森吉 泰生

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">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>

Following Part 1 of the previous study, this paper reports the structure's exciting force and summarize the overall research results. An experimental study was conducted to clarify the relationship between engine combustion and vibration, and to establish technology to suppress it. This study focused on the vehicle interior noise caused by combustion in which vibration transmission is the main component at high speed and high load region. A phenomenon in which both the combustion's exciting force and the structure's exciting force are combined is defined as vehicle interior noise caused by combustion. Conventionally, combustion and vibration are often discussed in terms of the average cycle, but considering the nonstationary property of vibration, in this paper analyzed the structure's exciting force characteristics for vibration in cycle-by-cycle. Analysis was conducted using the combustion indicators clarified in the previous study. The engine vibration is affected by piston specifications even with the same heat release characteristics. Based on the analysis results, the piston rotation angle and translational displacement are defined as indicators of the structure's exciting force. In this paper, after discussing the piston motion characteristics as the structure's exciting force and the indicators of vibration suppression, the results clarified by the research combined with the previous study are summarized.

This study focused on the vehicle interior noise caused by combustion in which vibration transmission is the main component at high speed and high load region. A phenomenon in which both the combustion's exciting force and the structure's exciting force are combined is defined as vehicle interior noise caused by combustion. Conventionally, combustion and vibration are often discussed in terms of the average cycle, but considering the nonstationary property of vibration, in this paper analyzed the combustion characteristics for cycle-by-cycle and investigated indicators for the combustion's exciting force. The engine vibration is affected by heat release characteristics even with the same engine structure specifications. The heat release characteristics were determined as indicators for the combustion's exciting force. Transfer Path Analysis (TPA) revealed that there is piston transmission in the target frequency band. Through eigenvalue analysis, it was found that there was no resonance with the eigenvalue of the structures in the target frequency band. Even with the same combustion characteristics, the engine vibration is affected by piston specifications. Piston motion characteristics were determined as indicators for the structure's exciting force. In this paper, after overview the impact of each exciting force on vibration, the heat release characteristics of the combustion's exciting force and the indicators for vibration suppression are mainly discussed.

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.

There is a growing need for low-emissions concepts due to stricter emission regulations, more stringent homologation cycles, and the possibility of a ban on new engines by 2035. Of particular concern are the conditions during a cold start, when the Three-Way Catalyst is not yet heated to its light-off temperature. During this period, the catalyst remains inactive, thereby failing to convert pollutants. Reducing the time needed to reach this temperature is crucial to comply with the more stringent emissions standards. The post oxidation by means of secondary air injection, illustrated in this work, is a possible solution to reduce the time needed to reach the above-mentioned temperature. The strategy consists of injecting air into the exhaust manifold via secondary air injectors to oxidize unburned fuel that comes from a rich combustion within the cylinder. This strategy can be implemented without major modifications to the engine's hardware or control system, making it an attractive option for retrofitting older engines or incorporating into new designs. The investigation was conducted experimentally and numerically, with test bench measurements and 3D-CFD simulations. The test bench data were helpful for validating and calibrating the 3D-CFD simulations, which employ two interrelated approaches. The first approach utilizes a full-engine mesh, which includes a 0D turbocharger model, to extrapolate reliable boundary conditions. The second approach uses a detailed exhaust model that includes the mentioned accurate boundary conditions and a chemical reaction mechanism. This paper presents the effects of post oxidation in two different engine operating points. Various secondary air injection strategies, including different temperatures and mass flows, and an alternative exhaust manifold design, are evaluated to assess potential improvements in post oxidation by means of 3D-CFD virtual development.

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．

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.

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.

Some SI (spark-ignition) engines fueled with gasoline for industrial machineries are designed based on the conventional diesel engine in consideration of the compatibility with installation. Such diesel engine-based SI engines secure a combustion chamber by a piston bowl instead of a pent-roof combustion chamber widely applied for SI engines for automobiles. In the development of SI engines, because knocking deteriorates the power output and the thermal efficiency, it is essential to clarify causes of knocking and predict knocking events. However, there has been little research on knocking in diesel engine-based SI engines. The purpose of this study is to elucidate knocking phenomena in a gasoline engine with a re-entrant piston bowl and swirl flow numerically and experimentally. In-cylinder visualization and pressure analysis of knock onset cycles have been experimentally performed. Locations of autoignition have been predicted by 3D-CFD analysis with detailed chemical reactions. The prediction accuracy of the location of autoignition has been examined by comparing with experimental results. Initial and boundary conditions for 3D-CFD are obtained by TPA (Three Pressure Analysis), which is a 1D engine cycle simulation using measured intake/exhaust and in-cylinder pressures as the input data. Locations and timing of autoignition have been observed through an endoscope attached to the cylinder head. The visualization area through the endscope is determined based on the location of autoignition predicted by 3D-CFD analysis. The in-cylinder pressure is also measured simultaneously, and the maximum amplitude of the pressure oscillations after applying a high-pass filter to the in-cylinder pressure is used as knock intensity (KI) to determine knock onset cycles. From results of the in-cylinder pressure measurements and analysis by TPA, the relationships between in-cylinder conditions and KI are analyzed. The comparison between visualized and calculated location of autoignition have been shown good agreement in the case that both the maximum and the low engine speed conditions.

