The 2D measurement of soot diameter and number density in a diesel engine using laser induced methods

It is necessary to diagnose accurately the characteristics of soot formation and oxidation in a diesel engine. Whereas past measurement techniques for soot concentration give limited information for soot, laser-based two-dimensional imaging diagnostics have a potential to provide temporally and spatially superior resolved measurements of the soot distribution. The technique using laser sheet beam has been applied to an optically accessible diesel engine for the quantitative measurement of soot. The results provided the information for reduction of soot from the diesel engine. Both LIS (Laser Induced Scattering) and LII (Laser Induced Incandescence) techniques were used simultaneously in this study. The images of LIS and LII showed the quantitative distribution of the soot concentration in the diesel engine. In this study, several results were obtained by the simultaneous measurements of LIS and LII technique. The diameter and number density of soot in combustion chamber of the test engine were obtained from ATDC 20 degree to 110 degree. The soot diameter increased about 37% between ATDC 20 degree and 110 degree. The number density of soot, however, decreased significantly between ATDC 40 degree and 70 degree.     

An investigation on effect of high pressure post injection on soot and NO emissions in a DI diesel engine

NO and Soot trade off is an important challenge for engineers in DI Diesel engines. This paper, introduces multiple injection as a strategy for simultaneous reduction of NO and Soot emissions on a DI diesel engine and also proposes a new concept of variable injection pressure and studies its effect on the engine emissions. To evaluate the benefits of multiple injection strategies and to reveal combustion mechanism, modified three dimensional CFD code KIVA-3V was developed. Results showed that using post injection with appropriate dwell between injection pulses has a great effect on simultaneous reduction of the emissions. Based on computational results, NO reduction formation mechanism in multiple injection strategy is as a single injection with retarded injection timing. It is shown that reduction in soot formation is because of the fact that in split fuel injection the soot, which is producing rich regions at the head of fuel spray, are not replenished by newly injected fuel in post injection pulse. Also increasing injection pressure in post injection will reduce the Soot emission dramatically while NO emission is in control for increase of fuel burning rate in post injection pulse.     

Combustion and radiation characteristics of oxygen-enhanced inverse diffusion flame

The characteristics of combustion and radiation heat transfer of an oxygen-enhanced diffusion flame was experimentally analyzed. An infrared radiation heat flux gauge was used to measure the thermal radiation of various types of flames with fuel, air and pure oxygen. And the Laser Induced Incandescence (LII) technique was applied to characterize the soot concentrations which mainly contribute to the continuum radiation from flame. The results show that an oxygen-enhanced inverse diffusion flame is very effective in increasing the thermal radiation compared to normal oxygen diffusion flame. This seems to be caused by overlapped heat release rate of double flame sheets formed in inverse flame and generation of higher intermediate soot in fuel rich zone of oxygen-fuel interface, which is desirable to increase continuum radiation. And the oxygen/methane reaction at slight fuel rich condition (φ=2) in oxygen-enhanced inverse flame was found to be more effective to generate the soot with moderate oxygen availability.     

Phenomenological combustion modeling of a direct injection diesel engine with in-cylinder flow effects

A cycle simulation program is developed and its predictions are compared with the test bed measurements of a direct injection (DI) diesel engine. It is based on the mass and energy conservation equations with phenomenological models for diesel combustion. Two modeling approaches for combustion have been tested; a multi-zone model by Hiroyasu et al (1976) and the other one coupled with an in-cylinder flow model. The results of the two combustion models are compared with the measured imep, pressure trace and NOx and soot emissions over a range of the engine loads and speeds. A parametric study is performed for the fuel injection timing and pressure, the swirl ratio, and the squish area. The calculation results agree with the measured data, and with intuitive understanding of the general operating characteristics of a DI diesel engine.     

Analytical study on soot formation in a diesel engine

The soot formation inside a diesel engine was studied by the analytical model. The soot is formed from gaseous carbon atoms by the phase change under the saturation condition. This soot model is implemented into the KIVA-3V code. From the results of the model, it is found that the fuel rich core of spray inside a flame is the main source of soot. The effect of injection timing is investigated by the soot model. When the injection timing is advanced, the formation of soot is suppressed because of high saturation pressure. The soot formation is increased when the injection timing is retarded mainly due to the decreased soot oxidation at low cylinder temperature.     

