An experimental study on spray and combustion characteristics of LPG for application in direct-injection

As an alternative fuel that can be used in SI engines, LPG is a clean fuel with larger H/C ratio compared to gasoline, low CO₂ emission, and small amount of pollutants such as sulfur compounds. In the Spark-ignition (SI) engine, Direct injection (DI) technology can significantly increase the engine volumetric efficiency and decrease the need for a throttle valve. DI allows engine operation with the stratified charge, which enables a relatively higher combustion efficiency. Stratified charge can be supplied to nearby spark plugs to allow for overall lean combustion, which improves thermal efficiency and can cope with problems regarding emission regulations. In this study, a visualization experiment system that consists of visualization combustion chamber, air supply control system, emission control system, LPG fuel supply system, electronic control system and image data acquisition system was designed and manufactured. For all cases for which ignition was successful, flame propagation image was digitally recorded using ICCD camera, and the recorded flame propagation characteristics were examined. This study, in its results, is expected to make a contribution in terms of important data for the design and optimization of a Spark-ignited direct injection (SIDI) LPG engine.

     

An experimental study on the effects of impingement-walls on the spray and combustion characteristics of SIDI CNG

Compressed natural gas (CNG) is regarded as one of the most promising alternative fuels, and maybe the cleanest fuel for the sparkignition (SI) engine. In the SI engine, direct injection (DI) technology can significantly increase the engine volumetric efficiency and decrease the need of throttle valve. During low load and speed conditions, DI allows engine operation with the stratified charge, and the use of extremely lean fuel-air mixture enables relatively higher combustion efficiency. In this study, a combustion chamber with a visualization system is designed. The spray development and combustion propagation processes SIDI CNG were digital recorded. It was found that high injection pressure reduced the ignition probability significantly because of quenching of flame kernel. To improve the ignition probability, three kinds of impingement-walls were designed to help the mixture preparation. It was found that the CNG-air mixture can be easily formed after spray-wall impingement and the ignition probability was also improved. The results of this study can contribute important data for the design and optimization of spark-ignition direct injection (SIDI) CNG engine.     

A study on fuel spray of spark-ignited direct injection engine using laser image technology

One of the important research for developing a spark-ignited direct injection engine is optimization of the fuel spray distribution and air flow field in the cylinder. Therefore, spray pattern and mean fuel droplet size of swirl injector were investigated using Laser Light Sheet Photography and PDPA' respectively. And, for the formation of stratified mixture with adequate strength near a spark plug at injection mode in compression stroke, spray distribution after impingement on flat piston or bowl piston in a transparent motoring engine was visualized for the three different injector positions. KIA Motors Corp.     

An experimental study on the spray characteristics of a dual-orifice type swirl injector at low fuel temperatures

The objective of this study is to investigate the effects of fuel temperature on the spray characteristics of a dual-orifice type swirl injector used in a gas turbine. The major parameters affecting spray characteristics are fuel temperature and injection pressure entering into the injector. In this study, the spray characteristics of a dual-orifice type swirl injector are investigated by varying fuel temperature from — 30°C to 120°C and injection pressure from 0.29 to 0.69 MPa. Two kinds of fuel having different surface tension and viscosity are chosen as atomizing fluids. As a result, injection instability occurs in the low fuel temperature range due to icing phenomenon and fuel property change with a decrease of fuel temperature. As the injection pressure increases, the range of kinematic viscosity for stable atomization becomes wider. The properties controlling the SMD of spray is substantially different according to the fuel temperature range.     

Comparison of experimental and predicted atomization characteristics of high-pressure diesel spray under various fuel and ambient temperature

The aim of this study is to investigate the effects of the fuel temperature and the ambient gas temperature on the overall spray characteristics. Also, based on the experimental results, a numerical study is performed at more detailed and critical conditions in a high pressure diesel spray using a computational fluid dynamics (CFD) code (AVL, FIRE ver. 2008). Spray tip penetration and spray cone angle are experimentally measured from spray images obtained using a spray visualization system composed of a high speed camera and fuel supply system. To calculate and predict the high pressure diesel spray behavior and atomization characteristics, a hybrid breakup model combining KH (Kelvin-Helmholtz) and RT (Rayleigh-Taylor) breakup theories is used. It was found that an increase in fuel temperature induces a decrease in spray tip penetration due to a reduction in the spray momentum. The increase of the ambient gas temperature causes the increase of the spray tip penetration, and the reduction of the spray cone angle. In calculation, when the ambient gas temperature increases above the boiling point, the overall SMD shows the increasing trend. Above the boiling temperature, the diesel droplets rapidly evaporate immediately after the injection from calculation results. From results and discussions, the KH-RT hybrid breakup model well describes the effects of the fuel temperature and ambient gas temperature on the overall spray characteristics, although there is a partial difference between the experimental and the calculation results of the spray tip penetration by the secondary breakup model.     

