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Low temperature plasma ignition has been proposed as a new ignition technique as it has features of good wear resistance, low energy release and combustion enhancement. In the authors’ previous study, lean burn limit could be extended slightly by low temperature plasma ignition while the power supply’s performance with steep voltage rising with time (dV/dt), showed higher peak value of the rate of heat release and better indicated thermal efficiency. In this study, basic study of low temperature plasma ignition system was carried out to find out the reason of combustion enhancement. Moreover, the durability test of low temperature plasma plug was performed to check the wear resistance.

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.

A newly developed small-sized IES (inductive energy storage) circuit with static induction thyristor at turn-off action was successfully applied to an ignition system. This IEC circuit can generate repetitive nanosecond pulse discharges. In this paper, the ignition system using repetitive nanosecond pulse discharges was investigated as an alternative to conventional spark ignition systems. The experiments were conducted using spherically expanding flame configuration for CH4 and C3H8-air mixtures under various conditions. In conclusions, the ignition system using repetitive nanosecond pulse discharges was found to extend lean flammability limits compared with conventional spark ignition systems. In addition, the ignition system using repetitive nanosecond pulse discharges could shorten ignition delay time.

Experimental studies are conducted on extinction of non-premixed dimethyl ether (DME) flames stabilized in the counterflow configuration. Studies are carried out by injecting a fuel stream made up of fuel and inert gas (N2 or CO2) from one duct and an oxidizer stream made up of O2 and inert gas (N2 or CO2) from the other duct. Critical conditions of extinction are measured by increasing the flow rate of the counterflowing streams until the flame extinguishes. Numerical studies are also performed using detailed chemistry at conditions corresponding to those used in the experiments and compared with measurements. The present study highlights the examination of the influence of flame temperature, flame structure and kind of inert gas on extinction properties of DME. To examine the effect of flame temperature, inert gas is introducing to both fuel and oxidizer sides in such a way that the stoichiometric mixture fraction, Zst, is not changed, which means flame structure is not changed.

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.

For recent high efficiency engine with high compression ratio and highly boosted technology, combustion occurs at resultant more elevated pressure condition, as compared to conventional engine, which is known to decrease laminar burning velocity and cause flame instability. Flame instability could play an important role in combustion performance, and so far many theoretical and experimental studies have been devoted to the relevant matters. In this study, effects of flame instabilities on the combustion properties, such as the topography of flame surface and the variation in flame speed, have been experimentally examined using a dual constant volume combustion chamber in consideration of elevated pressure combustion in state-of-art IC engine.

The purpose of this paper is to investigate the combustion properties of CH4/O2 mixtures diluted by CO2 compared to those of CH4/O2/N2 mixtures to study the feasibility of the new combustion method, which is expected to be effective in NOx reduction and the improvement of combustion. Both experimental and numerical studies are conducted to scrutinize the effects of flame stretch on the burning velocity, which plays an important role in combustion performance not only for laminar flames but also for turbulent flames. In this study, experiments are conducted by using a spherical combustion bomb for applications to internal combustion engines. Then the effects of flame stretch are also investigated numerically and quantitative discussion is made in terms of Markstein number which represents non-dimensional sensitivity of the burning velocity to flame stretch. As a result it is found that Markstein numbers for both methane mixtures decrease with decreasing equivalence ratio.

In combustion engines, turbulence generated by flow field motion in the cylinder affects the propagating flame initiated by a spark plug, resulting in the increase of heat release rate and thus power available from an engine of a given size. In this context the modeling and prediction of turbulent flame properties are of importance for smart control of engine performance. In the present work, turbulent burning velocities of outwardly propagating premixed flames for methane and propane are investigated under the framework of the flamelet concept. The primary objective of the present paper is to study experimentally the turbulent burning velocities and derive the fundamental equations.

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.