bluuebunny/crossref_metadata_2025 huggingface dataset:
An Efficient Strategy for the Design Optimization of Combustor Exit Temperature Profile
Authors: Motsamai Oboetswe S. , Visser Jan A. , Morris Montressor , de Kock Danie J.
Published: September 2008

A technique for design optimization of a combustor is presented in this study. The technique entails the use of Computational Fluid Dynamics (CFD) and mathematical optimization to minimize the combustor exit temperature profile. The empirical and semi-empirical correlations commonly used for optimizing Combustor Exit Temperature profile do not guarantee optimum. As experimental approach is time consuming and costly, use is made of numerical techniques. Using CFD without mathematical optimisation on a trial-and-error basis, however, does not guarantee optimal solutions. A better approach that is viewed as too expensive is a combination of the two approaches, thereby, incorporating the influence of the variables automatically. In this study the combustor exit temperature profile is optimised. The optimum (uniform) combustor exit temperature profile depends on mainly the geometric parameters. The combustor exit temperature profile is affected as soon as flow enters the combustor. However, in gas turbine applications where care has been taken on the influence of upstream flow related conditions, the combustor exit temperature profile is changed by dilution hole pattern and size. In this study dilution hole parameters have been used as optimization variables. The combustor in the study is an experimental liquid fuelled atmospheric combustor with turbulent diffusion flame. The CFD simulations uses the Fluent code with Standard k-ε model. The optimisation is carried out with Snyman’s Dynamic-Q algorithm, which is specifically designed to handle constrained problems where the objective or constraint functions are expensive to evaluate. The optimization leads to a more uniform combustor exit temperature profile as compared to the original.
Engine Data Logging of TxDOT Galveston Ferry Operations
Authors: Fritz Steven G. , Honc Randell , Chan Lit
Published: September 2008

This paper presents results from a study intended to generate engine operating profiles and exhaust temperature characteristics for the fleet of five ferries operated by the Texas Department of Transportation (TxDOT) between Galveston and Port Bolivar, Texas. Data logging of the TxDOT Galveston ferries was an important first step in assessing NOx reduction technologies. Based on the data logging, the following conclusions are drawn; While EMD and DDC engine exhaust temperatures monitored during in-use operations were below 260°C for a majority of the time, more than 70 percent of the EMD engine NOx emissions occurred at exhaust temperatures greater than 260°C during in-use operations. This is based on in-situ emissions data from an EMD engine of a ferry (Greer) in which emissions measurements were performed; the EMD 12-645-E6 propulsion engines operated well below their 1,120 kW rating; Actual in-use engine operating conditions of the EMD 12-645-E6 engines are not well represented by EPA E2 and E3 marine certification test cycles; EPA engine certification data may not be directly applicable for estimating in-use emissions; Emissions testing at two additional test points during EPA certification testing would capture TxDOT ferry actual operating modes.
Thermo-Fluid Dynamic Simulation of a S.I. Single-Cylinder H2 Engine and Comparison With Experimental Data
Authors: D’Errico G. , Onorati A. , Ellgas S. , Obieglo A.
Published: September 2008

This paper deals with the modelling and experimental work carried out on a BMW single cylinder spark ignition hydrogen engine. The authors have enhanced a 1D thermo-fluid dynamic simulation code in order to cope with the different chemical and physical aspects due to the fuelling of a spark ignition engine with hydrogen rather than with conventional gasoline. In particular the combustion module, which is based on a quasi-dimensional approach, has been extended by introducing the possibility of predicting the burning rate of the combustion of a homogeneous mixture of hydrogen and air. A fractal approach was followed for the turbulent flame speed evaluation, while an extend database for laminar burning velocities was created applying a kinetic simulation code for one-dimensional laminar flames. The modelling of the whole intake and exhaust systems coupled to the engine has been addressed, considering port-injection fuel system, in which hydrogen has been injected at very low temperature (cryogenic conditions). The fundamental 1D fluid-dynamic equations are solved by means of second order finite difference schemes; the working fluid is considered as a mixture of ideal gases, with specific heats depending on the gas temperature and the mole fractions of species, whose correlations for each specie (including para-hydrogen) have been extended in the region of low temperature. A first validation of the enhanced model is shown in the paper, comparing the computed results with the experimental data of in-cylinder pressures, intake and exhaust instantaneous pressure histories at different locations and NO emissions discharged by the cylinder.
Development of a Simulation Code for Hydrogen Fuelled SI Engines
Authors: Verhelst Sebastian , Sierens Roger , Verstraeten Stefaan
Published: September 2008

