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This paper reports a numerical and experimental analysis on a twin-cylinder turbocharged Spark Ignition engine carried out to investigate the cylinder-to-cylinder variability in terms of performance, combustion evolution and exhaust emissions. The engine was tested at 3000 rpm in 20 different steady-state operating conditions, selected with the purpose of observing the influence of cylinder-by-cylinder A/F ratio variations and the EGR effects on the combustion process and exhaust emissions for low to medium/high loads. The experimental outcomes showed relevant differences in the combustion evolution (characteristic combustion angles) between cylinders and not negligible variations in the emissions of the single cylinder exhaust and the overall engine one. This misalignment resulted to be due to differences in the injected fuel amount by the port injectors in the two cylinders, mainly deriving from the specific fuel rail geometry. The experimental data were then used to validate a 1D engine model, integrated with refined sub-models of turbulence, combustion, heat transfer and emissions. The model takes into account the in-cylinder production of noxious species, and their propagation in the exhaust system, up to the three-way catalytic converter. A satisfactory accuracy was reached in reproducing the overall engine performance and the combustion process in the two cylinders. In particular, the emission sub-models confirmed that the variations of the cylinder-out exhaust emissions (NOx, HC and CO) were mainly due to the non-uniform effective in-cylinder A/F ratio. The proposed numerical methodology has the potential to highlight unexpected combustion non-uniformities among different cylinders and represents a powerful support to the engine design and development. It also allows for the prediction of the overall exhaust emissions at different engine operating conditions up to the entire domain, thus assisting the engine calibration phase and reducing the experimental efforts.

Nowadays internal combustion engines can operate under lean combustion conditions to maximize efficiency, as long as combustion stability is guaranteed. The robustness of combustion initiation is one of the main issues of actual spark-ignition engines, especially at high level of excess-air or dilution. The enhancement of the in-cylinder global motion and local turbulence is an effective way to increase the flame velocity. During the ignition process, the excessive charge motion can hinder the spark discharge and eventually cause a misfire. In this perspective, the interaction between the igniter and the flow field is a fundamental aspect which still needs to be explored in more detail to understand how the combustion originates and develops. In this work, a combined experimental and numerical study is carried out to investigate the flow field around the spark gap, and its effect on the spark discharge evolution. Two different velocities of the flow field are explored and compared to the static configuration under ambient conditions in an air flow channel, investigating the effect of the orientation of a conventional J-type spark plug. Results of numerical simulations predict spark stretching that is in close agreement with experimental observations. The model results are used to provide insight into the spatial and temporal development of the spark discharge. This work provides a numerical tool that can be extremely useful to link the interaction between the in-cylinder charge motion and the spark discharge to the engine cycle-to-cycle variability prediction.

The electrochemical performance of a lithium-ion battery is strongly affected by the temperature. During charge and discharge cycles, batteries are subjected to an increment of temperature that can accelerate aging and loss of efficiency if critical values are reached. Knowing the thermal parameters that affect the heat exchange between the battery surface and the surrounding environment (air, cooling fins, plates, etc.) is fundamental to their thermal management. In this work, thermal imaging is applied to a laminated lithium-polymers battery as a noninvasive temperature-indication method. Measurements are taken during the discharge phase and the following cooling down until the battery reaches the ambient temperature. The 2d images are used to analyze the homogeneity of the temperature distribution on the battery surface. Then, experimental results are coupled with mathematical correlations. The derivation of the instantaneous heat generated in the battery and Newton's cooling law in transient conditions are used to estimate two main thermal parameters, as the convective heat transfer coefficient and the specific heat capacity, and then to calculate the heat generated by the battery. The experimentally-based derivation of the abovementioned thermal parameters will be useful in advanced thermal models for the design of batteries and battery cooling systems.

Mechanical friction and heat transfer in internal combustion engines have long been studied through both experimental and numerical simulation. This publication presents a continuation study on a Pressurized Motoring setup, which was presented in SAE paper 2018-01-0121 and found to offer robust measurements at relatively low investment and running cost. Apart from the limitation that the peak in-cylinder pressure occurs around 1 DegCA BTDC, the pressurized motoring method is often criticized on the fact that the gas temperatures in motoring are much lower than that in fired engines, hence might reflect in a different FMEP measurement. In the work presented in SAE paper 2019-01-0930, Argon was used as the pressurization gas due to its high ratio of specific heats. This allowed to achieve higher peak in-cylinder temperatures which close further the gap between fired and motored mechanical friction tests. In 2019-24-0141, Argon was mixed in different proportions with Air to synthesize gases with different ratios of specific heats in the aim of observing any abrupt transitions in the FMEP with different peak in-cylinder temperatures. In this publication, a higher loading test matrix to that published in 2019-24-0141 is presented, with an engine speed ranging from 1400 rpm to 3000 rpm and ratios of specific heats varying from that of Air (Î = 1.4) to that of Argon (Î = 1.67). The peak in-cylinder pressure was kept at a constant 103 bar. Results obtained in this work strengthen further the observations made in 2019-24-0141; where the measured FMEP is found to be insensitive to the different peak in-cylinder temperatures. In this study, a fast-response thermocouple of the eroding type was also fitted in the combustion chamber and gas-wall interface temperature histories were recorded. The transient heat flux was also computed through a spectral analysis and reported in this publication.

Improvement of performance and emission of future internal combustion engine for passenger cars is mandatory during the transition period toward their substitution with electric propulsion systems. In middle time, direct injection spark ignition (DISI) engines could offer a good compromise between fuel economy and exhaust emissions. Abnormal combustion and particularly knock and super-knock are some of the most important obstacles to the improvement of SI engines efficiency. Although knock has been studied for many years and its basic characteristics are clear, phenomena involved in its occurrence are very complex and are still worth of investigation. In particular, the definition of an absolute knock intensity and the precise determination of the knock onset are arduous and many indexes and methodologies have been proposed.

