Advances in Spray Nozzle Designs for Chemical Application

<div class="htmlview paragraph">A single nano-spark back light photography method has been developed to record the image of non-evaporating diesel sprays injected into high pressure nitrogen gas. Relatively clear image of fine droplets and spray was obtained. An image analysis method has been developed to quantify the droplet characteristics which are in focus, such as droplet size and shape. Spatial and temporal distribution of droplets has been clarified. It was observed that the number of droplets around the nozzle tip region decreases by time, however a large number of droplets were observed at X=13∼25 mm from nozzle tip at t=300∼700 μs from injection start. Double-nano spark photography of diesel sprays was carried out and relatively clear double exposure images of droplets were obtained on the same film. Two dimensional size and velocity measurement of droplets were simultaneously carried out based on these photographs. Distribution of droplets velocity was clarified and used to describe the droplets distribution. It was observed that at early period of injection droplets fly away from the spray at a certain angle. However, by time they lose their radial velocity and start to entrain into the spray.</div> <div class="htmlview paragraph">Variation of droplets velocity persuaded the authors to find out a relation between droplets and ambient gas velocity. Ambient gas around the diesel sprays was seeded by light particles and two-dimensional velocity measurement of ambient gas was carried out using a Particle Tracking Velocimetry (PTV) method. Velocity information of droplets and ambient gas was used to clarify the droplets-gas interaction. According to the results, there are two types of ambient gas flow around the diesel sprays. Around the nozzle tip region, ambient gas entrains steeply into sprays, however a vortex of ambient gas was observed around the spray tip. Maximum velocity of ambient gas was very low and about 1/5 of maximum droplet velocities. The velocity of droplets was also much lower than the penetration velocity of spray.</div>

<div class="htmlview paragraph">An experimental study was conducted to characterize the dynamics and spray behavior of a wide range of minisac and Valve-Covered-Orifice (VCO) nozzles using a high-pressure diesel common-rail system. The measurements show that the resultant injection-rate is strongly dependent on common-rail pressure, nozzle hole diameter, and nozzle type. For split injection the dwell between injections strongly affects the second injection in regards to the needle lift profile and the injected fuel amount. The minisac nozzle can be used to achieve shorter pilot injections at lower common-rail pressures than the VCO nozzle.</div> <div class="htmlview paragraph">Penetration photographs of spray development in a high pressure, optical spray chamber were obtained and analyzed for each test condition. Spray symmetry and spray structure were found to depend significantly on the nozzle type. The minisac class of diesel nozzle definitely exhibits superior characteristics regarding hole-to-hole spray symmetry, whereas the VCO class of diesel nozzles produce a more asymmetric, but more dispersed spray plume, with potentially better fuel-air mixing performance than the minisac nozzle. The dual-guided VCO class of nozzle does not significantly improve the spray symmetry over that of the single-guided nozzle. However measurement of spray tip penetration length shows that the dual-guided VCO nozzle provides higher spray-tip velocities than is achieved for single-guided tips. The results obtained show that the liquid spray tip penetration mainly depends on nozzle type, needle guiding strategy, injection pressure, and ambient gas pressure.</div> <div class="htmlview paragraph">Close to nozzle exit spray dynamics observation was carried out. The microscopic visualization results provide very interesting and dynamic information on spray structure, showing spray angle variations, injection-to-injection variation, and primary breakup processes not observed using conventional macroscopic visualization techniques. The near-field spray behavior is shown to be highly transient, strongly depend on the injector design, nozzle geometry, needle lift and vibration, and injection pressure which is a function of the injection system.</div>