Hydrogen is an attractive alternative energy carrier, which could make harmful emissions, global warming and the insecurity concerning oil supply a thing of the past. Hydrogen internal combustion engines can be introduced relatively easily, from a technological as well as from an economic point of view. This paper discusses the development of a model for the combustion of hydrogen in spark ignition engines, which has lead to a simulation program that can assist the optimization of these engines. The importance of a laminar burning velocity correlation taking stretch and instability effects into account is shown. The effects are particularly strong for the highly diffusive hydrogen molecule. In this paper, a laminar burning velocity correlation published previously by two of the authors is combined with a number of turbulent burning velocity models in a quasi-dimensional two-zone combustion model framework. After calibration of the combustion model for a reference condition, simulation results are compared with experimental cylinder pressure data recorded on a single cylinder hydrogen engine. Correspondence between simulation and measurement is shown for varying equivalence ratio, ignition timing and compression ratio. All models performed well for varying ignition timings and compression ratios; the real test proved to be the ability of the models to predict the effects of a varying equivalence ratio, this lead to a clear distinction in the models.
Exploring the Potential Advantages of Light-Weight Valves in Internal Combustion Engines
Authors: Miwa Jason T. , Buckley Richard T. , Stanglmaier Rudolf H. , Radford Donald W.
Published: September 2008

This paper presents an investigation into the potential efficiency and performance improvements in an internal combustion engine by changing the mass and stiffness of valve train components, specifically the mass of the valve and the stiffness of the valve spring. Changes in valve mass affect the dynamic response of the valve train, so changes in other components must be made to maintain reliable and efficient engine operation. In order to quantify the potential benefits of lightweight engine valves, a dynamic model of the complete valve train system was developed. This model was experimentally validated on a motored engine in which the valve motion was measured for different combinations of valve mass, spring stiffness and engine speed. This paper describes the development and validation of the dynamic model, and discusses the effects of varying the valve mass and valve spring stiffness. It was found that a 75% reduction in the mass of the valves (as expected through the use of fiber reinforced composites) could reduce the maximum camshaft drive torque and frictional power by about 60–70%.
Heat Transfers Characterisations in a Turbocharger: Experiments and Correlations
Authors: Cormerais M. , Hetet J. F. , Chesse´ P. , Maiboom A.
Published: September 2008

Unfortunately, the most turbocharger models included in a whole engine simulation rely typically on the direct use of the manufacturers’ maps and on the assumption of adiabaticity of the compressor and the turbine. However, experiments on a turbocharger test bench show that, contrary to general opinions, the heat transfers can influence the turbocharger performances. It seems essential to determine and correlate the different heat transfers occurring in a turbocharger. Furthermore one method is proposed to obtain compressor and turbine isentropic efficiencies, actual mechanical powers and outlet temperatures starting from the manufacturers’ performance maps. This method coupled with the heat transfers correlations obtained experimentally give results in relative good agreement with experimental measures in comparison to their easiness of use.
Investigation of Some Base Oil as Biodegradable Water-Cooling Two-Stroke Engine Oil
Authors: Tang Zhongping , Jin Peng , Sun Dingwei , Zhang Shaoming , Liu Weimin
Published: September 2008

According to statistics, a large portion of used lubricants remain as potential hazards for the environment. Particularly, about 30 to 50% lubricant used in outboard marine engines is not burned completely and released into the water. As a result, consumers demand environmentally compatible lubricants due to concern about loss of mineral oil-based lubricants to the environment which can result in water contamination and pose a threat to animal and plant life. To prevent bioaccumulation of these materials in aquatic plants and animals, many agencies are considering regulations toward to biodegradable two-stroke outboard marine engines oil. Vegetable oils and ester oils are very suitable to develop “green lubricants”. Ester oils usually show excellent high temperature stability, low temperature fluidity, high viscosity index, very low volatility, good miscibility and biodegradability, but they are expensive and also produce many poisonous materials to environmental during produce process. Vegetable oils are biodegradable, nontoxic and renewable, moreover, their cost is reasonable compared to ester oils. Accordingly, vegetable oils are considered as potential candidates to replace conventional mineral oil-based lubricating oils, but the poor oxidative stability limits their utilization in large scale. Investigation of this work have found that proper percentage rapeseed oil can meet the requirements of biodegradable water-cooling two stroke engine oil, futhermore this two-cycle engine oil has good miscibility without need any miscibility-enhancing solvents. Research results indicate that two-cycle engine oil, which comprised rapeseed oil, ester oil and low viscosity hydrocracked oil as well as functional additives, exhibits good oxidative stability, easy biodegradability and good miscibility.
Numerical Analysis of a Small Turbo-Charged Spark-Ignition Engine
Authors: Fontana Gustavo , Galloni Enzo , Palmaccio Roberto , Torella Enrico
Published: September 2008

