Search Results

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.

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.

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.