窪山 達也

Abstract Although prechamber (PC) is regarded as a promising solution to enhance ignition in lean-burn gas engines, a lack of comprehensive understanding of PC jet penetration dynamics remains. This study proposed a zero-dimensional (0D) model for PC jet penetration, considering the mixing of combustion products and unburned gases in jets and the floating ejection pressure. A combustion completion degree was defined by employing fuel properties and heat release to estimate the time-varying jet density. Pressure differences between the PC and the main chamber (MC) were referred to as the ejection pressure. Then, this model was validated against experimental data from a constant volume chamber (CVC) and a rapid compression and expansion machine (RCEM) with CH4-H2 blends at different equivalent ratios. Results showed that the proposed model can provide a good prediction in stationary and turbulent fields with the calibrated model coefficient. The overall jet penetration exhibits a t0.5 dependence due to its single-phase characteristic and the relatively lower density compared to the ambient gas in MC. The flame propagation speed and heat release in PC influence the combustion completion degree at the start of jet ejection. The mass fraction of burned gas in the ejected jet grows in response to the mixture equivalent ratio. Jet penetration is primarily driven by ejection pressure, with tip dynamics barely affected by the pressure difference after peaks. Tip penetration intensity rises with increasing fuel equivalent ratio and H2 addition, owing to the faster flame propagation. These findings can offer useful suggestions for model-based design and combustion model development for gas engines.

Experimental methods and numerical analysis were used to investigate the mechanism of high-speed knocking that occurs in small two-stroke engines. The multi-ion probe method was used in the experiments to visualize flame propagation in the cylinder. The flame was detected by 14 ion probes grounded in the end gas region. A histogram was made of the order in which flames were detected. The characteristics of combustion in the cylinder were clarified by comparing warming up and after warming up and by extracting the features of the cycle in which knocking occurred. As a result, regions of fast flame propagation and regions prone to auto-ignition were identified. In the numerical analysis, flow and residual gas distribution in the cylinder, flame propagation and self-ignition were visualized by 3D CFD using 1D CFD calculation results as boundary conditions and initial conditions. Flame propagation calculated by 3D CFD was found to be directional due to in-cylinder flow caused by scavenging flow. The calculated direction of flame spread was matched with the experimentally measured direction. It was also found that the first auto-ignition occurred in the high temperature region where the concentration of residual gas was high. Finally, numerical analysis was performed for the high compression ratio engine specifications. As a result, the mechanism of knocking was clarified as the first auto-ignition caused by the high-temperature residual gas, followed by the pressure wave inducing continuous auto-ignition. The flow formed during the scavenging process and the subsequent compression process determine the directionality of flame propagation and residual gas distribution at top dead center. Thus, the possibility of knocking avoidance by scavenging air shape and combustion chamber shape was suggested.

For the survival of internal combustion engines, the required research right now is for alternative fuels, including drop-ins. Certain types of alternative fuels have been estimated to confirm the superiority in thermal efficiency. In this study, using a single-cylinder engine, olefin and oxygenated fuels were evaluated as a drop-in fuel considering the fuel characteristic parameters. Furthermore, the effect of various additive fuels on combustion speed was expressed using universal characteristics parameters.

Liquid fuel attached to the wall surface of the intake port, the piston and the combustion chamber is one of the main causes of the unburned hydrocarbon emissions from a port fueled SI engine, especially during transient operations. To investigate the liquid fuel film formation process and fuel film behavior during transient operation is essential to reduce exhaust emissions in real driving operations, including cold start operations. Optical techniques have been often applied to measure the fuel film in conventional reports, however, it is difficult to apply those previous techniques to actual engines during transient operations. In this study, using MEMS technique, a novel capacitance sensor has been developed to detect liquid fuel film formation and evaporation processes in actual engines. A resistance temperature detector (RTD) was also constructed on the MEMS sensor with the capacitance sensor to measure the sensor surface temperature. The response and the sensitivity of the developed sensor were examined at the atmospheric conditions at first. As a result, it was found that though the sensor shows less sensitivity to pure commercial gasoline, it has enough sensitivity to gasoline fuel containing 20% ethanol (E20 gasoline). After the sensitivity test, the sensor was installed into the intake pipe of the single cylinder engine and examined to detect the liquid fuel film on the wall of the intake pipe. The engine was operated at a constant speed of 2000 rpm with E20 gasoline fuel. The sensor performed well during the engine operation, and the liquid fuel impingement and evaporation process could be monitored.