The reduction of green-house gas emissions, that is the reduction of engine fuel consumption, is becoming a primary requirement for the automotive industry as well as meeting current and future emission legislations. Performing high torque values with small displacement engines, the so-called “downsizing”, permits, in general, to limit some typical engine losses (for instance: pumping and friction losses), increasing the overall engine efficiency. This means to improve vehicle fuel economy and, as a consequence, the CO2 emissions avoiding a performance decrease. In this paper, the behavior of a small displacement turbocharged spark-ignition engine prototype, for medium size passenger cars, has been analyzed. 3-D numerical simulations have been carried out in order to achieve a lot of information on engine performance and control parameters. Thus, at different engine operating points, intake and exhaust manifold pressure, volumetric efficiency, high pressure curves, the flow field of the fresh charge within the cylinder, the air to fuel ratio distribution, the residual gas fraction distribution and so long have been calculated. Since, as usual, the turbocharged version of the engine under study derives from an existing naturally aspirated engine, the purpose of this investigation is to obtain a detailed picture of the variations produced by turbo-charging on engine main parameters. The increase of knock risk due to higher cylinder pressures has been evaluated as well. Thanks to the three dimensional analysis, sound information have been obtained, so that suggestions for modifying some geometric engine parameters, according to the variations imposed by turbo-charging, have been proposed. Computations have been performed by means of the 3-D AVL Fire code. Initial and boundary conditions have been evaluated by means of 1-D, unsteady computations running separately from the 3-D code. The model utilized in this study has been validated by comparing the obtained results to the measured data provided by the research center of the engine manufacturer.
Validating Phenomenological Smoke Model at Different Operating Conditions of DI Diesel Engines
Authors: Aghav Y. V. , Lakshminarayanan P. A. , Babu M. K. G. , Udin Azeem , Dani A. D.
Published: September 2008

A new phenomenological model that was published in ref [1] encompasses the spray and the wall interaction by a simple geometrical consideration. The current study extends this earlier work with investigations made on 16 different engines from 6-engine families of widely varying features applied to off-highway as well as on-road duty. A dimensionless factor was introduced to take care of the nozzle hole manufactured by hydro-erosion, (HE) as well as the conical shape of the nozzle hole (K factor) in case of valve closed orifice type of nozzles. The smoke emitted from the wall spray formed after wall impingement is the major contributor to the total smoke at higher loads. As the fuel spray impinges upon the walls of the combustion chamber, its velocity decreases. This low velocity jet contributes to the higher rate of the smoke production. Therefore, the combustion bowl geometry alongwith injection parameters play a significant role in the smoke emissions. The satisfactory comparison of predicted and observed smoke over the wide range of operation demonstrated applicability of the model in simulation study of combustion occurring in DI diesel engines.
Cycle-Resolved Detection of Combustion Start in SI Engines by Means of Different In-Cylinder Pressure Data Reduction Techniques
Authors: Baratta Mirko , d’Ambrosio Stefano , Spessa Ezio , Vassallo Alberto
Published: September 2008

An original technique for the detection of combustion start in SI engines on a cycle-by-cycle basis was proposed and applied to the analysis of pressure time-histories taken on a bi-fuel engine fueled by either gasoline or CNG. Such a technique locates the onset of combustion on the basis of the earliest release of chemical energy. It stems from the fact that, during the compression stroke, changes in the charge sensible energy, and thus in the cylinder pressure, are ruled only by work and heat exchanges with the combustion chamber walls. Hence, an imbalance in these three energies indicates the correspondent release of chemical energy, identifying combustion onset. The results of this technique were compared to those obtained through a direct analysis of in-cylinder pressure time-histories on logarithmic-coordinates p-V diagrams. More specifically, compression stroke appears like a segment on such diagrams and thus combustion onset can be defined by the detachment of in-cylinder pressure curve from linearity. The results of the different approaches for combustion start detection were compared on a wide range of working conditions of the bi-fuel SI engine under both gasoline and CNG fueling. The experimental matrix covered different engine speeds (N = 2000–4600 rpm), loads (bmep = 200–790 kPa), relative air-fuel ratios (RAFR = 0.80–1.60) and spark advances (SA ranging from 8 deg retard to 2 deg advance from MBT timing). 100 consecutive in-cylinder pressure traces were analyzed for each point in the test matrix. Particular attention was also given to the techniques applied for in-cylinder pressure filtering, which proved to be fundamental for accurate cycle-by-cycle investigation. Finally, on the basis of the experimental results obtained through the chemical-energy approach, two correlations for flame-development angle prediction are proposed, one for gasoline and the other for CNG. These correlations are based on cylinder-average thermodynamic properties at SA and can be usefully applied for triggering the flame propagation routines in indicated-cycle simulation codes.
Modeling the Performance of a Turbo-Charged S.I. Natural Gas Engine With Cooled EGR
Authors: Li Hailin , Karim Ghazi A.
Published: September 2008

