Mixture Formation Process Research Articles

Droplet size distribution and evaporation characteristics of fuel spray by a swirl type atomizer

Spray atomization and evaporation play extremely important roles in mixture formation and combustion processes of direct injection (DI) gasoline engines. In this study, the fundamental characteristics of a swirl spray injected into a constant volume vessel are investigated by means of several laser diagnostic techniques including the laser diffraction-based method for droplet size distribution, the laser induced fluorescence–particle image velocimetry for velocity distributions of droplets and spray-induced ambient air flow, and the two-wavelength laser absorption–scattering technique for concentration distributions of liquid and vapor phases in the spray. The results show that the droplets at outer zone of the spray exhibit larger diameter than those at inner zone under both ambient pressures 0.1 and 0.4 MPa. While this can be partially attributed to the effect of spray-induced ambient air flow, the strength of ambient air flow become small when increasing the ambient pressure from 0.1 to 0.4 MPa, indicating the strong influence of spray dynamics on the droplet size distribution. In the evaporating spray, there are higher vapor concentrations near the spray axis than at peripheral zones. At 4.0 ms after start of injection, spray droplets almost completely evaporate under ambient temperature 500 K and pressure 1.0 MPa, but there are significantly amount of fuels with equivalence ratio below 0.5 in the spray. Reduction in ambient pressure promotes the air entrainment and droplet evaporation, but lowered ambient pressure results in more fuel vapor of equivalence ratio above 1.3 along the spray axis.

Study of the mixture formation processes inside a modern direct-injection gasoline engine

The combustion process inside a direct injection spark ignition engine with charge stratification is a very complex process with a large number of variables existing for the definition of the engine characterization map. In this work, two different tracer-based laser-induced fluorescence techniques were applied to analyse the charge motion during the mixing process. For two different operation points with and without a complex in-cylinder flowfield, the two-line excitation LIF technique was applied for temperature and residual gas fraction imaging, and the FARLIF technique for fuel/air ratio imaging. It was found that the mixing of air and residual gas was very fast, and hence no inhomogeneities were found at ignition time. For the mixture preparation process, the swirl makes it difficult to position the fuel vapour cloud near the spark plug at ignition. As a solution to overcome this, a double-injection strategy was applied. With careful parameter choice, depending on the second injection mass and timing, the desired charge situation could be achieved.

감압비등을 이용한 혼합연료의 분무제어에 관한 연구

This study was conducted to assess the spray control of flash boiling with mixed fuel in consideration of HCCI (Homogeneous Charge Compression Ignition) engine condition. Mixed fuel existing in two phase regions can control the process of mixture formation under low temperature and density by using the spray resulting from flash boiling which is able to induce rapid evaporation of fuel spray as well as the evaporation of high boiling point component. Because HCCI engine injects the fuel early under ambient conditions, it can facilitate the chemical control of ignition combustion and physical control such as breakup and atomization of liquid fuel by flash boiling of mixed fuel which consists of highly ignitable light oil and highly volatile gasoline. This study was conducted by performing video processing after selected composition and molar fraction of the mixed fuel as major parameters and photographed Schlieren image and Mie scattered light corresponding to the flash boiling phenomenon of the fuel spray that was injected inside a constant volume vessel. It was found that flash boiling causes significant changes in the spray structure under relatively low temperature and density. Thus, we analyzed that the flash boiling spray can be used for HCCI combustion by controlling the mixture formation at the early fuel injection timing.

Analysis of Port Injected Fuel Spray Under Cross Wind Using 2-D Measurement Techniques

In a motorcycle gasoline engine the port fuel injection system is rapidly spread. Compared to an automotive engine the injected fuel does not impinge on the intake valve due to space restriction to install the injector. In addition as the air flow inside the intake pipe may become very fast and has large cycle‑to‑cycle variation it is not well found how the injector should be installed in the intake pipe to prepare good fuel‑air mixture inside the intake pipe. In this study the formation process of the fuel‑air mixture is measured by using ILIDS system that is a 2‑D droplets'size and velocity measurement system with high spatial resolution. Experiments with changing conditions such as flow speed and injection direction are carried out. As a result the effects of injection direction ambient flow speed and wall roughness on the fuel‑air mixture formation process was examined considering the three conditions of cold start light to medium load operation and high load operation.