Transported probability density function (PDF) methods are currently being pursued as a viable approach to model the effects of turbulent mixing and mixture stratification, especially for new alternative combustion modes as for example Homogeneous Charge Compression ignition (HCCI) which is one of the advanced low temperature combustion (LTC) concepts. Recently, they have been applied to simple engine configurations to demonstrate the importance of accurate accounting for turbulence/chemistry interactions. PDF methods can explicitly account for the turbulent fluctuations in species composition and temperature relative to mean value. The choice of the mixing model is an important aspect of PDF approach. Different mixing models can be found in the literature, the most popular is the IEM model (Interaction by Exchange with the Mean). This model is very similar to the LMSE model (Linear Mean Square Estimation). Other models are available in the literature, e.g. the MC model (Modified Curl model), the EMST model (Euclidian Minimum Spanning Tree) and the PMSR model (Pairwise Mixing Stirred Reactor). The IEM and the LMSE models relax scalar values in each particle to the mean with a characteristic time ?t computed by the intensity of scalar mixing. These deterministic models are attractive for engine combustion process modeling, because they are easy to implement and give reliable results with a short computational time. However, the numerical solution of the system is strongly linked to particles number and scalar dissipation rate. This latter requires modeling in order to take into account the physical phenomena it stands for. In a previous study, an IEM model has been used to describe the mixing in a stochastic reactor model that simulates the HCCI process (LTC combustion). In this study, the turbulent time scale ?t included in IEM model is modeled through the turbulent kinetic energy and its dissipation. Hence, a (k-?) turbulence model based on zero-dimensional energy cascade applied during the compression and the expansion cycle is presented. On another hand, the confidence interval introduced in this approach related to the initial heterogeneities amplitude of temperature and of species mass has been described as a function of the turbulent Reynolds number. The in-cylinder pressure predicted by the model was validated against the experimental results by using two different single cylinder engines. One engine was equipped with an optical access in order to follow the evolution of HCCI combustion process. For both engines HCCI combustion was applied by using early injection timings in order to ensure homogeneity of the in-cylinder charge. For both engines a good agreement has been observed in terms of in-cylinder pressure traces. At varying engine operating conditions, the mean relative error levels are lower than 3%.

In this paper, computation fluid dynamics (CFD) simulations are performed to describe the effect of in-cylinder flow structures on the formation and oxidation of soot in a swirl-supported light-duty diesel engine. The focus of the paper is on the effect of swirl motion and injection pressure on late cycle soot oxidation. The structure of the flow at different swirl numbers is studied to investigate the effect of varying swirl number on the coherent flow structures. These coherent flow structures are studied to understand the mechanism that leads to efficient soot oxidation in late cycle. Effect of varying injection pressure at different swirl numbers and the interaction between spray and swirl motions are discussed. The complexity of diesel combustion, especially when soot and other emissions are of interest, requires using a detailed chemical mechanism to have a correct estimation of temperature and species distribution. In this work, Representative Interactive Flamelets (RIF) method is employed to describe the chemical reactions, ignition, flame propagation and emissions in the engine. The CFD simulations are validated using experimental measurement of light-duty diesel engine at two different loads. A good agreement is achieved between the model results and the pressure, heat release rates and emissions from the experiment. These cases are considered as the base-line for the parameter study cases.

This paper evaluates a thermodynamic ice crystal icing model that has been previously presented to describe the possible mechanisms of icing within the core of a turbofan jet engine. The model functions between two distinct ice accretions based on a surface energy balance: freeze-dominated icing and melt-dominated icing. Freeze-dominated icing occurs when liquid water (from melted ice crystals) freezes and accretes on a surface along with the existing ice of the impinging water and ice mass. This freeze-dominated icing is characterized as having strong adhesion to the surface. The amount of ice accretion is partially dictated by a freeze fraction, which is the fraction of impinging liquid water that freezes. Melt-dominated icing occurs as unmelted ice on a surface accumulates. This melt-dominated icing is characterized by weakly bonded surface adhesion. The amount of ice accumulation is partially dictated by a melt fraction, which is the fraction of impinging ice crystals that melts. Experimentally observed ice growth rates suggest that only a small fraction of the impinging ice remains on the surface, implying a mass loss mechanism such as splash, runback, bounce, or erosion. The fraction of mass loss must be determined in conjunction with the fraction of freezing liquid water or fraction of melting ice on an icing surface for a given ice growth rate. This mass loss parameter, however, along with the freeze fraction and melt fraction, are the only experimental parameters that are currently not measured directly. Using icing growth rates from ice crystal icing experiments, a methodology that has been previously proposed is used to determine these unknown parameters. This work takes ice accretion data from tests conducted by the National Aeronautics and Space Administration (NASA) at the Glenn Research Center in 2018 that examined the fundamental physics of ice crystal icing. This paper continues evaluation of the thermodynamic model from a previous effort, with additions to the model that account for sub-freezing temperatures that have been observed at the leading edge of the airfoil during icing. The predicted temperatures were generally in good agreement with measured temperatures. Other key findings include the total wet-bulb temperature being a good first order indicator of whether icing is freeze-dominated (sub-freezing values) or melt-dominated (above freezing). Maximum sticking efficiency values, the fraction of impinging mass that adheres to a surface, was calculated to be about 0.2, and retained this maximum value for a range of melt ratios (0.3 to 0.65 and possibly higher), which is defined as the ratio of liquid water content to total water content. Higher air velocities reduced the maximum sticking efficiency and shifted the icing regime to higher melt ratio values. Finally, the leading edge ice accretion angle was found to be related to ice growth (lower growth rates for smaller angles) and melt ratio (smaller melt ratios resulted in smaller angles, likely due to erosion effects).

In order to meet the requirements in the stringent emission regulations, more and more research work has been focused on homogeneous charge compression ignition (HCCI) and partially premixed combustion (PPC) or partially premixed compression ignition (PCCI) as they have the potential to produce low NOx and soot emissions without adverse effects on engine efficiency. The mixture formation and charge stratification influence the combustion behavior and emissions for PPC/PCCI, significantly. An ultra-high speed burst-mode laser is used to capture the mixture formation process from the start of injection until several CADs after the start of combustion in a single cycle. To the authors' best knowledge, this is the first time that such a high temporal resolution, i.e. 0.2 CAD, PLIF could be accomplished for imaging of the in-cylinder mixing process. The capability of resolving single cycles allows for the influence of cycle-to-cycle variations to be eliminated. This ability to study individual cycles aids the understanding of the mixture formation process as well as the cycle-to-cycle variations. Strong air entrainment at the boundary layer can be clearly observed and followed as the mixing process progresses. The formation of eddies created by the shear force and their rotational motion can be continuously observed during the mixing process. The interaction between two adjacent spray plumes in the recirculation zone is well captured and studied. In addition, the mixing process resulting in the stratified fuel charge being located in the recirculation zone before the SOC while the areas along the original spray axis are leaned out after the end of injection, can be followed in one time sequence. Moreover, the auto-ignition position and early flame development can be studied, from the high-speed chemiluminescence imaging, together with the fuel distribution in the combustion chamber. (Less)

