Laser-induced fluorescence (LIF) for quantitative fuel concentration measurements in a combustion engine is a challenging task. Measuring close to the walls of the combustion chamber is even more challenging as both the incident laser light and the signal are strongly reflected on the walls of the combustion chamber. By using a new technique called Structured Laser Illumination Planar Imaging (SLIPI) such background effects, as well as unwanted multiply scattered light, can be suppressed allowing for higher measurement accuracy. In this article we demonstrate, for the first time, the feasibility of the SLIPI technique for gas phase LIF and in-cylinder measurements. Results from regular LIF and SLIPI measurements are also compared. The measurements were made on a non-reacting fuel-jet with acetone as a fuel tracer in a heavy duty diesel engine (Scania D12). It is observed that the equivalence ratio measured by SLIPI in the free part of the jet is only two thirds of that measured by regular LIF during the early jet development.

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Injection systems of modern diesel engines are the key to increase the fuel efficiency and to lower pollutant emissions. Therefore, a detailed understanding of the spray generated by the injector nozzle is crucial to optimize the process of the mixture formation and thus the combustion process. Up to now, the spray behavior in the near nozzle field is not completely understood. Standard optical diagnostic methods are known to fail visualizing the near nozzle region due to the high optical density of the diesel spray. One approach to address this challenge is the optical connectivity method, described by Charalampous et al.. It can be used to measure the length of the continuous liquid jet core in sprays. Here, the laser light is directed through the injection nozzle to illuminate the liquid jet internally. The spray breakup interrupts a further light transfer and thus limits the illuminated area to the liquid core. While so far a specially designed injector was necessary, in this work a new approach is invented where the laser light is guided by an optical fiber into the sack hole through one of the injector holes of an unmodified stock injector. The feasibility of this approach is demonstrated on a heavy duty diesel injector with fuel pressures up to 80 MPa, being adapted to the large high pressure injection chamber of the Institute of Technical Combustion in Hannover. Other than in, no additional tracer fuel was necessary, as the direct stray light yielded enough signal intensity. First results of the transient behavior of the liquid core length are discussed.

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In order to control the ignition timing and overall combustion rate of HCCI, it is important to have a firm understanding of the chemical reactions of fuel because HCCI can be characterized as controlled chemical auto-ignition process. One technique that can be employed to gain a better understanding of the HCCI combustion process is chemiluminescence, which is the light emission from the excited state of intermediates or radicals. The objective of this study is to experimentally investigate the correlation between chemiluminescence of the active species, which play important role in the ignition, and HCCI combustion characteristics for providing the way to control auto-ignition process. In addition, a combination of experimental and computational results is employed. The experiments were conducted using optical accessible engine, photo-multiplier and band-pass filters. Senkin application of the CHEMKIN-II kinetics rate code was used for computation. As the result, there was a precise correlation between the rate of heat release and chemiluminescence intensity of OH (307.4 nm) and all band (350-700 nm) by tracing the in-cylinder mass-averaged. The start timing of emitting luminescence in OH coincided with H_2O_2 dissociation, and the peak timing of emitting luminescence in all band corresponded to the CO-O recombination spectrum.

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In this work, the in-nozzle flow and primary breakup of fuel nozzles applied in large two stroke engines was analyzed by combined RANS and LES simulations. Intensive investigations have been performed to describe the influence of geometrical design features and flow conditions inside the nozzle on the droplet diameters, velocities and locations of origin. It is shown that the spray and droplet formation in large two stroke engines is highly unsymmetrical and depends on the nozzle geometry, location of the orifice and also on the upstream flow conditions. Disturbances and a sharp redirection of the flow into the nozzle orifice lead to a deflection of the dense fuel core, while an eccentricity of the nozzle bore induces a wrinkling up and rotation of the dense core around its central axis. Both phenomena lead to an asymmetrical disintegration of the liquid core. To describe the primary breakup and the aforementioned phenomena in CFD in-cylinder simulations, prior in-nozzle flow LES simulations are realistically not manageable and inefficient, as they require extensive computational effort. Hence, a statistical model to describe the primary breakup in Lagrangian spray simulations is introduced. Depending on thermodynamic conditions and nozzle geometry, droplet parcels are generated around the dense core by using probability density functions (PDF) for the droplet diameter, velocity and location. The PDFs as well as correlations for the dense core length, deflection of the spray and mean droplet diameter were derived from LES simulations.