Effect of Two-Stage Injection on Unburned Hydrocarbon and Carbon Monoxide Emissions in Smokeless Low-Temperature Diesel Combustion with Ultra-High Exhaust Gas Recirculation

The unburned hydrocarbon (UHC) and carbon monoxide (CO) emissions from smokeless low-temperature diesel combustion (LTC) with ultra-high exhaust gas recirculation (EGR) can be attributed to lowered combustion temperatures as well as to under-mixing of fuel-rich mixture along the combustion chamber walls, overly mixed fuel-lean mixture at the spray tails, and fuel missing the piston bowl and entering the squish zones. Two-stage injection has the potential to reduce UHC and CO emissions through decreasing the ratios of these mixtures. This study investigates the effects of two-stage fuel injection by varying the dwell between the two injections as well as the fuel quantity in each injection on the UHC and CO emissions, experimentally with a single-cylinder diesel engine. With the optimized dwell and injection ratio, two-stage injection can reduce the UHC and CO emissions, but these emissions are still at high levels in the ultra-high EGR smokeless LTC regime. Computational fluid dynamics simulations of the in-cylinder spray and mixture formation processes showed that with the two-stage injection, over-rich mixture in the squish zones can be significantly avoided but the over-lean mixtures at centre of the combustion chamber are little reduced, and these would likely be a significant source of UHC and CO emissions.

Gasodynamic characteristics of a combustion chamber in the integrated power plant with an asymmetric air intake

The results of experimental investigations of gasodynamic characteristics of a combustion chamber model in the integrated power plant (IPP) with an asymmetric air intake are presented. The influence of an angle of air supply into the chamber model on hydraulic losses and the flow structure is shown at different air flowrates, relative values of the minimal flow section area of the feeding air intake pipes, under changes of the flowrate of gas simulating gas generation products and geometric model parameters. A technique for measuring the concentration of carbon dioxide simulating IPP gas generation products in the combustion chamber air flow and the results of experimental investigations of a mixture formation process in the combustion chamber model are described.

Numerical investigation of the spray–mesh–turbulence interactions for high-pressure, evaporating sprays at engine conditions

This work presents a numerical methodology to simulate evaporating, high pressure Diesel sprays using the Eulerian–Lagrangian approach. Specific sub-models were developed to describe the liquid spray injection and breakup, and the influence of the liquid jet on the turbulence viscosity in the vicinity of the nozzle. To reduce the computational time and easily solve the problem of the grid dependency, the possibility to dynamically refine the grid where the fuel–air mixing process takes place was also included. The validity of the proposed approach was firstly verified simulating an evaporating spray in a constant-volume vessel at non-reacting conditions. The availability of a large quantity of experimental data allowed us to investigate in detail the effects of grid size, ambient diffusivity and used spray sub-models. In this way, different guidelines were derived for a successful simulation of the fuel–air mixture formation process. Finally, fuel injection and evaporation were simulated in an optical engine geometry and computed mixture fraction distributions were compared with experimental data.

Numerical study of the mixture formation process in a four-stroke GDI engine for two-wheel applications

Guidelines for managing the mixture formation process in a high-performance four-stroke Gasoline Direct Injection (GDI) engine for two-wheel applications are discussed, as derived from a multidimensional modelling of the in-cylinder processes. Gasoline adduction from a multi-hole injector is simulated by resorting to a properly developed model that accounts for the dependence of the initial droplets size distribution upon injection pressure. The model portability is preliminary demonstrated by comparison with experimental measurements carried out on sprays entering a confined vessel at controlled conditions. The simulation of different engine operating conditions highlights the capability to work under the so-called “mixed mode” boosting with spray guided mixture formation.

Correlation of Mixture Formation and Combustion Processes in D.I. Diesel Sprays

Correlation of Mixture Formation and Combustion Processes in D.I. Diesel Sprays

115 二段噴射を用いたディーゼル燃焼において噴射条件が混合気形成と燃焼の過程に及ぼす影響(OS-2 ディーゼル(1))

115 二段噴射を用いたディーゼル燃焼において噴射条件が混合気形成と燃焼の過程に及ぼす影響(OS-2 ディーゼル(1))

Correlation of Mixture Formation and Combustion Processes in D.I. Diesel Sprays

Correlation of Mixture Formation and Combustion Processes in D.I. Diesel Sprays

3D-CFD Simulation of Mixture Formation, Combustion and Heat Transfer Processes with AVL FIRE