<div class="htmlview paragraph">A multi-zone, direct-injection (DI) diesel combustion model, the so-called RK-model, has been developed and implemented in a full cycle turbocharged engine simulation code. The combustion model takes into account:</div> <div class="htmlview paragraph"> <ul class="list disc"> <li class="list-item"> <div class="htmlview paragraph">transient evolution of fuel sprays;</div> </li> <li class="list-item"> <div class="htmlview paragraph">interaction of sprays with swirl and walls;</div> </li> <li class="list-item"> <div class="htmlview paragraph">evolution of near-wall flow formed after spray-wall impingement depending on impingement angle and swirl;</div> </li> <li class="list-item"> <div class="htmlview paragraph">interaction of near-wall flows formed by adjacent sprays.</div> </li> </ul> </div> <div class="htmlview paragraph">In the model the fuel spray is divided into a number of zones with different evaporation conditions. The piston bowl is assumed to be a body of revolution with arbitrary side shape. Submodels of soot and NOx formation are included. The model has been validated by experimental data obtained for high-speed, medium-speed and low-speed engines over the whole operating range; a good agreement has been achieved without recalibration for different operating modes.</div> <div class="htmlview paragraph">Predictions of spray tip penetration, spray angle and ignition delay were validated by the published data obtained for different diesels including diesels with multiple injection system and injection timing after the TDC. Formulas for computation of these characteristics were derived.</div> <div class="htmlview paragraph">Computational research and optimization of sprayer nozzles orientation for different piston bowl shapes has been performed. Analysis of fuel sprays evolution in contact with walls as well as distribution of fuel in characteristic zones has been done for part load and full capacity. Conclusion about dependence of optimal piston bowl shape on BMEP was made.</div>

<div class="htmlview paragraph">In the past decade, SCR deNOx technology with urea injection has grown to maturity. European OEMs will apply SCR deNOx to meet future heavy-duty emissions legislation starting with EURO-4 (2005/2006). Numerous research programs in Europe and the US have shown a variety of system layouts and control strategies. The main differences are formed by:</div> <div class="htmlview paragraph"> <ul class="list disc"> <li class="list-item"><div class="htmlview paragraph">the engine-out NO<sub>x</sub> calibration</div> </li> <li class="list-item"><div class="htmlview paragraph">the application of an NO to NO<sub>2</sub> catalyst</div> </li> <li class="list-item"><div class="htmlview paragraph">open-loop or closed-loop urea dosage control.</div> </li> </ul> </div> <div class="htmlview paragraph">This paper gives an overview of possible SCR system configurations that are required for different stages of future emission legislation.</div> <div class="htmlview paragraph">Engine-out NO<sub>x</sub> emission is strongly influenced by ambient conditions. Projections in this study show that a combination of cold climate and a wintergrade fuel is the most severe: it may lead to 30% lower engine-out NO<sub>x</sub> emission with respect to laboratory conditions. The varying engine-out NO<sub>x</sub> emission requires a safety margin in the case of an open-loop controlled system in order to avoid excessive NH<sub>3</sub> slip.</div> <div class="htmlview paragraph">Calculations in this paper show that Euro 4 limits can be met with open-loop controlled urea dosage; an NO to NO<sub>2</sub> catalyst is even not required. For other future emission legislation (Euro 5, US 2007 and US 2010), it becomes difficult to safely achieve the limits with open-loop control. US 2007 and 2010 legislation require an NO to NO<sub>2</sub> catalyst because of the low average load and consequently low exhaust gas temperatures. Engines that are developed to meet US 2010 legislation need special measures to increase the exhaust gas temperature and to reduce engine-out NO<sub>x</sub> below 2 g/kWh.</div> <div class="htmlview paragraph">In all cases, optimal hydrolysis and mixing conditions are of major importance. High speed photography and droplet size measurements are presented as methods for characterizing and modeling aqueous urea spray patterns. The information from these measurements is used as input parameters for simulation tools. These consist of a 2D/3D CFD program for urea mixing analysis and a 1D SCR system model for development of dosage control and optimization of catalyst dimension.</div> <div class="htmlview paragraph">Finally, simulations with the SCR system model are compared with measurements on the engine test bench.</div>

<div class="htmlview paragraph">The surroundings around the diesel spray are entrained during the growth of the spray. The mixing process between the evaporated fuel oil and the entrained surroundings, that is, the entrainment, has a significant meaning for the combustion diesel engine. It is difficult to detect the movement of the entrainment because the diesel spray is the gas-liquid two-phase flow and the unsteady phenomenon within a few milliseconds. Then, in order to clarify and to generalize the movement of entrainment, following three experiments were done. 1)Two-dimensional steady water spray -flat spray- injected into the ambient atmosphere, using tuft and hot wire method. 2) Unsteady water jet injected into water, using tracer. 3)single diesel spray injected into the atmosphere with high pressure at room temperature, using smoke wire. According to the experimental results, it is characterized that the movement of the entrainment at the penetration parts of the diesel spray and the unsteady water jet where they show the characteristics of the steady flow is very much similar to that of the steady spray and the gas jet.</div>