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The KIVA-Waseda code which is based on the KIVA-3V and added the KH-RT spray model, the PaSR combustion model and other sub-models can predict pressure and ROHR histories of new generation diesel engines with a high pressure common rail injection system for passenger cars. Exhaust emissions, NO and soot, however still can not be predicted within acceptable precision. Thus the PaSR model was changed to chemical equilibrium calculation with Livengood-Wu integral and NO and soot prediction models. This modification is favorable to estimate engine performance and exhaust emission levels in practical time and precision. It is underlined that the method of solving chemical equilibrium using chemical species maps is unique. And furthermore, the KIVA code is coupled with an engine simulator which includes one-dimensional intake and exhaust gas dynamics simulation. Then this computational system is able to predict complete pressure histories during intake, compression, expansion and exhaust cycles, and eventually enables to figure out the engine performance by IMEP. The calculation results and the overview of the calculation system are shown here.

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In the last two decades, piston engine specifications have deeply evolved. Indeed, new challenges nowadays concern the reduction of pollutant (EURO, Tier, Japanese regulations) and CO2 emissions. To satisfy these new requirements, powertrains have become very complex systems including a large number of high technology components (high pressure injectors, turbocharger, Exhaust Gas Recirculation (EGR) loop, after-treatment devices...). A global CO2 emission decrease can also be achieved with an increasing use of oxygenated fuels. These two main ways of powertrain development require more complex control strategies. Few years ago, engine control strategies were mainly defined by experiments on engine test benches. This approach is not adapted to the complexity of future engines: on the one hand, tests are very expensive and on the other hand, they do not give many information to understand interactions between components. Today, a promising alternative to tests is the use of 0D/1D simulation tools. These methods have been widely used in the past ten years and allow to build engine control algorithms. However, they are generally based on empirical models and often suffer from a lack of predictivity. A solution for extending the range of application of the system simulation consists in developing more physical models based on the 3D calculations experience. This way has been recently followed at IFP Energies nouvelles, leading to the development and implementation of combustion and pollutant emissions models based on detailed tabulated chemistry methods, for both compression-ignition (CI) and spark-ignition (SI) engines. In this paper, a detailed description of an innovative tabulated chemistry method to predict CO and NOx emissions is proposed. Applications of this approach for both CI and SI combustions are presented and some validations are discussed, pointing out the combustion heat releases and cylinder pressures, but also the evolution of the pollutant emissions in front of load variations, in comparison with experimental data.

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This paper reports on the application of a simulation based Engine - Fuel Test Bench (EFTB) for studying performance of Diesel engine running on different fuels. The test bench is built around a zero-dimensional (0D) direct injection stochastic reactor model (DI-SRM) for engine in-cylinder processes simulation. Detailed kinetic models of fuel oxidation are used for emissions prediction. A general purpose optimizer supports the overall simulation process. To demonstrate capabilities of the test bench four different fuels have been simulated and compared to each other under Diesel conditions. Pure n-decane, pure n-heptane and blends of n-heptane with iso-octane and with toluene have been considered as of relevance to diesel fuel. The in-cylinder pressure, heat release rate, and exhaust emissions were the primary tracked engine parameters. Thanks to the low CPU costs, detailed description of fuel oxidation and high level of automation, the presented test-bench is well suited to investigate various aspects of engine-fuel interaction. In an efficient manner it allows comparing engine output performance and emissions depending on the applied fuel.

