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The rapid compression expansion machine (RCEM) was used to investigate the temporal variations of the spray flame and wall heat flux in the diesel engine combustion process by using 120 MPa and 180 MPa common rail pressure. A stepped cavity was applied to investigate spray and flame behavior under the pilot, pre and main multiple injection strategy. Wall heat flux sensors were installed in the piston cavity and the cylinder side. The injector has 3 holes with the neighboring angle in the left direction and another 3 holes in the right direction to simulate the spray interaction in the 10-hole injector combustion system in the actual diesel engine. The spray and flame behavior were taken by a high-speed video camera with direct photograph. A two-color analysis was applied to investigate gas temperature and KL factor distribution. The effect of locations and common rail pressure on heat transfer was investigated.

The high injection pressure and small cylinder volume of direct injection spark ignition (DISI) engines can result in flat-wall wetness on the surface of the piston, increasing fuel consumption and pollutant emissions. The characteristics of microscopic fuel adhesion are observed using refractive index matching (RIM). Fuel adhesion characteristics after wall impingement are evaluated with various cross-flow velocities under triple stage injection conditions. The results indicate that cross-flow has a beneficial effect on the diffusion of fuel spray. Average fuel adhesion thickness decreases with an increase in cross-flow velocities. Furthermore, cross-flow promotes the evaporation of fuel adhesion, which leads to a reduction in the fuel adhesion mass/mass ratio. The improvement of injection strategy has guidance on low-carbon future.

The fuel economy of recent small size DI diesel engines has become more and more efficient. However, heat loss is still one of the major factors contributing to a substantial amount of energy loss in engines. In order to a full understanding of the heat loss mechanism from combustion gas to cylinder wall, the effect of hole size and rail pressure at similar injection rate condition on transient heat flux to the wall were investigated. Using a constant volume vessel with a fixed impingement wall, the study measured the surface heat flux of the wall at the locations of spray flame impingement using three thin-film thermocouple heat-flux sensors. The results showed that the transferred heat was similar under similar injection rate profiles. However, in case of flame luminosity, temperature distribution, characteristic of local heat flux and soot distribution was also similar except the smaller nozzle hole size with higher injection pressure.

The air flow affects the spray feature and mixture significantly in gasoline engine. The effects of air flow with atmosphere and pressurized ambient pressure were investigated experimentally in the previous work, the gasoline spray characteristics and air flow are analyzed using CFD method in this study. By polishing the model of droplet breakup according to the experimental results, the simulations are taken with various air flow conditions. Modeling of spray injected under typical condition of crossflow is employed to compare the numerical results with experimental results, using the corrected model the more calculation are carried out simulating the real conditions. With changing the injection and air flow conditions, the spray feature, droplet size, droplet movement, and droplet distribution are calculated by a commercial software.

To get a better understanding of the characteristics of the high pressure gasoline sprays impinging on a wall, a fundamental study was conducted in a high-temperature high-pressure constant volume vessel under the simulated engine conditions of in-cylinder pressures, temperatures, and wall temperatures. The injection pressure was varied from 20 to 120 MPa. The spray tip penetration, vapor mass distribution, and vaporization rate were quantitatively measured with the laser absorption-scattering (LAS) technique. The velocity fields of the wall-impinging sprays under vaporizing conditions were measured with the particle image velocimetry (PIV) technique using silicone oil droplets as tracers. The effects of injection pressure and spray/wall interactions on spray characteristics were investigated. The results showed that the increased injection pressure improved penetration, vaporization, and turbulence of the sprays.

In direct injection spark ignition (DISI) engine, it is difficult to avoid the spray impingement of fuel on the cylinder wall and piston head, which is a possible source of hydrocarbons and soot emission. The injector nozzle geometry and injection pressure are essential components for the spray atomization and mixture formation. For better understanding the effects of injector hole diameters and injection pressure, the fuel spray and adhesion on a flat wall by different mini-sac injectors with a single hole was examined in this study. A flat-wall made of quartz glass was used as the impingement plate. Refractive Index Matching (RIM) method was applied to measure the thickness of fuel adhesion on the wall. All the cases performed in constant high-pressure chamber were under high temperature condition considering the real gasoline engine condition. Time-resolved behaviors of the fuel adhesion as well as adhesion mass, area and thickness were discussed.

Substantial amount of fuel energy input is lost by heat transfer through combustion chamber walls in the internal combustion engines. Thus, these heat losses account for reduced thermal efficiency, in that spray-wall impingement plays a crucial role in Direct Injection diesel engines. The objective of this study is to investigate the mechanism of the heat transfer from the spray/flame to the impinging wall under small diesel engine-like condition and how the spray characteristics are affected with regards to effect of injection pressure, nozzle hole diameter and impingement distance. The experiment results showed that injection pressure was predominant factor on spray-wall heat transfer.