Steady-flow characteristics and its influence on spray for direct injection diesel engine

Flow and spray characteristics are critical factors that affect the performance and exhaust emissions of a direct injection diesel engine. It is well known that the swirl control system is one of the useful ways to improve the fuel consumption and emission reduction rate in a diesel engine. However, until now there have only been a few studies on the effect of flow on spray. Because of this, the relationship between the flow pattern in the cylinder and its influence on the behavior of the spray is in need of investigation. First, in-cylinder flow distributions for 4-valve cylinder head of Dl (Direct Injection) Diesel engine were investigated under steady-state conditions for different SCV (Swirl Control Valve) opening angles using a steady flow rig and 2-D LDV (Laser Doppler Velocimetry). It was found that swirl flow was more dominant than that of tumble in the experimented engine. In addition, the in-cylinder flow was quantified in terms of swirl/tumble ratio and mean flow coefficient. As the SCV opening angle was increased, high swirl ratios more than 3.0 were obtained in the case of SCV -70ΰ and 90ΰ. Second, spray characteristics of the intermittent injection were investigated by a PDA (Phase Doppler Anemometer) system. A Time Dividing Method (TDM) was used to analyze the microscopic spray characteristics. It was found that the atomization characteristics such as velocity and SMD (Sauter Mean Diameter) of the spray were affected by the in-cylinder swirl ratio. As a result, it was concluded that the swirl ratio improves atomization characteristics uniformly.     

An experiment analysis of MILD combustion with liquid fuel spray in a combustion vessel

Mild combustion is characterized by its distinguished features, such as suppressed pollutant emission, homogeneous temperature distribution, reduced noise, and thermal stress. Recently, many studies have revealed the potential of MILD combustion in various power systems but most studies have been focused on gas phase fuel MILD combustion. Therefore, further study on MILD combustion using liquid fuel is needed for the application to a liquid-fueled gas turbine especially. In this work, we studied experimentally on the formation of liquid fuel MILD combustion under the condition of high dilution by burnt gas generated from a first premixed flame in two stages combustor which consists of the first premixed burner and secondary combustor. In particular, the effects of burnt gas velocity and oxygen level of burnt gas on the formation of liquid fuel MILD combustion were investigated. The results show that as the burnt gas velocity through the nozzle becomes higher, the color of flames was changed from yellow to pale blue and flames became very short. The OH radical measured by ICCD camera was uniformly distributed on the pale blue flame surface and its intensity was very low compared to conventional liquid diffusion flame. As burnt gas velocity is increased, local high-temperature region appeared to be diminished and the flame temperature became spatially uniform. And CO emission was sampled around 1 ppm and NOx emission was measured around 10 ppm under the overall equivalence ratio of 0.8 to 0.98 for 40 mm or less diameter of velocity control nozzle. This low NOx emission seems to be attributed to maintaining the average temperature in secondary combustor below the threshold temperature of thermal NOx formation. In view of the uniform temperature distribution, low OH radical intensity and low NOx emission data in the secondary combustor, formation of stable MILD combustion using kerosene liquid fuel could be verified at high burnt gas velocity.

     

An experimental study on combustion processes and nox emission characteristics of the air-staged burner

The combustion processes and emission characteristics in air-staged burner have been experimentally studied. The light fuel oil doped with pyridine(C₅H₅N) is used to investigate the fuel NO_X emission characteristics. Experiments are carried out for a wide range of operating conditions of single-staged and multi-staged burner. The detailed discussions are made for the flame structure of the air-staged burner as well as effects of excess air ratios, staged air flow percentage, and spray conditions on flame pattern and NO_X emission characteristics.     

A study on the characteristics of spray and combustion in a HCCI engine according to various injection angles and timings

Premixed diesel engines have the potential to achieve a more homogeneous, leaner mixture near TDC compared to conventional diesel engines. Early studies have shown that the fuel injection timing and injection angle affect the mixture formation in a HCCI (Homogeneous Charge Compression Ignition) engine. Therefore in this study, we investigated the relationship between combustion and mixture formations accordance with injection conditions in a common rail direct injection type HCCI engine using an early injection strategy. From this results, we found that the fuel injection timing and injection angle affect the mixture formation and in turn affect combustion in the HCCI engine. In addition, this study revealed that the injection angle of 100° is effective to reduce smoke emission without any sacrificing power in the early injection case.     