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The spray atomization mechanisms under the common conditions for Diesel engines are very complex and not completely understood. At the same time the detailed spray information is necessary to provide a better control of the combustion process. The main difficulty of numerical spray simulation is the correct representation of the two characteristic zones of the spray: dense near the nozzle and dilute downstream. Combining the advantages of Eulerian and Lagrangian approaches, ELSA model is able to continuously predict the whole spray evolution. In the dense zone the spray and its gaseous environment are presented as an effective single-phase fluid with a highly variable density. To describe the liquid dispersion, transport equations for the liquid mass fraction and for the liquid/gas interface density are solved. The transition to the Lagrangian calculation is applied when the spray is considered to be enough diluted. This complete Eulerian-Lagrangian spray atomization model has been implemented into the computational fluid dynamics code STAR-CD. The model implementation was validated by comparing predicted liquid and vapor penetrations with experimental data reported in literature. Once validated, the ELSA model was coupled with an inside nozzle simulation to study the impact of internal nozzle flow (geometry, cavitation formation) on the spray and its characteristics. Finally, the coupling with the ECFM-CLEH combustion model has been completed in this work. ECFM-CLEH stands for Extended Coherent Flame Model with Combustion Limited by Equilibrium Enthalpy. It simulates the different phases of Diesel combustion i.e. the auto-ignition, the premixed and the diffusion flame. In the premixed phase, combustion is mainly controlled by flame propagation while fuel and air mixing play an important role in the diffusion phase. The auto-ignition is modeled from tabulated fully detailed chemistry. The tabulated TKI (Tabulated Kinetics for Ignition) strategy proposed by IFP in combination with a presumed PDF using the temperature fluctuations for integration is used. Also a special attention has been made to improve the NOx formation considering the extended Zeldovich thermal NO. The set of sub-models presented above has been implemented in STAR-CD. Applications and validations for a full DI Diesel combustion process have been performed for typical automotive DI Diesel engines with variation of EGR level, Injection Timing and injector's nozzle diameter.

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A method has been developed that allows for performing reactive flow simulations using conditional moment closure (CMC) without spatial dimension reduction of the CMC grid. The CMC is performed for a progress variable and the emission scalars, using a progress variable parameterization of the combustion chemistry. The method has been implemented into a CFD software package. The proposed method has been tested for a simple spray bomb case, n-heptane spray injection into a constant volume vessel, and compared with the interactive flamelet model.

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A modified CFD code based on the KIVA family of codes incorporating several strategies for reducing the computational time required for diesel engine simulations is presented. These strategies, all of which may be applied simultaneously, include the following: (1) a dynamic maximum time step model, (2) spray models that reduce mesh dependencies, (3) a coarse axisymmetric non-polar sector mesh with relatively uniform cell sizes, (4) a parallel CHEMKIN combustion model using MPI with load balancing, and (5) a radius of influence chemistry cell grouping method. The average wall time required for a simulation of a Mitsubishi Heavy Industries heavy-duty diesel engine from IVC to EVO is reduced from 60 hours to 40 minutes through the use of 12 processors and the strategies described in this paper.

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In this study, a first application of a high fidelity Conditional Moment Closure (CMC) combustion model is presented for autoigniting Diesel sprays with dimensions and time-scales of large marine Diesel engines. Results have been compared with data available from an optically accessible large two-stroke marine Diesel engine reference experiment. A one-hole co-axial injector with an orifice diameter of 0.875 mm was employed. Four different test cases have been considered, where the gas temperature at start of injection (SOI) ranges from 730 to 910 K and the ambient density was kept constant at 33 kg/m^3. Validation is performed by means of ignition delay time, ignition location and flame lift-off length. Ignition delays were over/underpredicted by within 9 and 23 percent, whereas the highest errors for the flame lift-off length amounted to 13 percent. The trend of the ignition spot shifting to downstream locations for lower temperatures was correctly reproduced, while the accuracy of the predictions was within 40 percent. Experimental images of OH* chemiluminescence confirmed a flame region consistent with the simulation and the lateral deviation of the spray due to the characteristic swirling environment was well reproduced. The good agreement reported suggests that CMC is capable to reproduce the complex phenomenology of a lifted autoigniting spray flame also for a large injector size.

