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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 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.

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.

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.

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 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.

In recent years, the improvement in the fuel efficiency and reduction in CO2 emission from internal combustion engines has been an urgent issue. The lean burn technology is one of the key technologies to improve thermal efficiency of SI engines. However, combustion stability deteriorates at lean burn operations. The reduction in cycle-to-cycle and cylinder-to-cylinder variations is one of the major issues to adapt the lean burn technique for production engines. However, the details of the causes and mechanisms for the combustion variations under the lean burn operations have not been cleared yet. The purpose of this study is to control cylinder to cylinder combustion variation. A conventional turbocharged direct injection SI engine was used as the test engine to investigate the effect of engine control parameters on the cylinder to cylinder variations. The engine speed is set at 2200 rpm and the intake pressure is set at 58, 78, 98 kPa respectively.

The purpose of this paper is to find a way to extend the high load limit of homogeneous charge compression ignition (HCCI) combustion. This paper presents the effect of in-cylinder flow and stratified mixture on HCCI combustion by experiments and three-dimensional computer fluid dynamics coupled with a detailed chemical reaction calculation. The first study was conducted using a rapid compression and expansion machine (RCEM) equipped with a flow generation plate to create in-cylinder turbulent flow and with a control unit of in-cylinder wall temperature to create in-cylinder temperature distribution. The study assesses the effect of the turbulent flow and the temperature distribution on HCCI combustion. In the second study, the numerical simulation of HCCI combustion was conducted using large eddy simulation coupled with a detailed chemical reaction calculation. The study analyzes the interaction between in-cylinder turbulent flow and mixture distribution and HCCI combustion.

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.

Liquid fuel attached to the wall surface of the intake port, the piston and the combustion chamber is one of the main causes of the unburned hydrocarbon emissions from a port fueled SI engine, especially during transient operations. To investigate the liquid fuel film formation process and fuel film behavior during transient operation is essential to reduce exhaust emissions in real driving operations, including cold start operations. Optical techniques have been often applied to measure the fuel film in conventional reports, however, it is difficult to apply those previous techniques to actual engines during transient operations. In this study, using MEMS technique, a novel capacitance sensor has been developed to detect liquid fuel film formation and evaporation processes in actual engines. A resistance temperature detector (RTD) was also constructed on the MEMS sensor with the capacitance sensor to measure the sensor surface temperature.

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.

For the survival of internal combustion engines, the required research right now is for alternative fuels, including drop-ins. Certain types of alternative fuels have been estimated to confirm the superiority in thermal efficiency. In this study, using a single-cylinder engine, olefin and oxygenated fuels were evaluated as a drop-in fuel considering the fuel characteristic parameters. Furthermore, the effect of various additive fuels on combustion speed was expressed using universal characteristics parameters.

To investigate the heat transfer phenomena inside the combustion chamber of a diesel engine, a correlation for the heat transfer coefficient in a combustion chamber of a diesel engine was investigated based on heat flux measured by the authors in the previous study(8) using the rapid compression and expansion machine. In the correlation defined in the present study, thermodynamically estimated two-zone temperatures in the burned zone and the unburned zone are applied. The characteristic velocity given in the correlation is related to the speed of spray flame impinging on the wall during the fuel injection period. After the fuel injection period, the velocity term of the Woschni’s equation is applied. It was shown that the proposed correlation well expresses heat transfer phenomena in diesel engines.

The purpose of this paper is to find a way to extend the high load limit of homogeneous charge compression ignition (HCCI) combustion. A newly developed rapid compression and expansion machine (RCEM) was employed to reproduce the typical HCCI high load condition. The in-cylinder turbulence was created by the special piston which equipped with a flow guide plate. Meanwhile, the ambient temperature distribution in the cylinder was determined by the wall temperature controlling system which was controlled by the independent coolant passages. In addition, the numerical simulation by using large eddy method coupled with a detailed chemical reaction was conducted as well. The results show that HCCI mode is potential to be improved at high load condition in full consideration of in-cylinder temperature, flow, and turbulence.

It has been widely known that thermal and fuel stratifications of in-cylinder mixture are effective to reduce in-cylinder pressure rise rate during high load HCCI operations. In order to optimize a combustion chamber design and combustion control strategy for HCCI engines with wide operational range, it is important to know quantitatively the influence of the temperature and fuel concentration distributions on ignition and heat release characteristics. At the same time, it is important to know the influence of in-cylinder flow and turbulence on the temperature and fuel concentration distributions. In this study, a numerical simulation of HCCI combustion were conducted to investigate the effects of the in-cylinder flow and turbulence, and the distributions of temperature on ignition and combustion characteristics in HCCI combustion.

To realize stable combustion in lean or diluted conditions, reducing cycle-to-cycle variations of flow and fuel distribution is important. In this study, the effect of initial flow field was examined by simultaneous Time-Resolved PIV and visualization on two cross-sections in a fully optical-access engine under motoring and firing conditions with homogeneous pre-mixture. As a result, Omega index was defined and plotted on the correlation map between turbulence kinetic energy and CA10 (duration from ignition timing to 10% to the total accumulated heat). The omega index describes the strength of a horizontal flow field that resembles the shape of the Greek letter Omega. The plots with high Omega index were found frequently in the CA10 retarded cycles. On the other hand, the plots with low Omega index have simple tumble flows and the correlation was clearly found.

This study aimed to achieve both a high compression ratio and low knock intensity in a two-stroke engine. Previous research has suggested that knock intensity can be reduced by combining combustion chamber geometry and scavenging passaging design for the same engine specifications with a compression ratio of 13.7. In this report, we investigate whether low knock intensity can be achieved at compression ratios of 14.4 and 16.8 by adjusting the combustion chamber geometry and scavenging passage design. As a result, the mechanism by which combustion chamber geometry and scavenging passage design change knock intensity was clarified.

In internal combustion engine development, the ongoing research can be mainly classified into two categories based on the purpose: limiting exhaust emissions and searching for alternative fuels. One of the effective approaches reduce emissions is the improvement of thermal efficiency. Certain types of alternative fuels derived from renewable resources were estimated to confirm the thermal efficiency. This study uses a single-cylinder engine added with olefin and oxygenated additive fuel, such as 1-hexene, ethanol, and ETBE, to evaluate the parameters that affect thermal efficiency. Furthermore, the effects of various additive fuels are summarized and essential information is provided for determining next- generation fuel composition.