<div class="section abstract"><div class="htmlview paragraph">Lean combustion has been well known to be an effective method to improve the thermal efficiency. However, leaner mixture is prone to cause the unstable combustion and poorer unburned hydrocarbon (UTHC) emissions. Pre-chamber turbulent jet combustion has been proved to enhance the combustion stability under ultra-lean conditions. However, more NOx is formed during the combustion, resulting in the fact that the tailpipe NOx emission is too high to be still not available for the real application. In this report, in order to achieve a higher air excess ratio while keeping lower UTHC emissions, and especially NOx emission, a new combustion technique which combined pre-chamber jet combustion with fuel reforming was proposed and experimentally demonstrated on a pre-chamber engine.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Homogeneous charge compression ignition (HCCI) combustion is promising for not only high thermal efficiency but also reducing nitrogen oxides (NOx) and PM simultaneously. However, the operational range of the HCCI combustion is limited because of some issues, such as poor control of ignition timing and knocking by the excessive rate of pressure rise. In this study, a new combustion system based on the HCCI combustion process is proposed based on the authors' previous experimental work. This combustion system has a divided combustion chamber of two parts, one is small and the other is large. The most significant feature is the small chamber inside the piston. At first, combustion takes place in the small chamber, and then the burned gas is ejected into the large chamber to ignite the mixture in the large chamber. In this combustion system, the combustion in the large chamber takes the HCCI combustion process. 3D-CFD was conducted to predict HCCI combustion characteristics with small chamber inside the piston, varying the geometry of small chamber. Simulation results revealed that this combustion system can be achieve two-stage HCCI combustion with reduced pressure rise rate.</div></div>

<div class="section abstract"><div class="htmlview paragraph">This study aimed to achieve both a high compression ratio and low knock intensity in a two-stroke engine. Previous research has suggested that knock intensity can be reduced by combining combustion chamber geometry and scavenging passaging design for the same engine specifications with a compression ratio of 13.7. In this report, we investigate whether low knock intensity can be achieved at compression ratios of 14.4 and 16.8 by adjusting the combustion chamber geometry and scavenging passage design. As a result, the mechanism by which combustion chamber geometry and scavenging passage design change knock intensity was clarified.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Knocking is an important issue in improving the efficiency of spark ignition engines. It can be detected by photographing with high-speed cameras or measuring in-cylinder pressure or engine vibration or engine radiation sound. However, these methods each have the problems for example sensor damage risk or necessity of machining the engine. In this paper, we propose the efficient measurement method and the effective evaluation method with the restricted measurement results for engine knocking detection by utilizing the simultaneous measurement results of knocking with these sensors.</div></div>

<div class="section abstract"><div class="htmlview paragraph">In internal combustion engine development, the ongoing research can be mainly classified into two categories based on the purpose: limiting exhaust emissions and searching for alternative fuels. One of the effective approaches reduce emissions is the improvement of thermal efficiency. Certain types of alternative fuels derived from renewable resources were estimated to confirm the thermal efficiency. This study uses a single-cylinder engine added with olefin and oxygenated additive fuel, such as 1-hexene, ethanol, and ETBE, to evaluate the parameters that affect thermal efficiency. Furthermore, the effects of various additive fuels are summarized and essential information is provided for determining next- generation fuel composition.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Post-oxidation has been used to enhance the chemical reactions in the exhaust gas pipes, leading to the activations of the turbocharger and catalyst at cold state. In this research, a detailed study of the various mechanisms for post-oxidation is performed. For the post-oxidation activation, the unburned gas species (CO, THC, H2) in the exhaust manifold must be produced by some methodologies, such as scavenging, lambda-split, and post-injection. The required amount of O2 concentration can be either supplied by the scavenging (valve overlap tuning) or the secondary air injection (SAI) system. Mixing the species is also an important key to promoting post- oxidation, and an internal bypass adapter with a modified exhaust adapter shape was developed and evaluated.</div></div>

