森吉 泰生

NOx emissions from diesel passenger vehicles affect the atmospheric environment. It is difficult to evaluate the NOx emissions influenced by environmental conditions such as humidity and temperature, traffic conditions, driving patterns, etc. In the authors' previous study, real-driving experiments were performed on city and highway routes using a diesel passenger car with only an exhaust gas recirculation system. A statistical prediction model of NOx emissions was considered for simple estimations in the real world using instantaneous vehicle data measured by the portable emissions measurement system and global positioning system. The prediction model consisted of explanatory variables, such as velocity, acceleration, road gradient, and position of transmission gear. Using the explanatory variables, NOx emissions on the city and highway routes was well predicted using a diesel vehicle without NOx reduction devices. However, the prediction model had some limitations owing to the effects of NOx reduction devices. In this study, among various NOx reduction systems, a diesel vehicle with NOx storage catalyst (NSC) was chosen to predict the NOx emissions under a catalytic system. To improve the accuracy of the NOx emissions under the NSC, a catalyst model was added to the prediction model and used to predict the catalyst properties. By adding the catalyst model, the accuracy of NOx emissions of the prediction model was improved compared to the previous prediction model with individual explanatory variables. The NOx emissions were well predicted compared to the measured data.

To drastically improve thermal efficiency of a gasoline spark-ignited engine, super-lean burn is a promising solution. Although, studies of lean burn have been made by so many researchers, the realization is blocked by a cycle-to-cycle combustion variation. In this study, based on the causes of cycle-to-cycle variation clarified by the authors' previous study, a unique method to reduce the cycle-to-cycle variation is proposed and evaluated. That is, a bulk quench at early expansion stroke could be reduced by making slight fuel stratification inside the cylinder using the twin-tumble of intake flows. As a result, the lean limit was extended with keeping low NOx and moderate THC emissions, leading to higher thermal efficiency.

Among the emerging technologies in order to meet ever stringent emission and fuel consumption regulations, Exhaust Gas Recirculation (EGR) system is becoming one of the prerequisites particularly for diesel engines. Although EGR cooler is considered to be an effective measure for further performance enhancement, exhaust gas soot deposition may cause degradation of the cooling. To address this issue, the authors studied the visualization of the soot deposition and removal phenomena to understand its behavior. Based on thermophoresis theory, which indicates that the effect of thermophoresis depends on the temperature difference between the gas and the wall surface exposed to the gas, a visualization method using a heated glass window was developed. By using glass with the transparent conductive oxide: tin-doped indium oxide, temperature of the heated glass surface is raised. This new method was applied to an EGR cooler, which successfully enabled real-time visualization without soot deposition on the window surface. Consequently it was visually confirmed that the soot adheres to the heat exchanging surface. This observation also confirms that basic mechanism of the deposition is due to the thermophoretic phenomenon. Furthermore, there were notable findings observed in the experiment on running a diesel engine. First, position of water condensation occurrence depends on the local thickness distribution within the soot deposit. In addition, the size of the soot peeling area can be effectively increased by inducing high gas velocity with Vortex Generator fin (VG fin) when condensed water exists. The VG fin has heat transfer promoting effect by generated vortex along the gas flow direction on the heat transfer surface. In this paper, these observations are discussed in detail as well as the development of the visualization method.

To understand the mechanism of the combustion by torch flame jet in a gas engine with pre-chamber and also to obtain the strategy of improving thermal efficiency by optimizing the structure of pre-chamber including the diameter and number of orifices, the combustion process was investigated by three dimensional numerical simulations and experiments of a single cylinder natural gas engine. As a result, the configuration of orifices was found to affect the combustion performance strongly. With the same orifice diameter of 1.5mm, thermal efficiency with 7 orifices in pre-chamber was higher than that with 4 orifices in pre-chamber, mainly due to the reduction of heat loss by decreasing the impingement of torch flame on the cylinder linear. Better thermal efficiency was achieved in this case because the flame propagated area increases rapidly while the flame jets do not impinge on the cylinder wall intensively. This means that the optimization of orifice diameter and its number is quite important to enhance the flame propagation without increasing heat loss.

<p>The effects of fuel injection timing and coolant temperature on soot and particulate emissions at stoichiometric mixture condition under heating mode were examined in a single cylinder spark ignition direct injection gasoline engine. Single injection was employed and the start of fuel injection timing was adjusted in the intake stroke. The gross indicated mean effective pressure and the 50% heat release angle were set to 0.7 MPa and 9 deg.ATDC respectively by adjusting the intake air pressure, injected fuel mass and ignition timing. Regardless of coolant temperatures, with advancing the injection timing close to the top dead center, the exhausted soot mass concentration and particulate number are increased, mainly due to more liquid fuel impinging the combustion chamber walls and resulting in wider and more rich fuel-air mixture around the walls. Regardless of fuel injection timings, with decreasing coolant temperature, the exhausted soot mass concentration and particulate number are increased. To maintain the same load and combustion phasing, more amount of liquid fuel should be injected, due to the lower in-cylinder temperature and wall temperture with lower coolant temperature, resulting in more unevaperated fuel and wider zone for rich fuel-air mixture near the combustion chamber walls. Compared to coolant temperature, the injection timing should be well designed to decrease the particulate matter emission.</p>

<p>This article shows a research on the effect of in-cylinder flow on thermal stratified homogeneous charge compression ignition (HCCI) combustion to extend a high load limit of HCCI combustion. The study was conducted by three dimensional computational fluid dynamics coupled with simulation of chemical reactions. The in-cylinder temperature distribution was set as an initial condition. The in-cylinder flow was added before low temperature oxidation (LTO) and during high temperature oxidation (HTO), respectively. The results show that the in-cylinder flow before LTO leads to slow combustion due to heat loss to combustion chamber walls. The results also show that the in-cylinder flow during HTO is effective in fast combustion. This is mainly because in-cylinder flow expands hot burned mixture to unburned mixture, which accelerates the combustion.</p>

