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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.

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.

To increase thermal efficiency of internal combustion engines, dilution combustion systems, such as lean burn and exhaust gas recirculation systems, have been developed. These systems require spark-ignition coils generating large discharge current and discharge energy to achieve stable ignition under diluted mixture conditions. Several studies have clarified that larger discharge current increases spark-channel stretch and decreases the possibility of spark channel blow-off and misfire. However, these investigations do not mention the effect of larger discharge current and energy on the initial combustion period. The purpose of this study was to investigate the relation among dilution ratio, initial-combustion period, and coil specifications to clarify the control factor of the dilution limit.

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, CaCO3 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 CaCO3 again by absorbing CO2 during the intake and compression strokes. As this change is an exothermic reaction, the temperature of CaCO3 particle increases over 1000K of the chemical equilibrium temperature determined by the CO2 partial pressure.

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.

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.

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.

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. Experiments were conducted using constant volume chamber for CH₄ and C₃H₈-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 C₃H₈-air mixtures under various conditions. The mechanisms for improving the inflammability were discussed and the effectiveness of IES circuit under EGR condition was also verified.

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.

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.

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 was 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.

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.

Some SI (spark-ignition) engines fueled with gasoline for industrial machineries are designed based on the conventional diesel engine in consideration of the compatibility with installation. Such diesel engine-based SI engines secure a combustion chamber by a piston bowl instead of a pent-roof combustion chamber widely applied for SI engines for automobiles. In the development of SI engines, because knocking deteriorates the power output and the thermal efficiency, it is essential to clarify causes of knocking and predict knocking events. However, there has been little research on knocking in diesel engine-based SI engines. The purpose of this study is to elucidate knocking phenomena in a gasoline engine with a re-entrant piston bowl and swirl flow numerically and experimentally. In-cylinder visualization and pressure analysis of knock onset cycles have been experimentally performed. Locations of autoignition have been predicted by 3D-CFD analysis with detailed chemical reactions.

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

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.

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, CaCO3 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 CaCO3 again by absorbing CO2 during the intake and compression strokes. As this change is an exothermic reaction, the temperature of CaCO3 particle increases over 1000K of the chemical equilibrium temperature determined by the CO2 partial pressure.

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.

LSPI (Low speed pre-ignition) is a serious issue in highly boosted gasoline engines. The causes have been studied and lube oil affects the onset. In order to examine the effect of lubricating oil consumption on super knock caused by pre-ignition, measurements of in-cylinder pressure, temperature, oil consumption by sulfur trace at steady and transient conditions were conducted. Also, new piston ring pack was applied to reduce both of blow-by gas and oil consumption. As a result, accumulated oil during deceleration was found to cause pre-ignition after acceleration. The pre-ignition frequency is much higher than in steady condition, however, the amount of oil does not directly affect pre-ignition frequency, but dilution of oil and evaporation of oil/fuel and other parameters, such as temperature, pressure, and oil additives determine pre-ignition onset. In order to see the mechanism of pre-ignition onset, numerical simulations were conducted.

Experimental methods and numerical analysis were used to investigate the mechanism of high-speed knocking that occurs in small two-stroke engines. The multi-ion probe method was used in the experiments to visualize flame propagation in the cylinder. The flame was detected by 14 ion probes grounded in the end gas region. A histogram was made of the order in which flames were detected. The characteristics of combustion in the cylinder were clarified by comparing warming up and after warming up and by extracting the features of the cycle in which knocking occurred. As a result, regions of fast flame propagation and regions prone to auto-ignition were identified. In the numerical analysis, flow and residual gas distribution in the cylinder, flame propagation and self-ignition were visualized by 3D CFD using 1D CFD calculation results as boundary conditions and initial conditions.