A detailed investigation of post-oxidation phenomena by individual and combined effects of scavenging (VVT tuning) and secondary air injection (SAI) was performed. The 1-D simulation including a post-oxidation model developed by Stuttgart University as an international collaboration was used for investigation which includes the main exhaust gas species as CO, H₂, and O₂-based chemical reactions. Then, experimental validation was conducted on a 4-cylinder turbocharged gasoline direct injection (GDI) engine. From the results, it was noted that the post-oxidation can be actuated at limited operating conditions as higher overlap in moderated speed and load only when scavenging phenomena are considered. However, at lower overlap, it is restricted due to lower O₂ scavenging even though the exhaust temperature meets the post-oxidation requirement. Also, the in-homogeneity observed at higher overlap that restricts the significant post-oxidation before the turbocharger upstream. On the other hand, the SAI mechanism can actuate the post-oxidation even at lower overlap if enough O₂ concentration, exhaust temperature, and adequate mixing are attained. Hence, the post-oxidation zone can be extended to lower speed-load and overlap if both parameters as scavenging and SAI introduced together. This can possibly lead to better turbo-performance along with lower emissions. However, thermal efficiency needs to be compromised to some extent. It was also found that the effective post-oxidation can be actuated by SAI compared to scavenging-based phenomena if the same concentration of the O₂ and temperature are maintained by both mechanisms. This appeared due to the fresh air continuously injected at the exhaust port even at the time of exhaust valve opening duration in SAI mechanism that allows the better mixing of O₂ and hot unburned gas species. However, in scavenging-based phenomena, firstly, hot unburned gas passed through the exhaust manifold and then scavenged air follows which restricts mixing between scavenged air and unburned gas species.

To realize stable combustion in lean or diluted conditions, reducing cycle-to-cycle variations of flow and fuel distribution is important. In this study, the effect of initial flow field was examined by simultaneous Time-Resolved PIV and visualization on two cross-sections in a fully optical-access engine under motoring and firing conditions with homogeneous pre-mixture. As a result, Omega index was defined and plotted on the correlation map between turbulence kinetic energy and CA10 (duration from ignition timing to 10% to the total accumulated heat). The omega index describes the strength of a horizontal flow field that resembles the shape of the Greek letter Omega. The plots with high Omega index were found frequently in the CA10 retarded cycles. On the other hand, the plots with low Omega index have simple tumble flows and the correlation was clearly found. This means that not only turbulence but also mean velocity's pattern are important for the estimation parameter of cycle-to-cycle variation. As a result, it was found that the initial tumble should be given as "outside-fast"and then, a nearly homogeneous tumble was formed near spark timing without an Omega flow.

人工ニューラルネットワークを用いて，0次元ラジエータ熱収支モデルのモデルパラメータを同定する数値的方法を開発した．数値計算結果によれば，本法は，各モデルパラメータの同定，すなわち，ラジエータ・冷却水間とラジエータ・空気間の各熱コンダクタンス，および，ラジエータの熱容量の同定に応用可能である．

Human drivers seem to have different characteristics, so different drivers often yield different results from the same driving mode tests with identical vehicles and same chassis dynamometer. However, drivers with different experiences often yield similar results under the same driving conditions. If the features of human drivers are known, the control inputs to each driver, including warnings, will be customized to optimize each man–machine vehicle system. Therefore, it is crucial to determine how to characterize human drivers quantitatively. This study proposes a method to estimate the parameters of a theoretical model of human drivers. The method uses an artificial neural network (ANN) model and a numerical procedure to interpret the identified ANN models theoretically. Our approach involves the following process. First, we specify each ANN driver model through chassis dynamometer tests performed by each human driver and vehicle. Subsequently, we obtain the parameters of a theoretical driver model using the ANN model for the corresponding driver. Specifically, we simulate the driver’s behaviors using the identified ANN models with controlled inputs. Finally, we estimate the theoretical driver model parameters using the numerical simulation results. A proportional-integral-differential (PID) control model is used as the theoretical model. The results of the parameter estimation indicate that the PID driver model parameter combination can characterize human drivers. Moreover, the results suggest that vehicular factors influence the parameter combinations of human drivers.

Advanced combustion technologies, like highly boosted and lean or dilute combustion, have been employed to meet the demands of high efficiency and low emissions in SI engines, which have increased the challenges of ignition control. It is essential to find a suitable ignition strategy due to the need to develop a next-generation spark ignition system. In this study, simultaneous visualization by a high-speed infrared camera (FLIR X6900sc) and a conventional high-speed camera (FASTCAM SA-X) is carried out to obtain deeper insights into the ignition process in a constant volume combustion chamber (CVCC). Infrared images have provided a more accurate way of measuring the initial flame and are able to analyze quantitatively. Ignition performance is studied with various mixture dilutions, flow conditions, and discharge characteristics. Two types of ignition coils that have the same discharge energy were analyzed in particular. The results show that extending the discharge duration is more helpful in improving the ignition performance under the increasing dilution ratio, compared to the enhanced discharge current at the same discharge energy. However, the discharge current plays a more vital role in perfecting the ignition performance under the increasing local flow velocity than the discharge duration.