ディーゼル車の実路走行時における排出ガス性能の確保が急務である．本研究では，実路走行時の排出ガス評価手法の要件を明確化すべく，ディーゼル乗用車に車載式排出ガス分析計（PEMS）を搭載した実路走行試験を行い，とくにNOx 排出量における走行環境や車両条件等の因子による影響について考察した．

Reduction in the cycle-to-cycle variation (CCV) of combustion in internal combustion engines is required to reduce fuel consumption, exhaust emissions, and improve drivability. CCV increases at low load operations and lean/dilute burn conditions. Specifically, the factors that cause CCV of combustion are the cyclic variations of in-cylinder flow, in-cylinder distributions of fuel concentration, temperature and residual gas, and ignition energy. However, it is difficult to measure and analyze these factors in a production engine. This study used an optically accessible single-cylinder engine in which combustion and optical measurements were performed for 45 consecutive cycles. CCVs of the combustion and in-cylinder phenomena were investigated for the same cycle. Using this optically accessible engine, the volume inside the combustion chamber, including the pent-roof region can be observed through a quartz cylinder. CCV of in-cylinder flow for 45 continuous firing cycles were measured by Time-Resolved Particle Image Velocimetry (TR-PIV) technique. The in-cylinder flow was measured at intervals of 2 crank angle degrees from the intake to compression strokes using a dual-cavity, high-frequency Nd:YLF laser. In order to analyze the CCV, the measured instantaneous flow was converted to a time-averaged flow by low-pass filtering to remove the high-frequency component. Moreover, CCVs of fuel distribution at intake valve closing (IVC) and just before ignition timing were obtained by Planar Laser Induced Fluorescence (PLIF) technique. The fourth harmonic generation of a dual-cavity Nd:YAG laser was used as the excitation light source. 3-Pentanone, which was mixed with iso-octane and injected to the intake port, was used as a PLIF tracer. These two visualization techniques were applied simultaneously during the continuous firing cycles. As a result, it was confirmed that the CCVs of in-cylinder flow and fuel distribution significantly affect the CCV of combustion at low-load conditions. In particular, flow in a direction opposite to the tumble flow was observed in the lowest load cycle.

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 this study, we focused on observing the correlation between the torch flame and the main flame (which is a so-called “prechamber combustion”) as well as the knocking phenomena for various prechamber configurations.

可変容量ターボチャージャ（VGT）をガソリンエンジンに適用した際の燃費低減効果を検証するため，1.6L VGT ガソリンエンジンシミュレータ及びモード走行モデルを構築した．従来型のW/G ターボとVG ターボの燃費性能をモード走行燃費によって比較した結果，VG ターボとCooledEGR の組み合わせにより，燃費を低減できる可能性を示した．

In recent years, improvements in the fuel economy and exhaust emission performance of internal combustion engines have been increasingly required by regulatory agencies. One of the salient concerns regarding general purpose engines is the larger amount of CO emissions with which they are associated, compared with CO emissions from automobile engines. To reduce CO and other exhaust emissions while maintaining high fuel efficiency, the optimization of total engine system, including various design parameters, is essential. In the engine system optimization process, cycle simulation using 0-D and 1-D engine models are highly useful. To define an optimum design, the model used for the cycle simulation must be capable of predicting the effects of various parameters on the engine performance. In this study, a model for predicting the performance of a general purpose SI (Spark Ignited) engine is developed based on the commercially available engine simulation software, GT-POWER. The developed 1-D engine model was validated using a 3-D CFD (Computed Fluid Dynamics) simulation and experimental results. The effects of engine speed and load, air-fuel ratio (A/F), spark ignition timing on combustion characteristics were simulated. The simulation results were compared with experimental results to determine the accuracy of the developed model.

EGR適用範囲の高負荷側拡大を目的として各種コイルを評価し，高負荷条件において点火コイルの二次エネルギ増加によるEGR限界拡大効果がノック抑制に貢献することを明らかとした．ノック抑制による燃費低減効果は高負荷になる程大きく，点火強化の消費電力増加を上回る燃費低減効果が得られるポテンシャルがある．

本研究では，過給リーンバーンガソリン機関の希薄限界における燃焼特性を調査するため，単気筒ガソリン機関を用いて当量比0.6 の希薄燃焼を実現し，筒内圧力計測に基づく燃焼解析，エンドスコープを用いた火炎伝播とノッキングの高速度撮影を行い，燃焼特性，エネルギーバランス，ノッキングについて解析した．

An improvement of thermal efficiency of internal combustion engines is strongly required. Meanwhile, from the viewpoint of refinery, CO2 emissions and gasoline price decrease when lower octane gasoline can be used for vehicles. If lower octane gasoline is used for current vehicles, fuel consumption rate would increase due to abnormal combustion. However, if a Homogeneous Charge Compression Ignition (HCCI) engine were to be used, the effect of octane number on engine performance would be relatively small and it has been revealed that the thermal efficiency is almost unchanged. In this study, the engine performance estimation of HCCI combustion using lower octane gasoline as a vision of the future engine was achieved. To quantitatively investigate the fuel consumption performance of a gasoline HCCI engine using lower octane fuel, the estimation of fuel consumption under different driving test cycles with different transmissions is carried out using 1D engine simulation code. As a result, combining high compression ratio and Continuously Variable Transmission (CVT) can improve the fuel consumption in HCCI/SI combustion even using lower octane gasoline.

PFI (Port Fuel Injection) gasoline engines for motorcycles have some problems such as slow transient response because of wall wet of fuel caused by the injector's layout. Hence, it is important to understand the characteristics of fuel sprays such as droplet size and distribution of fuel concentration. Considering the spray formation in a port, there are three kinds of the essential elements: breakup, evaporation and wall impingement. However, it is difficult to observe three of them at the same time. Therefore, the authors have made research step by step. In the authors' previous study, the authors focused on the wall collision, droplet sizes, droplet speeds and the space distribution of the droplets. In this study, the authors focused on evaporation. A direct sampling method using FID (Flame Ionization Detector) for evaporating fuel was established and the concentration distribution of evaporating fuel in the port was measured and analyzed. As a result, it was found that higher velocity in the port increases fuel concentration with enhanced atomization and that evaporating fuel is easier to be affected by the flow and fuel distillation characteristics.