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A numerical model to predict pre-ignition phenomena in spark ignition engines is presented. The model is based on using a detailed chemistry model of a primary reference fuel (PRF) for gasoline. In order to save computational costs for calculating auto-ignition elementary reaction, a zonal chemistry approach is employed, thereby being able to simplify the description of the cylinder thermodynamic space. The model is embedded into a general CAE tool-chain including CFD for charge motion and mixture formation prediction and FEA heat load analysis for accurate wall temperature determination. By means of this approach, physical mechanisms due to the influence of hot surfaces and the effect of evaporated lubrication oil on promoting auto-ignition effects are numerically studied. Furthermore, other phenomena as the sensitivity study of stochastically occurring events are discussed. Results of the chemistry predictions are compared to experimental measurements from the single cylinder engine test bench.

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An accurate in-cylinder combustion model for SI-engines has been constructed by combining a stochastic reactor model with predictive turbulent flame propagation. The computational time for full cycle calculations is kept low through load balanced parallelization and particle clustering. This paper presents a two-zone zero dimensional transported probability density function model, utilizing a stochastic reactor for solution of the ordinary differential equations in each zone. A turbulent flame propagation model is applied, and laminar flame speed is achieved from a flame speed library built with detailed chemistry. The flame front is tracked with a CPU efficient polygon method. Knock and emissions are calculated using on-line detailed chemistry. The model has previously shown very good predictability of combustion as well as knock. In this work, the model calculation time has been decreased through load balanced distribution of the on-line chemistry calculations on a large number of CPU's. In addition, an algorithm for chemical state based particle clustering in each zone has been developed. Particles are clumped into groups based on user provided dispersion thresholds for any number of cluster tracking parameters. As a consequence, not all particles need to be treated during the chemistry step; only one cluster representative particle needs to be passed to the chemistry solver. The paper presents the clustering algorithm, and its verification. It is shown that a very limited number of clustering parameters can be used, and that the dispersion thresholds can be set high. On average, the clustering yields a factor 3-4 in speedup of chemistry calculations and CPU times of about a minute per cycle are achieved. Since chemistry and in-homogeneities are taken into account this yields a model suitable for e.g. fuel analysis and performance studies.

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In this work the G-equation combustion model has been implemented into StarCD code and coupled with an ODE-kinetic solver for predicting knock in a DISI engine based on the Shell autoignition model. The combustion model has been validated for selected engine operating points. A mesh sensitivity analysis highlighting the influences of mesh topology and grid type (hexahedral and polyhedral) is presented. To account for sensitivities of octane number and EGR ratio on knock behaviour, the governing parameters of the Shell model have been identified and optimized with the help of DoE. The knock models presented here can be operated in both a passive and an active way. The validation of both knock models with respect to temporal and local knock onset is done with fibre optical spark plug measurements and evaluation of statistical results of pressure trace analysis for a direct-injection spark-ignition engine. Both passive and active knock model approaches are compared in regards of pros and cons as well as engine performance. Finally the necessity of thin turbulent flame brushes realized with G-equation combustion model and their relevance for knock simulation is discussed.

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Combustion behaviors of gasoline rotary engines (hereinafter referred to as "RE") are different from those of reciprocating engines (that is conventional engines, and hereinafter referred to as "CE"), due to differences in its operating principle. So understanding of RE unique phenomena is essential to improve its thermal efficiencies. Thus, in order to understand the mechanism of RE combustion, Mazda has analyzed heat balance calculated from engine indicated pressure, visualized combustion state on a bench test engine, simulated their combustion properties, and created a combustion simulation model based on these experimental results. This paper will introduce findings from these activities, points of observations on characteristics of RE combustion, and examples of combustion improvements.