A comparison of spray characteristics was conducted between single- and multi-hole injectors. A commercial software (AVL FIRE) was used to investigate the internal flow inside the sac volume, as well as the initial spray behavior at 1 mm downstream of the nozzle exit. Microscopic imaging was applied to observe the spray dispersion angle (spray cone angle) at the vicinity of the nozzle. Laser absorption scattering (LAS) technique was implemented for measuring the mixture concentration. Three injection quantities, namely 0.5, 2.5, and 5.0 mg/hole, were selected to observe the differences between transient and quasi-steady spray. The vapor penetration at the initial stage of the injection was greater for single-hole than that of multi-hole injector due to faster fuel pressure build-up process inside the sac volume.

Increasing the injection pressure and splitting the injection stage are the major approaches for a diesel engine to facilitate the fuel-air mixture formation process, which determines the subsequent combustion and emission formation. In this study, the free spray was injected by a single-hole nozzle with a hole-diameter of 0.111 mm. The impinging spray, formed by a two-dimensional (2D) piston cavity having the same shape as a small-bore diesel engine, was also investigated. The injection process was performed by both with and without pre-injection. The main injection was carried out either as a single main injection with injection pressure of 100 MPa (Pre + S100) or a split main injection with 160 MPa defined by the mass fraction ratio of 3:1 (Pre + D160_3-1). The tracer Laser Absorption Scattering (LAS) technique was adopted to observe the spray mixture formation process. The ignition delay/location and the soot formation in the spray flame were analyzed by the two-color method.

Heat loss is more critical for the thermal efficiency improvement in small size diesel engines than large-size diesel engines. More than half of total heat energy in the internal-combustion engine is lost by cooling through the cylinder walls to the atmosphere and the exhaust gas. Therefore, the new combustion concept is needed to reduce losses in the cylinder wall. In a Direct Injection (DI) diesel engine, the spray behavior, including spray-wall impingement has an important role in the combustion development to reduce heat loss. The aim of this study is to understand the mechanism of the heat transfer from the spray and flame to the impinging wall. Experiments were performed in a constant volume vessel (CVV) at high pressures and high temperatures. Fuel was injected using a single-hole injector with a 0.133 mm diameter nozzle. Under these conditions, spray evaporates, then burns near the wall. Spray/flame behavior was investigated with a high-speed video camera.

The performance of a diesel engine largely depends on the spray behavior and mixture formation. Nozzle configurations and operating conditions are important factors that influence spray development. Using numerical and experimental methods, this study focused on the spray development of multi-hole nozzles under non-evaporating and evaporating conditions to compare the influence of nozzle hole diameter and injection pressure on spray characteristics. High-speed video observation was employed to study the properties of spray development under the non-evaporating condition, while the Laser Absorption Scattering technique was used in the observation and quantitative analysis of evaporating spray characteristics in the evaporating condition. In addition, computational fluid dynamics study results published previously [1] were correlated with the current experimental results to provide more detailed explanations about the mechanism of the characteristics of spray behavior.

With the aim of improving engine performance, recent trend of fuel injection nozzle design followed by engineers and researchers is focusing on more efficient fuel break up, atomization, and fuel evaporation. Therefore, it is crucial to characterize the effect of nozzle geometric design on fuel internal flow dynamics and the consequent fuel-air mixture properties. In this study, the internal flow and spray characteristics generated by the practical multi-hole (10 holes) nozzles with different nozzle hole length and hole diameter were investigated in conjunction with a series of computational and experimental methods. Specifically, the Computational Fluid Dynamics (CFD) commercial code was used to predict the internal flow variation inside different nozzle configurations, and the high-speed video observation method was applied to visualize the spray evolution processes under non-evaporating conditions.

The injection amount per stage in a multiple injection strategy is smaller than a conventional single-stage injection. In this paper, the effect of the injection amount (0.27mg, 0.89mg, 2.97mg) under 100MPa injection pressure and the effect of injection pressure (100MPa, 150MPa, 170MPa) under different injection amounts (0.27mg, 2.97mg) on the spray and mixture formation characteristics were studied by analyzing the vapor/liquid phase concentration distributions obtained under various conditions via using the tracer LAS technique. The spray was injected into a high-pressure and high-temperature constant volume vessel by using a single-hole nozzle with a diameter 0.133mm. The higher the injection pressure with a smaller injection amount is, the shorter the spray tip penetration and leaner air-fuel mixture occur. The combustion processes had been examined by a high-speed video camera with the two-color pyrometry method.

The effect of temporally-splitting high pressure injection on Diesel spray combustion and soot formation processes was studied by using the high-speed video camera. The spray was injected by the single-hole nozzle with a hole diameter of 0.11mm into the high-pressure and high-temperature constant volume vessel. The free spray and the spray impingement on the two dimensional (2D) piston cavity wall were examined. Injection pressures of 100 and 160 MPa for the single injection and 160 MPa for the split injection were selected. The flame structure and soot formation process were examined by using the two-color pyrometry. The soot generated in the flame under the split injection under 160 MPa becomes higher than that of the single injection under 160 MPa.