The concept of double compression, and double expansion engine (DCEE) for improving the efficiency of piston reciprocating engines was introduced in SAE Paper 2015-01-1260. This engine configuration has separate high, and low pressure units thereby effectively reducing friction losses for high effective compression ratios. The presence of an additional expander stage also theoretically allows an extra degree of freedom to manipulate the combustion heat release rate so as to achieve better optimum between heat transfer, and friction losses. This paper presents a 1-D modeling study of the engine concept in GT-Power for assessing the sensitivity of engine losses to heat release rate. The simulations were constrained by limiting the maximum pressure to 300 bar. The maximum motoring pressure was varied by, (a) constraining the compression ratio of the high pressure unit, and adapting the low pressure unit accordingly, (b) changing the compression ratio of the high pressure unit with a constant geometry for the low pressure unit. The effect of maximum pressure on the brake thermal efficiency was also investigated. A final set of simulations also compared the heat release rate of the model in SAE Paper 2015-01-1260 and two other models with the same start and end of combustion. The simulations were done at engine speed of 1900 rpm, and lambda 3. The results indicate the relative insensitivity of this concept engine's performance to the heat release rate when the maximum pressure constrained to a constant value of 300 bar, or even when lowering peak pressure down to 200 bar due to reduction in heat loss, and friction losses. The major limitations of the present study was the adoption of a constant convection heat loss multiplier for all the cases, and a simplistic friction model. (Less)

Prediction of spray droplet temperature is routinely performed within automotive engineering CFD simulation. Important applications include fuel spray modelling for in-cylinder combustion studies and urea-water spray modelling for SCR aftertreatment studies. Transient droplet surface temperature strongly influences droplet and spray evaporation rate and subsequent system performance. In this paper, different droplet temperature models are presented and compared for both single droplet modelling and a single-hole Lagrangian spray CFD simulation in OpenFOAM. The aim is to determine the complexity of implementation of the models and their effect on prediction accuracy for droplet surface temperature, evaporation rate and lifetime. A non-ideal multi-component droplet evaporation model using UNIFAC and NRTL for activity coefficient calculation is used. Model gasoline fuels containing varying quantities of ethanol are studied at conditions appropriate to gasoline direct injection. Three droplet temperature models are compared: a lumped thermal model typically employed in CFD packages; an effective thermal conductivity model (ETC) using the full heat equation; and an ETC model tracking the surface and centre temperature only. For droplet simulations, discrepancies of up to 13% in calculated droplet lifetime are found between the lumped thermal model and the effective conductivity models. The greatest discrepancy in lifetime is observed at conditions and compositions where rapid liquid thermal transients are encountered. This effect is characterized for the first time using the wet-bulb temperature, initial liquid temperature and fuel ethanol content, to guide modellers to an appropriate temperature model for the level of accuracy desired. The effect of droplet temperature modelling in spray CFD simulation is smaller, as measured by maximum changes in spray penetration (2%), evaporation rate (2%) and Sauter Mean Diameter (1.2%). A non-uniform temperature model is required when significant transient temperature change is expected, near-nozzle spray is studied or sub-models such as droplet collision and break-up are not in use.

International audience

International audience

The combustion process in a homogeneous charge compression ignition (HCCI) engine is mainly governed by ignition wave propagation. The in-cylinder pressure, heat release rate, and the emission characteristics are thus largely driven by the chemical kinetics of the fuel. As a result, CFD simulation of such combustion process is very sensitive to the employed reaction mechanism, which model the real chemical kinetics of the fuel. In order to perform engine simulation with a range of operating conditions and cylinder-piston geometry for the design and optimization purpose, it is essential to have a chemical kinetic mechanism that is both accurate and computational inexpensive. In this paper, we report on the evaluation of several chemical kinetic mechanisms for methanol combustion, including large mechanisms and skeletal/reduced mechanisms. These mechanisms are evaluated in terms of homogeneous ignition delay time, laminar flame speed, and multi-phase simulations of HCCI heavy-duty engine. The results are compared with experimental data and evaluated in terms of the accuracy and computational cost. It was found that scattering of ignition delay time predicted from different chemical kinetic mechanisms reported in the literature under homogeneous mixture ignition conditions give rise to a high sensitivity of the engine in-cylinder pressure prediction to the selected mechanism. (Less)

Open tanks and exterior surfaces of process heating equipment lose heat to the surroundings via convection, radiation, and/or evaporation. A practical way of reducing heat loss is by insulating or covering the surfaces. This paper presents methods to quantify heat loss and energy savings from insulating hot surfaces and open tanks. The methods include radiation and evaporation losses, which are ignored by simplified methods. In addition, thermal mass, such as refractory, conveyor and racking equipment, acts as a heat sink and increases heating energy use in process heating applications. This paper presents lumped capacitance and finite-difference methods for estimating heat loss to thermal mass, and savings from reducing this loss. The methods described above have been incorporated in free software, and are demonstrated using case study examples. The examples demonstrate the magnitude of the potential error from using simplified methods. INTRODUCTION This paper discusses and illustrates methods to quantify savings from insulating hot surfaces, covering open tanks and reducing thermal mass. A companion paper, Energy Efficiency Process Heating: Managing Air Flow, discusses improving process heating energy efficiency by managing air flow. Process heating systems lose heat through the systems’ shell. Heat is transferred through the shell by conduction, and then to the surroundings by convection and radiation. This heat loss can be reduced by insulating hot surfaces. Several methods exist to quantify the heat loss reduction from insulating hot surfaces. Most methods consider the thermal resistance of the insulation, but many do not consider the reduction in convection coefficient due to a cooler surface and do not explicitly consider radiation heat loss. Because of these deficiencies, simplified methods frequently underestimate the benefits of adding insulation. This paper describes a method to calculate energy savings from adding insulation, which increases the accuracy of the calculation by explicitly accounting for the reduction in convection due to decreased surface temperatures and radiation heat loss. Even more heat is lost from a process heating system if hot liquids are exposed to ambient air, such as in from a heated rinse tank, because evaporation heat loss takes place in addition to convection and radiation. Evaporation heat loss from uncovered tanks is between 2 and 6 times greater than convection and radiation heat loss combined. When an open heated tank is covered

An open jet wind tunnel can produce resonant acoustic conditions, some so large as to endanger the physical structure itself. A previous paper suggested a configuration for a collector with an inlet sloped at 45 degrees that eliminates these resonant conditions. The present paper expands on those earlier observations by presenting acoustic results for more collector configurations and also presents pressure distributions for test sections with lengths up to 8 nozzle diameters. Collector configurations with less slope are shown to be just as effective for conventional test sections (L/Dn∼3) as the earlier work. Collectors with steep slopes can avoid resonance even for very long test sections. Acoustic resonance is shown to correlate with test section pressure distribution and the area of constant pressure in the test section is maintained with the sloped collector. Test results show that long test sections with constant pressure and without resonance are possible.

The optimization of diesel engine performance and emissions can be achieved through a better understanding of the in-cylinder combustion process. Advanced non-intrusive optical techniques are providing new tools for investigating the thermo-fluid dynamics processes as well as they are contributing to develop predictive models for DI diesel combustion. High-speed images of spray and flame evolution as well as UV-visible chemiluminescence measurements were carried out in an optical 0.5-liter, single-cylinder, four-stroke, direct- injection diesel engine equipped with a prototype four valves cylinder head and a fully flexible CR injection system. In order to evaluate the effect of different injection strategies on the combustion process, measurements were performed varying injection parameters. The ignition location and time were individuated by combustion visualization and detection of radical species, obtained by chemiluminescence measurements. The spectral features of broadband flame emission characterized soot formation and its evolution.

