタイミングによる吸気バルブ（VVT）の遅閉じは、圧縮端の雰囲気温度を制御することができ、軽油の予混合化を促進した上での着火時期の制御が可能となることがわかった。この技術をEGR、過給と組み合わせることは、中高負荷運転域におけるNOxと黒煙の同時低減を実現するひとつの指針となりうることを示した。

Flash-boiling occurs when a fuel is injected into a combustion chamber where the ambient pressure is lower than the saturation pressure of the fuel. It has been known that flashing is a favorable mechanism for atomizing liquid fuels. On the other hand, alternative fuels, such as gaseous fuels and oxygenated fuels, are used to achieve low exhaust emissions in recent years. In general, most of these alternative fuels have high volatility and flash-boiling takes place easily in the fuel spray when injected into the combustion chamber of an internal combustion engine under high pressure. In addition the multicomponent mixture of high- and low-volatility fuels has been proposed in the previous study in order to control the spray and combustion processes in an internal combustion engine. It was found that the multicomponent fuel produces flash-boiling with an increase in the initial fuel temperature. Therefore, it is important to investigate these flash-boiling processes in fuel spray. In the present study, the submodels of a flash-boiling spray are constructed. These submodels consider the bubble nucleation, growth, and disruption in the nozzle orifice and injected fuel droplets. The model is implemented in KIVA3V and the spray characteristics of multicomponent fuel with and without flashing are numerically investigated. In addition, these numerical results are compared with experimental data obtained in the previous study using a constant volume vessel. The flashing spray characteristics from numerical simulation qualitatively show good agreement with the experimental results. In particular, it is confirmed from both the numerical and experimental data that flash-boiling effectively accelerates the atomization and vaporization of fuel droplets. This means that a lean homogeneous mixture can be quickly formed using flash-boiling in the combustion chamber. © 2006 Wiley Periodicals, Inc.

A variable valve timing (VVT) mechanism was applied to achieve premixed diesel combustion at higher load for low emissions and high thermal efficiency in a light duty diesel engine. By means of late intake valve closing (LIVC), compressed gas temperatures near the top dead center are lowered, thereby preventing too early ignition and increasing ignition delay to enhance fuel-air mixing. The variability of effective compression ratio has significant potential for ignition timing control of conventional diesel fuel mixtures. At the same time, the expansion ratio is kept constant to ensure thermal efficiency. Combining the control of LIVC, EGR, supercharging systems and high-pressure fuel injection equipment can simultaneously reduce NOx and smoke. The NOx and smoke suppression mechanism in the premixed diesel combustion was analyzed using the 3D-CFD code combined with detailed chemistry. LIVC can achieve a significant NOx and smoke reduction due to lowering combustion temperatures (LTC: Low Temperature Combustion) and avoiding local over-rich regions in the mixtures, respectively. Copyright © 2006 SAE International.

The 1997 Kyoto protocol came into effect in February, 2005 to reduce greenhouse gases within the period 2008-2012 by at least 5 % with respect to 1990 levels. Application of biodiesel fuel (BDF) to diesel engine is very effective to reduce CO2 emission, because BDF is carbon neutral in principle. The purpose of this project is to produce a light-duty biodiesel truck which can be suitable for emission regulation in next generation. The effect of BDF on the performance and emissions of modern diesel engine which was equipped with the aftertreatment for PM and NOx emissions was investigated without modifications of engine components and parameters, as a first step for research and development of biodiesel engine. Rapeseed oil methyl ester (RME) was selected in behalf of BDF, and combustion characteristics, engine performance and exhaust emissions were made a comparison between RME and petroleum diesel fuel by steady operation and Japan transient mode (JE05) tests. In particular, the flexibility of aftertreatment to BDF was analyzed by exhaust emission measurements in front and behind aftertreatment system. These experimental results revealed that the significant reduction of engine-out emissions by engine modification was necessary to achieve emission level below the future emission regulation, in addition to the optimization of aftertreatment system for biodiesel. These problems intend to be solved by the further research and development in this biodiesel project. Copyright © 2006 SAE International.

EGRによりNOxの生成を抑制したうえで、高圧噴射、過給および有効圧縮比の可変制御により燃料の予混合化を促進した。その結果、これまで極めて困難であった中速中負荷運転領域における市販軽油の使用を前提とした予混合ディーゼル燃焼を実現することができ、NOxと黒煙の大幅な同時低減を可能にした。

気泡核生成、成長、崩壊を考慮した低沸点・高沸点混合燃料の減圧沸騰噴霧モデルを構築し、KIVA3Vに組み込むことによりその数値解析を行った。その結果、噴霧先端到達距離の計算結果は、定量的に実験値とよく一致した。さらに、減圧沸騰効果により液滴径が大幅に減少し、混合燃料中のどちらの成分も良好な蒸発特性を示した。

Homogeneous Charge Compression Ignition (HCCI) is effective for the simultaneous reduction of soot and NOx emissions in diesel engine. In general, high octane number fuels (gasoline components or gaseous fuels) are used for HCCI operation, because these fuels briefly form lean homogeneous mixture because of long ignition delay and high volatility. However, it is necessary to improve injection systems, when these high octane number fuels are used in diesel engine. In addition, the difficulty of controlling auto-ignition timing must be resolved. On the other hand, HCCI using diesel fuel (diesel HCCI) also needs ignition control, because diesel fuel which has a low octane number causes the early ignition before TDC. The purpose of this study is the ignition and combustion control of diesel HCCI. The effects of parameters (injection timing, injection pressure, internal/external EGR, boost pressure, and variable valve timing (VVT)) on the ignition timing of diesel HCCI were investigated. Then, exhaust emissions were simultaneously measured at each operating condition. As a result, the combinations of these strategies made it possible to cause the ignition near TDC at each operating condition. In addition, low smoke and NOx emissions were realized without a drastic increase in THC and CO emission. These results show the possibility of diesel HCCI operation at wide load ranges. Copyright © 2005 SAE International.