In order to realize the high compression ratio and high dilution combustion toward improvement in thermal efficiency, the improvement in stability of ignition and initial phase of combustion under the high gas flow field is the major challenge. In terms of the shift on the higher power side of the operating point by downsizing and improvement of real world fuel consumption, the improvement of ignitability is increasingly expected in the wide operating range also including high load and high engine speed region. In this study, the effects of the gas pressure, gas flow velocity near the spark gap at ignition timing, and discharge current characteristics on spark channel formation were analyzed, focusing on restrike event and spark channel stretching in the spark channel formation process. And the relationship between the average discharge current until 1 ms and the EGR combustion limit was considered.

The effect of properties of lubricating oil on low speed pre-ignition (LSPI) was investigated. Three different factors of oil properties such as cetane number, distillation characteristics and Calcium (Ca) additive (with and without) are prepared and examined. Then actual engine test of LSPI was carried out to evaluate the effect and to clarify the mechanism and role of lubricating oil. Finally it is clarified that the oil cetane number and/or Ca additive strongly affect LSPI phenomena.

In this study, the effect of the low octane number fuel on HCCI engine performance was experimentally investigated using a slightly modified commercial four-cylinder gasoline engine. To operate the engine in HCCI strategy with wide operational range, the blowdwon supercharging (BDSC) system proposed by the authors was applied in the test engine. Research octane number (RON) of test fuels was varied from 90 to 78.5 as an experimental parameter. Experimental results showed that in the range of the present study, HCCI operational range, brake thermal efficiency and exhaust emissions during HCCI operation were little affected by the RON of the test fuels. In contrast, during SI operation, thermal efficiency was deteriorated with lower RON fuel because of knocking. In terms of "Well-to-Wheel" energy consumption, it is favorable to use gasoline without any additional treatment for increasing fuel octane number, because additional energy is necessary for increasing octane number of commercial gasoline. It is expected that the "Well-to-Wheel" CO emission can be reduced by application of high efficiency HCCI combustion into production engine operation with low octane number fuel. 2

The authors investigated the reasons of how a preignition occurs in a highly boosted gasoline engine. Based on the authors' experimental results, theoretical investigations on the processes of how a particle of oil or solid comes out into the cylinder and how a preignition occurs from the particle. As a result, many factors, such as the in-cylinder temperature, the pressure, the equivalence ratio and the component of additives in the lubricating oil were found to affect the processes. Especially, CaCO included in an oil as an additive may be changed to CaO by heating during the expansion and exhaust strokes. Thereafter, CaO will be converted into CaCO again by absorbing CO during the intake and compression strokes. As this change is an exothermic reaction, the temperature of CaCO particle increases over 1000K of the chemical equilibrium temperature determined by the CO partial pressure. The possibility of a preignition due to particles including CaCO particles is numerically simulated comparing with the experimental results. 3 3 2 3 2 3

In this study, in order to clarify the mechanism of preignition occurrence in highly boosted SI engine at low speed and high load operating conditions, directphotography of preignition events and light induced fluorescence imaging of lubricant oil droplets during preignition cycles were applied. An endoscope was attached to the cylinder head of the modified production engine. Preigntion events were captured using high-speed video camera through the endoscope. As a result, several types of preignition sources could be found. Preignition caused by glowing particles and deposit fragments could be observed by directphotography. Luminous flame was observed around the piston crevice area during the exhaust stroke of preignition cycles. This implies that the lubricant oil or mixture of oil and liquid fuel which is accumulated in the piston crevice area burns under low oxygen condition, and that the glowing particles which induce preignition would be produced in the oil combustion during the expansion stroke. Preignition induced by a lubricant oil droplet ignition was probably captured using fluorescence technique. Through the investigations, preignition which occurs at the piston crevice area was often observed. It was also found that preignition event often terminated in a single cycle in the present study and hardly occurred in the sequential manner including normal SI combustion as has been frequently reported in the previous studies. This is probably because a scavenging efficiency in the engine operating condition in this experiment is high. In the conventional boosted gasoline engine, an exhaust pressure increases, and some of the particles generated during first preignition cycle are not scavenged and remain inside the cylinder. The residual particles are heated during the subsequent combustion cycle and induce the preignition again. Preignition event continues until the residual particles are consumed. This would be one of the possible mechanism of the sequential preignition occurrence.

LSPI is an important issue to enable and enhance the effect of downsizing in SI engines. Experimental work was carried out by using 4 cylinder turbocharged gasoline engine, attaching the extra supercharger to get a higher boost pressure. Many parameters of driving condition, engine specification and lubricants were studied and some of them were extracted as the major items which affect the possibility of LSPI. Coolant temperature and Calcium (Ca) additive to lubricant had strong effect on the frequency of LSPI. Combustion strategy of strong miller cycle and LPEGR were also studied and compared in very high BMEP condition. Finally IMEPg of 3MPa at 1500rpm was achieved by using a single cylinder test engine equipped with 2-stage mechanically supercharged intake system.