This paper presents an investigation of a Volvo Direct Injection Spark Ignition (DISI) engine, where the fuel distribution and the in-cylinder flow field have been mapped by the use of laser techniques in an engine with optical access. Along with the experimental work, CFD-modelling of flow and fuel distribution has been performed.Laser Induced Fluorescence (LIF) visualisation of the fuel distribution in a DI-engine has been performed using an endoscopic detection system. Due to the complex piston crown geometry it was not possible to monitor the critical area around the sparkplug with conventional, through the piston, detection. Therefore, an endoscope inserted in the spark plug hole was used. This approach gave an unrestricted view over the desired area.In addition, the in-cylinder flow fields have been monitored by Particle Image Velocimetry (PIV) through cylinder and piston.The results from both the LIF and the PIV measurements have been compared with CFD-modelling at Volvo. The validation was made at part load when the engine was operating in stratified mode, i.e. late injection during the compression phase. Qualitative agreement was found between the calculated and measured fuel distribution around the spark plug prior to ignition.Also the PIV measurements showed a promising agreement with the flow fields obtained by CFD-modelling. In addition, the transportation properties of the fuel distribution that was monitored by LIF could to a great extent be explained by the results from the PIV measurement and the CFD-modelling.All three techniques showed promising agreements with each other and the measured properties could be used to further increase the accuracy of the CFD-modelling. The close collaboration and comparison between different techniques described in this paper increased the understanding of the processes going on in the combustion chamber. (Less)

Fuel supercriticality has recently received significant attention due to the elevated pressures and temperatures that directly-injected (DI) fuel sprays encounter in modern internal combustion (IC) engines. This paper presents a theoretical examination of conventional and alternative DI fuels at conditions relevant to the operation of compression ignition (CI) engines. The focus is to identify the conditions under which the injected liquid fuel can bypass the atomization process and directly transition to a diffusional mixing regime with the chamber gas. Evaluating the microscopic length-scales of the phase boundary associated with the injection of liquid nitrogen into its own vapor, it is found that the conventional threshold based on the interfacial Knudsen number (i.e. Kn = 0.1) does not adequately quantify the direct transition between sub- and supercriticality. Instead, a threshold that is an order of magnitude smaller is more appropriate for this purpose. Extending the analysis to a range of diesel fuel surrogates (e.g. n-heptane and n-dodecane), and alternative engine fuels that can be blended for use in CI engines (e.g. dimethyl ether and propane), it is then found that the local Knudsen numbers associated with the injection of conventional liquid fuels are significantly higher than those previously calculated in the literature, suggesting that those fuels will not directly transition to a dense-fluid mixing regime for all engine relevant conditions. However, the results show that the immediate transition to a single-phase regime may be relevant to lighter alternative fuels like DME and propane, which is attributed to the significantly lower critical temperature of these fuels, as well as their higher miscibility with the gas in the chamber.

This Paper is the continuation of the works concerning the heat pipe integration within lithium batteries as thermal control device. The previous work showed the high performance and ability of nickel/F11 grooved heat pipe to limit battery's temperature and reduce the internal thermal gradient when it operates in Zero G environment. In the present paper we analyze the performance of this concept during reentry phase of the spacecraft when it is subject to high acceleration. Theoretical study of heat pipe under body forces is performed and results are presented. An experimental assembly has been set up in laboratory to simulate an acceleration field by centrifugal concept. These studies show that heat pipe can be use to cool lithium batteries in the different phases of spacecraft flight and extension to other dissipating payload is tinkable. 5 refs.

Spark-ignition (SI) engines can derive substantial efficiency gains from operation at high dilution levels. Additionally, the use of exhaust gas recirculation (EGR) for charge dilution also maintains compatibility with three-way catalysts by allowing stoichiometric operation. However, running high dilution levels increases the occurrence of misfires and partial burns, which induce higher levels of cyclic-variability in engine operation. This variability has been shown to have both stochastic and deterministic components. Factors such as in-cylinder turbulence and mixing-variations can be classified as stochastic; while, charge composition is the major source of the deterministic component through its non-linear effect on ignition and flame propagation characteristics. The use of these deterministic components has been previously explored to construct next-cycle control approaches that would allow stable operation near the edge of stability. Building on that work, this paper aims to understand the effect of spark strategies, specifically the use of a second spark (restrike) after the main spark, on engine operation at high dilution levels that were achieved using both excess air (i.e. lean combustion) and EGR.

This paper assesses methane low pressure direct injection with stratified charge in a SI engine to highlight its potential and downsides. Experiments were carried out in a spark ignited single cylinder optical engine with stratified, homogeneous lean and stoichiometric operational mode, with focus on stratified mode. A dual coil ignition system was used in stratified mode in order to achieve sufficient combustion stability. The fuel injection pressure for the methane was 18 bar. Results show that stratified combustion with methane spark ignited direct injection is possible at 18 bar fuel pressure and that the indicated specific fuel consumption in stratified mode was 28% lower compared to the stoichiometric mode. Combustion and emission spectrums during the combustion process were captured with two high-speed video cameras. Combustion images, cylinder pressure data and heat release analysis showed that there are fairly high cycle-to-cycle variations in the combustion. Both blue pre-mixed flame and soot luminescence occurred in the combustion. The occurrence of soot luminescence was also supported by the emission spectrum. Soot formation sources were found to be localized randomly in the bulk flame but not on the piston nor in the vicinity of the spark plug. These findings illustrate the difficulty of achieving proper mixing between air and methane resulting in fairly high cycle-to-cycle variations in the combustion and fuel rich areas which create a source of soot.

Magneto-rheological (MR) fluid is a type of smart material which has ability to change its flow resistance on the application of magnetic field. This property of changing viscosity of the fluid due to application of magnetic field is utilized in the MR brake. MR brake typically consists of multiple rotating disks immersed in MR fluid and an enclosed electromagnet. The controllable yield stress produces shear friction on the rotating disks, generating the braking torque. Of late MR brakes have been explored for automotive applications. Literature review reveals that the torque output of MR brake is not sufficient for braking of mid-sized car. Hence, it is worthwhile to investigate its application for a two-wheeler where the braking torque requirement is low. This paper presents design and simulation of MR brake performance for its torque output. Design of MR brake involves deciding the configuration of MR brake in terms of number and sizing of disks, selection of MR fluid and design of magnetic circuit. The response of MR brake in terms of torque output with respect to influencing parameters like speed, current, number of disks, MR fluid properties and intensity of magnetic field can be observed with the help of simulation in order to save cost and time associated with experimental testing. MATLAB/SIMULINK software environment has been used for this simulation. Introduction of MR Fluid Magneto-rheological (MR) fluid is the material that responds to an applied magnetic field with a dramatic change in rheological behavior. MR fluid is in a free-flowing liquid state in the absence a magnetic field, but under a strong magnetic field its viscosity can be increased by more than two orders in a very short time (milliseconds) and it exhibits solid-like characteristics [1]. The magnetizable particles (mainly iron) are suspended in an appropriate carrier liquid. The carrier fluid serves as a dispersed medium and ensures the homogeneity of particles in the fluid. A variety of additives (stabilizers and surfactants) are used to prevent gravitational settling and promote stable particles suspension, enhance lubricity and change initial viscosity of the MR fluid [2]. Figure 1 Chain-Like Structure Formation in Controllable Fluids [3] In the presence of an applied magnetic field, the iron particles acquire a dipole moment aligned with the external field which causes particles to form linear chains aligned to the magnetic field, as shown in Figure