Based on selected examples the present status of 3D-CFD related to internal combustion engine applications is presented. The focus is on highlighting the current status of model validation and on demonstrating specific application methodologies using the CFD code AVL FIRE. From the broad area of diesel engine combustion system development, results of the analysis and optimization of mixture formation, combustion and pollutant formation are shown for conventional as well as alternative diesel combustion. The results quality related to the prediction of the in-cylinder pressure trace, heat release rate and pollutants is discussed in the context of related experimental data. In the field of gasoline engine development, the present possibilities related to 3D-CFD calculation of premixed flame propagation for the analysis and optimization of full load SI-engine combustion performance is presented. The applicability of the adopted models as well as their predictive capabilities are demonstrated based upon selected results of calculated flame propagation and knock onset characteristics and comparison of the results with related experimental data. Finally, the possibilities of 3D-CFD in the context of the analysis and optimization of the thermal loading of structural components are presented. The application of novel models for the calculation of the gas- and water-side heat transfer including coupled fluid / thermal calculations is demonstrated for the thermal analysis of the head-block compound of a passenger car SI-engine.

수치해석을 이용한 가솔린연료 분무 거동특성 연구

The focus of this study is placed on the behavior characteristics of gasoline spray under condition field of room temperature and pressure. To analyze the behavior and flow characteristics of injected fuel spray is important in speculation of mixture formation process. Also the exhausted emissions from actual engines can be controlled by the analyzed results. The φ(degree of freedom) and K(energy ratio of particle motion) are selected as the simulation parameter. The factors affect characteristics of spray structure, and the factors are included in the sub-program of the KIVA-II code. In this study, the simulation study by modified KIVA-II code was conducted and the calculated results obtained by the modified KIVA-II code show good agreements with experimental results. As a result, applying the improved TAB model with φ=8 and K=2 to simulation analysis of the KIVA-II code is sufficiently useful for analyzing the macro characteristics in spray structure, such as the spray tip penetration of injected fuel spray.

Study of spray impingement and a squish combustion system for diesel engines

In order to improve fuel/air mixture homogeneity and enhance air motion in the combustion chamber, a new spray impingement and squish combustion system (SISCS) is developed. The mixture formation and combustion processes in three different combustion chambers are simulated using the AVL-FIRE code. Simulation results show that the passage width has great influence on combustion and emissions. Compared with the original engine the NO and soot emissions can be reduced by using the combustion chamber of the case B.

A study of the mixture formation process for a third-generation conical spray applied in HCCI diesel combustion

The purpose of this study is to investigate the mixture formation processes of a third-generation spray (TGCS), an impinging spray that is intended to be applied in mixture preparation for homogeneous charge compression ignition (HCCI) diesel combustion. The spray visualization is performed in a constant-volume vessel by high-speed photography, to investigate the characteristics of the TGCS, and also to provide a validation for numerical models. Then the behaviors of spray and mixture formation process in a constant-volume vessel and diesel in-cylinder conditions were examined numerically by FIRE v8.5 package. Results of the high-speed photography indicated that the TGCS is characterized by a flexible spray tip penetration and circumferential angle, depending on the impinging angle of the TGCS nozzle. Findings of the numerical simulations in a constant-volume vessel under the spray visualization conditions revealed that after the fuel jets had impinged on the guide wall, the TGCS has a much smaller fuel mass fraction compared with a free spray. Furthermore, simulation results under diesel engine conditions demonstrated that for the TGCS, the fuel–air mixture can achieve circumferential homogeneity at 2° CA after the start of injection (ASOI), and form a comparatively homogeneous lean mixture at 20° CA ASOI.

Laser analyses of mixture formation and the influence of solute on particle precipitation in the SAS process

Laser based Raman and elastic light scattering measurements were performed to study the process of mixture formation and the influence of the solute paracetamol onto the phase behaviour of the pseudo-binary system ethanol/CO 2 in the supercritical antisolvent process. From the Raman based technique, mole fraction and partial density distributions of CO 2 were obtained. The mole fraction distributions indicate a rapid mixture formation with fast supersaturation of the solute. At the same time, the increase of the CO 2 partial density at conditions considerably above the mixture critical point (MCP) indicate a change from a homogeneous supercritical to a multi-phase subcritical flow. This phase change goes along with particle precipitation. Thus, the results of our investigations proof, why past approaches failed to generate amorphous paracetamol nanoparticles with the system paracetamol/ethanol/CO 2 above the MCP. Process parameters like injection pressure (20.0–35.0 MPa), chamber pressure of CO 2 (7.5–17.5 MPa), temperature (313–333 K) and solute concentration (0–5 wt%) were varied.

