鈴木 隆

Recently, ammonia (NH3), which has a higher energy density than hydrogen, has gained attention for zero-carbon emission goals in the transportation sector. However, in a conventional internal combustion engine (ICE), NH3 combustion mechanism is still under investigation. In this paper, to further expand the knowledge on the adoption of NH3 in ICEs, authors conducted NH3/gasoline co-combustion experiments in a modified, 17.7:1 compression ratio, naturally aspirated spark-assisted CI engine with sub-chamber. The sub-chamber was chosen in order to enhance the combustion speed of NH3. In addition, the sub-chamber was equipped with glow and spark plugs to overcome the high auto-ignition temperature of NH3. Engine performance and NOX emissions were studied under three different intake air temperatures. During the experiments, NH3 content was increased gradually where the engine was run under lean conditions. Although higher NH3 content was achieved compared to our previous work, increasing the intake air temperature resulted in decreased charging efficiency. In addition, corrosion was found on the piston ring after 120 h of operation, negatively affecting the engine performance. Furthermore, NH3/gasoline co-combustion duration was shortened drastically with the influence of the sub-chamber, where the longest combustion duration under the present conditions was found to be 17°CA.

The overreliance on fossil fuels to generate energy is not sustainable because of their carbon emissions that are harming our environment. To substitute the fossil fuels with a more sustainable options, alternative fuels, such as carbon-free ammonia has been gaining worldwide attention. To allow the application of ammonia in internal combustion engines, its performance as an engine fuel need to be investigated. Ammonia as fuel has some shortcomings that can be outlined as slow combustion rate and corrosion due to the generation of hydrogen which makes it difficult to utilize in conventional internal combustion engines. In this study, an engine equipped with sub-chamber feature was used to overcome slow combustion rate of lean-burn condition of iso-octane/air mixture. Iso-octane was chosen as the fuel specifically since in lean-burn conditions, where the excess air ratio is near 1.8, its laminar burning velocity is similar to that of ammonia. The study was conducted using a single cylinder modified diesel engine which features spark plug and glow plug in a sub-chamber. The investigations varied the engine speeds (1000 and 1500 RPMs), glow plug voltages (6 V and 10 V), excess air ratios (1.4 to 1.8), and ignition timings (362 °CA to 365 °CA). The results suggested improved engine performances with a lower excess air ratio and higher glow plug voltage due to more complete and stable combustion. By increasing the engine speed, the lean burn limit was extended as seen from the improved engine performances. Because of the subchamber feature, advancing the ignition timing, with respect to the after top dead centre, resulted in lower engine performances. Larger excess air ratio was found to increase the sensitivity of the engine performances with the ignition timing. The brake mean effective pressure for all conditions has a coefficient of variation of less than 5%, indicating stable combustion. The results suggested that the current setup can be used to investigate ammonia blended fuel and direct ammonia combustion in future works.

To improve the cooling system of internal combustion engines, the utilization of the nucleate boiling heat transfer is desired. Our previous study revealed the relationship between the water nucleate boiling heat flux and dimensionless numbers. By using 50% ethylene glycol aqueous solution (EG50%) as coolant, the nucleate boiling heat flux was measured on the corroded heating surface and compared with the experimental data of water as coolant. Subsequently, dimensional analyses were done to investigate the necessary dimensionless numbers affecting the forced flow nucleate boiling. Two new models are proposed for water and EG50% as coolants, and predicted heat flux results were found to be in an average error of 9.7% and 10.1%, respectively.

Intake airflow characteristics are essential for the performance of diesel engines. However, previous investigations of these airflow characteristics were mostly performed on two-valve engines despite the difference between the airflow of two-valve and four-valve engines. Therefore, in this study, particle image velocimetry (PIV) investigations were performed on a four-valve diesel engine. The investigations were conducted under different engine speeds and helical port openings using a swirl control valve (SCV). The results suggest that the position of the swirl center does not significantly shift with different engine speeds and helical port openings, as the dynamics of the flow remained closely similar. The trends of the airflow characteristics can be best observed during the compression stroke. A higher engine speed increases the angular velocity of the engine more compared to the increase of the airflow velocity and results in a lower swirl ratio of the flow. On the other hand, a higher engine speed leads to a higher mean velocity and the variation of velocity results in a larger turbulence intensity of the flow. Increasing the helical port opening brings a reduction in the swirl ratio and turbulence intensity as more airflow from the helical port disturbs the airflow from the tangential port.