CO2希釈ガスはこれまで比熱が高くガス温度を低減するという効果に注目されてきたが，燃焼に与える影響を詳細に把握するためには，定量的な実験と解析が必要である．分離膜を使った窒素分離が実用化され，希釈率を下げて，N2やCO2など希釈剤の影響を調査した例は殆ど見あたらず，本研究の対象とした．

In this research, the improvement of mixing and pulsation in exhaust manifold with a design and implementation of bypass adapter at exhaust port were deeply investigated. This in-turn can improve the post-oxidation phenomena and hence emissions and engine performance could be enhanced. This research investigation includes 1-D, 3-D simulations and experimental validation on a 4-cylinder turbocharged spark ignition (SI) engine. Firstly, the 1-D and 3-D simulation models were developed and calibrated with the experimental results. Then, the simulations were used for the detailed investigation of mixing and pulsation in exhaust manifold with and without bypass adapter. Thereafter, experimental test for the post-oxidation were conducted with and without consideration of the bypass adapter and results were compared. From the simulation and experimental results, it was proven that by using bypass adapter at the exhaust port, the mixing of exhaust gas species was observed to be significantly improved to some extent. Also, the unbalance between exhaust port and turbocharger upstream gas species were reduced. This also reduced the exhaust gas pulsation. By the improvement of mixing between scavenged O₂ and unburned gas species, the post-oxidation reaction was also noted to have improved and consequently the emissions and turbo-speed were found to be better that led to an improved IMEP and thermal efficiency of the engine.

Abstract In recent years, automobile exhaust gas regulations have become stricter due to environmental problems such as global warming. A project by the Cabinet Office called the Strategic Innovation Promotion Program (SIP) began in 2014. SIP has 11 themes in total. One of them, innovative combustion technology, aimed to improve the thermal efficiency of automobiles from the existing 40% to 50%. To improve the thermal efficiency of the automobile, it was essential to improve the efficiency of the turbocharger. In this study, we developed a turbocharger for gasoline and diesel engines. First, to confirm the efficiency of the conventional turbocharger, experiments and CFD analysis of a commercial turbocharger were performed. ANSYS-CFX was used as a numerical code. To confirm the accuracy of the CFD, the CFD results were compared with the experimental results, and it had good agreement with the experimental results. From the analysis results, the loss region of the conventional turbocharger was clarified. The designed turbocharger compressor was tested as a prototype compressor. The results of the compressor had good agreement with CFD results, so it was confirmed that the accuracy of CFD and design method was valid. Finally, A one-dimensional simulation using GT-Power which is a system analysis software for automobiles was performed to evaluate the developed turbocharger on the engine. In the fifth year of the project, the target efficiency of 50% was achieved.

直噴ガソリンエンジンの始動条件において，燃料噴射時期と微粒子排出量の関係を調べた結果に対して数値計算を行い，モデルの評価を行う．すす生成モデルには，ガソリンサロゲート燃料に対して衝撃波管実験を用いて検証したコンパクトなモデルを用い，始動時特有のバスタブ特性について再現性の検討を行った．

A detailed investigation of ignition and injection timing influence on post-oxidation phenomenon which in-turn can improve turbo-performance along with the emissions of a turbocharged (SI) engine. In this research a novel methodology by adopting the scavenging-based post-oxidation phenomenon was investigated.Firstly, 1-D simulation model was developed, and the model was validated with the experimental results. Then, the simulation was used for the investigation of ignition and injection timing influence on post-oxidation. Thereafter, experimental tests for the post-oxidation were conducted. From the results, it can be stated that the retard of ignition timing shifts the combustion phase towards late which increased the exhaust pressure and temperature. This could increase the chances of the actuation of the post oxidation reaction in the exhaust manifold. Moreover, it was also found that the injection of fuel during the overlap phase and after overlap had significant influence on the post-oxidation process. Fuel injection during the overlap can increase the possibility of scavenging a fraction of fuel and promote post-oxidation reaction. In both cases, it was found that the emissions and turbo-performance become better at late spark and early injection timing due to oxidation reaction. However, thermal efficiency was affected which will be optimized in the future. (C) 2020 Elsevier Ltd. All rights reserved.