주위조건 변화에 대한 증발 디젤분무 거동특성 연구

디젤자유분무 Diesel-Free Spray( ), 증발분무 Abstract To analyze the mixture formation process of evaporating diesel spray is important for emissions reduction in actual engines. Then the effects of change in density of ambient gas on spray structure in high temperature and pressure field have been investigated in this study. The ambient gas density was changed from ρa=5.0kg/m 3 to ρa=12.3kg/m 3 with CVC(Constant Volume Chamber). Also, simulation study by modified KIVA-II code was conducted and compared with experimental results. The ambient temperature and injection pressure are kept as 700K and 72MPa, respectively. The images of liquid and vapor phase in the evaporating free spray were simultaneously taken by exciplex fluorescence method. As experimental results, with increasing ambient gas density, the tip penetration of the evaporating free spray decreases due to the increase in the drag force from ambient gas. The spatial structure of a diesel spray can be verified as 2-regions consisted of liquid with momentum decrease and vapor with large-scale vortex. The calculated results obtained by modified KIVA-II code show good agreements with experimental results.

증발디젤분무의 혼합기 형성과정에 대한 열역학적 접근

The focus of this work is placed on the analysis of the mixture formation process under the evaporative diesel-free spray conditions. In order to examine homogeneity of mixture within the vapor phase region of the injected spray, image analysis was carried out based on the entropy of statistical thermodynamics. As an experimental parameter, the injection pressure and ambient gas density were selected, and effects of the injection pressure and density variation of ambient gas on the mixture formation process in the evaporative diesel spray were investigated. In the case of application of the thermodynamic entropy analysis to evaporative diesel spray, the value of the dimensionless entropy always increases with increase in time from injection start. Consequently, the dimensionless entropy in the case of the higher injection pressure is higher than that of lower injection pressure during initial injection period.

An investigation of mixture formation and in-cylinder combustion processes in direct injection diesel engines using group-hole nozzles

Mixture properties of the transient fuel spray injected by group-hole nozzles were quantitatively studied in a constant volume chamber via the laser absorption scattering (LAS) technique, and compared with conventional single-hole nozzles. Specific areas investigated included non-evaporating and evaporating ambient conditions, and the conditions of free spray and spray impinging on a flat wall. The particular emphasis was on the effect of one of the key parameters of the group-hole nozzle structure, namely, the interval between orifices. Subsequently, in-cylinder ignition and combustion processes were investigated by direct flame visualization in a single-cylinder optical research engine using the group-hole nozzle and the standard multi-hole nozzle, together with heat release analysis. Results show that the group-hole nozzle can produce a smaller Sauter mean diameter (SMD) of droplets under the non-evaporating condition. Under the evaporating condition, for the free spray cases, there exists a trade-off between the fuel evaporation and the spray penetration in the application of the group-hole nozzle. With the increase in interval between orifices, the ratio of evaporation increases, but the spray tip penetration decreases. For the spray impinging on a flat wall, the group-hole nozzle can enhance the spray tip penetrations to some extent compared with the single-hole nozzles. Flame images taken in a direct injection optical engine show that the enhancement of the fuel atomization and evaporation by the group-hole nozzle may contribute to a decrease in overall flame luminosity level, suggesting reduced soot formation in diesel engines.

An experimental and numerical study on sprays injected from two-hole nozzles for DISI engines

The objective of this study is to investigate the mixture formation process of sprays injected from two-hole nozzles for direct-injection spark-ignition (DISI) engines. Spray characteristics were examined for vapor and liquid mass distributions, spray tip penetration and spray angle using the laser absorption–scattering (LAS) technique and the computational fluid dynamics (CFD) simulation. Other characteristics including: the vapor phase concentration distribution, droplet spatial distribution and pressure distribution were acquired from the CFD simulation results. Comparison of measured and calculated results showed that as the hole-axis-angle (HAA) of the two-hole nozzle decreased, the droplet coalescence increased and vapor mass decreased. The spray with the HAA of 10° had the longest spray tip penetration and the spray with the HAA of 15° had the shortest one. The two jets of the two-hole nozzle spray had a tendency of offsetting to the central region of the spray. From 10 to 15 MPa, the increase in the injection pressure increased the vaporization rate and the spray tip penetration rate very much, but no such tendency was found when the injection pressure increased from 15 to 20 MPa.