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A three dimensional numerical analysis is made of in-cylinder process in a typical four-cycle reciprocating spark ignition engine with an off-center intake valve. The conservation equations of mass, momentum and energy are solved on the basis of the finite volume method. The ordinary two-equation model is employed as the turbulence model. Fuel is injected into the intake port, and fuel vapor, fuel droplets and air flow into the cylinder through the valve clearance during the intake stroke. As the inlet boundary condition, the inflow velocity distribution, mass fractions of fuel vapor and droplets are given around the intake valve periphery. For simplicity, it is assumed that fuel droplets move with the gas and have the rates of evaporation which are estimated by the classical quasi-steady theory of a single droplet evaporation. Calculation is made from TDC of intake stroke to TDC of compression stroke at every 10 degrees crank angle.

Laser Rayleigh scattering was applied for the remote, nonintrusive measurements of fuel vapor concentration in the combustion chamber of an automotive SI engine with the multipoint fuel injection. The fuel was simulated by Freon-12, which was injected intermittently or continuously into the flow of dust-free dry air through an intake port. The measurements were made of the time histories of instantaneous fuel vapor concentration at a location in the vicinity of a spark plug in the combustion chamber of the engine motored at 650 rpm for various air fuel ratios, fuel injection durations and fuel injection timings. The measured results were analyzed to derive an ensemble-averaged mean concentration, a cyclic variation of the temporal mean concentration and a temporal concentration fluctuation in a specific cycle.

Exciplex-based planar fluorescence technique was applied for two-dimensional visualization of the fuel spray including the region close to the nozzle tip. A spray doped with small amount of naphthalene and TMPD was discharged from a diesel nozzle into a pressurized gaseous nitrogen inside the test chamber installed with glass windows. The fuel spray was also allowed to evaporate in high temperature gaseous environments produced by combustion of the homogeneous mixture of methane and air in the test chamber. Photographs of the temporally frozen two dimensional image of the fuel spray were processed using an image analyzer. The image in the longitudinal cross section passing through the center axis of the spray demonstrated that the high density portion of liquid fuel appeared almost periodically downstream and that the axial distance between the neighboring high density portion increased with an increase in the downstream distance.

The authors have observed diesel spray structures by laser sheet Miescattering methods at room temperature under several ambient pressures(from 0.0 KPa to 2.1 MPa), and measured spray penetrations, spray-anglesand spray inner structures of light diesel oil. The results of spray-anglemeasurements showed that the spray-angle increased with an increase in theambient pressure near a nozzle tip. The spray-angle far from the nozzletip had the minimum value of spray angle at about 0.6 MPa ambientpressure. The spray structure had periodic high density portions occurringat a constant frequency (about 80 KHz). The frequency was time invariantand independent of ambient pressure. These results suggested that theperiodic portions were caused by the inner structure of the injector orthe structure of the nozzle.

An experimental study was made to investigate in-cylinder flow field in a natural gas fueled spark ignition engine and the effects of engine specifications on in-cylinder flow field. The instantaneous two-dimentional flow fields in a single-cylinder visualization engine, which has 75mm bore and 62mm stroke, were measured in various cross sections perpendicular to the cylinder axis by using the laser light sheet PTV method at various crank angles during intake, compression, and expansion strokes over the wide range of piston combustion chamber configuration, top clearance, and nominal swirl ratio. Flow fields during compression and expansion strokes were also calculated using KIVA2 simulation code for better understanding of the measured results. The results showed that induction-generated swirl is getting concentric to the cylinder center in compression stroke, and is shifted in the radial direction in expansion stroke.

An experimental study was made to investigate the effect of combustion chamber configuration, top clearance, nominal swirl ratio, and spark plug position on in-cylinder combustion in a spark-ignited natural gas engine, which is converted from a direct injection diesel engine. Flame propagation in a single-cylinder visualization engine was measured from the cylinder axis direction by the high speed schlieren method, over the wide range of combustion chamber configuration, top clearance, nominal swirl ratio, and spark plug position. The results showed that flame does not propagate concentrically to the spark plug, but is shifted by swirl, which is the main flow in this engine. Smaller piston cavity diameter led to more rapid flame propagation, resulting in larger heat release rate and larger cylinder pressure. Piston cavity diameter does not affect the initial combustion until TDC.