The authors investigated the reasons of how a preignition occurs in a highly boosted gasoline engine. Based on the authors' experimental results, theoretical investigations on the processes of how a particle of oil or solid comes out into the cylinder and how a preignition occurs from the particle. As a result, many factors, such as the in-cylinder temperature, the pressure, the equivalence ratio and the component of additives in the lubricating oil were found to affect the processes. Especially, CaCO included in an oil as an additive may be changed to CaO by heating during the expansion and exhaust strokes. Thereafter, CaO will be converted into CaCO again by absorbing CO during the intake and compression strokes. As this change is an exothermic reaction, the temperature of CaCO particle increases over 1000K of the chemical equilibrium temperature determined by the CO partial pressure. The possibility of a preignition due to particles including CaCO particles is numerically simulated comparing with the experimental results. 3 3 2 3 2 3

Highly efficient natural gas engines have been widely used in wide range of sectors from industry and transportation. However, because combustion process in gas engines with a pre-chamber is very complicated, it is difficult to experimentally investigate the combustion process including flame propagation from the pre-chamber. In this study, combustion characteristics in the gas engine with a pre-chamber were numerically investigated by using three-dimensional numerical simulation with detailed chemical reactions. Torch flame combustion brings about high temperature and strong turbulence to the main chamber. Combustion processes of the natural gas engine with pre-chamber can be categorized in three stages. The first stage is high speed flame propagation induced by flame torches from the pre-chamber. The second stage is simple flame propagation in the main-chamber. This flame propagation speed is relatively lower than the first stage combustion, because turbulence kinetic energy is lower than that during the first stage. The curvature of rate of heat release relates to the surface area of flame front and excess air ratio in the flame front. The third stage is autoignition of the unburned mixture in the end gas region. Autoignition in the main-chamber occurs between the torches. The intensity of pressure oscillation and rate of heat release depend on both the mass of the unburned mixture in the end gas region and the onset positions of autoignition.

The analysis of preignition in a boosted gasoline engine is an important issue to improve the engine power and thermal efficiency. One of the convincing mechanisms is an autoignition of oil-gasoline droplets. The oil-gasoline droplets formation process that are adhered to the piston top-land in film is simulated by giving the acceleration of the piston motion. Using VOF method, the effects of several physical parameters, such as oil film thickness, fuel dilution rate, and top-land length on the droplet formulation which disperses in a combustion chamber are investigated. As a result, it was found that droplets formation have three steps and the oil film thickness is the most effective factor. Next, the possibility of ignition of the oil droplet inside the cylinder was examined. However, it was found difficult to cause autoignition. Therefore, CaCO3 included in the oil as an additive may be changed to CaO by heating during expansion and exhaust strokes and then, CaO may be converted into CaCO3 again by absorbing CO2 during the intake and compression strokes. As this change is an exothermic reaction, the temperature of the particle increases determined by CO2 partial pressure. The CaO particle may be a cause of preignition.

直噴ガソリンエンジンから排出されるPMは，主に筒内に付着した燃料に起因する．冷間始動時，蒸発性が低い燃料成分は複数サイクルにわたって残存，暖気後に蒸発してすすを生じると予想される．本研究では数値解析を用い，単一サイクル内の圧力・温度変化，複数サイクルでの壁温変化がすす排出特性に及ぼす影響を検討した．

Closed-loop control is vital for an application of HCCI engines in passenger cars. This paper introduces a simplified control-oriented model for control of combustion phasing and IMEP of a Blowdown Supercharge Engine (BDSC). Despite the complexity of this particular engine, the model has been found to match not only the steady state values in high load HCCI, but also to reproduce the transients. This model takes advantage of the knowledge of non-dynamic processes within the engine that can be derived from steady state values, while the main dynamics are achieved by dynamically modelling of cyclic coupling via in-cylinder temperature alone and mean exhaust pressure dynamics. Furthermore, a simplified combustion model has been found to be accurate enough for the region of interest. An automated tuning scheme helps to match the model to the respective target values. With this model and the tuning scheme, the model can be easily tuned for every possible case. A model-based MIMO state controller, based on Sliding-Mode Control theory has been designed and tested on a detailed 1-D simulation code.

HCCI combustion can realize low NOx and particulate emissions and high thermal efficiency. Therefore, HCCI combustion has a possibility of many kinds of applications, such as an automotive powertrain, general-purpose engine, motorcycle engine and electric generator. However, the operational range using HCCI combustion in terms of speed and load is restricted because the onset of ignition and the heat release rate cannot be controlled directly. For the extension of the operational range using either an external supercharger or a turbocharger is promising. The objective of this research is to investigate the effect of the intake pressure on the HCCI high load limit and HCCI combustion characteristics with blowdown supercharging (BDSC) system. The intake pressure (Pin) and temperature (Tin) were varied as experimental parameters. The intake pressure was swept from 100 kPa (naturally aspirated) to 200 kPa using an external mechanical supercharger. The experimental results showed that the maximum load successfully increased with increasing the intake pressure. The highest load in this study was 935kPa in IMEPg at the condition of 200 kPa in Pin and 32 ŶC in Tin. The maximum load of boosted BDSC-HCCI engine can be achieved comparable to the full load of naturally aspirated SI engine. In addition, for conditions with above 200 kPa in Tin, A/F and G/F could be almost the same. The comparison of heat release rate between with and without BDSC showed that the peak value of heat release rate decreased and the combustion duration was prolonged with BDSC by thermal stratification. Not only the pressure rise rate but also the peak cylinder pressure could be reduced by BDSC system. Moreover, the intake temperature was decreased while maintaining the conditions of G/F and intake pressure to investigate the intake temperature on heat release. The results showed that the dP/dθ max is reduced with Tin less than 50 ŶC. © 2013 SAE Japan and © 2013 SAE International.

In this paper, the necessary in-cylinder conditions for the transition from spark ignion (SI) to homogeneous charge compression ignition (HCCI) are analyzed. The hereby important factors for ignition time are investigated analytically. A control oriented combustion model, that is validated by experimental data, is used for sensivity analysis and a Monte-Carlo approach is taken to identify the important factors for transient HCCI and combustion mode switch.As a result, it was shown that the in-cylinder temperature plays a major role, exceeding other factors, such as the air-fuel ratio. The analytical conclusions are illustrated by numerical simulations after which the feasibility for actuation will be discussed. Final goal is to ensure a stable combustion in each cycle without crossing unstable combustion conditions.