Atomization characteristics and prediction accuracy of LISA-DDB model for gasoline direct injection spray

In this paper, the spray atomization characteristics of a gasoline direct-injection injector were investigated experimentally and numerically. To visualize the developing spray process, a laser sheet method with a Nd :YAG laser was utilized. The microscopic atomization characteristics such as the droplet size and velocity distribution were also obtained by using a phase Doppler particle analyzer system at the 5 MPa of injection pressure. With the experiments, the calculations of spray atomization were conducted by using the KIVA code with the LISA-DDB breakup model. Based on the agreement with the experimental results, the prediction accuracy of LISA-DDB breakup model was investigated in terms of the spray shapes, spray tip penetration, SMD distribution, and axial mean velocity. The results of this study provides the macroscopic and microscopic characteristics of the spray atomization, and prediction accuracy of the LISA-DDB model.     

An investigation on the spray characteristics of DME with variation of ambient pressure using the common rail fuel injection system

We investigated the DME spray characteristics about varied ambient pressure and fuel injection pressure using the common rail fuel injection system when the nozzle holes diameter is varied. The common rail fuel injection system and fuel cooling system were used since DME has compressibility and vaporization at atmospheric temperature. The fuel injection quantity and spray characteristics were measured. The spray was analyzed for spray shape, penetration length, and spray angle at the six nozzle holes. There are two types of injectors: 0.166 mm diameter and 0.250 mm diameter. The ambient pressure, which was based on gage pressure, was 0, 2.5, and 5 MPa. The fuel injection pressure was varied by 5 MPa from 35 to 70 MPa. By comparing with the common injector, using the converted injector it was shown that the DME injection quantity was increased 127% but it didn??t have the same low heating value. Both the common and converted injectors had symmetric spray shapes. In case of converted injector, there were asymmetrical spray shapes until 1.2 ms, but after 1.2 ms the spray shapes were symmetric. Also, the converted injector had shorter penetration length and wider spray angle than the common injector.     

An experimental study on the combustion characteristics of a low nox burner using reburning technology

The combustion characteristics of a low NO_x burner using reburning technology have been experimentally studied. The reburn burner usually has three distinct reaction zones which include the primary combustion zone, the reburn zone and the burnout zone by provided secondary air. NO_x is mainly produced in a primary combustion zone and a certain portion of NO_x can be converted to nitrogen in the reburn zone. In the burnout zone, the unburned mixtures are completely oxidated by supplying secondary air. Liquefied Petroleum Gas (LPG) was used as main and reburn fuels. The experimental parameters investigated involve the main/ reburn fuel ratio, the primary/secondary air ratio, and the injection location of reburn fuel and secondary air. When the amount of reburn fuel reaches to the 20-30% of the total fuel used, the overall NO reduction of 50% is achieved. The secondary air is injected by two different ways including vertical and parallel injection. The injector of secondary air is located at the downstream region of furnace for a vertical-injection mode, which is also placed at the inlet primary-air injection region for a parallel-injection mode. In case of the vertical injection of the secondary air flow, the NO_x formation of stoichiometric condition at a primary combustion zone is nearly independent of the reburn conditions (locations, fuel/air ratios) while the NO_x emission of the fuel-lean condition is considerably influenced by the reburn conditions. In case of the parallel injection of the secondary air, the NO_x emission is sensitive to the air ratio rather than the fuel ratio and the reburning process often coupled with the multiple air-staging and fuel-staging combustion processes.     

An investigation of the spray characteristics of diesel-DME blended fuel with variation of ambient pressure in a constant volume combustion chamber

We compared the spray characteristics of a typical fuel (100% diesel, DME) and diesel-DME blended fuel in a constant volume combustion chamber (CVCC). The typical fuel (100% diesel, DME) and diesel-DME blended fuel spray characteristics were investigated at various ambient pressures (pressurized nitrogen) and fuel injection pressures using a common rail fuel injection system when the fuel mixture ratio was varied. The fuel injection quantity and spray characteristics were measured including spray shape, penetration length, and spray angle.     

An experimental study on the effects of spring stiffness on the combustion and dynamic characteristics of a linear engine

We investigated the effects of the stiffness of springs applied to linear compressor chambers experimentally. The applied springs could prevent conflict between the engine piston head and engine head cover as well as be available to save the regenerative energy. The linear engine bore size was 30 mm, the maximum stroke was 31 mm and effective stroke volume of a cylinder was 25.45 cc. The spring stiffness was varied: 0, 0.5, 1.00, 2.9 and 14.7 N/mm. The linear engine was fueled with a pre-mixture combined with LPG (propane 99%) and air. As an experimental result, higher spring stiffness affected growth in regenerative energy and stroke. Also, IMEP was increased by rising stroke. Finally, increased IMEP and regenerative energy made more electricity than no spring.     