<div class="section abstract"><div class="htmlview paragraph">The improvement of vehicle soiling behavior has increasing interest over the past few years not only to satisfy customer requirements and ensure a good visibility of the surrounding traffic but also for autonomous vehicles, for which soiling investigation and improvement are even more important due to the demands of the cleanliness and induced functionality of the corresponding sensors. The main task is the improvement of the soiling behavior, i.e., reduction or even prevention of soiling of specific surfaces, for example, windows, mirrors, and sensors. This is mostly done in late stages of vehicle development and performed by experiments, e.g., wind tunnel tests, which are supplemented by simulation at an early development stage. Among other sources, the foreign soiling on the side mirror and the side window depend on the droplet detaching from the side mirror housing. That is why a good understanding of the droplet formation process and the resulting droplet diameters behind the side mirror is necessary, including all the possible influencing factors. A first fundamental study was already investigated by the authors at a vehicle side mirror using a modified wind tunnel soiling test rig [<span class="xref">1</span>].</div><div class="htmlview paragraph">In the current study, a generic plate with a defined edge for droplet detachment is placed inside the open jet of a calibration wind tunnel. The aim of the investigation is to test different parameters of the detachment process and to analyze the resulting droplet sizes behind the generic edge. Parameters such as the radius of the detachment edge, the liquid, and the volumetric flow rate are varied and their influence on the atomization as well as soiling processes is analyzed using shadowgraphy measuring technique and high-speed video recording.</div><div class="htmlview paragraph">Our results show that the droplet detachment behind a generic plate can be divided into two separate topics: the detachment position and the detachment process. The detachment position is dependent on the air velocity and the edge radius. With an increased radius and an increased velocity, the water can stay longer wall-bound and detach further downstream. The detachment process at the edge shows two different ligament formation processes independent of the air velocity: ligament formation and ligament-bag formation. A secondary breakup process may occur for droplets in the air, where four different processes are observed, covering vibration breakup, bag breakup, bag-and-stamen breakup, and sheet thinning. In all tested variations, most of the droplets show a diameter of about 65 μm.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Proton Exchange Membrane (PEM) Fuel Cell (FC) presents itself as a promising technology in view of zero-tailpipe emission vehicles. In addition, the constant development of renewable energy sources will lead to an increase in green hydrogen availability, and thus completely eliminate emissions for devices that use H2 as an energy vector. However, PEM FCs are still far from being fully developed as a technology: thermal and water management are the main issues that researchers are studying through experiments and Computational Fluid Dynamics (CFD) simulations. For the numerical approach, H2O removal models often consider a simplified flat surface, but the microgeometry of the Gas Diffusion Layer (GDL) has a leading role in determining the critical dimension for droplet detachment and how much resistance the surface poses to water sliding.</div><div class="htmlview paragraph">The aim of this paper is to investigate the influence of droplets number on a GDL. The GDL has been characterized through optical analysis (5 μm/pixel spatial resolution) and the key features of the interlaced structure has been determined by using an approach typical of the textile industry. Droplet size (diameter ranging from 200 to 600 μm) and reciprocal distance have been parametrized and their behavior has been observed under the effect of 10 m/s cross airflow in a closed PEM FC channel layout. A different texture has been generated with the aim of evaluating the influence of the microstructure on water removal rates.</div></div>

<div class="htmlview paragraph">Various single and split injection schemes are studied to provide a better understanding of fuel distribution during cold starting in DI diesel engines. Improved spray-wall interaction, fuel film and multicomponent vaporization models are used to analyze the combustion processes.</div> <div class="htmlview paragraph">Better combustion characteristics are obtained for the split injection schemes than with a single injection. An analysis of the fuel impingement processes identifies the mechanisms involved in producing the differences in vaporization and combustion of the fuel. A greater amount of splashing occurred for the split injections compared to a single injection. This behavior is attributed to the decreased film thickness (less dissipation of impingement energy), the decreased impingement area (obtained by increasing the impingement Weber number), and most importantly, the reduced frequency of drop impingement. In comparison, the single injection scheme resulted in an impingement time between drops (i.e., drop frequency) that was considerably smaller than the time required for splashing. Thus, subsequent impinging drops interfered with the splashing process, resulting in a greater quantity of adhered fuel on the walls. The increased splashing for the split injection schemes reduced the overall droplet size, which further aided vaporization and combustion. The partitioning of the injected fuel and the dwell between injection pulses have shown to provide better combustion characteristics for cold starting.</div> <div class="htmlview paragraph">One common approach to improve startability is to increase the amount of fuel injected. This type of strategy was also modeled. However, the results indicate that better combustion characteristics may be achieved through the optimization of the injection scheme as an alternative to overfueling.</div>