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One-dimensional flame propagation and the behavior of the end gas in a constant volume tube-shaped vessel were observed with schlieren and direct photography for n-C_7H_<16>/O_2/Ar mixtures in order to investigate the knock phenomea. The experiments were carried out varying the initial temperature from 430 to 550 K. The strong pressure oscillation occurred at 480K. The occurrence of low temperature flame in the end gas and the deceleration of the propagation flame formed by the spark ignition were observed before the occurrence of pressure oscillation. The intense light emission which was considered to be caused by the auto-ignition or the rapid flame propagation occurred near the flame formed by the ignition. The auto-ignition near the flame formed by ignition or the rapid flame propagation seemed to cause the pressure oscillation. The occurrence of the auto-ignition or the rapid flame propagation followed by pressure oscillation was discussed based on the properties of ignition delay obtained by the numerical simulations.

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Knocking characteristics for various flame propagation velocity was investigated by changing turbulence in the combustion chamber. The use of the super rapid compression machine (SRCM) provides an opportunity to investigate the behavior of intense knocking. The behavior of flame propagation and spontaneous ignition of end gas were observed and flame propagation velocity and the volume fraction for flame propagation could be estimated through the experiments using a high-speed direct and schlieren photography. As a result, it was found that knocking intensity takes peak value in the cases where the volume fraction for flame propagation is 60-70%, when the volume fraction was changed by changing flame propagation velocity. In the highest flame propagation velocity case, compression and combustion time corresponded to engine speed of about 6000 rpm. The wrinkles in schlieren images of end gas and pressure oscillation caused by heat release of low temperature reaction appeared before knocking occurrence. On the other hand, they did not appeared in high flame propagation velocity cases.

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Conversion of pollutants in the catalyst initiates when a minimum catalyst temperature is reached. Retarding the ignition timing beyond top dead centre firing is a widely used method for effective catalyst heating using the engine exhaust enthalpy. The emissions during these first seconds of engine use dominate cumulative tailpipe emissions over typical drive cycles. Furthermore, downsizing, combined with turbocharging, leads to extended catalyst light-off times, as the exhaust enthalpy must also heat the turbocharger casing. However, future legislation will tighten the emission standards. In particular, the particulate emissions of gasoline direct injection engines have increased in importance in recent years, primarily because the number of particles emitted by a vehicle will be regulated by the upcoming Euro 6 exhaust gas emission standards. This paper discusses the impact of injection pressures above the standard of 200 bar on the catalyst heating operation. Direct injection with a centrally positioned injector enables a wide range of parameters for both injection splitting and injection timing. For example, the possibility to inject a small quantity of fuel close to the ignition timing stabilizes ignition and combustion robustness but also can increase soot formation. So, optimizing mixture formation by managing evaporation rates and fuel penetration depths is essential to avoid or minimize particle formation, especially under cold engine conditions. Increasing the injection pressure is a promising approach to improve the catalyst heating performance of gasoline direct injection spark ignition engines while maintaining low particulate emissions.

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An experimental study was carried out to investigate the effects of injection timing on spray and combustion characteristics in a spray guided direct injection spark ignition (DISI) engine under lean stratified operation. In-cylinder pressure analysis, exhaust emissions measurement, and visualization of the spray and combustion were applied. Combustion in a stratified DISI engine was found to have combustion characteristics of both lean premixed and diffusion controlled flame. The stratified mixture characteristics corresponding injection timing condition was verified as a dominant factor of these flame characteristics. For the early injection timing, non luminous blue flame and low combustion efficiency were observed due to the lean homogeneous mixture formation. On the other hand, luminous sooting flame was shown at the late injection timing because of under-mixed mixture formation. In addition, smoke emission and incomplete combustion products were increased at the late injection timing due to increased locally rich area. On the other hand, nitrogen oxides (NOx) emissions were decreased and indicated mean effective pressure (IMEP) was increased as the injection timing was retarded. Combustion phasing resulted by the injection timing was verified as the reason in this observation.