An experimental study on CWM combustion in fluidized bed combustor

In this study, CWM is combusted and combustion phenomena are investigated in fluidized bed combustor which has 140mm I.D. and 2300mm height. The bed material is sand of mean diameter 0.405mm and fixed bed height is 200mm. CWM is injected either over-or in-bed through water-colled injector by positive displacement pump. The exhaust gas composition, the elutriation rates, and the unburned carbon contents in elutriated ash are measured. The combustion efficiencies are also investigated according to the CWM injector locations, excess air ratios, and air preheat temperatures. When CWM injector is used, the combustion of CWM is proceeded in agglomeration condition regardless of the CWM injector positions. The contents of unburned carbon and the elutriation rates are lower for the case of over-bed injection than for in-bed injection. And the combustion efficiencies according to the excess air ratios show the same tendency regardless of the positions of CWM injector, when the fluidizing velocities are low.     

An experimental study on ejection forces of injection molding

In injection molding, the ejection forces decrease when the surface roughness of mold decreases. However, the ejection forces increase contrary in the area of surface roughness is less than 0.2 μmRa. Several kinds of PVD films are coated on the mold cores to prevent the increasing of ejection forces. Some of these PVD films showed effective prevention of increasing of ejection forces.     

The experimental study of atomization characteristics of gasoline spray impinging on glow plug

In order to reduce the exhaust emissions of a spark ignition engine, it is important not only to improve the catalyst conversion efficiency, but also to directly reduce the engine-out exhaust emissions during a cold starting of the engine and warm up periods. The purpose of this study is to evaluate feasibility of a glow plug for an early fuel evaporator. In order to promote atomization, gasoline is injected on the glow plug with room temperature (20°C) and high temperature (250°C). To analyze the spray behavior characteristics, a PMAS is used to measure the SMD and the dropsize distribution of an impinging spray and a free spray. Results show that the evaporation rate of the impinging spray on the high temperature surface of the glow plug was higher than that of the free spray on the room temperature surface.     

Effect of the injection parameters on diesel spray characteristics

The characteristics of the diesel spray have affected certain aspects of engine performance, such as the power, fuel consumption, and emissions. Therefore, this study was performed to investigate the effects of various injection parameters. In order to obtain the effect of injection parameters on diesel spray characteristics, the experiment is performed by using a high temperature and pressure chamber. The behaviors of the spray are visualized by using a high speed video camera, spray angle, penetration, and various other things.     

Numerical and experimental study on hollow-cone fuel spray of highpressure swirl injector under high ambient pressure condition

A hybrid breakup model was proposed as a trustworthy prediction of hollow-cone fuel spray in the present study and the atomization process of the hollow-cone fuel spray of a high-pressure swirl injector in a Gasoline Direct Injection (GDI) engine under high ambient pressure conditions was studied by a new hybrid breakup model. The proposed hybrid breakup model is composed of the Linearized Instability Sheet Atomization (LISA) model as a primary breakup process. The Aerodynamically Progressed Taylor Analogy Breakup (APTAB) model, instead of the Taylor Analogy Breakup (TAB) model, was used as a secondary breakup process. The effects of the droplet deformation on a droplet aerodynamic external force are considered in the APTAB model. In addition, we replaced the x ² distribution function used in previous the APTAB model by the Rosin-Rammler distribution function to improve the prediction precision. The Laser Induced Exciplex Fluorescence (LIEF) technique and the Phase Doppler Anemometry (PDA) system were used to produce a set of experimental data for the model validation. The estimation of the prediction ability of the LISA+APTAB model was carried out, and spray characteristics, which are difficult to obtain by experimental method, were calculated and discussed. The suggested hybrid breakup model showed better prediction capability compared with the previous model (LISA+TAB model). From the calculated results, the effect of the ambient pressure on the SMD (Sauter Mean Diameter) and droplet velocity could be discussed quantitatively.     

The effect of injection pressure and fuel viscosity on the spray characteristics of biodiesel blends injected into an atmospheric chamber

An experimental study was conducted to examine the effect of injection pressure and fuel type on the spray tip penetration length and the angle of spray injected into atmospheric chamber. The objective of the present study is to formulate empirical correlations of the spray tip penetration and the spray angle for non-evaporative condition. The experiment was performed by a common rail type high-pressure injector for the diesel engine at the injection pressure 40??100 MPa and four different fuels (D100, BD25, BD45, and BD65). The results showed that the biodiesel content increased the spray tip penetration and decreased the spray angle. The correlation of spray tip penetration is expressed for each region before and after spray break-up time in terms of injection pressure, fuel viscosity and time after start of injection. The correlation is also obtained for spray angle equation terms of injection pressure and fuel viscosity.