Computer software, which simulates the thermodynamic and gas dynamic of internal combustion engines, are used extensively during design and development process. This paper analyzes the 1D boundary multi-pipe junctions calculations using the Method of Characteristics (MOC). Sonic flows can be encountered in the exhaust manifolds of internal combustion engines (especially racing engines) and in the model a check if the flow is sonic or not have been made. Flows with more than one manifold have flow toward the junction, need an equivalent "Datum" manifold, with an airflow as the sum of all flows, an averaged area and stagnation enthalpy has been defined in order to calculate the pressure loss when crossing the junction. The pressure loss terms have been calculated as function of the flow-ratio of the gas flowing to the manifold to the total incoming flow and the pipe angle. Such terms take into account of the flow ratio referred to the "Datum" flow and the pipe angle term is the average of all the pressure losses of every duct with incoming flow. The main model used to calculate the wave actions in the manifolds is the Two Step Lax-Wenfroff scheme, second order in space and time with the TVD flux limiter, needed to smooth the instabilities typical of second order hyperbolic schemes. Two set of tests have been designed in order to show the advantages of the present formulation. The first is "Y" junction with an inlet duct. Increasing the inlet pressure, the flow increase up to reach the sonic flow. The second test is a Y junction with 2 inlet ducts with the third duct that goes to sonic flow. A racing engine has also been simulated comparing the results with those from a dynamometer, showing good accordance between model and measured data. Copyright © 2013 SAE International.

"Progress in hole drilling technique is opening new perspectives in diesel nozzle design. In such a scenario, research on unconventional hole shapes looks worthwhile, in order to evaluate their influence on fuel flow features within the nozzle. In the present paper, investigations have been based on modeling. Moving from a standard hole configuration towards oval shaped holes, 3D-CFD campaigns have been devoted to highlight the hole layout influence on diesel nozzle flow. The investigations have been focused both on the fuel flow pattern at hole inlet and on the flow features at hole exit section; in such a modeling process, transient data concerning spatial distribution of velocity, turbulent kinetic energy and cavitation behavior at hole exit have been computed, highlighting the perturbations induced by the unconventional hole shape on the fuel flow; once the flow behavior has been explored, results have been resumed indicating how flow pattern properties are reflected at hole exit, quantitatively"

Controlling ignition delay is the key to successfully enable partially premixed combustion in diesel engines. This paper presents experimental results of partially premixed combustion in an optically accessible engine, using primary reference fuels in combination with artificial exhaust gas recirculation. By changing the fuel composition and oxygen concentration, the ignition delay is changed. To determine the position of the flame front, high-speed visualization of OH-chemiluminescence is used, enabling a cycle resolved analysis of OH formation. A clear correlation is observed between ignition delay and flame location. The mixing of fuel and air during the ignition delay period defines the local equivalence ratio, which is estimated based on a spherical combustion volume for each spray. The corresponding emission measurements using fast-response analyzers of CO, HC and NOX confirm the decrease in local equivalence ratio as a function of ignition delay. Furthermore multiple injection strategies are investigated, applying pilot as well as post injections, in combination with a main injection at constant load. From these results it is concluded that both pilot and post injections result in an increase of unburned hydrocarbon and CO emission and a slight decrease of nitric oxide emissions.

A novel method of measuring cylinder gas temperature in an internal combustion engine cylinder is introduced. The physical basis for the technique is that the flow rate through an orifice is a function of the temperature of the gas flowing through the orifice. Using a pressure transducer in the cylinder, and another in a chamber connected to the cylinder via an orifice, it is shown how the cylinder temperature can be determined with useful sensitivity. In this paper the governing equations are derived, which show that the heat transfer characteristics of the chamber are critical to the performance of the system, and that isothermal or adiabatic conditions give the optimum performance. For a typical internal combustion engine, it is found that the pre-compression cylinder temperature is related to the chamber pressure late in the compression process with sensitivity of the order of 0.005 bar/K. Copyright © 2010 SAE International.

This paper explores the combined effects of boosting, intake air temperature, trapped residual gas fraction, and dilution on the Maximum Pressure Rise Rate (MPRR) in a boosted single cylinder gasoline HCCI engine with combustion controlled by negative valve overlap. Dilutions by both air and by cooled EGR were used. Because of the sensitivity of MPRR to boost, the MPRR constrained maximum load (as measured by the NIMEP) did not necessarily increase with boosting. At the same intake temperature and trapped residual gas fraction, dilution by recirculated burn gas was effective in reducing the MPRR, but dilution by air increased the value of MPRR. The dependence of MPRR on the operating condition was interpreted successfully by a simple thermodynamic analysis that related the MPRR value to the volumetric heat release rate., United States. Dept. of Energy (University Consortium on Low Temperature Combustion)

This paper proposes a method of determining residual gas fraction (RGF) by sampling the CO 2 concentration in the exhaust manifold of a single cylinder HSDI diesel engine. During a skip-fire event, the CO 2 concentration in the exhaust gas for the last firing cycle and the subsequent motoring cycle were measured using a fast-response emissions analyzer. The ratios of these two values are shown to be indicative of the RGF. To simulate the increase in exhaust pressure found with EGR or aftertreatment systems, the exhaust back pressure was elevated using an exhaust throttle. The intake pressure was held constant over a range of engine speed and load conditions. The results demonstrate that the RGF increases linearly with increasing exhaust back pressures for all engine operating conditions. The backflow of exhaust gas into the cylinder and intake manifold during the valve overlap period is found to be the most significant cause of the higher RGFs, especially at higher exhaust back pressures. The measured RGFs are used to validate the results obtained from a commercial 1-D engine flow simulation package. Analysis of the experimental in-cylinder pressure shows the effects of the residual gas on the combustion. With increased RGF, the ignition delay is reduced due to the higher endof-compression temperature caused by the hot residual gases. The offsetting effects of charge dilution on ignition delay are insignificant since the RGF never exceeds 9% of the charge. Pumping losses increase linearly with increasing exhaust back-pressure, reducing net indicated thermal efficiency. However, the gross indicated thermal efficiency is not significantly influenced by exhaust throttling.