A study on the measurement of temperature and soot in a constant-volume chamber and a visualized diesel engine using the two-color method

In this study, the measurements of soot and temperature were used to investigate the turbulent diesel diffusion flame in a constant-volume chamber and a visualized direct injection (D.I.) diesel engine using the two-color method and a high-speed camera. Through these experiments, we effectively acquired information on the temperature and soot by the two-color method in a turbulent diesel diffusion flame. In addition, this experiment revealed that the KL factor was high on the parts of the chamber where the temperature dropped. On the other hand, the KL factor was low where the temperature increased rapidly. Also, the highest temperatures of the flame in a constant-volume chamber and in a D.I. diesel engine were approximately 2300K and 2400K, respectively. This study suggests the measurement of not only the temperature but also the soot of a diffusion flame of the diesel engine through an optical methodology.     

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.     

Combustion characteristics of a swirl chamber type diesel engine

A numerical model that utilizes Computational Fluid Dynamics (CFD) techniques is simulated for the analysis of a swirl chamber type diesel engine. This research also reveals the effects of swirl chamber passage hole geometry on the combustion characteristics of a swirl chamber type diesel engine depending on the shape, angle, and area of the jet passage. Turbulence kinetic energy is generated by compound effects of the pressure, heat release, NOx concentrations, and soot concentrations. Results show that combustion characteristics are affected by the passage hole areas and the passage hole inclination angles.     

热重分析仪测量柴油机油烟炱含量

利用2950型TGA热重分析仪测量柴油机油中烟炱的含量,以便调整柴油发动机的供油提前角,使机油中的烟炱含量达到规定值。     

Numerical modeling of combustion processes and pollutant formations in direct-injection diesel engines

The Representative Interactive Flamelet (RIF) concept has been applied to numerically simulate the combustion processes and pollutant formation in the direct injection diesel engine. Due to the ability for interactively describing the transient behaviors of local flame structures with CFD solver, the RIF concept has the capabilities to predict the auto-ignition and subsequent flame propagation in the diesel engine combustion chamber as well as to effectively account for the detailed mechanisms of soot formation, NO_X formation including thermal NO path, prompt and nitrous NO_X formation, and reburning process. Special emphasis is given to the turbulent combustion model which properly accounts for vaporization effects on the mixture fraction fluctuations and the pdf model. The results of numerical modeling using the RIF concept are compared with experimental data and with numerical results of the commonly applied procedure which the low-temperature and high-temperature oxidation processes are represented by the Shell ignition model and the eddy dissipation model, respectively. Numerical results indicate that the RIF approach including the vaporization effect on turbulent spray combustion process successfully predicts the ignition delay time and location as well as the pollutant formation.     

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.     

The experimental investigations of recirculated exhaust gas on exhaust emissions in a diesel engine

The effects of recirculated exhaust gas on the characteristics of NOx and soot emissions under a wide range of engine loads were experimentally investigated by using a four-cycle, four-cylinder, swirl chamber type, water-cooled diesel engine operating at three engine speeds. The purpose of this study was to develop the EGR-control system for reducing NOx and soot emissions simultaneously in diesel engines. The EGR system is used to reduce NOx emissions, and a novel diesel soot removal device with a cylinder-type scrubber for the experiment system was specially designed and manufactured to reduce soot contents in the recirculated exhaust gas to the intake system of the engine. The experiments were performed at the fixed fuel injection timing of 4° ATDC regardless of experimental conditions. It was found that soot emissions in exhaust gases were reduced by 20 to 70% when the scrubber was applied in the range of the experimental conditions, and that NOx emissions decreased markedly, especially at higher loads, while soot emissions increased owing to the decrease in intake and exhaust oxygen concentrations, and the increase in equivalence ratio as the EGR rate is elevated.     

Simulation of combustion in a porous-medium diesel engine

The future internal-combustion (IC) engines should have minimum emissions level under lowest feasible fuel consumption. This aim can be achievable with a homogeneous combustion process in diesel engines. We used a porous medium (PM) to homogenize the combustion process. This research studies simulation of a direct-injection diesel engine, equipped with a chemically inert hemispherical PM. Methane is injected into a hot PM, assuming mounted up the cylinder in head. Combustion with lean mixture occurs inside PM. A numerical model of PM engine was carried out using a modified version of the KIVA-3V code. PM results were evaluated with experimental data of unsteady combustion-wave of methane in a porous tube. The results show the mass fraction of methane, CO, NO and temperature in solid and gas phases of the PM and in-cylinder fluid. Also presented are the effects of injection timing and compression ratio on combustion.