Injection characteristics play an important role in the emission and overall thermal efficiency of an engine. Several methods have been proposed for analyzing different fuel injection characteristics. This study focused on the interferometric laser imaging for droplet sizing (ILIDS) technique to investigate the effects of droplet size and velocity under different conditions of water-glycerin mixtures. These effects were evaluated using intermittent spray flows in both ambient and pressurized constant volume spray chamber conditions. The initial results were compared to those reported by previous studies and used to determine the Sauter mean diameter (SMD), arithmetic mean diameter (AMD), droplet velocity, and probability density function of the spray droplet size. SMD and AMD tended to decrease as the plate temperature, injection pressure, and viscosity were increased at specific observation areas. The average velocity of the droplet increased with higher plate temperature and injection pressure at specific observation areas. The distribution of the smaller droplet increased with higher plate temperature and injection pressure. For the water-glycerin mixture, as the glycerin ratio increased, more viscous droplets were created. This was followed in higher nozzle shear force at the outlet of the fuel injector, which decreased the particle size and generated more atomized fuel sprays. This result can enable the reduction in hydrocarbon and carbon monoxide emissions from internal combustion engines.

In order to get better results in the Formula SAE of Japan, it is necessary to develop a small displacement engine with an ideal fuel consumption rate. Therefore, the authors started to improve an existing engine by combining with glow plug heated sub-chamber and lean burn. Lean burn conditions are usually adopted in gasoline engines, having the advantages of high specific heat ratio, low pump loss, and low cooling loss due to requiring a decreased combustion temperature. The combination of these elements can be expected to vastly improve thermal efficiency and fuel consumption. Unfortunately, however, when the mixture becomes lean, the ignition delay increases, and the flame propagation speed reduces. This leads to an increase in combustion fluctuation. The authors intend to solve this problem by installing a glow plug in a newly designed sub-chamber. This type of device would usually be used to heat the sub-chamber of a diesel engine to solve the cold start problem. Experiments were conducted on a modified single-cylinder four-stroke CI engine (YANMAR TF120V) to operate as an SI engine with a higher compression ratio than conventional SI engines- 15.1:1. The engine is operated at a constant speed of 1000 and 1500 rpm, and temperature variation is created by varying excess air ratio and the glow plug's voltage. The coefficient of variation of BMEP was calculated to ensure the engine's cycle-by-cycle variation. According to the experimental results of glow plug voltage, when the excess air ratio is between 1.2 and 2.0, stable combustion can be achieved at excess air ratios up to 1.96 - this value is shown as the maximum lean burn limit in this study. Also, when compared to a system with the same conditions except without the glow plug, the brake thermal efficiency has been improved by up to 5.0 points, the brake specific fuel consumption rate also has been reduced by up to 17.4%. In the follow-up experiments on the ignition timing, it can be found that in case of ignition in the sub-chamber, MBT is after top dead center and the variation of ignition time has a limited effect on brake thermal efficiency or brake specific fuel consumption at a fixed glow plug voltage.