A variety of gaseous fuels and wide range of cooled EGR could be used in turbocharged S.I. gas engines. This makes experimental investigation of knocking behavior both unwieldy and uneconomical. Accordingly, it would be attractive to develop suitable effective predictive model that can be used to improve understanding the role of various design and operating parameters and achieve a more optimized turbo-charged engine operation. A two-zone predictive model developed mainly for naturally aspirated S.I. engine applications of natural gas and validated earlier, was extended to consider applications employing turbochargers, after-coolers and cooled EGR. A suitably detailed kinetic scheme involving 155 reaction steps and 39 species for the oxidation of natural gas is employed to examine the pre-ignition reactions of the unburned natural gas-air mixtures that can lead to knock before being fully consumed by the propagating flame. The model predicts the onset of knock and its intensity once end gas auto-ignition occurs and considers the effects of turbo-charging and cooled EGR on the total energy to be released through auto-ignition and its effect on the intensity of the resulting knock. The consequences of changes in the effectiveness of after- and EGR-coolers when fitted, lean operation and reductions in the compression ratio on engine performance parameters, especially the incidence of knock were examined. The benefits, limitations and possible penalties of the application of fuel lean operation combined with cooled EGR are also examined and discussed.
1D Engine Simulation of a Small HSDI Diesel Engine Applying a Predictive Combustion Model
Authors: Cerri T. , Onorati A. , Mattarelli E.
Published: September 2008

The paper analyses, by means of a parallel experimental and computational investigation, the performances of a small HSDI turbocharged Diesel engine. As far as the numerical approach is concerned, an in-house ID research code for the simulation of the whole engine system has been enhanced by the introduction of a multi-zone quasi-dimensional combustion model, tailored for multi-jet direct injection Diesel engines. This model takes into account the most relevant issues of the combustion process: the spray development, the in-cylinder air-fuel mixing process, the ignition and formation of the main pollutant species, such as nitrogen oxides and particulate. The prediction of the spray basic patterns requires the previous knowledge of the fuel injection rate. Since the direct measure of this quantity at each operating condition is not a very practical proceeding, an empirical model has been developed in order to provide reasonably accurate injection laws from a few experimental characteristic curves. The results of the simulation at full load are compared to experiments, showing a good agreement on brake performance and emissions. Furthermore, the combustion model tuned at full load has been applied without any change to the analysis of some operating conditions at partial load. Still, the numerical simulation provided results which qualitatively agree with experiments.
Emission and Performance Effects of Biodiesel Blends of B5, B20 and B100 in a Single-Cylinder Medium-Speed Diesel Engine
Authors: Moshiri Mohammad R. , Payne Malcolm L. , Vasquez Manuel
Published: September 2008

Biodiesel blends from two different origins (Canola and Frying oil) were prepared and tested at B5, B20 and B100 concentrations on single cylinder medium-speed research engine at ESDC Inc. The effect of these six fuels (three concentrations, B5, B20 and B100 of each source) on exhaust emissions, fuel consumption (BSFC) and engine horsepower were compared to those of Low Sulphur # 2 Petro-diesel fuel. The engine was tested under three different test settings; Idle, 50% Load and 100% Load. The results showed: reduction in emissions (except NOX) for B5 and B20 of Canola and Frying oil blends while maintaining engine power and fuel efficiency in an acceptable range (within 2%). For B100 blends, reductions were more significant for CO and Smoke opacity but significant increase for NOX and PM emissions. Engine break horsepower was also decreased by %8–%9 with B100 blends. Engine Heat Value Release rate and Fuel Injection Pressure were also recorded for better assessment of fuel efficiency and emission results.
HCCI Combustion and Cyclic Variation for Lean Mixture Operation
Authors: Liu C. , Karim G. A. , Soharabi A. , Xiao F.
Published: September 2008

The characteristics of HCCI combustion were investigated experimentally in a variable compression ratio CFR engine when operating on lean mixtures of n-heptane and n-pentane in air. The effects of changes in equivalence ratio, compression ratio, the addition of nitrogen, carbon dioxide, and methane into the intake charge on the cyclic variation in the ignition and the development of the combustion processes were investigated. The limiting conditions that produce ignition in one cycle only among many, repeated ignition in every cycle, and knock were identified. It was found that HCCI combustion and the range of its operating conditions are limited by the extent of non-homogeneity of the intake charge, both in mixture quality and temperature. The optimum values for the addition of nitrogen, carbon dioxide, and natural gas to produce higher indicated work and reduce cyclic variation and the intensity of energy release depend on the intake mixture strength and specific operational conditions.
One Dimensional Modeling of Catalyst for Internal Combustion Engine Simulation
Authors: Chalet David , Galindo Jose´ , Climent He´ctor
Published: September 2008