An improvement of thermal efficiency is strongly demanded for gasoline engines. In this study, experiments were earned out to investigate the effects of intake air temperature and coolant temperature on brake thermal efficiency, heat loss and friction loss in a spark ignition gasoline engine. Experimental results showed that, intake air temperature has a little effect on brake thermal efficiency during partical load operation. During high load operation, a decrease in intake air temperature improved brake thermal efficiency due to an improvement in indicated thermal efficiency and decrease in exhaust loss. It was also revealed that the combination of high temperature cooling water for the engine block and low temperature cooling water for the cylinder heat is effective for improving brake thermal efficiency.

In order to extend the operational range with a gasoline fueled multi-cylinder homogeneous charge compression ignition engine, a blowdown supercharge system and an exhaust gas recirculation guide was developed. The concept was to provide a large amount of diluted mixture and a strong in-cylinder thermal stratification for decreasing nitrogen oxide emissions and pressure rise rate during high-load homogeneous charge compression ignition operation. Secondary air injection was also proposed to reduce a cylinder-to-cylinder variation in ignition timing, which is one of the limiting factors of multi-cylinder homogeneous charge compression ignition operation. In advance of experimental works, the blowdown supercharge system and the exhaust gas recirculation guide were proved to be effective to reduce pressure rise rate for high-load operation using three-dimensional in-cylinder flow simulations and zero-dimensional multi-zone simulations with detailed chemical kinetics. Based on the simulation results, experiments were conducted using a slightly modified production four-cylinder gasoline engine. At first, the effects of the proposed techniques were experimentally investigated by focusing on one cylinder out of four. Then, a four-cylinder homogeneous charge compression ignition operation test using the new techniques was carried out. The one-cylinder measurements revealed that the blowdown supercharge system with an exhaust gas recirculation guide is capable of extending the homogeneous charge compression ignition operating range up to a net indicated mean effective pressure of 590 kPa for naturally aspirated conditions. In addition, secondary air injection was experimentally demonstrated as a technique for reducing a cylinder-to-cylinder variation in ignition timing. Reducing the cylinder-to-cylinder variation in ignition timing, four-cylinder homogeneous charge compression ignition operation with a net indicated mean effective pressure of 570 kPa was successfully achieved with the blowdown supercharge system and the exhaust gas recirculation guide. © IMechE 2012.

The objective of this study is to develop a practical technique to achieve homogeneous charge compression ignition operation with a wide operating range using a blowdown supercharge system, which has been previously demonstrated as an effective technique to extend the upper load limit of acceptable homogeneous charge compression ignition operation. The valve actuation strategy to attain acceptable homogeneous charge compression ignition operation in a wide operating range has been newly developed and experimentally examined. The proposed strategy provides high in-cylinder temperature and a relatively small amount of in-cylinder mixture during low-load operations to improve the combustion stability while providing a large amount of diluted mixture for high-load operations to keep the in-cylinder pressure rise rate and nitrogen oxide emissions low. In addition, thermal efficiency and exhaust emissions for various homogeneous charge compression ignition operating loads using the blowdown supercharge system were experimentally investigated. Experimental results showed that the proposed valve actuation strategy, in which early intake valve closing and relatively late exhaust gas recirculation valve opening occurred, was effective to increase combustion stability during low-load conditions, and a stable homogeneous charge compression ignition operation at a net indicated mean effective pressure of 140 kPa was achieved. Compared to conventional spark-ignition operation, 14% to 35% improvement in brake specific fuel consumption rate was attained with more than 99% reduction in nitrogen oxide emissions for homogeneous charge compression ignition operation using the blowdown supercharge system. © IMechE 2012.

Gasoline direct injection (GDI) systems have higher power and fuel efficiency than multi-point injection (MPI) systems. The direct injection of fuel into the combustion chamber leads to improved fuel economy because intake air is cooled by fuel evaporation. Direct fuel injection also improves knock resistance and volume efficiency. Furthermore, spray-guided direct injection (DI) combustion systems allow stratified lean combustion operation due to their ability to eliminate wall-wetting and form ignitable stratified mixtures near spark plugs.In this research, a spray-guided combustion system with a piezo-type gasoline direct injector was investigated for its applicability to stratified lean combustion engines. Tests were conducted at constant engine speeds and load conditions (2000 rpm, IMEP 0.28 MPa) that reflect typical operating conditions for passenger vehicles. Fuel economy and combustion stability were evaluated for various injection pressures at each excess air ratio. It is possible to create a sufficiently rich mixture for ignition in the vicinity of the spark plug, even under overall ultra-lean mixture conditions (λ = 3.0). Exhaust gas recirculation (EGR) and retarded ignition timing were considered to achieve a reduction in nitrogen oxide (NO ) emissions. EGR with optimized ignition timing was most effective when a spray-guided combustion system was employed. © 2012 Elsevier Ltd. x

To extend the operating range of a gasoline HCCI engine, the blowdown supercharging (BDSC) system and the EGR guide were developed and experimentally examined. The concepts of these techniques are to obtain a large amount of dilution gas and to generate a strong in-cylinder thermal stratification without an external supercharger for extending the upper load limit of HCCI operation whilst keeping dP/dθ and NO emissions low. Also, to attain stable HCCI operation using the BDSC system with wide operating conditions, the valve actuation strategy in which the amount of dilution gas is smaller at lower load and larger at higher load was proposed. Additionally to achieve multi-cylinder HCCI operation with wide operating range, the secondary air injection system was developed to reduce cylinder-to-cylinder variation in ignition timing. As a result, the acceptable HCCI operation could be achieved with wide operating range, from IMEP of 135 kPa to 580 kPa. Compared to conventional SI operation, BSFC was improved by 14 % ~ 35 % with more than 99 % reduction in NO emissions. Copyright 2011 Society of Automotive Engineers of Japan, Inc. and SAE International. max x x