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The effects of fuel properties, fuel pressure, fuel temperature, and ambient pressure on spray characteristics have been studied extensively by various researchers. Expressed in terms of the primary forces, such as inertia force, surface tension force, viscous force and aerodynamic drag force, many empirical and non-dimensional formulations of spray characteristics such as spray penetration, spray-plume angle, and Sauter Mean Diameter (SMD) have been established. However, these formulations have been primarily developed for use in diesel sprays, and they are generally not directly applicable for spark ignition engine fuel sprays of gasoline and alcohol fuels. In this study, non-dimensional correlations of the microscopic characteristics of the sprays such as drop size for spark-ignition direct-injection (SIDI) engines are obtained in terms of non-dimensional numbers such as the Weber number and Reynolds number. Phase Doppler Interferometry (PDI), combined with Mie-scattered high speed imaging, is applied to measure the drop size distributions of a multi-hole spray over a wide range of test conditions which simulate different operation modes in SIDI engines. Four types of fuels, namely, gasoline, ethanol, butanol and pentanol were used in this study. Based upon the engine conditions, a wide region of Weber number and Reynolds number was chosen to reveal how the dominating forces govern the liquid-jet breakup and spray atomization processes. In addition to the generalized non-dimensional correlations of spray penetration and spray-plume angle for gasoline and alcohol fuels developed in our previous work, the non-dimensional drop size correlations of multi-hole sprays have also been established. Together with the previously derived non-dimensional correlations of spray penetration and spray-plume angle, these generalized non-dimensional correlations of macroscopic and microscopic spray characteristics are found to be very useful for providing the physical insights of modeling the multi-hole sprays in SIDI engine applications.

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Ethanol and gasoline blended fuel sprays injected by a single hole-type injector for D.I. Gasoline Engine were measured by using the Laser Absorption Scattering technique that simultaneously measures the spatial concentration distributions of the liquid and vapor phases in the fuel spray. The effects of the blended ratio of the ethanol and gasoline on the spray development and the mixture formation were investigated. The measurement results were verified by using the numerical analysis aiming to clarify the spray development and the mixture formation.

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It is becoming evident that the fuel-air mixing process in high pressure multiple-injection CRDI engines is different from the conventional single injection such that a simultaneous reduction between NOx and soot particulate emissions is realizable. As a novelty, this paper explores the physics behind the mixing processes in multiple-injection technique using a comprehensive phenomenological model developed and validated by the authors for predicting combustion and emissions characteristics of multiple-injection CRDI engines. Towards this objective, the paper predicts and relates the variations in mixing rates for double and triple injection schedules with their observed combustion and emission characteristics. These quantitative predictions of mixing rates in multiple-injection substantiate the cause of soot reduction during later part of CRDI combustion. The predictions of fuel evaporation, fuel air mixing and emission characteristics of high pressure multiple-injection CRDI engines obtained from the model are found to reveal features useful in understanding CRDI engine performance. The trends and relationship of injection and its related processes observed in this study conform to the experimental observations of several multiple-injection CRDI engine studies. The predictions from the model suggest that there must be an optimal injection schedule in order to achieve the simultaneous reduction of nitric oxide and soot particulate emissions with the minimum sacrifice on fuel economy.

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In order to obtain further understandings of physical and chemical characteristics of multi-component fuel spray, one-dimensional spray vaporization and ignition model has been proposed. In this model, Wakuri's momentum theory was employed to take into account the amount of air entrainment with heat quantity into the fuel spray. The temperature rise and phase equilibrium of dual-component fuel were estimated by use of SUPERTRAPP code. The ignition delay was calculated based on Livengood-Wu integral. The prediction results of this model were able to capture the trends concerning to vaporization and ignition processes observed in experiments.