The aim of this paper consists of establishing a methodology for oxidation catalyst modeling based on experimental tests and the development of a theoretical model with zero and one dimensional elements. Related to the theoretical work, the main aspects of such modeling are presented. It consists of describing the inner catalyst geometry by a combination of volumes and simple pipes network. The gas properties in volumes are calculated with a filling and emptying approach whereas the unsteady flow in pipes elements is considered to be one-dimensional and solved by using a finite difference scheme. Concerning the experimental tests, a study is carried out on a shock tube bench. The advantage of this experimental test bench is to study the propagation of a shock wave in the catalyst under controlled and convenient conditions, i.e. cold and non steady flow. Later, the model is set up by comparing the upstream and downstream pressure signals with the simulation results. Since the model lacks of relevant information of pressure losses at the inlet and outlet of the channels, which are rather difficult to compute due to the complex phenomena and flow maldistributions if the use of a 3D CFD code is avoided, the calibration of the model to match the experimental data is the decided approach. In this context, the shock wave test bench is used in order to excite the catalyst with non-steady flow conditions rather than to reproduce the conditions that will appear in real engine operation. The comparison shows good agreement between one-dimensional and experimental results. In order to validate this new modeling on a real engine configuration, an experimental validation is carried out in a four-stroke turbocharged Diesel engine. This experimental test bench allows to measure the main engine characteristics and performance as well as the instantaneous pressure upstream and downstream the catalyst. A simulation code has been also set up to model the engine and the comparison in terms of exhaust pressure pulses propagation inside the catalyst shows good agreement between the one-dimensional model and the experimental results.
Analytical and Experimental Investigation of Medium-Speed Diesel Engine Using a Kerosene Fuel
Authors: Chen Gong , Gamble James N. , McAndrew Dennis W. , McGowan John , Lynch John R.
Published: September 2008

This paper summarizes the analytical and experimental investigation of fuel-injection-controllable medium speed diesel engines using kerosene fuels. The investigation focuses on analyzing and testing the effects of using JP-8 kerosene fuel for an engine of this type, on engine fuel injection, in-cylinder combustion, and output performances and exhaust emissions. Main properties of JP-8 fuel compared to those of conventional 2-D diesel in affecting the engine processes are identified and analyzed in connection with the engine processes. The consequent effects are analytically predicted prior to actual engine testing. Results from testing a medium-speed diesel engine using 2-D diesel and JP-8 fuel separately are presented and agree closely in the trends of variation with the analysis and prediction.
Hydraulic Circuit Design Keys to Remove the Dependence of the Injected Fuel Amount on Dwell Time in Multi-Jet C.R. Systems
Authors: Baratta Mirko , Catania Andrea Emilio , Ferrari Alessandro
Published: September 2008

In Multijet Common Rail (C.R.) systems, the capability to manage multiple injections with full flexibility in the choice of the dwell time (DT) between consecutive solenoid current pulses is one of the most relevant design targets. Pressure oscillations triggered by the nozzle closure after each injection event induce disturbances in the amount of fuel injected during subsequent injections. This causes a remarkable dispersion in the mass of fuel delivered by each injection shot when DT is varied. The present works aims at investigating hydraulic circuit design keys to improve multiple injection performance of C.R. systems, by virtually removing the dependence of the injected fuel amount on DT. A Multi-Jet C.R. of the latest solenoid-type generation was experimentally tested at engine-like operating conditions on a high performance test bench. The considerable influence that the injector supplying pipe can exert on induced pressure oscillation frequency and amplitude was widely investigated and a physical explanation of cause-effect relationships was found by energetics considerations, starting from experimental tests. An optimization study was carried out to identify the best geometrical configurations of the injector supplying pipes so as to minimize pressure oscillations. The analysis was carried out with the aid of a previously developed simple zero-dimensional model, allowing the evaluation of pressure wave frequencies as functions of main system geometric data. Purposely designed orifices were introduced into the rail-pipe connectors or at the injector inlet, so as to damp pressure oscillations. Their effects on injection system performance were experimentally analyzed. Hydraulic circuit solutions that apply both optimized injector inlet-pipe sizes and oscillation damping orifices at the rail outlet were thoroughly investigated. Finally, the influence of the rail volume on pressure wave dynamics was studied to evaluate the possibility of severely reducing the rail capacitance. This would lead to a system, not only with reduced overall dimensions, but also with a prompter dynamic response during engine transients.
Development of a Misfire Detection’s Technique Based on an Engine’s Torsional Model
Authors: Moro Davide , Pantaleoni Stefano , Serra Gabriele
Published: September 2008