予混合気の自着火燃焼に対する非平衡プラズマの自着火促進作用を検討することを目的として，詳細な反応モデルを用いたシミュレーションを実施した．また，非平衡プラズマで生成される化学種の自着火促進効果を比較した．これらより，非平衡プラズマの自着火促進メカニズムや最適な適用条件について検討を加えた．

To clarify the mechanism of high brake thermal efficiency of HCCI combustion compared to SI combustion, the contributions of pumping loss, friction loss and gross indicated thermal efficiency were investigated. Also, independent effects of heat loss, specific heat ratio, heat release profile and combustion timing on gross indicated thermal efficiency in HCCI combustion were analyzed in detail. As a result, high gross indicated thermal efficiency is found to be the main contributors to improvement in brake thermal efficiency. Also, it is found that heat loss in HCCI combustion is lower than SI combustion leading to the increase in gross indicated thermal efficiency. The improvement in gross indicated thermal efficiency in HCCI operation is mainly caused by lower heat loss in HCCI compared to SI combustion.Copyright © 2012 by the Japan Society of Mechanical Engineers.

It is expected that liquid fossil fuels will be replaced by gaseous fuel within twenty years, and hydrogen may be of great importance by the mid-twenty-first century. However, recently, it has been difficult to secure a hydrogen economy, which starts from the establishment of a hydrogen infrastructure and leads to production, storage, and application. A transitional strategy should be prepared, and it is believed that a kind of partial application, such as reforming hydrocarbon fuel, could be a technical bridge to a hydrogen economy. Natural gas as an energy source for transportation has the advantage of emission at low levels. However, more technical researches should be carried out to hold a dominant position of clean fuel over well-developed diesel vehicles. Hydrogen/natural gas blends (HCNG) are promising fuels for solving the problems of present natural gas vehicles. It may possibly meet reinforced emission regulation, and North America and some European countries have already begun the development of an HCNG vehicle and the supply project of an HCNG station. The HCNG research project of Korea started in 2009 for developing an HCNG bus that meets the EURO-VI standard. In order to study the performance and emission characteristics of an HCNG engine, an 11-L, heavy duty, lean burn engine was used. The level of nitrogen oxides (NOx), the most important component of emissions, is closely related to operation strategy. Therefore, operating parameters, including excess air ratio and spark advance timing, were optimized, and other parameters for high thermal efficiency were also examined. Copyright © 2012 by the Japan Society of Mechanical Engineers.

To find an ignition and combustion control strategy in a gasoline fueled HCCI engine equipped with the BlowDown SuperCharging (BDSC) system which is previously proposed by the authors, a one-dimensional HCCI engine cycle simulator capable of predicting the ignition and heat release of HCCI combustion was developed. The ignition and the combustion models based on Livengood-Wu integral and Wiebe function were implemented in the simulator. The predictive accuracy of the developed simulator in the combustion timing, combustion duration and heat release rate were validated by comparing to experimental results. Using the developed simulator, the control strategy for the engine operating mode switching between HCCI and SI combustion was explored with focus attention on transient behaviors of air-fuel ratio, A/F, and gas-fuel ratio, G/F. The simulation result showed that the one-step variations in the amount of recharged EGR gas and G/F can be attained by activation or deactivation of the EGR valve lift with the BDSC system. It is considered that this one-step variation in G/F allows the one-step transition from the HCCI operation to the SI operation with small torque fluctuation. However, in the combustion mode transition from SI to HCCI, the combustion timing during the transient HCCI combustion was excessively advanced. The excessively advanced ignition timing leads to the increase in in-cylinder pressure rise rate, dP/dθ. In the strategies examined in the present study, only intake throttle valve, exhaust throttle valve and EGR valve lift switching were used to control mixture conditions in terms of A/F and G/F during combustion mode transition. The results obtained suggest that additional devises to control mixture conditions during the combustion mode transition is necessary to attain the smooth transition from SI to HCCI combustion. Copyright © 2012 SAE International.

Fuel economy can be significantly improved in a gasoline direct-injection (GDI) engine owing to the stratified mixture formation strategy which guarantees stable combustion under ultra-lean air fuel mixture conditions. In the GDI engine, it is widely accepted that the spray-guided direct-injection system, which is characterized by a close configuration between the centrally mounted injector and the spark plug, is regarded as a promising technology among the efforts to realize stratified lean combustion. With this configuration, the split injection can be an effective fuel injection scheme because of its potential to modulate the spray characteristics as well as to create a combustible mixture in the proximity of the spark plug. In this study, the split-injection strategy was assessed as a way to achieve ultra-lean operation in a GDI engine and the resulting lean-combustion characteristics were investigated in terms of the engine performance and emissions. The engine was tested at constant operating conditions (an engine speed of 3000 r/min and an indicated mean effective pressure of 0.4 MPa) with a change in the fuel injection pressure ranging from 10 MPa to 20MPa. The excess air ratio l varied from stoichiometry to the lean flammability limit, which turned out to be extended in the GDI approach. The engine test results show that the split injection of fuel allowed the formation of an adequately stratified mixture in lean-combustion conditions, and thus stable combustion was guaranteed. These results indicate that an excess air ratio was one of the important factors affecting the thermal efficiency and nitrogen oxide (NOx) emissions and was significantly extended to λ = 2.0 by the split-injection scheme. In addition, several fuel injection parameters such as the injection quantity, the split ratio, and the number of splits were examined with an emphasis on their impact on the fuel economy and emissions. The results demonstrate that there exists a trade-off between the NOx reduction and the efficiency, and therefore it is required to choose an appropriate injection strategy depending on the engine operating conditions in order to satisfy emission regulations. © 2011 Authors.