<div class="htmlview paragraph">A study of fuel spray characteristics for diesel fuel from a multi-hole nozzle injector was performed yielding tip penetration length and spray cone angle for each of the spray plumes from a six hole injector. The main feature of the system used was that analysis of all the fuel plumes could occur at one time, as all the plumes were imaged on the same piece of film. Spray behavior was examined for two injection pressures (72 MPa and 122 MPa) and for ambient temperatures up to 523 K (250°C).</div> <div class="htmlview paragraph">The results in this paper show how the spray plumes behave as they leave each of the six holes of the injector. The characteristics of each hole differs during injection. The variations of spray cone angle and tip penetration length between holes are small, but significant. These variations in tip penetration and cone angle changed as the temperature of the chamber changed, but the overall characteristics of the spray plumes changed only slightly for the temperatures used in this paper.</div>

<div class="htmlview paragraph">This paper presents an atomization mechanism of a spray injected into the low-pressure field, as the subject of injection system in a suction manifold of gasoline engine. Pure liquid fuel, which is n-Pentane or n-Hexane is injected into quiescent gaseous atmosphere at room-temperature and low- pressure through pintle type electronic control injector. Fuel sprays are observed by taking photographs for variation of the back pressure and the changes in spray characteristics with the back pressure below atmospheric pressure are examined in detail. In particular, in the case of the back pressure below the saturated vapor pressure of fuel, the atomization mechanism is discussed from a viewpoint of flash boiling phenomena, those are bubble growth rate and so on. The results show that the saturated vapor pressure of fuel is the most significant factor and the spray characteristics can be arranged with the pressure difference between the back pressure and the saturated vapor pressure for various fuels, corresponding to the intensity of the flash boiling. Then, in the case of the back pressure below the saturated vapor pressure, the atomization process can be explained in terms of the nucleation process and the growth rate of cavitation vapor bubbles due to the flash boiling, corresponding to the pressure difference between the back pressure and the saturated back vapor pressure. Further a certain model describing the fuel vapor formation rate is proposed considering the distribution of initial bubble nuclei in the fuel and the bubble growth process, based upon the cavitation bubble analysis in the flash boiling phenomena.<span class="xref">*</span> Number in bracket designate references at end of paper.</div> <div class="htmlview paragraph">RECENTLY, A MULTI-POINT INJECTION SYSTEM has become to be applied in gasoline engines predominantly owing to its high response and control quality of fuel supply. In this system, liquid fuel is injected into the relative low-pressure atmosphere through an electronic control injector. And in some operating conditions of engine, a great deal of unburnt hydrocarbon is emitted with exhaust gas because of its low quality of the spray atomization. Therefore, it is important to reveal the atomization process of the spray injected into the low-pressure field and especially to examine the changes in spray characteristics with the surrounding back pressure with reference to performance and exhaust emissions of the engine.</div> <div class="htmlview paragraph">In general, injected fuel from the pintle type injector appears in the form of fuel film with conical shape near the injector and the breakup of fuel film into droplets is not completed immediately. In fact, aerodynamic forces and the instability of fuel film due to the turbulence provided at the injector exit and the resistance by the atmospheric density cause unstable wave growth leading to the disruption of the film flow resulting to liquid ligaments and to droplets. However, when liquid fuel is injected into the back pressure below the equilibrium pressure, so-called the saturated vapor pressure, for the liquid temperature, the liquid spray disintegrates into fine droplets by evolution of the vapor owing to flash boiling. The flash boiling phenomena, that is vapor bubble growth by cavitation, occur when a liquid, initially in a subcooled state, is rapidly depressed to a pressure below the saturated vapor pressure to initiate a rapid boiling process.</div> <div class="htmlview paragraph">In connection with the flash boiling fuel injection, superheated liquid jets have often been researched as the subject of the study. For instance, Brown & York [<span class="xref">1</span>]<span class="xref">*</span> have described the relation between the droplet mean size and the growth rate constant of the bubbles, and Lienhard & James [<span class="xref">2</span>] have presented the breakup length of the flashing superheated jets. And then, Sudo et al. [<span class="xref">3</span>] have measured the droplet size distribution in Methanol flash boiling spray. Further, the effects of the nuclei number and the idle time of bubble growth rate on the atomization process have been reported by Suzuki et al. [<span class="xref">4</span>], and research on analytical bubble growth rate for practical injectors has been conducted by Oza & Sinnamon [<span class="xref">5</span>].</div> <div class="htmlview paragraph">This study is intended for investigating the atomization mechanism of the spray injected into room-temperature and low-pressure field through a pintle type electric control injector. In particular, the change in spray characteristics with the back pressure below the atmospheric pressure are examined in detail. And, when the back pressure is below the saturated vapor pressure of fuel, the spray characteristics are discussed from a viewpoint of flash boiling, consisting the nucleation process and the bubble growth rate. In addition, a model which describes the fuel vapor formation rate is proposed by considering the distribution of initial bubble nuclei in the fuel and the bubble growth process, based upon the cavitation bubble analysis in the flash boiling phenomena. Experiments were performed using two fuels, n-Pentane and n-Hexane.</div>