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Diesel spray characteristics are largely governed by the atomization phenomenon. Atomization phenomenon in the computational fluid dynamics (CFD) may be described using a breakup model. Previously, diesel spray analysis has been done using a breakup model such as Kelvin-Helmholtz and Rayleigh-Taylor (KH-RT) model. KH model and RT model are modeled for high Weber number conditions. Even if the fuel is injected with high pressure, the downstream region of spray is corresponding to relatively low Weber number conditions. To overcome this problem, we develop the KH-MTAB model. This is a hybrid breakup model where the KH model and Modified Taylor Analogy Breakup (MTAB) model are used to model the primary and secondary breakup respectively. MTAB model is more suitable for the description of secondary breakup, compared to RT model. In this report, in order to validate the KH-MTAB model at high density fields, it is calculated in conditions of non-evaporation and evaporation spray. It is found that LES is in good agreement with experimental results such as macroscopic characteristic like penetration, and microscopic characteristic like SMD in non-evaporation spray. Furthermore LES is in good agreement with vapor penetration and liquid penetration in evaporative spray.

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Numerical simulation of internal flow in VCO nozzle with respect to eccentric location of a needle is performed and compared with the experiment. Cavitation is created in the vicinity of the nozzle hole entrance, and swirl flow is generated in the nozzle hole by the eccentricity. As increasing the swirl, the type of the flow in the nozzle hole changes from solid state to hollow state due to an air entrainment into the nozzle hole. The swirl number and the spray cone angle are decreased in the hollow state. The simulation results indicate qualitative agreement with the experiment.

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In a direct injection diesel engine, combustion characteristics are greatly influenced by the mixture formation behavior of diesel spray. This behavior depends on various conditions such as nozzle geometry, injection pressure and ambient gas density. Recently, boost pressure of a diesel engine is set to increase in order to meet downsizing of the engine. Consequently, compressed air density in the cylinder is becoming high as compared with the density of a conventional diesel engine, and it seems that the compressed air density affects more strongly the mixing process of diesel spray. Therefore, under high ambient gas condition, it is necessary to understand precise spray behavior in terms of velocity distribution inside a diesel spray. In this study, time-resolved particle image velocimetry (PIV) was applied to sequential images of diesel spray in order to assess velocity distribution inside the spray in high density gas surroundings. As the results obtained, it was clear that spray width increased with increasing ambient gas density and injection pressure. PIV analysis shows the detail velocity distribution inside the spray. Ambient gas density effect on the spray width was larger than injection pressure effect. Moreover, local position of intense mixing zone shifted from spray periphery to inside a spray with an increase of ambient gas density and injection pressure.

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As recent vehicle industry has focused on global warming and air pollution, high thermal efficiency and eco-friendly engines with low CO2 emission levels have become more attractive. To meet strict future emission regulations, diesel engines are increasing interests due to its high efficiency. Higher injection pressure and multiple injections enable an improvement of air-fuel mixing characteristics and it makes increase of thermal efficiency and reduction of vehicle emissions. Therefore in these days, a piezo type injector with common-rail which has fast response and possibilities of multiple injections in shorter time is adopted for diesel engines instead of solenoid type injector. More powerful performance and accurate engine control are predicted with using piezo injector. Therefore in this paper, injection rate and spray image of multiple injections which are important design parameters for a piezo type injector have been investigated. Interval of injections and a number of injections in multiple injection strategy has been controlled to verify interaction of each injection. Characteristics of multiple injections have been researched through optical process with a high speed camera in a high pressure chamber. Also a method of RMS(Root Mean Square) process has been used for comprehending the distribution of injection easily. As a result, in case of piezo type injector, rapid response of injection was confirmed and spray characteristics of multiple injections were improved; multiple injections were possible in a shorter time interval between each injection. Penetration lengths become shorter and characteristics of evaporation get better.