For improving the thermal efficiency and the reduction of hazardous gas emission from IC engines, it is crucial to model the heat transfer phenomenon starting from the intake system and predict the intake air's mass and temperature as precise as possible. Previously, an empirical equation was constructed using an experimental setup of an intake port model of an ICE, in order to be implemented into an engine control unit and numerical simulation software for heat transfer calculations. The empirical equation was based on the conventional Colburn analogy with the addition of Graetz and Strouhal numbers. Introduced dimensionless numbers were used to characterize the entrance region, and intermittent flow effects, respectively. In this study, further improvement of the model was done by characterizing the effect of backflow gas on intake air temperature by the introduction of the Euler number. 1-D engine simulations were done to analyze the valve-overlap and displacement backflow gas phases' effect on the intake air temperature. Additionally, engine test-bench experiments were conducted to validate the in-house built model and its applicability into engine control unit algorithm. The outlet temperature of the intake manifold was measured and results were compared to the various correlations. The in-house built equation showed the best accuracy when compared with the conventional approach, Colburn analogy. Maximum and average errors between the measured and estimated outlet temperatures were found to be 2.7% and 0.8%, respectively. The coefficient of variation for the in-house built equation was found to be 6.2%, which is considered to be a strong correlation. The average calculation time for the model is found to be 32 microseconds which satisfies the requirement for the current engine control unit technology.

To improve the thermal efficiency of ICEs, effective control of in-cylinder temperature is important. Utilization of nucleate boiling phenomenon to model the heat transfer is one of the measures that can be used for this purpose. Surface heat flux and bubble departure frequency measurements were done under the different wall superheat, coolant flow-rate, and temperature conditions. Subsequently, dimensional analyses were done to investigate the necessary dimensionless numbers acting on the heat flux model. The addition of power and exponential function of Jakob number was found to be effective, resulting in an average and minimum errors of 11.2% and 6.5%, respectively.

Utilization of crude palm oils (CPO) as biodiesel faces difficulty due to their high level of viscosity. Mixing crude eucalyptus oils (CEO) with CPO may reduce the viscosity due to the presence of aromatic compounds in CEO. The single droplet analysis was performed to determine the characteristics of mixing CPO with the CEO. The results showed that the addition of CEO decreased the viscosity due to the presence of intermolecular attractions, thereby leading to more active molecules in the CPO-CEO mixture. Furthermore, the aromatic compound in the CEO helped in decreasing the CPO flash point, while the aromatic compound in the triglyceride molecule weakens the bonds between molecules. The addition of CEO to CPO tends to reduce the ignition delay due to the presence of cineol content in the CEO, which weakens the van der Waals bond in CPO.

ディーゼル機関のモデルベースト燃焼制御器では，冷却損失を考慮した圧縮ポリトロープ指数の予測にこれまで実験式を用いてきた．著者らは，実験数を軽減するため，新たに物理モデルを開発し，制御器に実装した．実機にて過渡運転性能を評価したところ，実験値と比較して，モデルの予測誤差は0．３１％と評価された．

Improving thermal efficiency of internal combustion engines has been a priority in the automotive industry. It is necessary to model the heat transfer phenomenon at the intake system and precisely predict intake air's mass flow rate into the engine cylinder. In the previous studies, the heat transfer at the intake system was modeled as quasi-steady state phenomenon, based on Colburn analogy. Authors developed two empirical equations with the introduction of Graetz and Strouhal numbers. In the present study, further improvements were done by the addition of pressure ratio between the intake manifold and atmospheric pressure, along with Reynolds number in order to characterize the backflow gas effect on intake air temperature. Compared with the experimental results, maximum and average errors of intake air temperature estimations inside the manifold found to be 2.9 % and 0.9 %, respectively.

ディーゼル機関の過渡運転性能向上には，モデルベースト制御によるサイクル毎の燃料噴射量と時期の予測が有効である．本研究では，燃焼室の局所壁温度履歴および局所壁面熱流束履歴を測定し，著者らが構築したオンボード用筒内壁温度推定モデルおよび壁面熱伝達モデルの予測精度を評価したので報告する．

A new equation, which was dependent on physical principles, was developed for the study of heat transfer in CI engines which needs turbulence of gas flows to calculate heat flux. Proposed approach was implemented into a 1-D engine simulation, which was used to determine heat flux between in-cylinder gas and wall. Results from the suggested equation were compared to the previous conventional equations; Morel and Hohenberg, and to the engine experiments. The proposed equation showed better accuracy when compared with the conventional equations due to detailed representation of in-cylinder gas flow by dividing the combustion chamber into 6 different regions.