<div class="section abstract"><div class="htmlview paragraph">Light-duty diesel vehicles that make use of a diesel particulate filter (DPF) generally require periodic active regenerations. This is achieved by late, in-cylinder post-injections designed to add unburned fuel into the exhaust system to raise the DPF temperature and burn off the soot. These late injections do not atomise and evaporate as readily as during normal combustion causing a portion of this fuel to impinge on the cylinder wall and wash down, with the engine oil, into the sump. This can result in degradation of the engine oil which could lead to increased engine wear and/or engine failure.</div><div class="htmlview paragraph">When investigating which fuel properties have an effect on oil dilution, most literature suggests high final boiling point fuels increase fuel addition rates to engine oil. Through the use of accelerated oil dilution testing on an engine test bench, the findings of this paper suggest that a fuel with low viscosity, density and surface tension, and high front-end volatility (which are linked to fuel spray droplet size and associated in-cylinder droplet evaporation rates) is better correlated with low fuel addition rates to engine oil.</div><div class="htmlview paragraph">Fuel subtraction is where fuel is evaporated out of the engine oil during elevated oil temperatures which is a different phenomenon to fuel addition. Fuel subtraction rates were shown to follow the derivative of the back-end of a fuel's distillation curve (percentage volume distilled with respect to temperature).</div><div class="htmlview paragraph">Blends and neat forms of diesel fuels derived from crude oil, gas-to-liquids (GTL), coal-to-liquids (CTL), rapeseed methyl ester (RME) and soya bean methyl ester (SME) were used. GTL and CTL diesel resulted in significantly reduced oil dilution when compared to the other fuels used in this study.</div></div>

<div class="htmlview paragraph">A diesel spray model has been developed and validated against experimental data obtained for different injection and surrounding gas conditions to allow investigation of the relative importance of the different physical processes occurring during the spray development. The model is based on the Eulerian-Lagrangian approximation and the Navier-Stokes equations, simulating the gas motion, are numerically solved on a collocated non-uniform curvilinear non-orthogonal grid, while the spray equation is solved numerically using a Lagrangian particle tracking method. The injection conditions are determined by another recently developed model calculating the flow in the fuel injection system, the sac volume and injection holes area which accounts for the details of the injection velocity, the fuel injection rate per injection hole and occurrence of hole cavitation. Thus, differences between the sprays from inclined multihole injectors can be simulated and analysed.</div> <div class="htmlview paragraph">Several spray sub-models have been implemented into the code, and their influence on the predicted droplet characteristics was evaluated. These models account for liquid core atomization, droplet secondary breakup, droplet collisions, droplet impingement, droplet turbulent dispersion and droplet evaporation. Aerodynamic-induced atomization, jet turbulence-induced atomization and cavitation-induced atomization introduced by a new sub-model are the three mechanisms considered to be responsible for the liquid core primary break-up; the vibrational, bag, chaotic, stripping and catastrophic break-up regimes are taken into account using different droplet secondary break-up models reported in the literature. A new sub-model based on the maximum entropy formalism is used for the calculation of the droplet size distribution. Coalescence, bouncing and separation are the mechanisms accounting for droplet-droplet interaction and a model assuming isotropic turbulence is used for the calculation of the gas turbulence effects on droplet diffusion. Evaporation has been considered assuming both uniform droplet temperature and its variation within the volume of the droplet. Effects attributed to droplet deformation, as calculated by the break-up model, frequently neglected in other existing spray models, are found to play an important role on the fuel evaporation rate; heat and mass transfer correlations for the flow around spheroids were used for these calculations. In the case of spray impingement on a wall, the rebounding, splashing and sticking regimes were considered, representing different physical assumptions adopted for the simulation of droplet-wall interactions; these models account for the effects of wall roughness, presence of wall film and wall temperature on the properties of the secondary droplets ejected from the wall.</div> <div class="htmlview paragraph">Experimental test cases used for model validation include free atmospheric sprays injected into quiescent or cross flowing air, impinging sprays and diesel sprays in engine cylinders. Extensive comparison between computational and experimental results has been performed for the temporal and spatial variation of the droplet size and droplet velocities, the spray tip penetration and the global spray structure. The results revealed that the dominant parameters influencing diesel spray development and its mixing with the surrounding air are hole cavitation, injection velocity and droplet deformation.</div>