The paper describes a novel method for calculating the residual gas fraction and the trapping efficiency in a 2 stroke engine. Assuming one dimensional compressible flow through the inlet and exhaust ports, the method estimates the instantaneous mass flowing in and out from the combustion chamber; later the residual gas fraction and trapping efficiency are estimated combining together the perfect displacement and perfect mixing scavenging models. It is assumed that when the intake port opens, the fresh mixture is pushing out the burned charge without any mixing and after a multiple of the time needed for the largest eddy to perform one rotation, the two gasses are instantly mixed up together and expelled. The result is a very simple algorithm that does not require much computational time and is able to estimate with high level of precision the trapping efficiency and the residual gas fraction in 2 stroke engines. The tuning and the validation of this algorithm are performed by measuring the trapping efficiency. These measurements are conducted with an innovative technique which consists in measuring the inlet and exhaust temperature, and calculation of the blow down temperature from the pressure trace. The model was tested using a mini high speed 2 stroke HCCI engine fuelled with diethyl ether between 10,800 and 19,000 [rpm]. (Less)

This paper deals with the numerical investigation of a Diesel engine high pressure DI system in which the influence of needle motion characteristics on the internal injector flows is evaluated; a radial perturbation of the axial needle motion has been imposed to analyze its role over the nozzle flow features. The developed model is based on the coupling of two computational tools. With the former one, AMESim code, the injector has been modeled; the results obtained from the injector simulation, in terms of injection needle lift time evolution, have been used to initialize the latter computation tool, FIRE code, in which 3D flow numerical investigation of the internal injector flows has been performed. Details of the adopted modeling strategy are presented and the results of each simulation step are shown.

This paper presents a combustion stability index derived from an in-cylinder ionization signal to control the engine maximum EGR limit. Different from the existing approaches that use the ionization signal values to gauge how much EGR was added during the combustion, the proposed method concentrates on using the ionization signal duration and its stochastic properties to evaluate the end result of EGR on combustion stability. When the duration index or indexes are higher than pre-determined values, the EGR limit is set. The dynamometer engine test results have shown promise for closed loop EGR control of spark ignition engines. INTRODUCTION Exhaust Gas Recirculation (EGR) is a well-known practice to improve engine fuel economy and reduce NOx emissions in certain operating regimes. For EGR, a portion of the exhaust gas is either recirculated back to intake manifold through a link between the intake and exhaust manifolds (external EGR) or trapped inside the cylinder through valve timings (internal EGR) for engines having a variable valve timing mechanism in order to mix with the fresh air for the next combustion event. Dilution of the fresh air-charge mixture with the inert exhaust gas lowers the combustion temperature and therefore suppresses the NOx formation. Currently, the EGR setting for a given engine operating condition is generally pre-determined by extensive engine calibrations and implemented in real time utilizing the stored maps in an open loop control setting. The amount of EGR for each operating condition needs to be determined based on the emission and combustion stability considerations. The addition of EGR not only reduces NOx emissions, but also allows better fuel economy until excessive dilution starts to deteriorate the combustion quality. Generally speaking, as long as the combustion stability is within the desired operating range, the higher the EGR content, the better the fuel economy and the lower the NOx emission results for a steady state condition. Combustion stability is often measured by the COV of IMEP (COVariance of Indicated Mean Effective Pressure). The lower the COV value, the better the combustion stability. However, there is no direct method to obtain the COV of IMEP for an operating condition without an in-cylinder pressure sensor. Therefore, the closed loop control of EGR, lean limit, idle spark timing, or any other stability related engine control, is challenging in the absence of an in-cylinder pressure measurement. Without having an online measurement, all the settings are pre-calibrated and generally applied as they are for all the engines of the same type during the engine’s lifetime. For an SI (Spark Ignition) engine, when the combustion stability is beyond the desired stability limit, the crank angles for the combustion to reach a certain fraction of fuel burned or for the combustion to complete usually become greater compared to a normal combustion event. The standard deviations for the corresponding angles also get larger [1]. Furthermore, both the initial flame development (05% burned) and main combustion durations (10-90% burned) increase when EGR increases (see [2], among others). Therefore, the COV of IMEP is not the only indicator of combustion stability for an SI engine, how long the combustion process takes in crank angle degrees could also be an alternative indicator as well. However, the burn duration calculation still relies on an in-cylinder pressure measurement. On the other hand, in-cylinder ionization signals have recently gained a lot of attention for combustion/engine control purposes. An example of a 300-cycle average ionization signal is shown in Figure 1. It usually consists of two peaks following the ignition pulse. The first peak represents the flame kernel growth and development around spark plug (chemical ionization), and the second peak is the re-ionization (thermal ionization) due to the in-cylinder temperature increase as a result of both pressure increase and flame development in the cylinder. The thermal ionization may disappear at operating conditions with light loads or high EGR rates. Nevertheless, an ionization signal provides a detailed fingerprint about the combustion process. It shows when a flame kernel is formed and propagates away from the spark plug gap, when the combustion is 2005-01-3751 Closed Loop Maximum Dilution Limit Control using In-Cylinder Ionization Signal Ibrahim Haskara, Guoming Zhu, Chao Daniels and Jim Winkelman Visteon Corporation Downloaded from SAE International by Brought To You Michigan State Univ, Saturday, April 04, 2015

In order to study differences between Diesel nozzle holes, four methodologies have been tested. The techniques compared in this paper are: the internal geometry determination, hole to hole mass flow measurement, spray momentum flux and macroscopic spray visualization. The first one is capable of obtaining the internal geometry of each of the orifice of the nozzle; the second one is capable of measuring the mass flow of each nozzle hole in both, continuous and real injections. The third one gives the momentum flux of each orifice, and finally, with the macroscopic spray visualization, the spray penetration and spray cone angle of each hole, are obtained. Generally, all these techniques can be used in order to determine the hole to hole dispersion due to different angle inclination of the holes, different internal geometry of orifices, deposits, nozzle needle off-center, needle deflection, etc. Moreover, the results obtained from theses techniques are a very useful tool in order to study the injection process. Special attention deserves the new capability developed to carry out the hole to hole mass flow measurement. In fact, although Diesel nozzle mass flow measurement, either injection rate or continuous mass flow, is a technique widely used, it has the disadvantage that the complete nozzle mass flow is characterized without a distinction between the mass flow from each of the orifices. Here, a new test rig is presented in order to achieve this kind of measurements.

The basic elements of the Thermal Transient Anemometer (TTA) have been presented by Foss, et al. (Meas. Sci. Technology, 12, 2004). This measurement system has been developed to identify the spatially averaged temperature and the similarly averaged velocity over "cells" or segments of a flow area. Specific applications include underhood cooling airflows and HVAC flow paths. Advancements in the temperature measurements and the anemometer's velocity transfer function at different ambient temperature conditions are reported in this paper.