The diesel engines are superior in terms of power efficiency and fuel economy compared to gasoline engines. In order to optimize the performance of direct injection diesel engine, the effect of various intake pressure (boost pressure) from supercharging direct injection diesel engine was studied at various engine rotation. A single cylinder direct injection diesel engine was used in this experiment. The bore diameter of the engine used was set to 85 mm, the stroke length was set to 96.9 mm, and the compression ratio was set to 16.3. The variation of engine rotation started from 800 rpm to 2 000 rpm with 400 rpm increment. The variation of boost pressure is bounded from 0 kPa boost pressure (naturally aspirated) to the maximum of 60 kPa boost pressure with 20 kPa boost pressure increment. The performance of the engine is evaluated in terms of in-cylinder pressure and heat release rate as the most important performance characteristics of the diesel engine. The in-cylinder pressure and heat release rate of direct injection diesel engine are increased with the elevation of boost pressure at various engine rotation. The raise of engine rotation resulted in the decrease of maximum in-cylinder pressure and heat release rate.

本稿ではMAP作成の手間を自動化し, かつ環境変化に対するロバスト性を有する制御系設計法として, フィードバック誤差学習を用いたモデルベースト制御を提案する. また, 制御器の学習機構として小脳演算モデルコントローラを用いることで計算負荷を低減することができる. そして, 本手法の有効性を実機試験にて検証する.

Overall efficiency of internal combustion engines are heavily depended on intake air temperature which is directly related to the heat transfer inside an intake system. Previously, authors developed an equation by using port model setup to calculate Nusselt number with introduction of Graetz and Strouhal numbers. This study modified the port model equation to improve its accuracy in a real engine experimental setup. Predicted intake air temperature was compared to the measured data with a maximum error of 5.6%. Additionally, 100 K of temperature difference was found between the boost pressure values of 944hPa and 678hPa from 1-D engine simulation results.

© 2018 SAE International. All Rights Reserved. An empirical equation was developed for modeling the heat transfer phenomena taking place in an intake manifold which included the backflow gas effect. In literature, heat transfer phenomenon at intake system is modeled based on steady flow assumptions by Colburn analogy. Previously, authors developed an equation with the introduction of Graetz and Strouhal numbers, using a port model experimental setup. In this study, to further improve the empirical equation, real engine experiments were conducted where pressure ratio between the intake manifold and engine cylinder were added along with Reynolds number to characterize the backflow gas effect on intake air temperature. Compared to the experimental data, maximum and average errors of intake air temperature estimated from the new empirical equation were found to be 2.9% and 0.9%, respectively. Furthermore, Colburn analogy and suggested empirical equation were consecutively implemented to 1-D engine simulation software on gasoline and diesel engine setups. Naturally aspirated gasoline engine simulations revealed the importance of the backflow gas effect in line with the real engine experiments. Maximum and average temperature differences between the Colburn analogy and suggested equation showed 36.0 K and 28.7 K, respectively. In turbocharged diesel engine simulations, intake air temperature's effect on auto ignition timing was analyzed. At engine speed of 2250 rpm, in-cylinder air temperature difference at IVC was found to be 5.8 K. This difference corresponded to an advanced auto-ignition timing by 1.15 deg. CA, which could be interpreted an estimated reduction of CO2 gas by 0.28%.

本論文は，実機エンジンの吸気管にて温度測定を行い，吸気システムでの伝熱現象を検討した．その際，流れの非定常性および温度境界層の発達を考慮し，Nu数をRe数，Gz数，St数で表した実験式を導出した．また，熱力学モデルに基づきシリンダに吸入される空気温度を推定したところ，5.6%の誤差で推定可能であることがわかった．

ディーゼル機関の過渡性能向上にはオンボード・モデルベースト制御による着火時期の予測が重要である．著者らは，筒内ガス温度をサイクルごとに予測するため，低計算負荷の圧縮ポリトロープ指数予測モデルを開発した．過渡運転条件に適用し，１Ｄ数値計算と比較した結果，構築したモデルの有用性が認められたので報告する．