In this study, an experimental investigation on a naturally aspirated (NA), 8-L spark ignition engine fueled by biogas with various methane concentrations - which we called the N dilution test - was performed in terms of its thermal efficiency, combustion characteristics and emissions. The engine was operated at a constant engine rotational speed of 1800 rpm under a 60 kW power output condition and simulated biogas was employed to realize a wide range of changes in heating value and gas composition. The N dilution test results show that an increase of inert gas in biogas was beneficial to thermal efficiency enhancement and NO emission reduction, while exacerbating THC emissions and cyclic variations. Then, as a way to achieve stable combustion for the lowest quality biogas, H addition tests were carried out in various excess air ratios. H fractions ranging from 5 to 30% were blended to the biogas and the effects of hydrogen addition on engine behavior were evaluated. The engine test results indicated that the addition of hydrogen improved in-cylinder combustion characteristics, extending lean operating limit as well as reducing THC emissions while elevating NO generation. In terms of efficiency, however, a competition between enhanced combustion stability and increased cooling energy loss was observed with a rise in H concentration, maximizing engine efficiency at 5-10% H concentration. Moreover, based on the peak efficiency operating point, a set of optimum operating conditions for minimum emissions with the least amount of efficiency loss was suggested in terms of excess air ratio, spark ignition timing, and hydrogen addition rate as one of the main results. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 2 2 x 2 2 x 2 2

The objective of this study is to develop a practical technique to achieve HCCI operation with wide operation range. To attain this objective, the authors previously proposed the blowdown supercharge (BDSC) system and demonstrated the potential of the BDSC system to extend the high load HCCI operational limit. In this study, experimental works were conducted with focusing on improvement of combustion stability at low load operation and the reduction in cylinder to cylinder variation in ignition timing of multi-cylinder HCCI operation using the BDSC system. The experiments were conducted using a slightly modified production four-cylinder gasoline engine with compression ratio of about 12 at constant engine speed of 1500 rpm. The test fuel used was commercial gasoline which has RON of 91. To improve combustion stability at low load operation, the valve actuation strategy for the BDSC system was newly proposed and experimentally examined. With the newly proposed valve actuation strategy, only intake valve lift was varied and EGR and exhaust valve lifts were fixed with variation in target load. Compared to the previously proposed valve actuation strategy for the BDSC system, relatively late EGR valve opening timing with early intake valve closing timing is applied at low load condition in the proposed strategy. This provides high in-cylinder temperature and relatively rich fuel concentration at low load operation while providing a large amount of diluted mixture at high load operation. Additionally, effect of coolant water temperature on combustion stability was experimentally investigated. Coolant water temperature was varied from 85°C to 105°C. Experimental result showed that for low load HCCI operation, the valve timing with early intake valve closing and relatively late EGR valve opening was effective to increase combustion stability due to increases in in-cylinder temperature and fuel concentration. With early intake valve closing and relatively late EGR valve opening, a stable HCCI operation at net IMEP of 200 kPa was achieved. However, brake thermal efficiency was slightly deteriorated due to increase in pumping work utilized to increase in in-cylinder temperature. The increase in coolant water temperature also improved combustion stability and extends the low load operational limit due to increase in in-cylinder temperature. With a cooling water temperature of 105°C, the low load HCCI with net IMEP of 134 kPa was attained. In addition, to reduce the cylinder to cylinder variation in ignition timing which restricts HCCI operating range with multi-cylinder operation, the secondary air injection system in which air is injected into an exhaust port of each cylinder to control recharged EGR gas temperature using gas fuel injector was proposed and examined to control ignition timing of each cylinder independently. As a result, the cylinder to cylinder variation in ignition timing was successfully reduced and the high load HCCI operational limit with four-cylinder operation was extended up to net IMEP of 570 kPa. Compared to conventional SI operation, brake thermal efficiency was improved by about 15 % using the newly proposed strategy with more than 99% reduction in NO emission. © 2011 SAE International. x

Because blending hydrogen with natural gas can allow the mixture to burn leaner, reducing the emission of nitrogen oxide (NO ), hydrogen blended with natural gas (HCNG) is a viable alternative to pure fossil fuels because of the effective reduction in total pollutant emissions and the increased engine efficiency. In this research, the performance and emission characteristics of an 11-L heavy duty lean burn engine using HCNG were examined, and an optimization strategy for the control of excess air ratio and of spark advance timing was assessed, in consideration of combustion stability. The thermal efficiency increased with the hydrogen addition, allowing stable combustion under leaner operating conditions. The efficiency of NO reduction is closely related to the excess air ratio of the mixture and to the spark advance timing. With the optimization of excess air ratio and spark advance timing, HCNG can effectively reduce NO as much as 80%. © 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. x x x

To extend the operating range of a gasoline HCCI engine, the blowdown supercharging (BDSC) system and the EGR guide were developed and experimentally examined. The concepts of these techniques are to obtain a large amount of dilution gas and to generate a strong in-cylinder thermal stratification without an external supercharger for extending the upper load limit of HCCI operation whilst keeping dP/dθ and NO emissions low. Also, to attain stable HCCI operation using the BDSC system with wide operating conditions, the valve actuation strategy in which the amount of dilution gas is smaller at lower load and larger at higher load was proposed. Additionally to achieve multi-cylinder HCCI operation with wide operating range, the secondary air injection system was developed to reduce cylinder-to-cylinder variation in ignition timing. As a result, the acceptable HCCI operation could be achieved with wide operating range, from IMEP of 135 kPa to 580 kPa. Compared to conventional SI operation, BSFC was improved by 14 % ∼ 35 % with more than 99 % reduction in NO emissions. © Copyright 2011 Society of Automotive Engineers of Japan, Inc. and SAE International. max x x

