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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.

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.

To drastically improve thermal efficiency of a gasoline spark-ignited engine, super-lean burn is a promising solution. Although, studies of lean burn have been made by so many researchers, the realization is blocked by a cycle-to-cycle combustion variation. In this study, based on the causes of cycle-to-cycle variation clarified by the authors’ previous study, a unique method to reduce the cycle-to-cycle variation is proposed and evaluated. That is, a bulk quench at early expansion stroke could be reduced by making slight fuel stratification inside the cylinder using the twin-tumble of intake flows. As a result, the lean limit was extended with keeping low NOx and moderate THC emissions, leading to higher thermal efficiency.

This paper details the air-fuel mixing process in a gasoline direct injection (DI) engine. Laser measurement techniques such as particle image velocimetry (PIV) and laser induced fluorescence (LIF) were employed on the optical engine with a transparent cylinder to analyze the in-cylinder flow and fuel vapor concentration. In addition, firing tests were conducted using an actual engine. Test results showed that the multi-stage injection is effective for air-fuel mixing and improvement of combustion stability.

Air velocities in the cylinder of motored engine were measured by laser Doppler anemometer (LDA) and particle image velocimetry (PIV) to make the standard database that will be used for verification of the numerical simulation. A 4-stroke, 4-valve test engine with transparent cylinder was operated with engine speed of 600rpm. The velocities on that condition were measured individually in vertical- and swirl-direction. The distributions of mean- and RMS- velocities are obtained from the measured data. Flow velocity through the intake valve was also measured at the top of the cylinder. As the results, the flow structure by each crank angle can be clarified. The present data can be commonly used for some numerical research group of RC238 in JSME for verification of numerical simulation results. The effect of the tumble generation valve (TGV) is evaluated by velocity distributions.

A new combustion method of high compression ratio SI engine was studied and proposed in order to achieve higher thermal efficiency of SI engine comparable to that of CI engine. Compression ratio of SI engine is generally restricted by the knocking phenomena. A combustion chamber profile and a cranking mechanism are studied to avoid knocking with high compression ratio. Since reducing the end-gas temperature will suppress knocking, a combustion chamber was considered to have a wide surface at the end-gas region. However, wide surface will lead to high heat loss, which may cancel the gain of higher compression ratio operation. Thereby, a special cranking mechanism was adopted which allowed the piston to move rapidly near TDC. Numerical simulations were performed to optimize the cranking mechanism for achieving higher thermal efficiency. An elliptic gear system and a leaf-shape gear system were employed in the simulations.

The chemiluminescence emission intensity can be measured with high temporal resolution, leading to understanding the chemical reaction. Time-series chemiluminescence measurements of OH*, CH* and C2* were carried out to understand flame propagation speed, its thickness and A/F ratio of combustion status. The optical piston head (quartz) allows us to visualize combustion chamber. It is found that the chemiluminescence intensity ratio of CH*/OH* and C2*/OH* can estimate local A/F. The A/F measured by O2 sensor was used for evaluation and the results indicate this method can be applicable to estimate A/F.

The in-cylinder bulk flow and turbulence characteristics in a spark ignition engine were examined using two particle image velocimetry (PIV) systems. The effects of a turbulence-generating valve (TGV) bulk flow and turbulence characteristics were investigated. The results show that both the motion and location of turbulent flow can be controlled by a TGV valve. This could be used to reduce the level of unburned hydrocarbons produced during a cold start. The time history and scales of turbulence [1, 2 and 3] were compared with those obtained using laser Doppler velocimetry. The developed PIV systems were accurate, and the measured data were reliable enough to permit discussion of the cycle-resolve and cycle-to-cycle variation of in-cylinder flow. At top dead center, the measured turbulence scales of motion in the flow with the TGV closed were two thirds of those obtained with the TGV open.

Stereoscopic photography using four mirrors and a 16 mm high speed camera has been developed to observe in-cylinder gas motion three dimensionally. The one-camera system can simultaneously produce both left and right pictures under the same optical conditions. The measurable range of the system is from 400 to 500 mm and the resolution is 1.7mm. In-cylinder phenomena can be observed cycle-by-cycle without any modification of a cylinder head. To confirm its effectiveness, the system was applied to a bottom view type single-cylinder S.I engine with four valves. The bore and stroke are 92mm and 75mm, respectively. The rotation speed in a test was 1500rpm and a volume efficiency was 40%. The film speed of the high speed camera ranged from 3,000 to 6,000 pictures per second. In-cylinder gas motion during combustion was examined three-dimensionally by tracking bright flame spots produced by a sodium compound added to the fuel.