The recent OBD requirements enforce the misfire’s diagnosis and the isolation of the cylinder where the missing combustion took place. Most of the common-used techniques developed are based on the engine’s angular speed, that is derived by the signal usually measured with an inductive or Hall-effect sensor already used for the engine’s control. The presence of single or multiple misfires (several misfires within the same engine’s cycle) induces torsional vibration in the powertrain, requiring specific filtering of the diagnostic signal to avoid false alarms. This paper presents some preliminary results, related to a 4 cylinder 1.2 liter engine mounted on an eddy-current brake test bench, obtained by a new diagnosis technique based on two speed sensors, placed near the toothed wheels used respectively for the engine and current brake’s control. The signals coming from the two sensors, applied to an equation derived by a torsional model of the engine powertrain, allow to evaluate an index based on the difference between engine and brake’s torque that highlights the misfire presence. It will be shown that this index does not require any particular calibration procedure. Experimental tests, in which single and multiple misfires are induced in several operating conditions, show clearly the algorithm’s robustness in misfire detection, especially in multiple misfire tests, where the misfiring cylinders are exactly detected.
Individual Cylinder Knock Detection Based on Ion Current Sensing: Correlation Analysis
Authors: Cavina Nicolo` , Po Giacomo , Poggio Luca , Zecchetti Daniele
Published: September 2008

This paper addresses issues related with the measurement, analysis and real-time control of knocking combustions in high-performance spark-ignition engines. In particular, the relationship between output torque and knock intensity has been investigated. Issues examined include a methodology for identifying target knocking levels, and a critical comparison of different signals for extracting knock-related information. When considering high-performance spark-ignition engines, individual cylinder spark advance management that allows maximum output torque while protecting engine components from knock-related damage, is particularly complex. The first part of the activity is focused on an analysis aimed at the identification of a knocking level that allows reaching maximum performance while protecting engine components: For a given engine operating condition, such knocking level is shown to be constant for all the engine cylinders, and it is directly measurable through knock intensity indexes obtained by post-processing the in-cylinder pressure signal. If such knocking level is to be achieved during on-board operation, it is necessary to real-time reconstruct individual cylinder pressure-based knock indexes values. One of the main objectives of this work is therefore the evaluation of the impact that the adoption of an ion current sensing system would have on the performance of such a spark advance controller. The background of the second part of the work is the knocking-related information that can be extracted by real-time processing engine block vibration signals. The main drawbacks of such approach are related to the definition of the minimum number of sensors to be installed, to the evaluation of their optimal position, and to the signal-to-noise ratio typical of such systems, which becomes critical especially at high engine speeds. Possible solutions are the use of in-cylinder pressure or ion current sensors installed on board the vehicle. This work is mainly focused on ion sensing application, due to the still existing cost and reliability problems associated with the onboard application of in-cylinder pressure measuring systems. The second part of the work therefore deals with the correlation analysis between pressure based and ion current based knock intensity indexes. The experimental tests have been performed on a V12 6.0 liter and on a V12 6.2 liter high performance engines: Large spark advance sweeps were performed for each speed breakpoint, while acquiring 6 in-cylinder pressure and 6 ion current signals. Several indexes were extracted from both type of signals, in order to achieve both maximum correlation levels and physical consistency with knock-related damage. The results are particularly encouraging, since the correlation levels between pressure-based and ion current-based knock indexes are very high, thus allowing the definition of a closed-loop individual cylinder spark advance controller able to achieve the target knocking level.
Development and Validation of an Ignition Model for SI Engines
Authors: Falfari Stefania , Bianchi Gian Marco
Published: September 2008

