窪山 達也

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 order to extend the HCCI high load operational limit, the effects of the distributions of temperature and fuel concentration on pressure rise rate were investigated through theoretical and experimental methods. The Blowdown Supercharge (BDSC) system and the EGR guide parts are employed simultaneously to enhance thermal stratification inside the cylinder. Also, direct fuel injection system was also used to control the distribution of fuel concentration. As a result, pressure rise rate during high load HCCI operation was successfully reduced with the thermal stratification enhanced by the EGR guide. It is also found that the uniformed fuel concentration distribution generated by a direct fuel injection had less effective to reduce pressure rise rate. Because directly injected fuel into hot EGR gas decreased EGR gas temperature leading to reduce thermal stratification generated by the EGR guide.

The objective of this study is to extend the HCCI operational range while maintaining high thermal efficiency of a HCCI engine using the blowdown supercharge (BDSC) system. Two different compression ratios of 11.7 and 14.1 were tested by replacing the piston. The effect of compression ratio on both the HCCI operational range and thermal efficiency were investigated. The experimental results showed that the HCCI operational limit and the fuel consumption at the low load operation were successfully improved by increasing compression ratio. On the other hand, high load operational limit was hardly affected by compression ratio. Also, it was found that the BDSC-HCCI engine with higher compression ratio improves thermal efficiency of the whole HCCI operation range. © 2013 The Japan Society of Mechanical Engineers.

The objective of this research is to investigate the effect of the EGR guide, employed to generate a strong in-cylinder thermal stratification, on the recharged EGR gas flow into the cylinder in a gasoline HCCI engine equipped with the blowdown supercharging (BDSC) system. The recharged EGR gas flow was visualized using an optical access engine. A steady gas flow and an unsteady gas flow in motoring from the exhaust port into the cylinder were visualized via PIV method. The effect of the pressure difference between the exhaust port and the cylinder and the geometry of the EGR guide on the recharged gas flow was investigated. The results indicate that the flow field pattern is largely affected by the EGR guide height, and that an increase in the EGR guide height is effective to generate a strong in-cylinder thermal stratification. And then, the reduction of maximum pressure rise rate (dp/dθ) was investigated with a larger EGR guide height. Also, the in-cylinder thermal stratification was investigated by numerical simulation. The results indicate that thermal stratification gets stronger by a higher EGR guide. However, it was found that the reduction of maximum pressure rise rate takes a peak at a height of EGR guide. ©2013 The Japan Society of Mechanical Engineers.

An improvement of thermal efficiency is strongly demanded for gasoline engines. In this study, experiments were carried 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 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.

The variable valve lift and duration (in the following: VVLD) devices, some have been mass-produced already in the world, are necessary to be assembled with the variable cam phaser (in the following: VCP) to optimize open and close valve timing. On the other hand, with the variable valve phase and lift (in the following: VVPL) mechanism, the valve event is advanced with decreasing the valve lift and duration. Hence, no additional VCP is required when using the VVPL for throttle-less operation. A new VVPL has been developed as a mechanical, swing-cam actuation mechanism. The mechanisms of the conventional production VVLD devices are investigated and the functional analysis of the possible mechanisms is carried out to identify and design a simple mechanism for the new VVPL. The designed VVPL system is capable of continuously varying the valve lift from 0 mm to 10 mm, with the higher valve lift for any of the given duration. CAE oriented study, conducted before the production of the prototype, predicted the unexpected problems of the system at the design stage. By the multi-body dynamic simulation, predicting the dynamic behavior of the system, the requirement for the design to obtain the stable operation in the entire operation range was clarified. The trial manufactured VVPL was tested on the 4-cylinder test bench after the single cylinder test, and successfully operated up to 7000rpm of engine speed. The accuracy of the multi-body dynamic simulation was evaluated with the measured dynamic behavior. It was found that the high speed limitation of the system was sufficiently predicted by the multi-body simulation. Following the functional test, the newly designed VVPL system was installed into the 4-cylider gasoline engine and its effect on fuel efficiency was evaluated on the firing test bench. As a result, a large improvement in fuel efficiency was obtained with the developed VVPL system, as expected. Copyright © 2013 SAE International.

