Search Results

Experiments and modeling of a spray impinged onto a cavity wall of a simulated piston were performed under simulated diesel engine conditions (pressure and density) at an ambient temperature. The diesel fuel was delivered from a Bosch-type injection pump to a single-hole nozzle, the hole being drilled in the same direction as the original five-hole nozzle. The fuel was injected into a high-pressure bomb in which an engine combustion chamber, composed of a piston, a cylinder head and a cylinder liner, was installed. Distributions of the spray impinged on the simulated combustion chamber were observed from various directions while changing some of the experimental parameters, such as combustion chamber shape, nozzle projection and top-clearance. High-speed photography was used in the constant volume bomb to examine the effect of these parameters on the spray distributions.

Three-Dimensional visualization technique based on volume rendering method has been developed in order to translate a calculated result of diesel combustion simulation into an realistically spray and flame image. This paper presents an overview of diesel combustion model which has been developed at Hiroshima University, a description of the three-dimensional visualization technique, and some examples of spray and flame image generated by this visualization technique.

A calculative investigation was performed in order to examine the effects of injection rate profile and air entrainment characteristics on exhaust emission using a phenomenological spray combustion model. The calculations were made of an engine with a bore of 114 mm and a stroke of 130 min while changing the injection rate profile and the air entrainment characteristics. As a result of the calculations, effective measures were found for simultaneous reduction of NOx and smoke emissions.

In order to measure the droplets and vapor concentration inside a fuel spray, a dual-wavelength laser absorption-scattering technique was developed using the second harmonic (532nm) and the fourth harmonic (266nm) of a Nd:YAG laser and using dimethylnaphthalene as the test fuel. The investigation results show that dimethylnaphthalene, which has physical properties similar to diesel fuel, is almost transparent to visible light near 532nm and is a strong absorber of ultraviolet light near 266nm. Based on this result, the vapor concentration in a fuel spray can be determined by the two separate measurements: a transmission measurement at a non-absorbing wavelength to detect the droplets optical thickness and a transmission measurement at an absorbing wavelength to detect the joint vapor and droplets optical thickness. The droplets density can be determined by extinction imaging through the transmission at the non-absorbing wavelength.

The two-dimensional distributions of the liquid phase temperatures in diesel sprays injected into high-pressure and high-temperature environments were measured using the laser-induced fluorescence technique. The liquid fuel (n-hexadecane) was doped with pyrene(C16H10). The fuel spray doped with pyrene was injected under a high-pressure of 3.1MPa and a high-Temperature of 773K. The evaporating diesel spray was excited by laser radiation at 266nm, and the resulting fluorescence was imaged by an intensified CCD camera. The fluorescence intensity ratios of the pyrene monomer and excimer emissions have temperature dependence, and were used to determine the liquid phase temperatures in the diesel sprays. The cross-sectional distribution of the liquid phase temperature was estimated from the fluorescence images by the temperature dependence of the intensity ratio.

The fuel injection characteristics of Dimethyl Ether(DME) were calculated and compared with the calculated results of diesel fuel using a simulation model of an in-line diesel injection system in order to clarify the differences between the injection characteristics of the two fuels. Moreover, numerical analyses for the DME injection were performed while changing the fuel parameters and the injection system parameters in order to estimate the effects of these parameters on the fuel injection characteristics. The effects of some of these parameters were evaluated by experimental results conducted in a constant volume vessel. Furthermore, the spray tip penetration was calculated using the computed results of the injection pressure. As a result of this study, the injection characteristics of the DME fuel are basically confirmed. By the macroscopic analyses of these spray characteristics, the DME spray behavior in a combustion chamber can be estimated.

This paper presents a Stratified Three zone Diesel Combustion Model consisting of “No. 1-burning zone,” “No.2-burned zone,” and “No.3-low temperature air zone,” based on the hypothesis proposed by one of the authors (Matsuoka)(1) (2) (3). This hypothesis accounts for the re-entrainment of its own burnt gas (REOBG) into the diesel spray flame. The air from zone 3 is entrained into zone 1 and zone 2, where it is partially entrapped by zone 2. The burned gas of zone 2 also re-entrains and mixes in zone 1 forming each stratified layer. Parametrical study results compared with the measured data show that such entrainment has a significant physical effects on the main combustion phase. As a result, it causes a drop in the acceleration rate of heat release, also an increase of pyrolyze that in turn promotes the soot formation. Chemical reactions caused by this REOBG that appears in the later combustion stage are also considered.