     

Soot measurements in a chlorinated counterflow diffusion flame using a laser scattering and extinction technique

The effects of the presence of chlorinated species on soot formation have been studied in laminar diffusion flames burning chlorinated hydrocarbons. Measurements have been made of the structure of a chlorinated laminar, diffusion flame that is stabilized in a stagnation point flow around a porous cylinder. Comparisons have been made between a pure methane flame and a flame of 50% methane and 50% methyl chloride. Temperature profiles were obtained with a thermocouple. Laser Doppler velocimetry was used to measure the velocity of the gas along the streamline. Laser extinction and scattering techniques were employed to characterize the soot aerosol. It was found that the addition of the methyl chloride to methane caused soot production, as measured by the soot volume fraction, to increase by at least an order of magnitude.     

缸内直喷汽油机冷启动燃烧与排放光学试验研究

结合光学单缸机和激光诱导荧光测量技术对直喷汽油机冷怠速工况缸内油气混合与燃烧过程进行了可视化试验研究。试验采用了屋脊形透明缸套和双侧激光,利用统计图像评估方法得到了缸内混合气浓度和燃烧火焰分布图像,通过缸压传感器和燃烧分析仪对燃烧稳定性进行了分析,采用废气分析仪和光学传感器分别对碳氢和碳烟排放进行了分析评估。研究表明：燃烧稳定时燃油与缸套碰壁是碳氢排放产生的主要原因,碳烟排放则主要由活塞顶部燃油碰壁造成;适当推迟第二次喷油时刻有利于点火时刻火花塞附近稳定浓混合气的形成,继而提高燃烧稳定性,同时减少碳氢排放,过迟喷射会导致碳烟明显增加,过早喷射会造成缸内失火,碳氢排放增加。     

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.     

Effects of piston shapes and intake flow on the behavior of fuel mixtures in a GDI engine

The purpose of this study is to investigate the stratification of fuel vapor with different in-cylinder flow, piston cavity and injection timings in an optically accessible engine. Three different piston shapes that are F(Flat), B(Bowl) and R(Re-entrance) types were used. The images of liquid and vapor fuel were captured under the motoring condition using Laser Induced Exciplex Fluorescence technique. As a result, at early injection timing of 270° BTDC, liquid fuel was evaporated faster by tumble flow than swirl flow, where most of fuel vapor were transported by tumble flow to the lower region and both sides of cylinder for the F-type piston. At late injection timing of 90° BTDC, tumble flow appears to be moving the fuel vapor to the intake side of the cylinder, while swirl flow convects the fuel vapor to the exhaust side. The concentration of mixture in the center region was highest in the B-type piston, while fuel vapor was transported to the exhaust side by swirl flow in F and Rtype pistons. At the injection timing of 60° BTDC, the R-type piston was better for stratification due to a relatively smaller bowl diameter than the others.     

A study on the characteristics of soot formation and oxidation in free fuel droplet array

In this study, it was attempted to obtain the fundamental data for the formation and oxidation of soot from a diesel engine. Combustion of spray injected into a cylinder is complex phenomenon having physical and chemical processes, and these processes affect each other. There are many factors in the mechanism of the formation and oxidization of soot and it is necessary to observe spray combustion microscopically. In order to observe with that view, free fuel droplet array was used as an experimental object and the droplet array was injected into an atmospheric combustion chamber with high temperature. Ambient temperature of the combustion chamber, interdroplet spacing, and droplet diameter were selected as parameters, which affect the formation and oxidation of soot. In this study, it was found that the parameters also affect ignition delay of droplet. The ambient temperature especially affected the ignition delay of droplet as well as the flame temperature after self-ignition. As the interdroplet spacing that means the local equivalence ratio in a combustion chamber was narrow, formation of soot was increased. As diameter of droplet was large, surface area of the droplet was also broad, and hence evaporation of the droplet was more active than that of a droplet with relative small diameter.     