<div class="htmlview paragraph">Hydrocarbon emissions during cold start and subsequent engine warm-up constitute the majority of hydrocarbons emitted during an FTP test. Reducing HC emissions during this portion of the test is necessary to meet current and future HC emissions regulations. This paper summarizes the results of a study which quantified the influence of fuel injector configuration and engine calibration on HC emissions prior to catalyst light-off, in a contemporary four-valves-per-cylinder engine. The fuel-injector parameters investigated included dual versus single spray, air-assist versus non-air-assist, and different spray characteristics (cone angle, droplet size). Control parameters investigated included injection timing, air-fuel ratio, and spark timing. Design and calibration merits were assessed according to combustion stability, cumulative hydrocarbon emissions during cold start and warm-up, and catalyst light-off time.</div> <div class="htmlview paragraph">For all injector configurations tested, closed-intake-valve injection always produced more favorable results than open-intake-valve injection. In addition, when fuel was injected on closed intake valves, neither the use of dual sprays nor air-assist provided significant benefits.</div>

<div class="section abstract"><div class="htmlview paragraph">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. The effects of air flow on spray are clearer by numerical method than that in experimental measurements, the bended spray outline is varied with changing air flow speed, ambient pressure and injection angle, the penetration decreases when the cross-flow speed is increased and better second droplet breakup; Droplet size increases when the ambient pressure is increased, the tiny droplets appears in the area downstream the air flow even after the spray column near nozzle, the coalescence between droplets happens, which case large droplets appear downstream air flow; the small droplets are easy to be mingled with air flow, which is distinct in bottom of spray, the air flow field is also changed by the spray, turbulence appears downstream flow after spray; air flow most enhance the distribution of spray when the spray angle is 90°, decreasing or increasing the spray angle case the more weaken distribution of spray. The numerical results agree with the experimental measurement, it is meaningful to optimize the air flow parameters during design and control.</div></div>

<div class="htmlview paragraph">For better understanding of the in-cylinder combustion characteristics of DME, combustion radicals of a direct injection DME-Fueled compression ignition engine were observed using a spectroscopic method. In this initial report, the emission intensity of OH, CH, CHO, C<sub>2</sub> and NO radicals was measured using a photomultiplier. These radicals could be measured with wavelength resolution (half-width) as about 3.3 nm. OH and CHO radicals appeared first, and then CH radical emission was detected. After that, the combustion radicals were observed using a high-speed image intensified video camera with band-pass filter. All of radicals were able to observe as images with half-width as 6 or about 10 nm. Rich DME leaked from nozzle was burning at the end of combustion. Therefore, the second light emission of C<sub>2</sub> radical after the main combustion was observed. The light of OH emitted all over the DME spray at the combustion started, then the dim light expanded in combustion chamber, so that CH radical emitted at the spray tip. After that the light intensity around the combustion chamber wall became strong with advancing the combustion. The light of NO radical emitted at around the tip of spray, which area seems to be stoichiometric combustion area.</div>