窪山 達也

<p>Cycle-to-cycle variation (CCV) of in-cylinder flow occurs in internal combustion engines. It is necessary to analyze CCV of flow to separate averaged-flow (as low frequency / low wave number) from turbulence (as high frequency / high wave number), because an averaged flow varies from cycle to cycle. Two averaging methods are used for the extraction of mean component from instantaneous flow. One is temporal-averaging method, the other is spatial-averaging method. In the temporal -averaging method, a fluctuation of flow is captured at fixed point in Eulerian, turbulence is regarded as the high frequency component, and it is removed by a low pass filtering. In the spatial-averaging method, the turbulence in spatial arrangement of flow velocity is directly averaged by using vortex scale as a threshold (e.g. Moving-averaging filter and Gaussian-averaging filter). However, the temporal-averaging and the spatial-averaging have completely different characteristics. Therefore, it is necessary to clarify the difference of filtering characteristics in each averaging filter. In this study, comparisons of averaged flow patterns of temporal-average and spatial-average are carried out. Moreover, variable sized spatial filter which is based on Taylor's frozen-turbulence hypothesis is proposed. As a result, variable sized filtering is found close to the filter characteristic of the time average method.</p>

実路走行時におけるNOx排出量を予測するシミュレーションについて，著者らは既研究で，NOx低減触媒を装着していない車両で実路走行時の予測を可能とした．本研究では， NOx吸蔵還元触媒を装着した車両を対象に，簡易な予測モデルを検討し，実路走行時の排出量と比較・検証を行った.

ディーゼル機関の後燃え要因である噴霧先端の過濃混合気塊生成抑制のため，主燃料分割噴射の効果を調査した．分割によりメイン噴射量が低減しキャビティ内の過濃混合気塊生成が抑制されること，及びアフター噴射燃料は高温場で余剰空気と共に急速燃焼することで後燃えが低減し，熱効率向上要因となっていることが判明した．

火花点火機関の高希釈高過給化により，点火環境は厳しくなる一方である．スパークプラグでの放電路挙動と予混合気への点火性能の関係を明らかにすることが重要である．本研究では定容燃焼容器を用い，希釈流動場における放電と着火性の関係を調査した．各放電パラメータの着火性への寄与度は，流動強度により差異が確認された．

直噴ガソリンエンジンのすす生成モデルの構築のための基礎データとして、エンジン実験におけるすす測定の安定化を試みた。測定位置や圧力変動低減のためチャンバーの有無などを変化させることで、すす排出挙動の異なる条件であってもすすの排出量と粒子数および粒径分布を安定かつ再現性よく測定することが可能となった。

導入が予定されているRDE試験は排出ガス規制である一方、同時に燃費の測定も可能である。その際に得られる燃費は、モード燃費や実燃費と比較してどのような水準となると見込まれるのか、直噴ターボガソリン車を用いてRDE試験法に準拠したコースを走行して比較を行い、とくに実燃費との関係について考察した。

<p>DI Gasoline engine tends to increase the particulate mass concentration in the case of cold start, warming-up process and high load condition. In this study, PM emission was investigated from cold start to warming-up stage. The engine coolant temperature is set to 8°C, 30°C and 80°C, and start of fuel injection is changed from -320 deg.ATDC and -90 deg.ATDC. The excess air ratio, the load (gross indicated mean effective pressure, Gross IMEP) and the combustion phase (CA 50) was adjusted to 1.0 and 0.7 MPa, ≈ 9 deg. ATDC, respectively. The fuel injection pressure was kept constant at 10 MPa. As a result, when the coolant temperature was changed to 8°C, 30°C and 80°C, it was found that the soot at the coolant temperature of 8°C increased. In addition, it was found that soot was less affected by coolant temperature from -300 deg. ATDC to -120 deg. ATDC. Soot tends to increase at the injection condition -320 deg. ATDC and -90 deg. ATDC where the piston top surface is approaching the injector. The soot increased because fuel adhered to the piston top surface and pool combustion occurred. Also at -90 deg.ATDC, soot formation from the rich region due to mixing failure is considered to be an influencing factor.</p>

<p>Cycle-to-cycle variation (CCV) of combustion is an important issue because it affects emissions and drivability. Improvement of CCV of combustion has been carried out using electronic controls (e.g. ignition timing, fuel injection and variable valve timing) in motor vehicle's engines. However, electronic devices are hardly used for motorcycle's engines because of limited space and cost. Therefore, the engine performance itself must be improved to reduce CCV of combustion in motorcycle. Though CCV of combustion is caused by CCV of in-cylinder flow pattern, fuel distribution, temperature and residual gas, and ignition energy, it is difficult to measure and analyze these factors. In this study, the simultaneous measurement of high-speed PIV and direct photographing of flame propagation was carried out. CCV of in-cylinder flow was evaluated as temporally-averaged flow that was obtained by instantaneous flow using low-pass filtering and cut-off frequency. As a result, in-cylinder temporally-averaged flow pattern fluctuated between individual cycles. Especially, the flow pattern on the surface of piston at BDC was different between the highest and the lowest cycle in IMEP. This difference is considered to be due to the location offset of tumble flow. Also the fluctuation of turbulence kinetic energy (TKE) is caused by tumble flow offset. TKE distribution near the spark plug at ignition timing affected the direction and speed of flame propagation.</p>