In recent years, the improvement in the fuel efficiency and reduction in CO2 emission from internal combustion engines has been an urgent issue. The lean burn technology is one of the key technologies to improve thermal efficiency of SI engines. However, combustion stability deteriorates at lean burn operations. The reduction in cycle-to-cycle and cylinder-to-cylinder variations is one of the major issues to adapt the lean burn technique for production engines. However, the details of the causes and mechanisms for the combustion variations under the lean burn operations have not been cleared yet. The purpose of this study is to control cylinder to cylinder combustion variation. A conventional turbocharged direct injection SI engine was used as the test engine to investigate the effect of engine control parameters on the cylinder to cylinder variations. The engine speed is set at 2200 rpm and the intake pressure is set at 58, 78, 98 kPa respectively. In-cylinder pressure, intake pressure, and exhaust pressure are measured in each cylinder by the piezoelectric and piezo-resistive pressure transducers. The ignition timing and fuel injection timing is varied as experimental parameters to investigate the effects of the combustion phase and the fuel distribution on combustion stability. At 78 kPa condition, it was seen that the tendency of COV of IMEP was slightly different in each cylinder Also, it was seen a few cycles of sudden decline IMEP in the third cylinder at lean burn operation. So, COV of IMEP was different in each cylinder and COV of IMEP of first cylinder lower than the third cylinder. Moreover, combustion phase was different in each cylinder when ignition timing was same. Therefore, it is considered that optimized ignition timing and fuel injection timing is different in each cylinder.

Knocking occurs within the high-speed range of small two-stroke engines used in handheld work equipment. High-speed knock may be affected by the engine speed and delivery ratio. However, evaluation of these factors independently using experimental methods is difficult. Therefore, in this study, these factors were independently evaluated using numerical calculations. The purpose of this study was to clarify the mechanism by which the intensity of high-speed knocking that occurs in small two-stroke engines becomes stronger. The results suggest that temperature inhomogeneity due to insufficient mixing of fresh air and previously burned gas may induce high-speed knocking in the operating range at high engine speeds.

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．

As an effective method to improve engine performance at low engine speed, and reduce fuel consumption, VGT has been widely used in diesel engines. However, due to the higher exhaust temperature of the gasoline engines, it still has challenges of application in the turbocharged gasoline engines. As the high temperature of exhaust gas could damage the components of the complex variable structure in VGT, which may result in being deteriorated after long-term use of VGT. To improve the durability of VGT, researchers have been considering enhancing the high-temperature stability and durability by new components of the variable structure or advanced material for VGT production. In this study, a kind of porous material was installed before the turbine to study the effects on VGT application in a 4-cylinder turbocharged gasoline engine. As a result, using porous material, under the steady condition of medium load at 3200 RPM, a fuel economy improvement of about 1% was obtained due to the higher turbine efficiency and less pumping loss, and a 33 ℃ turbine inlet temperature decrease occurred due to the extra heat loss by adding porous material. In addition, under a high load of 4000 RPM, due to the decreased turbine inlet temperature by using of porous material, the stoichiometric combustion range of the engine was expanded, and peak torque was increased by a 25 ℃ lower turbine inlet temperature with porous material than the highest turbine inlet temperature limit. As a result, porous Si-SiC material could improve the fuel economy, high-temperature durability, and peak torque of the VGT engines.

The introduction of real driving emissions cycles and increasingly restrictive emissions regulations force the automotive industry to develop new and more efficient solutions for emission reductions. In particular, the cold start and catalyst heating conditions are crucial for modern cars because is when most of the emissions are produced. One interesting strategy to reduce the time required for catalyst heating is post-oxidation. It consists in operating the engine with a rich in-cylinder mixture and completing the oxidation of fuel inside the exhaust manifold. The result is an increase in temperature and enthalpy of the gases in the exhaust, therefore heating the three-way-catalyst. The following investigation focuses on the implementation of post-oxidation by means of scavenging in a four-cylinder, turbocharged, direct injection spark ignition engine. The investigation is based on detailed measurements that are carried out at the test-bench. Due to the complexity of the investigated phenomenon, the analysis at the test-bench has been sustained by 3D-CFD simulations. At first a 3D-CFD full-engine model has been implemented to reproduce the complete engine from the air-box up to the turbine inlet. This model is able to simulate all the relevant full-engine effects like scavenging, cylinder-to-cylinder interaction and local inhomogeneity inside the cylinder. The second implemented model focuses on the exhaust manifold, from the exhaust valve up to the turbine volute, and it is characterized by a fine computational grid and by the implementation of a chemical reaction mechanism. Both models have been validated using the detailed measurements of the test-bench. The simulation matched precisely the measurements and enabled a better interpretation of experimental data. The simulation methodology has been applied also to other engine operating points enabling a mapping of post-oxidation, the development of a post-oxidation model for 1D engine simulation and the implementation of a simplified model for the full-engine simulation.