In this paper, a constitutive modeling of the metal powder compaction is presented as a first step of ongoing research of a multiscale and multistage mathematical based model concept for powder metallurgy component design and performance prediction using the finite element method. In recent years, techniques such as finite element analysis have received wide attention for their high applicability to powder metallurgy (PM) industry. These techniques provide a valuable tool in predicting density and stress distributions in the pressed compact prior to the actual tooling design and manufacturing process. However, the accuracy of FE prediction highly depends on the possibility to obtain appropriate experimental data to calibrate and validate the powder material model. Within the framework of continuum mechanics, the plasticity model depends on external and internal state variables such as temperature, stress, hardening, relative density and contact between metal powder particles. The material model considers different microstructural and mechanical aspects such as dislocation dynamics, friction, porosity/density evolution, pressure dependent yield surface, particle size/shape distribution, and rate effects related to press speed. To represent the powder densification, we describe a double-surface plasticity model, based on a combination of a convex yield surface consisting of a failure envelope, such as a Mohr-Coulomb yield surface and, a hardening cap model with the use of internal state variables that capture the structure of the structure-property relations. The model is aimed to be implemented in the finite element program. The Molecular Dynamics is also introduced in this multiscale methodology as numerical experiments to study the metal compaction and sintering processes at the nanoscale level. These numerical experimental data are aimed to determine and correlate the micrpstructure-plasticity relationships at the macroscale.

In this paper, the local stress intensity factor solutions for kinked cracks near spot welds in lap-shear specimens are investigated by finite element analyses. Based on the experimental observations of kinked crack growth mechanisms in lap-shear specimens under cyclic loading conditions, three-dimensional finite element models are established to investigate the local stress intensity factor solutions for kinked cracks emanating from the main crack. The three-dimensional finite element computational results show that the critical local mode I stress intensity factor solution increases and then decreases as the kink depth increases. When the kink depth approaches to 0, the critical local mode I stress intensity factor solution appears to approach to that for vanishing kink depth based on the global stress intensity factor solutions and the analytical kinked crack solutions for vanishing kink depth. Finally, the implications of the local stress intensity factor solutions for kinked cracks on fatigue life prediction are discussed.

This paper focuses on ways of improving the spray formation from spray-guided multi-hole gasoline direct injection injectors. Work has been done both experimentally using laser diagnostic tools and numerically using Computational Fluid Dynamics. Laser Induced Exciplex Fluorescence (LIEF) measurements in a constant pressure spray chamber and optical engine measurements have shown that injectors with 6-hole nozzles and 50-degree umbrella angles are unsuitable for stratified combustion because they produce steep air-fuel ratio gradients and create a spray with overly-deep liquid fuel penetration as well as presence of liquid fuel around the spark plug. In order to study injector performance, numerical calculations using the AVL FIRE™ CFD code were performed. The numerical results indicate that by increasing the injector umbrella angle, the extent of piston wall wetting can be decreased. Also, changing the pattern of holes in the nozzle changes the spray pattern, enabling its optimization with respect to ignition and flame propagation. Furthermore, PDA and Direct Imaging experiments showed that increasing the l/d ratio by reducing the hole diameter resulted in a decrease in the mean droplet sizes (D32). The spray angle was found to increase with decreasing l/d ratios. It has also been shown that by choosing a suitable l/d ratio it is possible to control the local AFR and cross-flow velocity at the spark plug. Copyright © 2005 SAE International.

A model to simulate the mass loss due to splashing by large droplets impinging on an airfoil surface has been developed and successful validated for a single airfoil 1 : MS(1)-317 at angle of attack (AOA) of 0°. The published results on the comparison between experimental and predicted droplet impingement efficiency values have shown good agreement. Droplet impingement characteristic is essential for simulating ice shapes. Although current icing codes can predict ice buildup for Appendix C droplet sizes with acceptable degree of accuracy, they were less successful with supercooled large droplets (SLD) due to the droplet splashing effects. The proposed mass loss model accounts for this effect by including a splash parameter term into the computation of the droplet impingement efficiency. This parameter is a function of the droplet median volume diameter (MVD) and impact parameter (K), which is related to the droplet impact velocity (and angle). This paper presents further application of this mass loss model to the MS(1)-317 airfoil at AOA of 8°, and the GLC-305 airfoil at AOA of 1.5°.

The paper presents a study of the influence of fuel pressure supply fluctuations on the upstream side of the fuel injector atomizer. The study is performed over a wide range of pressures (70 to 130 Mpa) with two different common-rail (CR) high-pressure fuel injectors. The common atomizer is a VCO-type equipped with conically shaped atomizer bores. With the injector tip (nozzle) mounted in a counterpressure vessel the pressure fluctuations in the fuel-rail and in the injector body are recorded simultaneously with stroboscopic Schlieren-visualization of the time-resolved spray behavior. It is demonstrated that not only the instantaneous mass flow is affected. As a function of rail-pressure, pulse-width and injection strategy the pressure fluctuations change the spray hard-core structure and its break-up behavior. In order to quantify the impact on the combustion process the spray behavior visualizations in the pressure vessel are completed with analytical considerations of the spatial and temporal spray behavior obtained by the use of the 3D-numerical simulation code NCF-3D. The predicted combustion data for the different injectors are correlated to measured data from a 1.3-liter turbocharged passenger car diesel engine.

This paper describes the flow characteristics in the near throat region of a poppet valve under steady flow conditions. An experimental and theoretical procedure was undertaken to determine the total pressure at the assumed throat region of the valve, and also at a downstream location. Experiments of this type can be used to accurately determine the flow performance of a particular induction system. The static pressure recovery was calculated from the near throat region of the valve to the downstream location and was shown to be dependent on valve lift. Total pressure profiles suggest that for this particular induction system, the majority of pressure loss occurs downstream of the valve for lift/diameter ratios up to 0.1, and upstream of the valve for lift/diameter ratios greater than 0.1. Negligible pressure recovery was shown to exist from the cylindrical periphery of the valve head to the downstream location for all valve lifts, indicating that the flow had probably separated completely from the trailing edge of the valve seating face. The calculated discharge coefficients, based on the geometric throat static pressure measurements on the seating face, were in general less than those determined using the downstream static pressure, by as much as 12% in some instances towards the valves lower mass flow rate range.