著者らは既報で，ガソリンサロゲート燃料に適用可能なコンパクトなすす生成モデルを提案した．本研究では，直噴ガソリンエンジンの始動条件において，異なる冷却水温度の実験結果に対してモデル検証を行った．また，下死点近傍で燃料を噴射した場合にすす排出量が増加する傾向に対し，数値解析によって現象評価を試みた．

超高過給ダウンサイジングコンセプトを実現するため，低回転から高回転まで超高過給運転を可能とし，正のポンプ仕事を得ることでエンジン熱効率を改善することを狙って，システムの検討を行い，2段過給システムを試作した．検討内容と実験結果について報告する．

In this research, simulation and experimental investigation of H2 emission formation and its influence during the post-oxidation phenomenon were conducted on a turbo-charged spark ignition engine. During the post-oxidation phenomenon phase, rich air-fuel ratio (A/F) is used inside the cylinder. This rich excursion gives rise to the production of H2 emission by various reactions inside the cylinder. It is expected that the generation of this H2 emission can play a key role in the actuation of the post-oxidation and its reaction rate if enough temperature and mixing strength are attained. It is predicted that when rich combustion inside the cylinder will take place, more carbon monoxide (CO)/ Total Hydro Carbon (THC)/ Hydrogen (H2) contents will arrive in the exhaust manifold. This H2 content facilitates in the production of OH radical which contributes to the post-oxidation reaction and in-turn can aid towards increasing the enthalpy. Through simulations, it was also investigated that higher H2 levels influences the ignition delay of the post-oxidation reaction significantly. In addition, the experimental investigation of H2 formation with different overlap and spatial distribution were also analyzed. It was noted that the H2 formation always came to be higher at high overlap (90 deg. overlap) due to significant scavenging in the exhaust manifold that leads in-cylinder mixture rich. Also, the H2 concentration firstly increases when we move from exhaust port to Turbocharger (TC) upstream. This is due to the inhomogeneity that occurred between exhaust port to TC upstream. Furthermore, as we move from TC upstream to TC downstream, the H2 level decreases due to the consumptions of H2 in post-oxidation reaction.

To increase thermal efficiency of internal combustion engines, dilution combustion systems, such as lean burn and exhaust gas recirculation systems, have been developed. These systems require spark-ignition coils generating large discharge current and discharge energy to achieve stable ignition under diluted mixture conditions. Several studies have clarified that larger discharge current increases spark-channel stretch and decreases the possibility of spark channel blow-off and misfire. However, these investigations do not mention the effect of larger discharge current and energy on the initial combustion period. The purpose of this study was to investigate the relation among dilution ratio, initial-combustion period, and coil specifications to clarify the control factor of the dilution limit. Four coils having different current profiles were evaluated under 2000 rpm and 6-bar net-indicated mean effective pressure under a diluted mixture condition through combustion-performance and in-cylinder optical-measurement tests on a single cylinder engine. The combustion-performance test results indicate a correlation between the dilution limit and initial combustion period. The in-cylinder optical-measurement test results indicate that the initial combustion period has a correlation with spark stretch before the 1st restrike and spark-stretch rate. These results also indicate that variation in the initial combustion period depends on the temporal flow velocity change during discharge and long initial-combustion-period cycles are caused at slow velocity during discharge.

ダウンサイジング過給エンジンの高負荷領域を拡大するため，低回転超高過給運転を試み，正味平均有効圧3MPaを1750rpmで達成した．また拡大した高負荷領域における燃費率を改善した．本研究のコンセプトと実験結果について述べる．

本研究ではオイル添加剤の調整がLSPI発生頻度に与える影響を明確するため，Ca, Mg, Mo三種類の添加剤の組合せをベースに，各々の添加剤の量を2水準設定し，その組合せの計8種類の試作オイルを用意した．特にこれまでに報告例がない，IMEP 2.4MPaの超高負荷運転において，オイル添加剤がLSPI発生に与える影響を調査した．

<p>It is required to reduce both the friction and lubricant oil consumption (LOC) in order to reduce CO₂ in internal combustion engines. In addition, as the requirement to reduce particulate number (PN) may be realized by reducing LOC, the relationship between LOC and PN should be examined. Elucidation of the mechanism of LOC belongs to a basic and applied field and a common subject, however, only the LOC is measured by the weight method in steady conditions and the mechanism is not clarified so far. Thereby, the relationship between LOC and PN was measured in a wide operation area including transient conditions using a production engine in this study.</p>