The objective of this study is to develop a practical technique to achieve HCCI operation with wide operation range. To attain this objective, the authors previously proposed the blowdown supercharge (BDSC) system and demonstrated the potential of the BDSC system to extend the high load HCCI operational limit. In this study, experimental works were conducted with focusing on improvement of combustion stability at low load operation and the reduction in cylinder to cylinder variation in ignition timing of multi-cylinder HCCI operation using the BDSC system. The experiments were conducted using a slightly modified production four-cylinder gasoline engine with compression ratio of about 12 at constant engine speed of 1500 rpm. The test fuel used was commercial gasoline which has RON of 91. To improve combustion stability at low load operation, the valve actuation strategy for the BDSC system was newly proposed and experimentally examined. With the newly proposed valve actuation strategy, only intake valve lift was varied and EGR and exhaust valve lifts were fixed with variation in target load. Compared to the previously proposed valve actuation strategy for the BDSC system, relatively late EGR valve opening timing with early intake valve closing timing is applied at low load condition in the proposed strategy. This provides high in-cylinder temperature and relatively rich fuel concentration at low load operation while providing a large amount of diluted mixture at high load operation. Additionally, effect of coolant water temperature on combustion stability was experimentally investigated. Coolant water temperature was varied from 85 °C to 105 °C. Experimental result showed that for low load HCCI operation, the valve timing with early intake valve closing and relatively late EGR valve opening was effective to increase combustion stability due to increases in in-cylinder temperature and fuel concentration. With early intake valve closing and relatively late EGR valve opening, a stable HCCI operation at net IMEP of 200 kPa was achieved. However, brake thermal efficiency was slightly deteriorated due to increase in pumping work utilized to increase in in-cylinder temperature. The increase in coolant water temperature also improved combustion stability and extends the low load operational limit due to increase in in-cylinder temperature. With a cooling water temperature of 105 °C, the low load HCCI with net IMEP of 134 kPa was attained. In addition, to reduce the cylinder to cylinder variation in ignition timing which restricts HCCI operating range with multi-cylinder operation, the secondary air injection system in which air is injected into an exhaust port of each cylinder to control recharged EGR gas temperature using gas fuel injector was proposed and examined to control ignition timing of each cylinder independently. As a result, the cylinder to cylinder variation in ignition timing was successfully reduced and the high load HCCI operational limit with four-cylinder operation was extended up to net IMEP of 570 kPa. Compared to conventional SI operation, brake thermal efficiency was improved by about 15 % using the newly proposed strategy with more than 99% reduction in NO emission. © 2011 SAE International. x

To improve thermal efficiency of gasoline engines, the effect of coolant system on fuel consumption rate is studied in this report. The authors tried to control the flow of cooling water to find an optimized flow system to improve thermal efficiency, especially for the cold start condition. Experiments were carried out using a four-cylinder SI engine. Three test conditions of i) normal cold start, ii) cold start without operating the water pump and iii) cold start but with heated engine oil were measured. Temperatures of cooling water at some positions were measured during the warming-up time. Secondly, the effect of cooling water temperature on thermal efficiency at a steady state condition was examined. As a result, a higher temperature causes an improvement of thermal efficiency due to a reduction in mechanical friction. © 2011 SICE.

To avoid knocking phenomena, a special crank mechanism for gasoline engine that allowed the piston to move rapidly near TDC (Top Dead Center) was developed and experimentally demonstrated in the previous study. As a result, knocking was successfully mitigated and indicated thermal efficiency was improved [1],[2],[3],[4]. However, performance of the proposed system was evaluated at only limited operating conditions. In the present study, to investigate the effect of piston movement near TDC on combustion characteristics and indicated thermal efficiency and to clarify the knock mitigation mechanism of the proposed method, experimental studies were carried out using a single cylinder engine with a compression ratio of 13.7 at various engine speeds and loads. The special crank mechanism, which allows piston to move rapidly near TDC developed in the previous study, was applied to the test engine with some modification of tooling accuracy. Experimental result showed that indicated thermal efficiency as improved at 1000 r/min from low to high load, and at 1600, 2000 r/min high load by Leaf-shape mechanism. Improvement of indicated thermal efficiency at 1000 r/min was due to the reduction of cooling loss and at 1600, 2000r/min high load due to the recovery of the degree of constant volume. Also it was found that high load operation with compression ratio of 13.7 without knocking was realized using the proposed piston movement mechanism. Auto-ignition occurred at high load conditions even though the proposed piston movement was applied, but auto-ignition was not followed by high frequent in-cylinder pressure oscillation shown in the case of knocking. © Copyright 2011 Society of Automotive Engineers of Japan, Inc. and SAE International.

Direct-injection diesel engines have become prime candidates for future transportation needs owing to their high thermal efficiency. However, the increase in nitrogen oxides (NO ) within local high-temperature regions and the increase in particulate matter within the diffusion flame region during diesel combustion are problematic and must be resolved. The utilization of NO -absorbing catalysts, based on the concept of NO storage and release, is one of the most promising techniques able to reduce NO emissions within net oxidizing gas conditions. This type of NO removal system, called the lean NO trap (LNT) catalyst, absorbs NO under lean exhaust gas conditions and releases NO under rich conditions. This technology provides the advantage of high NO conversion efficiency; however, the correct amount of reducing agent must be supplied within the catalytic converter under appropriate conditions in order to guarantee a high NO reduction efficiency. In this research, the performance characteristics of an LNT, using a hydrogen-enriched gas as a reductant, were examined via various injection strategies and rich exhaust gas conditions. Although the hydrogen concentration of hydrogen-enriched gas also affects the LNT performance, the composition of hydrogen-enriched gas was fixed as a similar composition to that for the ideal re-forming of diesel fuel. The NO reduction efficiency is closely connected to the injection timing and duration of reductant flow. When the injection was introduced 1.5s after throttling, the LNT NO conversion was maximized. However, the LNT NO conversion decreased when the injection timing was earlier or later than 1.5s. Because the actual rich duration of the exhaust gas is limited at a specific point during the rich operation for 3s, the LNT NO conversion was maximized when the hydrogen-enriched gas was injected at the minimum air-to-fuel ratio observed at the LNT inlet. By optimizing the control of this flow, the system encounters only a 1.9 per cent fuel penalty while maintaining a 90 per cent NO reduction efficiency. x x x x x x x x x x x x x x x