Size distributions and number concentrations of particles from the DOC and CDPF

Particulate matters (PM) from diesel combustion comprise the major portion of harmful components of air in urban areas. In this study, the effects of DOC and/or CDPF on the size distributions and catalytic reactions of these nano-sized particles were investigated to clarify the exhaust mechanism and to minimize the emission of the nano-sized PM. Parameters of interest in the investigation included sulfur content of the fuels used, air-fuel equivalence ratio, fuel injection pressure, and the engine speed. The number concentration of the particles in diluted exhaust gas was measured by a SMPS in the diametric range of 10–385 nm. The number of nanometer-sized particles increased when the engine was operated at high equivalence ratio with diesel fuel that contained 500 ppm of sulfur. As the sulfur concentration in the fuel increased, the number of the particles smaller than 30 nm increased upon passing DOC and CDPF in the exhaust system of the common-rail diesel engine.     

Numerical simulation on soot deposition process in laminar ethylene diffusion flames under a microgravity condition

A numerical study on soot deposition in ethylene diffusion flames has been conducted to elucidate the effect of thermophoresis on soot particles under a microgravity environment. Time-dependent reactive-flow Navier-Stokes equations coupled with the modeling of soot formation have been solved. The model was validated by comparing the simulation results with the previous experimental data for a laminar diffusion flame of ethylene (C₂H₄) with enriched oxygen (35% O₂ + 65% N₂) along a solid wall. In particular, the effect of surrounding air velocity as a major calculation parameter has been investigated. Especially, the soot deposition length defined as the transverse travel distance to the wall in the streamwise direction is introduced as a parameter to evaluate the soot deposition tendency on the wall. The calculation result exhibits that there existed an optimal air velocity for the early deposition of soot on the surface, which was in good agreement with the previous experimental results. The reason has been attributed to the balance between the effects of the thermophoretic force and convective motion. This paper was recommended for publication in revised form by Associate Editor Ohchae Kwon Jae Hyuk Choi received his B.S. and M.S. degrees in Marine System Engineering from Korea Maritime University in 1996 and 2000, respectively. He then went on to receive a Ph.D. degrees from Hokkaido university in 2005. Dr. Choi is currently a BK21 Assistant Professor at the School of Mechanical and Aerospace Engineering at Seoul National University in Seoul, Korea. Dr. Choi’s research interests are in the area of reduction of pollutant emission (Soot and NOx), high temperature combustion, laser diagnostics, alternative fuel and hydrogen production with high temperature electrolysis steam (HTES). Junhong Kim received his B.S., M.S., and Ph. D degrees in Mechanical Engineering from Seoul National University in 1998, 2000, and 2004, respectively. His research interests include lifted flames, edge flames, and numerical simulation. Sang Kyu Choi received his B.S. degree in Mechanical Engineering from Seoul National University in 2004. He is a Ph. D student in the School of Mechanical Engineering, Seoul National University. His research interests include edge flames, oxy-fuel combustion, and numerical simulation. Byoung ho Jeon received his B.S degrees in Mechanical Engineering from kangwon University in 1998, and M.S., Ph. D. degrees in Mechanical Engineering from Hokkaido University in 2002, 2008, respectively. Dr Jeon is working at Korea Aerospace Research Institute from 2007. June. as Gasturbine engine developer. Jeon’s research interests are in the area of reduction of pollutant emission (Soot and Nox), High temperature combustion, combustion system (Furnace, Combine Generation system, IGCC, CTL), and Fire safety in building. Osamu Fujita received his B.S., M.S., and Ph. D. degrees in Mechanical Engineering from Hokkaido University in 1982, 1984, and 1987, respectively. Prof. Fujita is currently a Professor at the division of Mechanical and space Engineering at Hokkaido University in sapporo, Japan. Prof. Fujita’s research interests are in the area of reduction of pollutant emission (Soot and Nox), solid combustion, catalytic combustion, high temperature combustion, alternative fuel and fire safety in space. Suk Ho Chung received his B.S. degree in Mechanical Engineering in 1976 from Seoul National University, and his M.S. and Ph. D. degree in Mechanical Engineering in 1980 and 1983, respectively from Northwestern University. He is a professor since 1984 in the School of Mechanical and Aerospace Engineering, Seoul National University. His research interests cover combustion fundamentals, pollutant formation, and laser diagnostics.