In a direct injection diesel engine, fuel spray was auto-ignited by an elevated temperature and pressure atmosphere in a combustion chamber. Since an ignition might appear in which a suitable mixture for exothermic reaction was prepared and flame might be developing to a combustible mixture, a settlement of ignition in time and space could control the entire combustion. The ignition position was usually investigated with photometric observations such as high-speed video systems. However plane observations could not inform the exact position of the ignition because spray had the 3D structure. In this paper, a new trial for the measurement of the ignition position was reported. A single shot diesel spray injected into a test chamber was ignited by elevated temperature and pressure atmosphere in the chamber. The chamber had an impingement plate so as to measure an ignition delay of a wall impingement diesel spray. Stereoscopic observation was realized using the two-way fiber optical system that was specially designed. Front and side views of ignition phenomena were captured. Using these images, the ignition position was settled in the 3D space on the impingement wall. As the result, it was confirmed that the ignitions took place at a side periphery of the spray and some times they appeared on the impingement wall. The ignition position of a wall impingement spray was greatly affected by the distance form nozzle to impingement wall. Further, difference of the onset positions of luminous and non-luminous flame kernels was discussed in this report.

This paper presents a follow on study from earlier work investigating the influence of fuel parameters on the deposit formation and emissions from a direct injection stratified charge spark ignition engine. It was shown that injector fouling was the main reason for the increase in unburned hydrocarbon emissions and spray visualizations supported these results. The hypothesis is that the deposit buildup in the injector caused the increased hydrocarbon emissions due to an increased wall film formation. To further verify the findings, Phase Doppler Anemometry measurements at simulated engine conditions, were performed. Measurements recorded on the injector axis 20 mm downstream from the injector orifice, showed that the initial pre-jet velocity was 30% higher and the drop mean diameter was 5% larger in the case of a used injector compared to a new injector. Based on these investigations, spray files were set-up in the 3-D CFD-code AVL FIRE. A moving calculation mesh, capturing the main geometrical features from the Mitsubishi GDI® combustion system, was created. With this calculation mesh, the influence of important parameters on the mixture formation was studied for the two injectors. Simulations showed that the mass of fuel captured in the wall film with a new injector was equivalent to 10% of the total injected fuel mass. With a fouled injector this rose to around 30%. This supports the hypothesis that the injector fouling makes a significant contribution to the increased amounts of hydrocarbon emissions found in engine tests.

This paper presents an original three dimensional model for fluid flow and soot deposition in the overall wall flow honeycomb DPF. First, hot-wire experimental velocity measurements carried out along the DPF outlet crosssection are shown to highlight the flow heterogeneity. Then coupled 1D local momentum and mass balance equations to describe a bundle of channels are proposed and discussed. The model is applied to simulate the loading of a bundle of channels. Two typical cases are considered to illustrate heterogeneity problems: (i) a transverse wall permeability gradient and (ii) the initial blockage of two entrance channels. In this latter case, the heterogeneity effect is found to be confined in the neighbor channels. Finally, a macroscopic form of this set of 1D local equations, obtained using a method of volume averaging applied on a cross-section filter element which consists of several unit elements, is described. First simulations of loading of a square cross-section DPF, having an initial spatial distribution of wall permeability, are performed. Results clearly show the heterogeneity distribution of both the flow and soot deposition through the DPF.

Spray characteristics such as spray shape and spatial distribution of droplet diameter remarkably influences on output and exhaust emissions of direct injection gasoline engines. Especially, spatial distribution of the droplet diameter after impingement of a spray against a piston cavity is one of the most important factors for output and exhaust emissions, but is not revealed sufficiently because of the difficulties of measurement. In this paper, a new laser holography method that can obtain spatial distribution of droplet diameter over the spray in a short time was developed. And with this method, differences of spatial distribution of Sayter mean diameter (SMD) of droplets between before and after impingement on a flat wall in a high-pressure chamber were revealed using a prototype injector. Effects of impinging angle and distance against the wall on spatial SMD distribution were also investigated.

A comprehensive analysis of combustion, heat release, heat transfer and performance of a low heat rejection diesel engine was carried out for its potential development over the conventional diesel engine. A model for the prediction of combustion and heat felease has been formulated and developed, based on the two zone combustion modelling concept of WHITEHOUSE.N.D/WAY.R.J., and BALUWAMY.N. The combustion model takes into consideration on a zonal basis, the details of spray formation under non-swirl and swirling conditions, spray wall interaction, heat transfer, preparation and reaction rates. The penetration, deflection and growth of the spray are calculated based on the momentum added due to entrainment under swirl and non-swirl conditions. The combustion parameters were calculated based on the first law of thermodynamics using energy and enthalpy coefficients. The gas-wall heat transfer calculations are based on ANNAND.W.J.D, ANNAND. W.J.D & MA.T.H, LE FEUVRE.T., and WOSCHNI.G., heat transfer models for IC engines. A wall heat transfer model for the combustion chamber components along with the insulation coating was developed and formulated to simulate the low heat rejection condition. This model is coupled along with the above combustion and gas-wall heat transfer models to predict the effect of increased instantaneous wall temperature on heat release, gas-wall heat transfer, heat transfer through the engine components such as piston, cylinder head & cylinder liner and overall performance of a low heat rejection direct injection diesel engine. In this paper, the overall heat transfer on performance of conventional and operating conditions are simulated and analysed. To validate the predicted results, experimental investigation were carried out under identical conditions on a six cylinder direct injection Automotive diesel engine under conventional and insulated conditions using partially stabilized zirconia coating of thickness 0.5 mm and 1 mm for the combustion chamber components and outside surface of the cylinder liner. The predictions by the computer model, the experimental results and the capability of the model in predicting engine heat release, cylinder peak pressure, temperature and heat transfer details on zonal and cumulative basis are demonstrated, and the correlation are highly satisfactory.

Results from plant growth experiments utilizing particulate growth media during space flight revealed difficulties associated with providing reliable reproducible gaseous and water supply to plant roots. These limitations were attributed to insufficient understanding of liquid configuration and growth media transport processes in reduced gravity. The objective of this NASA-funded research program is to develop a framework for modeling and quantitative characterization of physical processes associated with flow of wetting and non-wetting phases in particulate plant growth media in microgravity. This paper provides an overview of research plans and current status of research activities. Characterization and modeling of substrate water retention and transport properties in microgravity is key to management and control of gas and liquid fluxes within plant root zones. Modeling efforts will focus on both 1) a pore network model for describing discontinuous fluid phase transport (ganglia/blobs) and 2) a statistical distribution model describing water retention and hydraulic conductivity as functions of various pore configurations. Minimizing hydrostatic forces within porous media by using thin samples on earth may provide an approximation to microgravity conditions. In our preliminary study we have used Magnetic Resonance Imaging (MRI) to detect and track the evolution of liquid configuration and dynamics within thin slices of opaque porous media (Aquafoam with mean pore size of 50 μm). Both twoand three dimensional temporal MRI imaging has been performed in thin Aquafoam slices positioned vertically and horizontally (to simulate the effect of gravity). The wetting front exhibited percolation-type patterns and fingering. Preliminary results show that gravity dominates liquid flow even for low Bond numbers. Although the capillary forces are very strong the small hydrostatic pressure built in the initial liquid volume determines the subsequent evolution of the wetting front.