In the downsizing concept, the turbocharger (T/C) is one of the key devices for improving thermal efficiency and exhaust emissions of internal combustion engines for automobiles. In order to maximize the supercharged engine performance, the size of the T/C applied for the given engine system has been optimized by using a 1-D engine cycle simulation. For this reason, T/C performance prediction model for engine cycle simulation is required to be accurate over a wide operating range. In the conventional T/C performance prediction model, the turbine performance was predicted by extrapolating from the efficiency map measured under steady flow. However, the accuracy of the extrapolation method is uncertain, and it has been pointed out that the prediction accuracy is low in the low load operations. In this study, a 1-D T/C model developed based on hydrodynamics and thermodynamics was used. Using the 1-D T/C model, a grid efficiency map over the entire operating range was calculated and the grid map was applied to 1-D engine cycle simulation. The accuracy of the T/C model was verified by comparing the experimentally measured efficiency under steady flow.

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.

Exhaust gas energy recovery systems have shown great potential in improving internal combustion engine’s fuel consumption. The use of porous Si-SiC material as heat storage medium to improve the turbine performance and fuel consumption of the engine has not been investigated. In order to study the effect of porous Si-SiC material as heat storage medium on the fuel consumption for a turbocharged gasoline engine, steady and transient engine conditions were considered. A one-dimensional flow dynamic model of the porous heat storage material was established and comprehensively validated by experimental data. Then, this model was applied to predict the performance of the engine with heat storage medium under various conditions, including steady operation condition at targeted torque and transient operation conditions following the worldwide harmonized light vehicles test cycles. As a result, under steady operation conditions, using heat storage medium, a fuel consumption reduction of about 1.1% was obtained due to increased turbine efficiency and reduced pumping loss. Moreover, the simulation under worldwide harmonized light vehicles test cycle driving cycle achieved fuel consumption saving up to 6.6% at medium vehicle speed due to the reuse of recovered exhaust gas energy in the heat storage medium. Thus, to use of the porous Si-SiC material as a kind of heat storage medium can be deemed as a prominent way to improve the turbine efficiency and engine performance of turbocharged gasoline engines.

A transparent model engine was developed which can generate an axially symmetrical flow field in the cylinder and which allows easy access to optical measurements of the in-cylinder air motion. Experimental data on flow characteristics such as mean velocity, turbulent velocity and turbulent scale in the entire space of the cylinder obtained with this engine are expected to be available for evaluating the reliability of the mathematical models popular at present. This paper describes the design concept and details of the structure of the engine, and offers some experimental data measured by both a flow visualization technique and laser Doppler velocimetry.

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.

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．

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．

<p>The prechamber combustion characteristics were studied using a rapid compression and expansion machine (RCEM) to improve the efficiency of cogeneration natural gas engines. The torch flames generated by a prechamber were used to investigate the effect that a prechamber has on the main combustion. In our previous study, we observed the correlation between the torch flame and the main flame (which is a so-called "prechamber combustion"). In this study, the effects of prechamber parameters such as initial pressure and nozzle diameter of injection holes, equivalence ratio on prechamber combustion characteristics were investigated in detail. Especially, by comparing the combustion characteristics of methane, which is the main component of natural gas, and propane, which is a representative of small-volume components, the effects of fuel types on the ignition and combustion characteristics of pre-chamber ignition system were investigated to elucidate of the effect of fuel property. In conclusions, regarding the mechanism of prechamber-ignition combustion, it was inferred that the jet erupted from the prechamber did not directly propagate in the main chamber but included the "ignition phenomenon" of the main chamber due to the jet. In addition, under the experimental conditions of this study, it was found that the ignition delay time and the combustion period can be predicted by simple calculation, which can lead to the important guideline for the pre-chamber design.</p>

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.

Low temperature plasma ignition has been proposed as a new ignition technique as it has features of good wear resistance, low energy release and combustion enhancement. In the authors' previous study, lean burn limit could be extended slightly by low temperature plasma ignition while the power supply's performance with steep voltage rising with time (dV/dt), showed higher peak value of the rate of heat release and better indicated thermal efficiency. In this study, basic study of low temperature plasma ignition system was carried out to find out the reason of combustion enhancement. Moreover, the durability test of low temperature plasma plug was performed to check the wear resistance.