Evaporating diesel spray distributions in the combustion chamber of a direct injection diesel engine were calculated using a phenomenological simulation model, and the calculated results were described three dimensionally using a 3-D volume rendering application which has been developed by the authors. The evaporating diesel spray distributions in the combustion chamber were measured using a technique based on the extinction of ultraviolet (wavelength of 280nm) and visible (wavelength of 560nm) laser lights. The measured results were compared with the predicted spray distributions in order to verify the simulation model. The calculated results show reasonably good agreement with the experimental results, and the validity of this spray model as a practical computational tool for estimating diesel spray behavior is confirmed by this comparison.

Among the alternative fuels, dimethyl ether (DME), one of the oxygenated fuels, attracts attention as an alternative fuel for the Diesel engine since the properties of the DME are fitted to the Diesel engine combustion and the know-how development has been made of the mass production of the DME from a natural gas. In this study, experiments were performed of ignition characteristics of the DME and Diesel fuel sprays injected by a D.I. Diesel injector into a high-pressure, high-temperature vessel. The fuel injection was made by a Bosch type injection system. A schlieren optical system was adopted for visualizing the ignition process as well as the vaporization process of the DME and Diesel fuel sprays. The ignition delay was measured by using a photo-sensor which had a sensitivity in the wavelength range from visible to ultraviolet. Pressure and temperature of the ambient air and the oxygen concentration of the ambient air were changed as experimental parameters.

An experimental study was conducted to investigate the flame propagation characteristics in the presence of a heterogeneous concentration distribution of a fuel-air mixture in order to provide fundamental knowledge of the effects of gaseous mixture concentration heterogeneity on the combustion process. Different propane-air mixture distributions were produced by the reciprocating movements of a pair of perforated plates in a constant volume combustion chamber. The mean equivalence ratio of the fuel-air mixture was varied from 0.7 on the lean side to 1.6 on the rich side, the turbulence intensity in the combustion chamber was also varied at levels of 0.185 m/s, 0.130 m/s, 0.100 m/s, and 0.0 m/s. By an independent control of the mixture distribution and the turbulence intensity in the combustion chamber, the flame structure and flame propagation speed at various heterogeneous levels of the mixture distribution were investigated in detail.

Distributions of non-evaporating diesel sprays impinging on a simulated combustion chamber wall were observed from various directions while changing some of the experimental parameters, such as nozzle projection and top-clearance. High-speed photography was used in this study to examine the effects of these parameters on the spray distributions. Moreover, the spray distributions were predicted by using a spray model based on a multi-package model. The calculated distributions were displayed three-dimensionally using a volume rendering application developed by the authors. The predicted spray distributions were compared with the experimental results observed from various directions in order to evaluate the spray model.

Although mixture formation is considered important in actual spark ignition engines, A full understanding of the combustion characteristics of a heterogeneous mixture has not yet been achieved. In this study, in order to clarify the effects of a heterogeneous concentration distribution of the fuel-air mixture on the flame propagation process, different degrees of heterogeneously distributed mixtures were created by the motion of a pair of perforated plates in a constant volume combustion chamber. The laser Rayleigh scattering method was applied for quantitative visualizations of these mixture distributions. To control the distribution of the mixture concentration and the turbulence intensity independently, the flow in the chamber and its turbulence intensity were also measured by a laser sheet method and the LDV technique.

A phenomenological spray-combustion model of a D.I. Diesel engine was applied to study the engine parameters with potential for reducing NOx and smoke emissions. The spray-combustion model, first developed at the University of Hiroshima in 1976, has been sophisticated by incorporating new knowledge of diesel combustion. The model was verified using data from an experimental, single cylinder, D.I. diesel engine with a bore of 135mm and a stroke of 130mm. After the verification process, calculations were made under a wide range of the engine parameters, such as intake air temperature, intake air pressure, intake swirl ratio, nozzle hole diameter, injection pressure, air entrainment rate into the spray, and injection rate profile. These calculations estimated the effects of the engine parameters on NOx, smoke and specific fuel consumption. As a result of the calculations, an approach for the low NOx and smoke emission engine was found.

Cross-sectional distributions of the liquid phase temperatures in fuel sprays were measured using a laser-induced fluorescence technique. The liquid fuel (n-hexadecane or squalane) was doped with pyrene(C16H10). The fluorescence intensity ratios of the pyrene monomer and excimer emissions has temperature dependence, and were used to determine the liquid phase temperatures in the fuel sprays. The measurements were performed on two kinds of sprays. One was performed on pre-heated fuel sprays injected into surrounding gas at atmospheric conditions. The other was performed on fuel sprays exposed to hot gas flow. The spray was excited by laser radiation at 266nm, and the resulting fluorescence was imaged by an intensified CCD camera. The cross-sectional distribution of the liquid phase temperature was estimated from the fluorescence image by the temperature dependence of the intensity ratio.