In SI engines the ignition process strongly affects the combustion process. Its accurate modelling becomes a key issue for a design-oriented CFD simulation of the combustion process. Different approaches to simulate ignition have been proposed. The common base is decoupling the physics related to the very first ignition phase when a plasma is formed from that of the development of the flame kernel. The critical point of ignition models is related to the capability of representing the effect of ignition system characteristics, the criterion used for flame deposit and the initialisation of the combustion model. This paper aims to present and validates extensively an ignition model suited for CFD calculation of premixed combustion. The ignition model implemented in a customized version of the Kiva 3 code is coupled with ECFM Flamelet combustion model. The ignition model simulates the plasma/kernel expansion based on a lump evaluation of main ignition processes (i.e., breakdown, arc-phase and glow phase). A double switch criterion based on physical and numerical consideration is used to switch to the main combustion model. The Herweg and Maly experimental test case has been used to check the model capability. In particular, two different ignition systems having different amount of electrical energy released during spark discharge are considered. Comparisons with experimental results allowed testing the model with respect to its capability to reproduce the effects of mixture equivalence ratio, mean flow, turbulence and spark energy on flame kernel development as never done before in three-dimensional RANS CFD combustion modelling of premixed flames.
Experimental and Numerical Investigations of Jet Impingement Cooling of Flat Plate for Controlling the Non-Tail Pipe Emissions From Heavy Duty Diesel Engines
Authors: Goyal Sandeep Kumar , Agarwal Avinash Kumar
Published: September 2008

The continuous increase in power density has led to higher thermal loading of pistons of heavy duty diesel engines. Material constraints restrict the maximum operating temperature of a piston. High piston temperature rise may lead to engine seizure because of piston warping. To avoid this, pistons are usually cooled by oil jet impingement from the underside of the piston in heavy duty diesel engines. Impingement heat transfer has been used extensively because of the high rates of cooling it provides. The associated high heat transfer rate is due to the oil jet that impacts hot impingement surface at high speed. However, if the temperature at the underside of the piston, where the oil jet strikes the piston, is above the boiling point of the oil, it may contribute to the mist generation. This mist significantly contributes to non tail-pipe emission (non-point source) in the form of unburnt hydrocarbons (UBHC’s). This paper presents and discusses the results of a numerical and experimental investigation of the heat transfer between a constant heat flux flat plate and an impinging oil jet. Piston boundary conditions are applied to the flat plate. Using the numerical modeling, heat transfer coefficient (h) at the underside of the piston is calculated. This predicted value of heat transfer coefficient significantly helps in selecting right oil grade, oil jet velocity, nozzle diameter and distance of the nozzle from the underside of the piston. It also helps to predict whether the selected grade of oil will contribute to mist generation. Using numerical simulation (finite element method) temperature profiles are evaluated by varying heat flux. Infrared camera is used to investigate and validate the temperature profile of the flat plate. High speed camera is used to capture the mist generation and oil jet breakup due to impinging jet.
Turbocharging a Bi-Fuel Engine to Achieve Equal Power in Natural Gas and Gasoline Modes
Authors: Andalibi Parham , Ahmadi Mahdi
Published: September 2008

In bi-fuel engines, in which thermodynamic and mechanical design concepts are entirely based on gasoline mode, torque and power values are lower in natural gas mode than gasoline one. This problem is directly related to volumetric efficiency reduction in natural gas (NG) mode. Volumetric efficiency in natural gas is lower because of gaseous form of natural gas entering the engine and differences between thermo-chemical properties of natural gas and gasoline; e.g. stoichiometric air-fuel ratio and heat of vaporization. On the other hand, natural gas stoichiometric air-fuel ratio is generally greater than gasoline one and theoretically, more air should be supplied in NG mode. Although the effect of volumetric efficiency reduction is more important than another, both of them state the amount of charged air should be increased in NG mode to prevent power fall in this mode.
Two-silane chemical vapor deposition treatment of polymer (nylon) and oxide surfaces that yields hydrophobic (and superhydrophobic), abrasion-resistant thin films
Authors: Saini Gaurav , Sautter Ken , Hild Frank E. , Pauley Jerry , Linford Matthew R.
Published: September 2008

This article describes a two-silane, chemical vapor deposition (CVD) approach to creating hydrophobic (or even superhydrophobic), abrasion-resistant coatings on silicon oxide and polymer (nylon) substrates. This multistep approach employs only reagents delivered in the gas phase, as follows: (i) plasma cleaning/oxidation of the substrate, (ii) CVD of 3-isocyanatopropyltriethoxysilane, which is used as an adhesion promoter for the substrate, (iii) hydrolysis with water vapor, and (iv) CVD of (tridecafluoro-1,1,2,2-tetrahydrooctyl)trichlorosilane (the “Rf-Cl silane”). Surfaces are characterized by wetting, spectroscopic ellipsometry, x-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). This work has the following unique features. First, the authors explore an all gas phase deposition of a new silane coating that is scientifically interesting and technologically useful. Second, the authors show that the presence of an adhesion promoter in the process leads to thinner films that are more robust in abrasion testing. Third, results obtained using plasma/deposition equipment that is relatively inexpensive and/or available in most laboratories are compared to those obtained with a much more sophisticated, commercially available plasma/CVD system (the YES-1224P). The entire deposition process can be completed in only ∼1h using the industrial equipment (the 1224P). It is of significance that the polymer surfaces modified using the 1224P are superhydrophobic. Fourth, the thickness of the Rf-Cl silane layer deposited by CVD correlates well with the thickness of the underlying spin coated nylon surface, suggesting that the nylon film acts as a reservoir of water for the hydrolysis and condensation of the Rf-Cl silane.
Ultralow k films by using a plasma-enhanced chemical vapor deposition porogen approach: Study of the precursor reaction mechanisms
Authors: Castex A. , Jousseaume V. , Deval J. , Bruat J. , Favennec L. , Passemard G.
Published: September 2008