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.

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.

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.

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.

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/dθmax and NOx 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 NOx emissions. Copyright 2011 Society of Automotive Engineers of Japan, Inc. and SAE International.

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 x emission. © 2011 SAE International.

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 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.

In order to extend the HCCI high load operational limit, the effects of the distributions of temperature and fuel concentration on pressure rise rate (dP/dθ) were investigated through theoretical and experimental methods. The Blow- Down Super Charge (BDSC) and the EGR guide parts are employed simultaneously to enhance thermal stratification inside the cylinder. And also, to control the distribution of fuel concentration, direct fuel injection system was used. As a first step, the effect of spatial temperature distribution on maximum pressure rise rate(dP/dθmax) was investigated. The influence of the EGR guide parts on the temperature distribution was investigated using 3-D numerical simulation. Simulation results showed that the temperature difference between high temperature zone and low temperature zone increased by using EGR guide parts together with the BDSC system. Experiments were conducted by using a four-cylinder gasoline engine equipped with the BDSC with EGR guide system to investigate the effect of the EGR guide on the heat release rate and the in-cylinder pressure rise rate. Experimental results showed that 50% and 90% mass fraction burned timing (CA50 and CA90) were delayed and combustion duration became longer when the EGR guide was used to enhance thermal stratification. As a result, the maximum pressure rise rate could be decreased and the HCCI high load limit successfully extended. Meanwhile10% mass fraction burned timing (CA10) was not affected by the thermal stratification generated by the EGR guide. This is probably because the fuel is also spatially stratified such that the fuel concentration becomes lean in the high temperature zone. Next, the effect of the fuel distribution on high load HCCI operation was investigated. Numerical analysis using a multi-zone combustion model considering detailed chemical reactions was carried out. The simulation results showed that the maximum pressure rise rate was decreased by 27% when the fuel distribution was uniform with temperature distribution generated by the BDSC with EGR guide system. Then, to obtain a uniform fuel distribution while keeping the temperature distribution generated by the BDSC with EGR guide system, a direct injection system was employed and the effect of fuel direct injection on maximum pressure rise rate was experimentally investigated. As a result, if 20% of the total fuel was injected directly into the cylinder during the exhaust stroke, the spatial distribution of the fuel concentration (G/F fuel mass ratio to the total mass of in-cylinder mixture) became more homogeneous and maximum pressure rise rate was decreased by 10%. And also, 20% of the total fuel directly injected during the compression stroke, maximum pressure rise rate was decreased by 20%. Finally, a simple method to predict the ignition timing using Livengood-Wu integral and 1-D numerical simulation code was examined. It was found that the proposed method can predict the ignition timing with small deviation around ±2 degrees. © 2010 SAE International.

A newly developed small-sized IES (inductive energy storage) circuit with a semiconductor switch at turn-off action was successfully applied to an ignition system. This IES circuit can generate repetitive nanosecond pulse discharges. An ignition system using repetitive nanosecond pulse discharges was investigated as an alternative to conventional spark ignition systems in the previous papers [ 1 ][ 2 ]. Experiments were conducted using constant volume chamber for CH4 and C3 H8 -air mixtures. The ignition system using repetitive nanosecond pulse discharges was found to improve the inflammability of lean combustible mixtures, such as extended flammability limits, shorted ignition delay time, with increasing the number of pulses for CH4 and C3 H8 -air mixtures under various conditions [ 1 ]. The mechanisms for improving the inflammability were discussed and the effectiveness of IES circuit under EGR condition was also verified [ 2 ]. Moreover, an application of this ignition system to a SI engine was conducted preliminarily and the effectiveness of IES circuit for the real engine was also confirmed [ 2 ]. Following previous studies, the present study moves to more realistic development stage using two experimental configurations same as former studies a constant volume chamber and single cylinder SI engine. With a constant volume chamber, the effectiveness of IES circuit for Iso-octane (C 8 H18) and conventional ignition plug is investigated, and the flame kernel formation process was observed using schlieren photography with a high speed camera to make the difference of the ignition mechanism between IES circuit and conventional ignition circuit clear. With a single cylinder SI engine, two experiments are carried out to qualify the difference of the inflammability between IES circuit and conventional ignition circuit. The operational limit of lean combustion is investigated. The result shows that the lean limit is extended from 20 to 23 in A/F at IMEP 440 kPa by replacing the ignition system from a conventional one. Also, the diluted limit is investigated. The result shows that the diluted limit is extended from 17.5 % to 22.5 % in EGR ratio at IMEP 630 kPa and that thermal efficiency is improved by 5%. The ignition delay and the combustion duration are decreased and the cycle-to-cycle variation of the ignition timing and IMEP are decreased. Copyright © 2010 SAE International.

