Laser-induced Exciplex Fluorescence Research Articles

1226 DIディーゼル機関の初期燃焼およびすす生成に与える燃料蒸気濃度の影響(OS-3 ディーゼル燃焼とガスエンジン)

The purpose of this study is to clarify the effect of vapor concentration on early ignition and soot formation process. The concentration of liquid- and vapor-phase fuel during a mixture formation process in a DI diesel engine has been investigated using planar laser induced exciplex fluorescence (LIEF) technique. Measurement has been made in a small-sized DI diesel engine. The experimental results show that: The relatively well-diffused vapor phase fuel, which has been passed through the active turbulent mixing process prior to ignition, affects the first ignition and initial soot formation. Ignition is occurred at the moment when the spatial distribution of fuel vapor formed in ignition delay period becomes homogeneous gradually. It was confirmed that a great deal of vapor phase fuel with relatively high concentration is distributed at the area between the fuel spray and cylinder head, where the vortex motion is promoted. It could be deduced that the vortex flow plays an role to promote the mixing and ignition process. It is probable that the region between the cylinder head and fuel spray axis is a good candidate for ignition and initial soot formation.

LIQUID AND VAPOR SPRAY STRUCTURE IN HIGH-PRESSURE COMMON RAIL DIESEL INJECTION

Diesel spray structure is studied using optical diagnostics. A single-hole common rail diesel injector is used to enable high injection pressures up to 150 MPa. The spray is observed in a high-pressure, high-temperature cell that reproduces the conditions existing in a combustion chamber of a diesel engine during injection. The liquid phase of the spray is studied using laser-induced exciplex fluorescence (LIEF). The vapor phase is studied using an innovative measurement technique for which a high-boiling-point tracer is added to the fuel. The vaporized part of the spray is visualized by tracer droplet light scattering of a laser sheet. The technique is made quantitative with an appropriate calibration method. These two diagnostic methods are then used to build a database of liquid-phase visualizations and of quantitative two-dimensional distributions of fuel vapor concentration, with varying injection parameters. A detailed analysis of the structure of sprays is done. It is found that the liquid spray exhibits an area of high optical density at the outlet of the nozzle, with an abrupt transition to a fully atomized spray within a few nozzle orifice diameters. The structure of the fully atomized spray is comparable to a bundle-like structure, and is found to be the consequence of transient phenomena occurring in the nozzle. The structure of the vapor plume is similar, showing evenly distributed areas with steep gradients at the edges. This result is deducted from single-shot measurements and is found to contrast significantly with the more progressive structure of multipulse averages. This structure of the fuel vapor is expected to be responsible for the location of autoignition that occurs at multiple points nearly simultaneously. Finally, the effect of injection pressure is discussed. An increase of injection pressure is found to enhance the atomization at the nozzle outlet, resulting in a more distributed vapor phase, hence resulting in better mixing.

Investigation of the mixture formation inside a gasoline direct injection engine by means of linear Raman spectroscopy

Linear Raman scattering has been used for the investigation of the mixture formation inside an optically accessible gasoline direct injection spark ignition engine. The concentrations of O 2 , N 2 , H 2 O, and isooctane have been measured simultaneously and cycle resolved along a line of nearly 1 cm at three different locations inside the combustion chamber. By means of polarization-resolved detection optics, it was possible to separate the highly polarized Raman signals from unpolarized contributions from light emissions by stray light from surfaces, background luminescence, or laser-induced fluorescence. A separation between pure air and air/fuel mixture spectra was possible, indicating the influence of air entrainment on mixture formation. As all droplet influences on the taken spectra could be suppressed successfully, only pure gasphase spectra enter the air/fuel ratios evaluated. At the three selected locations (underneath the spark plug and displaced about 1.6 cm toward the intake and toward the outlet valve), the concentrations of all major species have been detected with high spatial and temporal resolution to observe the mixture formation process in a wide area inside the cylinder starting at fuel injection until shortly before ignition. Comparison with two-dimensional laser-induced exciplex fluorescence (LIEF) images allows improved interpretation of the phenomena taking place during mixture formation.

