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In the multiple-ion probe method, multiple ion probes are installed on the combustion chamber wall, and each individual ion probe detects flame contact and records the time of flame arrival. From the recorded data, it is possible to reconstruct the dynamic behavior of the flame surface and, for example, indirectly visualize the inside of the combustion chamber as a moving image. In this study, 32 ion probes were used to record flames propagating in a 2-stroke SI engine, and various analysis and evaluation methods other than indirect visualization was investigated and evaluated. Although it is possible to extract local flame propagation velocity, direction of propagation, etc. from the reconstructed flame propagation in the engine, an analysis method that aims to find the characteristics of the overall combustion in the actual combustion during a single cycle from a single feature, rather than local data, was investigated.

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.

The propagating flame in a 2-stroke gasoline engine under WOT or transient operating conditions was measured with up to 12 ion probes. Flame arrival time data obtained from multiple-ion probes were statistically compared between arrival time data obtained by different ion probes or between data obtained by the same ion probe for different cycles to investigate the spatial and temporal characteristics of flame propagation behavior. Spatial statistical data analysis revealed that the propagating flame is strongly influenced by the in-cylinder flow prior to ignition. Temporal statistical data analysis revealed that the state of flame propagation, starting from any given cycle and continuing in subsequent cycles, shows a tendency similar to that of the initial cycle for some time, and that the original tendency is completely lost after about 50 cycles.

Multiple-ion probe method is one of the beneficial method to obtain the detailed information about explosive combustion such as knocking. Our group has been trying to expand the measurement ability on multiple ion probe method from highly-controlled combustion in combustion test tube studied by previous studies to highly-unstable combustion such in spark ignition engines. The previous studies showed that multiple-ion probe method was able to capture the movement of propagating flame in 2-stroke gasoline engine in limited conditions. It requires that more reliable detection of propagating flame in the engine to capture the flame movement more stably. In the present study, the effects of the shape of the ion probe on flame detection characteristics in 2-stroke gasoline engine was investigated. Tested parameters of the shape in the ion probe were projection length and diameter of an ion probe wire. Projection length was changed as 0, 0.5, 1.0, 1.5mm.

Multiple ion-probes method provides fine measurement on propagating flame by using multiple ion-probes installed tow-dimensionally on the wall surface of confined chamber. Each ion-probe detects the arrival of propagating flame and the detecting time is recorded. The data set of flame detecting times is able to re-generate the temporary and spatially detailed behavior of flame propagation. Because ion-probe itself generally has physical and thermal strength, multiple ion-probe method is suitable method for detailed measurement of the combustion resulting pulsatile high pressure such as in reciprocating piston engines. In the present study, flame measurement technic by multiple ion-probes has been experimentally introduced for measuring the combustion in 2-stroke gasoline engine. The present paper reports the detailed results of measurement on propagating flame in the engine. In addition, newly clarified technical issues of this technic is also mentioned.

Multiple ion-probes method has an advantage for detailed measurement on high-intensity combustion including engine combustion, oscillation combustion in gas turbine or burner. Multiple ion-probes are installed individually on the surface of the confinement wall in combustion chamber. Detailed behavior of the flame propagation along the chamber wall can be reproduced by the datasets of the flame arrival time detected by individual ion-probes. Main target of this study is to clarify the measurement performance of this multiple ion-probes method for various type of propagating flames generated in confined combustion tube. The characteristics of the flame is largely varied by changing the ratio of dilution with nitrogen on methane-oxygen stoichiometric mixture. No dilution, which means methane-oxygen stoichiometric mixture only, results fastest speed and relatively stable propagation.

A new technic to measure the propagating flame precisely by using densely installed multiple ion-probes has been developed. This system targets the high-intensity and pulsatile combustion, including knocking in gasoline engine, and oscillating combustion in burner or gas turbine combustor. In such environment, observation of details in the combustor by visualization is generally limited because of the strength of observation window. In contrast, ion-probe is physically and thermally strong enough to endure such environment. In the present study, characteristics of the combustion measurement were investigated using the different types of propagating flame with various LPG-oxygen-nitrogen mixtures. The composition of the mixture was stoichiometric LPG-oxygen diluted with nitrogen. Nitrogen dilution ratio was varied to control the flame propagation velocity.

The mixture formation prior to the ignition process is a key element in the diesel combustion because it significantly influences throughout the combustion process and exhaust emissions. Purpose of this study is to clarify the effects of ambient temperature, oxygen concentration and air entrainment into the spray on the heat release process during ignition delay periods. This study investigated diesel combustion fundamentally using a rapid compression machine and high speed digital video camera. The detail behavior of spray evaporation, spray interference and mixture formation during ignition delay period was investigated using the schlieren photography system. Ignition process, flame development and images of the spray ignition with extremely dark flame were investigated by light sensitivity direct photography method. Heat release processes were analyzed by pressure measurement in the chamber.

Evolution of evaporating diesel spray is complex phenomena; however, it is important process for ignition, combustion and emission formation in diesel combustion. In this research, droplets evaporation process at spray boundary was experimentally investigated focusing on the behavior of evaporating droplets during ignition delay period. In the experiment, nano-spark shadowgraph photography technique was applied to a rapid compression machine. This study developed a new optical system to observe spray evaporation process. The existing systems can hardly analyze transitional behavior of vapor phase of spray and droplets behavior in high number-density region. The new technology that is named dual nano-spark shadowgraph photography method can record both macro-scale and micro-scale continuous spray images clearly at very short time interval of 15µsec on normal photographic black and white film.

Many technologies for reducing exhaust emissions of wide variety of diesel engines from small size to large size ones have been considered with the improvement throughout the combustion process. To reduce emissions, mixing of fuel and air is still important phenomena. Purpose of this study is to clarify the relation between mixture formation during the ignition delay period and burning process in diesel combustion that strongly affects the exhaust emissions. In this study, a rapid compression machine was used to simulate actual phenomenon inside the combustion chamber with changing ambient density. In addition, swirl velocity and injection pressure were changed as experimental parameters to improve mixture formation at high ambient density. This study constructed schlieren photography system with a high-speed digital video camera to investigate the detail behavior of mixture formation during ignition delay period.