Spray combustion processes of palm oil biodiesel (PO) and conventional diesel fuels were simulated using the CONVERGE CFD code. Thermochemical and reaction kinetic data (115 species and 460 reactions) by Luo et al. (2012) and Lu et al. (2009) (68 species and 283 reactions) were implemented in the CONVERGE CFD to simulate the spray and combustion processes of the two fuels. Tetradecane (C14H30) and n- heptane (C7H16) were used as surrogates for diesel. For the palm biodiesel, the mixture of methyl decanoate (C11H20O2), methyl-9-decenoate (C11H19O2) and n-heptane was used as surrogate. The palm biodiesel surrogates were combined in proportions based on the previous GC-MS results for the five major biodiesel components namely methyl palmitate, methyl stearate, methyl oleate, methyl linoleate and methyl linolenate.

The effects of spray/wall interaction on diesel combustion and soot formation in a two-dimensional piston cavity were studied with a high speed color video camera in a constant volume combustion vessel. The two-dimensional piston cavity was applied to generate the impinging spray flame. In the cavity, the flat surface which plays a role as the cylinder head has a 13.5 degree angle with the injector axis and the impinging point was located 30 mm away from the nozzle tip. Three injection pressures of 100, 150, and 200 MPa and a single hole diesel injector (hole diameter: 0.133mm) were selected. The flame structure and combustion process were examined by using the color luminosity images. Two-color pyrometry was used to measure the line-of sight soot temperature and concentration by using the R and B channels of the color images. The soot mass generated by impinging spray flame is higher than that of the free spray flame.

Spray characteristics are of great importance to achieve fuel economy and low emissions for a D.I. gasoline engine. In this study, the characteristics of the fuel spray as well as its interaction with a cross-flow were investigated. The fuel was injected by a VCO injector into an optically accessible rectangular wind tunnel under the normal temperature and pressure, in which the direction of the injection was perpendicular to the direction of the cross-flow. The velocity of the cross-flow varied from 0 to 10 m/s while the injection pressure was 5 and 10 MPa. With using the high speed video camera and the PIV system, the spray profile, velocity distribution and the penetration distance were measured. The lower penetration distance can be obtained with the lower injection pressure and the increased velocity of the cross-flow, however the injected fuel expands along the direction of the cross-flow, which indicates that spray atomization and mixing of fuel and air are enhanced.

Previous research has shown that the reduced nozzle hole diameter and elevated injection pressure are effective for preparing a uniform fuel-air mixture in a direct injection (D.I.) Diesel engine. A micro-hole nozzle with a hole diameter of 0.08 mm and an ultra-high injection pressure of 300 MPa have been employed to investigate the mixture formation process under various conditions. The aim of the current work is to clarify the effect of nozzle hole diameter and injection pressure on flame lift-off and soot formation processes. The free sprays from the micro-hole and conventional nozzles were investigated at a high-temperature, high-pressure constant volume vessel. A high-speed video camera system was employed to record the non-vaporizing sprays and combustion. The direct photography of OH chemiluminescence was used to provide information about the high temperature combustion process and to measure the flame lift-off length.

The fuel-ambient gas interaction process of the free diesel spray injected from the micro-hole nozzle (0.08 mm) into the quiescent and engine-like ambient gas condition was investigated by means of the laser-induced fluorescence - particle image velocimetry (LIF-PIV) technique in non-evaporating condition. Direct photography with high speed video camera and two color pyrometry were applied to analyze the evaporation spray and flame characteristics. Three injection pressures from 100, 200 to 300 MPa and two ambient gas densities of 11 and 15 kg/m₃ were selected as testing conditions. The entrained mass flow rate of the ambient gas through the whole spray boundary, the ratio of the total ambient gas entrainment rate to the fuel injection rate, etc., were calculated by using the ambient gas velocity data obtained by the LIF-PIV technique and used to correlate the combustion behavior.

The effect of injection pressure ranging from 100 to 300MPa on the ignition, flame development and soot formation characteristics of biodiesel fuel spray using a common rail injection system for direct injection (D.I.) diesel engine was investigated. Experiments were carried out in a constant volume vessel under conditions similar to the real engine condition using a single hole nozzle. Biodiesel fuels from two sources namely; palm oil (BDFp) and cooked oil (BDFc) with the commercial JIS#2diesel fuel were utilized in this research. The OH chemiluminescence technique was used to determine the ignition and the lift-off length of the combusting flame. The natural luminosity technique was applied to study the flame development and the two color pyrometry was applied for the soot formation processes. Ignition delay decreased as the injection pressure progressed from 100 to 300MPa. This was as a result of the enhanced mixing achieved at higher injection pressures.