98/01518 Mixture of triethylamine (TEA) and benzene as a new seeding material for the quantitative two-dimensional laser-induced exciplex fluorescence imaging of vapor and liquid fuel inside SI engines: Fröba, A. P. et al. Combustion and Flame, 1997, 112, (1/2), 199–209

98/01518 Mixture of triethylamine (TEA) and benzene as a new seeding material for the quantitative two-dimensional laser-induced exciplex fluorescence imaging of vapor and liquid fuel inside SI engines: Fröba, A. P. et al. Combustion and Flame, 1997, 112, (1/2), 199–209

Multicomponent liquid and vapor fuel measurements in the cylinder of a port-injected, spark ignition engine

Fuel distribution measurements in the cylinder of a port-injected, spark ignition (SI) engine are presented with a discussion of the effects of injection timing, swirl, and engine speed. Planar laser-induced exciplex fluorescence (PLIEF) was used to study the liquid-and vapor-phase fuel distributions. Optical access to the cylinder was provided by placing a fused silica cylinder between the head and block of a production engine and using a Bowditch-type piston extension. Separate measurements were made with fluorescent tracers indicative of the light and heavy components of gasoline. A blend of four pure fuels mixed in proportions to give a distillation curve similar to that of gasoline was used for all measurements to achieve consistency in the base fuel as well as similarity with the vaporization characteristics of gasoline. These measurements indicate that the vapor-phase fuel distribution is strongly affected by the presence of liquid fuel in the cylinder, the amount of which varies with injection timing. The liquid that enters the cylinder is composed mostly of the heavy components of the fuel. Variations in the amount of swirl indicate that the vapor-phase fuel distribution also is affected by the bulk velocity field. Engine speed, over the range from 200 to 1200 rpm, did not exert a significant influence on the fuel distribution.

Mixture of triethylamine (TEA) and benzene as a new seeding material for the quantitative two-dimensional laser-induced exciplex fluorescence imaging of vapor and liquid fuel inside SI engines

A mixture of triethylamine (TEA) and benzene in iso-octane has been proven to be a suitable seeding material for the study of the gasoline fuel mixture and evaporation processes under engine-like conditions. Laser-induced fluorescence (LIF) of the exciplex-forming mixtures of TEA and benzene has been investigated using a KrF-excimer laser at 248 nm as an excitation source. The dopants have physical and chemical properties that match well with the model fuel iso-octaine and show only low absorption at the excitation wavelength. These are important criteria for materials to be used as tracer substances for the study of evaporation and mixture formation processes in SI engines. In the liquid phase, the mixture of the two tracer substances with iso-octane shows a broadband fluorescence spectrum which is red-shifted with respect to the vapor-phase fluorescence. This allows a spectrally separated detection of the local distributions of the liquid and the vapor phases by using appropriate bandpass filters. Vapor-phase fluorescence in the presence of synthetic air, oxygen, nitrogen, carbon dioxide, and water vapor under variation of pressure, concentration, and temperature was measured in a heatable high-pressure chamber. It has been found that oxygen is the only molecular species which induces collisional quenching of the fluorescence emissions. Hence, using the described tracer system, a quantitative detection of vapor-phase concentrations and fuel/air-ratios under engine like conditions is possible. It is demonstrated that the fluorescence intensity is directly proportional to the fuel/air-ratio and independent of pressure for pressures higher than 3 bar. The temperature dependence of the fluorescence intensity has been studied in a temperature range from 398 to 523 K. With increasing temperature, a systematic decrease of the fluorescence intensity has been detected, which, however, is still directly proportional to the fuel/air ratio. An application of the newly developed tracer combination for the quantitative two-dimensional imaging of the fuel/air-ratios in the vapor-phase and the simultaneous, spectrally separated detection of the liquid phase inside an SI engine is presented.