Taketoshi Fujikawa

Analysis of cycle-by-cycle variation in a direct injection gasoline engine using a laser-induced fluorescence technique

Abstract To analyse the cycle-by-cycle variation of combustion in a direct injection gasoline engine equipped with a fan-shape spray nozzle and operated with exhaust gas recirculation (EGR), the fuel mixture distribution was measured at a time of spark and during the combustion period by the laser-induced fluorescence (LIF) technique. It was found that in the case of advanced or retarded injection timing, the initial combustion period tends to extend and the indicated mean effective pressure (i.m.e.p.) becomes low when lean mixtures appear at the spark position and at the spark timing. This suggests that the cycle-by-cycle variation of combustion under these conditions is dominated by the fuel concentration at the spark position and spark timing. In contrast to this, for the best injection timing, which allows the lowest cycle-by-cycle variation, the i.m.e.p. fluctuation is affected not by the initial combustion period but by the main combustion period. The observation of LIF images revealed that the i.m.e.p. fluctuation at this condition is strongly correlated to the unburned mixture quantity at the side area of the piston cavity during the latter half of the combustion period. It was shown by a computational fluid dynamics (CFD) calculation that the combination of a uniform spray pattern and a compact cavity shape is effective to reduce the over-lean mixture region in the edge of the piston cavity, which is responsible for the cycle-by-cycle variation of combustion at the condition of best-tuned injection timing.

Photographic and Three Dimensional Numerical Studies of Diesel Soot Formation Process

Soot formation process was examined by high speed photographs, using a single combustion diesel engine with a transparent swirl chamber. Fuel-air mixture and flames, and soot clouds were visualized by the schlieren method and the back-illuminated method, respectively. A three dimensional simulation program with soot formation and oxidation models was developed to clarify diesel soot formation processes. The models consist of several models previously proposed and partly improved in this study. Good agreement was obtained between calculated and experimental results. The following points were clarified through observation and numerical studies: The main soot area is considerably smaller than luminous flame area, especially in the initial soot formation process; the main soot cloud first appears in the tip region of fuel-air mixture, downstream of ignition position a few submilliseconds after the ignition. It is the soot carried down from the ignition position by a gas flow; and temperature is more influential in soot formation, rather than fuel vapor concentration.

Development of transparent cylinder engines for schlieren observation

A square piston engine and a side-view collimating (SVC) cylinder engine are developed for side-view schlieren visualization of in-cylinder processes. The square piston engine has a square cylinder with two flat quartz windows permitting optical access to the entire cylinder volume. Compression sealing is provided by three polyimide ring assemblies which maintain the windows clean during the actual observational. In contrast with the square piston engine, the SVC cylinder engine permits to take schlieren photographs in practical engine geometries. This is made possible by designing the SVC cylinder so that it does not disperse parallel light rays.

Simulation and experiments of the laser induced breakdown of air for femtosecond to nanosecond order pulses

3D + 1 dimensional simulations and experimental results for the laser induced breakdown of air are presented. The simulations include the laser propagation, multi-photon and impact ionization and heating of the electrons using accurate atomic and molecular data. For laser pulses of duration from 100 fs to 1 ns mechanisms for the breakdown of air based on the pulse duration and intensity ranging from optical field ionization to electron impact ionization are found. The laser energies at which the breakdown occurs are found to be in good agreement with experimental results.

Schlieren Observation of Spark-Ignited Premixed Charge Combustion Phenomena Using a Transparent Collimating Cylinder Engine

The schlieren photographs of in-cylinder processes in a spark-ignited premixed charge gasoline engine were observed via a transparent collimating cylinder and were presented in comparison with a pressure analysis. The schlieren photographs of the spark, the initial flame and the unburned gas ejection from the piston crevice, which is unable to be observed by direct photography, were clearly taken. It shows that the small difference in the initial combustion process among cycles is intensified by the movement of the piston during the expansion stroke. Finally, this difference appears as the cycle by cycle variation in the pressure and the rate of heat release. The observed flame size increased faster and was larger than the burned gas estimated from the pressure. The difference between them is large enough and can not be explained without considering the mixing of burned and unburned gases inside the flame front.

Laser-Induced Breakdown of Air with Double-Pulse Excitation

Experimental investigation of air-breakdown induced by double-pulse laser with nanosecond pulse duration is conducted. The effects of pulse interval and energies on laser absorption and plasma brightness are presented.

Simulation and Experiments of the Laser Induced Breakdown of Air for Femtosecond to Picosecond Order Pulses

Simulations including the laser propagation, multi-photon and impact ionization, and heating of the electrons and experimental results for the laser induced breakdown of air for pulses of duration from femtoseconds to picoseconds are presented.