A newly developed small-sized IES (inductive energy storage) circuit with semiconductor switch at turn-off action is successfully applied to an ignition system of a small gasoline internal combustion engine. This IES circuit can generate repetitive nanosecond pulse discharges. An ignition system using repetitive nanosecond pulse discharges is investigated as an alternative to a conventional spark ignition system. The present study focuses on the extension of the operational limits for lean and diluted combustion using the repetitive nanosecond pulse discharges. First, in order to investigate the flame kernel formation process when the repetitive nanosecond pulse discharges are used, the initial flame kernel is observed using Schlieren photography with a high speed camera. As a result, the flame kernel generated by repetitive pulse discharges is larger than by a conventional ignition system. Then, an application of repetitive nanosecond pulse discharges to a single cylinder SI engine is conducted and the operational limit of lean combustion is investigated. The result shows that the lean limit is extended from 20 to 23 in A/F at IMEP 440 kPa by replacing the ignition system from a conventional one. Also, the diluted limit is investigated. The result shows that the diluted limit is extended from 17.5% to 22.5% in EGR ratio at IMEP 630 kPa and that thermal efficiency is improved by 5%. The ignition delay and the combustion duration are decreased and the cycle-to-cycle variation of the ignition timing and IMEP are decreased. © 2009 SAE International.

本研究では，新たに開発した小型の誘導エネルギー蓄積式パルス電源により生成される，繰り返しパルスを用いることで，効率的に生成した活性化学種雰囲気下の混合気に対して，短パルスアーク放電することにより，希薄燃焼時の着火特性の改善を図る．本論文は第二報であり，点火機構の解明と実機への応用を試みた．

A newly developed small-sized IES (inductive energy storage) circuit with semiconductor switch at turn-off action is successfully applied to an ignition system of a small gasoline internal combustion engine. This IES circuit can generate repetitive nanosecond pulse discharges. An ignition system using repetitive nanosecond pulse discharges is investigated as an alternative to a conventional spark ignition system. The present study focuses on the extension of the operational limits for lean and diluted combustion using the repetitive nanosecond pulse discharges. First, in order to investigate the flame kernel formation process when the repetitive nanosecond pulse discharges are used, the initial flame kernel is observed using Schlieren photography with a high speed camera. As a result, the flame kernel generated by repetitive pulse discharges is larger than by a conventional ignition system. Then, an application of repetitive nanosecond pulse discharges to a single cylinder SI engine is conducted and the operational limit of lean combustion is investigated. The result shows that the lean limit is extended from 20 to 23 in A/F at IMEP 440 kPa by replacing the ignition system from a conventional one. Also, the diluted limit is investigated. The result shows that the diluted limit is extended from 17.5 % to 22.5 % in EGR ratio at IMEP 630 kPa and that thermal efficiency is improved by 5%. The ignition delay and the combustion duration are decreased and the cycle-to-cycle variation of the ignition timing and IMEP are decreased. Copyright © 2009 SAE International.