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The development of quantitatively robust spray measurements is important for advancing model development and fundamental understanding. However, the physical interpretation of both experimental measurements and model predictions needs to be carefully considered when making comparisons between them. One such example occurs in the measurement of liquid-phase of sprays injected under an evaporating environment. Various experimental techniques are applied to quantify the maximum liquid penetration, but the selection of the measurement technique and the details of the experimental arrangement may significantly influence the results. Moreover, the liquid length measured through one experimental setup may not be consistent with the definition used in a model, making a comparison between the two indirect. Hence, there is still a need to assess the physical meaning of experimentally measured liquid lengths in order to provide a direct relationship with model-based predictions. The aim of this work is to experimentally study the liquid penetration and steady liquid length in diesel sprays by applying diffused back-illumination imaging. Compared to Mie scattering, diffused back-illumination offers advantages because a reference image without the injected spray provides an intensity reference that can be used to calculate light extinction; thus leading to a better standardization of the measurement among researchers. Recent standards developed for gasoline sprays along with a suggestion made by the Engine Combustion Network call for diffused back-illumination imaging to evaluate liquid length. An analysis of the results provided by this technique has been carried out to evaluate the potential to measure liquid length of evaporating diesel sprays injected in a high-pressure, high-temperature optical vessel. The results of this study showed that the diffused back-illumination provides measurements of the liquid penetration that are fairly consistent with Mie scattering experiments in capturing the trends. On the other hand, the experiments showed that the effects of beam-steering limited the technical capabilities to extract quantitative measurements of the liquid length under diesel engine conditions and that a methodology must be implemented to satisfactory measure the liquid-phase of the sprays.

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The spray and combustion characteristics of biodiesel (BDF) and diesel fuels injected by a micro-hole nozzle of 0.08 mm diameter under increasing injection pressure up to ultra-high value of 300 MPa were investigated in this research. The LIF-PIV (Laser Induced Fluorescence- Particle Image Velocimetry) technique was used to investigate the spray and entrained gas characteristics of the fuels while the OH chemiluminescence and two color techniques were utilized to study the ignition and combustion characteristics of the spray flames. From the research it was observed that at all injection pressures, due to inferior atomization processes, the normal velocity and total mass of the entrained gas by BDF was less compared to diesel. As a result of higher cetane number the BDF's flame ignition delay was shorter compared to diesel. The ratio of the mass flow rate of gas entrained to mass flow rate of injected fuel by BDF was less compared to diesel. Oxygen content in the BDF played a greater role in soot reduction as against the gas entrained.

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In this study, Spray and Combustion Characteristics of Diesel Fuel in the Medium Speed Engines (High ambient pressure and larger nozzle hole diameter compared to Automotive Engines) were clarified. To simulate the ambient density and ambient temperature conditions of the actual engine, optical accessible Rapid Compression Expansion Machine (RCEM) was used. As a result, increasing ambient density and nozzle hole diameter increases spray cone angle. Increase of Spray cone angle shortens ignition delay and ignites upstream of spray. From these results, spray and combustion characteristics on medium speed engines were clarified, which were different from automotive engines.

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This was accomplished with a prototype injector that achieves a faster injection rate of approximately 80% or more than a mass-production model piezo-driven common rail injector that complies with EURO 5 standards by enhancing the injection rate from the opening of the nozzle needle up to full lift while keeping the nozzle hole diameter small. The prototype injector achieved this by making the fuel-air mixture leaner without increasing the fuel injection pressure, or in other words without an adverse effect on fuel consumption due to increased work by the fuel pump, and thus yielded a reduction in harmful emissions. This was confirmed by evaluation of the spray characteristics and by combustion experiments using a single-cylinder engine, the results of which were reported. In this paper, the influence of orifice diameter using a micro orifice nozzle is described by spray measurement and engine combustion. With the use of practical multi-hole nozzles, whose orifice diameter are 0.08mm, 0.10mm and 0.12mm respectively, spray form observation, fuel droplet size measurement and combustion experiment using single-cylinder engine were conducted. Downsizing of nozzle orifice diameter provides short liquid phase penetration, narrow spray angle and small size fuel droplets. But soot from engine with 0.08mm nozzle is higher than those of 0.10mm and 0.12mm nozzles. This is considered that the influence on the combustion due to the reduced spray penetration is greater than atomization by the decreased diameter of the nozzle hole

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