火炎伝播の過程を観察する手法としてシュリーレン法が広く知られている．しかし火花放電による着火の場合，プラズマ形成や予熱による密度変化の影響で初期火炎の形状や大きさが判別できない．そこで本稿では可視域高速度カメラと赤外高速度カメラを用い，放電路と初期火炎の形成の様子を捉えることを試みた．

<p>It is required to examine the characteristics of turbochargers for automobiles using one-dimensional simulation from the viewpoint of estimating total engine performance. In this study, a mathematical model to predict mechanical loss generated in a turbocharger is proposed. Friction works generated in a journal bearing and a thrust bearing are modeled, separately. As for the calculation of the friction work with the thrust bearing, the thrust force is calculated from the fluid force which is formulated analytically and calculated numerically based on one-dimensional flow taking account of relevant boundary conditions. According to the developed model, the friction work generated in a journal bearing is larger than that in a thrust bearing. Difference of thrust force and flow rate of oil has less impact on the friction works in a turbocharger. Finally, calculated total friction work based on the model proposed in the present study is compared with that obtained from the oil temperature method.</p>

ディーゼル機関の後燃え低減による熱効率向上を目指し，市販のディーゼル機関の燃焼を紫外自発光撮影手法により可視化することで，後燃えの熱発生領域を調査した．三次元数値計算結果と共に考察した結果，後燃え期間中の熱発生は，噴霧火炎先端に形成された過濃混合気が滞留し，その外周部で発生している．

<p>To increase thermal efficiency of internal combustion engine, lean burn and EGR (Exhaust Gas Recirculation) system have been developed with spark ignition coils generating larger discharge current and discharge energy than current mass production coils. Several researches clarified that larger discharge current increases discharge channel extension and decreases possibility of discharge channel blow-off and possibility of misfire. However, these investigations don't mentioned effect of larger discharge current and energy on air-fuel ratio and combustion period. Then purpose of this research is to investigate relation among air-fuel ratio, combustion period and coil specification in order to clarify control factor of air-fuel ratio of lean burn. In this study, five coils having different current profiles were evaluated under 2000 rpm and 0.6 MPa NMEP (Net indicated Mean Effective Pressure) at lean mixture condition by combustion test and in-cylinder optical measurement test with research single cylinder engine. The combustion test results showed a correlation between lean limit air-fuel ratio and initial combustion period. Moreover, optical measurement test showed that initial combustion period has a correlation with discharge energy before 1st restrike and discharge channel extension rate and variation of initial combustion period under stable control condition doesn't depend on discharge current.</p>

今後乗用車に導入される可能性があるパワートレイン関連の新技術を導入した場合のWLTC走行時の燃費改善効果を予測するために，燃費シミュレーションツールに新たなモデルを導入し，その予測精度について実機を用いて検証を行った．次いで，このモード走行燃費シミュレーションコードを使って，各新技術の燃費改善効果を評価した．

大気環境のさらなる改善のためにディーゼルエンジン排出ガスからの大幅なNOx低減が求められる中、弊社は平成28年排出ガス規制に適応したNOxの還元剤として軽油を用いる尿素フリーの後処理システム（DPR-II）を実用化した。本システムの排出ガス低減技術を発表する。

車両燃費シミュレーションではトランスミッション等のサブシステムをモデル化する必要がある．本研究は，実車での計測により車両燃費シミュレーションに必要なトランスミッション等のモデルを簡易に構築する手法を検討した．さらに，本シミュレーションを活用してタイヤ性能の違いが燃費に及ぼす影響を定量的に評価した．

This study concerns a quantitative analysis of late-cycle soot oxidation in diesel engines that focuses on two-dimensional KL factor images obtained by the two-color method. The spatially integrated KL factor was converted into the in-cylinder soot mass using a new formula of diesel soot emissivity. This methodology was applied to two combustion systems: a heavy-duty optical engine which was tuned for a higher fuel-air mixing capability and a rapid compression and expansion machine which had a lower mixing performance. The in-cylinder soot mass history during the last stage of soot oxidation phase was converted into a normalized soot mass history and was used for comparison with simulated soot mass history. A model calculation of in-cylinder soot mass history which was based on oxidation of a primary soot particle was performed with the surface-specific soot oxidation rate as a parameter. A value of the surface-specific soot oxidation rate was specified from the curve fitting approach between the experimental and simulated in-cylinder soot mass traces. The resultant soot oxidation rates plotted on the Arrhenius diagram were found to lie in domains with different oxidation mechanisms. The reason for the scattered plots was discussed referring to model predictions of soot oxidation in the literature, and it was concluded that the higher oxidation rates could be attributed to well-mixed soot oxidizer structure.

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.

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.

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.

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.

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&lt inf&gt 3&lt /inf&gt 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&lt inf&gt 3&lt /inf&gt again by absorbing CO&lt inf&gt 2&lt /inf&gt during the intake and compression strokes. As this change is an exothermic reaction, the temperature of CaCO&lt inf&gt 3&lt /inf&gt particle increases over 1000K of the chemical equilibrium temperature determined by the CO&lt inf&gt 2&lt /inf&gt partial pressure. The possibility of a preignition due to particles including CaCO&lt inf&gt 3&lt /inf&gt particles is numerically simulated comparing with the experimental results.

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.

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.

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.