We developed an analytical method for the detection of nitric oxide (NO), nitrogen dioxides (NO ) and ozone (O ) simultaneously with high time resolution (1 s). The fast analytical method was applied for the observation at the Fuji mountain roadside at an altitude of 2300 m. We successfully observed the concentrations of NO and NO in emissions from each vehicle at a roadside, and the O concentration decreased due to the reaction with NO. Relative amounts of NO emissions and primary NO emission ratios of each vehicle driven on the road were estimated by the concentrations observed with high time resolution. 2 3 2 3 x 2

In this report, the effect of injection specification, such as droplet size, lengths of nozzle tip and spray angle, on the engine performance was investigated using a 1.2 L port fuel injection (PFI) four-cylinder gasoline engine. The experimental conditions were selected to cover the daily operating mode, including the cold start and catalyst heating process. The experiments were conducted by varying not only the injectors but also the injection timing which was shifted from the exhaust to intake stroke. The results were evaluated by the fuel consumption and exhaust gas emissions. When these tests were conducted on a production engine, a carefully designed tumble generator was installed at the intake port to enhance the intake air flow. As a result, the injection specifications showed a potential to obtain less fuel consumption and lower engine-out emissions was evaluated.

Cycle-to-cycle variation (CCV) of combustion in low load operation is a factor that may cause various problems in engine operation. Variable valve timing and variable ignition timing are commonly used as a means to reduce this variation. However, due to mountability and cost constraints, these methods are not feasible for use in motorcycle engines. Therefore, development of an engine with minimal CCV without utilizing complicated mechanisms or electronic control is required. CCV of combustion may be caused by fluctuations in in-cylinder flow, air-fuel mixture, temperature, residual gas and ignition energy. In this study, the relationship between CCV of combustion, in-cylinder flow fluctuation and air-fuel mixture fluctuation was the primary focus. In order to evaluate in-cylinder flow fluctuation, Time Resolved Particle Image Velocimetry (TR-PIV) technique was utilized. In addition, Planar Laser Induced Fluorescence (PLIF) technique was used to measure spatial distribution of the mixture. These two visualization techniques were used together to measure continuous combustion cycles. The fluctuation of net IMEP can be explained by the fluctuation of Turbulence Kinetic Energy (TKE) and fuel concentration. In most cycles, net IMEP was correlated with TKE. In the remaining cycles, net IMEP was correlated with fuel concentration. The contribution of each factor towards net IMEP is to be discussed. It has been also confirmed that TKE fluctuation is caused by fluctuation in the tumble vortex structure, as shown in the authors' previous study [2] [13].

Porous materials, which have large surface areas, have been used for heat storage. However, porous Si-SiC material, as heat storage medium to be applied to a turbocharged gasoline engine has not been investigated extensively. In this study, porous Si-SiC material was used in the upstream of the turbine as heat storage medium and a model was thereby developed for further study. Substrate surface area and substrate volume of Si-SiC were calculated for structure model calibration. Following these calculations and test results, the pressure loss and thermal model were validated. Results show that the weaken exhaust gas pulsation amplitude by porous Si-SiC leads to better turbine performance and BSFC in steady engine condition for a turbocharged gasoline engine. In addition, its transient operation response needs to be improved under transient engine conditions. Hence the possibility of improving the transient response is investigated with characteristics of porous Si-SiC material. It was observed that less time was required for the engine to reach the target torque in transient conditions.

The purpose of this paper is to find a way to extend the high load limit of homogeneous charge compression ignition (HCCI) combustion. A newly developed rapid compression and expansion machine (RCEM) was employed to reproduce the typical HCCI high load condition. The in-cylinder turbulence was created by the special piston which equipped with a flow guide plate. Meanwhile, the ambient temperature distribution in the cylinder was determined by the wall temperature controlling system which was controlled by the independent coolant passages. In addition, the numerical simulation by using large eddy method coupled with a detailed chemical reaction was conducted as well. The results show that HCCI mode is potential to be improved at high load condition in full consideration of in-cylinder temperature, flow, and turbulence.

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．

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．

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．

<p>Research on internal combustion engine using gaseous fuel is getting popular. In order to reduce exhaust gas emissions including CO₂, heavy oil is replaced by gas fuel, especially for ships and stationary generators. Demand of natural gas is rapidly increased due to the clean exhaust gas emissions and the price. Moreover, combustion study of hydrogen and ammonia is also getting active as both fuels can be made from green energy. In this article, combustion technologies using natural gas are mainly focused, such as abnormal combustion, ignition method, methane slip and combustion analogy. Many research papers are reviewed and discussion from both experimental and numerical viewpoints are briefly described.</p>