本研究では，新たに開発した小型の誘導エネルギー蓄積式パルス電源により生成される，繰り返しパルスを用いることで，効率的に生成した活性化学種雰囲気下の混合気に対して，短パルスアーク放電することにより，希薄燃焼時の着火特性の改善を図る．本論文は第二報であり，点火機構の解明と実機への応用を試みた．

A newly developed small-sized IES (inductive energy storage) circuit with semiconductor switch at turn-off action was successfully applied to an ignition system. This IES circuit can generate repetitive nanosecond pulse discharges. An ignition system using repetitive nanosecond pulse discharges was investigated as an alternative to conventional spark ignition systems. Experiments were conducted using spherically expanding flame configuration for CH4 and C3H8-air mixtures under various conditions. The ignition system using repetitive nanosecond pulse discharges was found to improve inflammability of lean combustible mixtures, such as extended flammability limits, shorted ignition delay time, with increasing the number of pulses. The authors seek for the mechanisms for improving the inflammability in more detail to optimize ignition system, and verify the effectiveness of IES circuit in EGR condition, for real engine use. Moreover, an application of this ignition system to a SI engine was conducted. As a result, the lean limit was extended from 20 to 23 in A/F at IMEP 440 kPa by replacing the ignition system from a conventional one, and indicated thermal efficiency was improved by 11%. © 2009 SAE International.

The objective of this study is to extend the high load operation limit of a gasoline HCCI engine. A new system extending the high load HCCI operation limit was proposed, and the performance of the system was experimentally demonstrated. The proposed system consists of two new techniques. The first one is the "Blow-down super charging (BDSC) system", in which, EGR gas can be super charged into a cylinder during the early stage of compression stroke by using the exhaust blow-down pressure wave from another cylinder phased 360 degrees later/earlier in the firing order. The other one is "EGR guide" for generating a large thermal stratification inside the cylinder to reduce the rate of in-cylinder pressure rise (dP/dθ) at high load HCCI operation. The EGR guides consist of a half-circular part attached on the edge of the exhaust ports and the piston head which has a protuberant surface to control the mixing between hot EGR gas and intake air-fuel mixture. The experiments were carried out using a 4-cylinder port fuel injection engine with a compression ratio of 12. As a result, HCCI operation at high loads, up to an IMEP of 650 kPa at an engine speed of 1500 rpm, was achieved. Copyright © 2009 SAE International.

In order to clarify the mechanism of heat loss in DI diesel engines, total amount of heat loss to the combustion chamber and local heat flux at various locations on the piston head were measured by using a rapid compression and expansion machine. High-speed direct photography of spray flame was carried out and flame temperature was obtained by two-color method. In order to investigate the effects of the flow induced by the spray and its impingement on the chamber wall on heat loss, swirl ratio was varied from 0 to 5 and two different fuel injection nozzles (φ0.15mm×4 and φ0.10mm×10) were used. The measured local heat flux exhibited more uniform distribution with the φ0.10mm×10 nozzle than with the φ0.15mm×4 nozzle, and at higher swirl ratio. The heat loss amount during the single cycle increased with the increase in swirl ratio due to the increased heat loss after the combustion period. The heat loss amount during the combustion period was almost constant regardless of the swirl ratio. The heat loss amount during the single cycle and the combustion period were not very different between the two different nozzle cases. The magnitude of heat flux at flame impinging point did not significantly vary with the nozzle orifice diameter. This is because the effect of the reduced impinging velocity is cancelled out by the effect of the increased flame temperature in the case of smaller orifice diameter on the heat flux.

In order to clarify the mechanism of heat loss in DI diesel engines, total amount of heat loss and local heat flux at various locations on the piston head were measured by using a rapid compression and expansion machine. High-speed direct photography of spray flame was carried out and flame temperature distribution was obtained by two-color method. In order to investigate the effects of combustion characteristics, such as flame temperature, on heat loss, oxygen volume fraction was varied as experimental parameter in two different ways. In the first way, the oxygen volume fraction was varied from 21% to 15% at a constant intake gas pressure (0.1MPa). In the second way, the oxygen volume fraction was varied from 21% to 15% by adding nitrogen at a constant amount of oxygen in the cylinder. Measurement results in the first case showed that the flame temperature decreased and the heat loss slightly decreased with decrease in oxygen volume fraction. However, the ratio of the heat loss to the gross heat release was almost constant regardless of the oxygen volume fraction. On the other hand, in the second case, the heat loss and the ratio of the heat loss to the gross heat release decreased with decrease in oxygen volume fraction. This decrease of the heat loss is due to the lower flame temperature and the reduced area and period of direct contact between the flame and the chamber wall, caused by the higher heat capacity and density of the ambient gas.