As interconnects are scaled down, much effort is made to achieve ultralow k material with a dielectric constant lower than 2.5. Thus, many new precursors are investigated in plasma-enhanced chemical vapor deposition. This is particularly true with the porogen approach where two molecules are used: an organosilicon to create the silicon matrix and an organic molecule “porogen” that creates material porosity during a post-treatment such as annealing. In this article, the influence of the organosilicon molecular structure is investigated. Two “matrix precursors” with different structures are therefore compared. The first one, referred to as D5, has a ring structure (decamethyl pentacyclosiloxane); the second one, referred to as DEOMS, has a star structure (diethoxymethyl silane). The porogen organic molecule, referred to as CHO, is cyclohexen oxide. The fragmentation paths of the precursor molecules in the plasma are investigated by quadrupole mass spectroscopy and the film structure is studied by Fourier transform infrared spectroscopy. The mass spectroscopy analysis shows that the fragmentation in plasma is highest for DEOMS, intermediate for CHO, and lowest for D5 in comparable process conditions. At the maximum plasma power setting, the loss rate, which yields molecule consumption, is 43%–81% for the D5-CHO mixture, respectively, and 73%–37% for the DEOMS-CHO mixture, respectively. This is related to higher bond-dissociation energy for the siloxane (SiOSi) link in D5 than silane (SiH), silylethoxyde (SiOC2H5) in DEOMS, or CC and epoxy cycle in CHO. Indeed, a higher electron-energy relative threshold for dissociation under electron impact is measured for D5 (around 7eV) than for DEOMS and CHO (around 4eV). Moreover, the fragment structures differ from one precursor to another. Methyl groups are abstracted from D5 and a few polysiloxane chains are produced from pentacycle opening and fragmentation. In the case of DEOMS, many single silicon-atom-bearing species are produced. Consequently, the D5-based films have significant retention of siloxane cycles and a less diverse silicon environment than DEOMS-based films. The porogen incoporation (organic phase) was evidenced through alkyl group absorption and is more important with DEOMS than D5 as a matrix precursor. Moreover, the epoxy moiety of the porogen seems scavenged by the plasma and is not retained in the films. These results confirm other studies that discarded D5-CHO chemistry for porous dielectric achievement in an industrial reactor, whereas DEOMS-CHO leads to porous films with an ultralow dielectric constant. Eventually, this study shows that the usefulness of cyclosiloxane precursors is not straightforward.
Capillary flow meter for calibrating spinning rotor gauges
Authors: Berg Robert F.
Published: September 2008

This article describes a capillary flow meter whose maximum flow rate of 0.2μmol∕s (∼0.2cm3∕min at ambient conditions) covers the range that is useful for calibrating spinning rotor gauges. Knowing the input pressure, output pressure, and temperature of the capillary yields the gas flow rate with a relative standard uncertainty as small as 0.04%. The flow meter, which requires no moving parts aside from valves, comprises a ballast tank, a coil of quartz capillary with an inner diameter of 0.1mm, and a commercial instrumentation package. Measurements near 0.1μmol∕s showed agreement with an independent primary flow meter to within 0.2%, comparable to the combined relative standard uncertainty of 0.11%. Additional measurements showed that operating the capillary flow meter with an exit pressure less than 1kPa allowed the flow to stabilize within minutes. However, the small exit pressure caused an unexpected enhancement of the slip correction in the hydrodynamic model of the capillary.
Reduction in hydrogen outgassing from stainless steels by a medium-temperature heat treatment
Authors: Park C. D. , Chung S. M. , Liu Xianghong , Li Yulin
Published: September 2008

The authors carried out heat treatments, in-vacuum or in-air at 400 °C, to reduce the hydrogen outgassing rate from stainless steels. An outgassing rate as low as 2×10−14 Torr ℓ s−1 cm−2 was routinely achieved by a medium-temperature bakeout, but it took much longer time than reported to perform intensive thermal treatment. The result shows that the diffusion process governs degassing only at the early stage of degassing while the recombination limits outgassing at low concentrations. Air baked chambers had somewhat lower outgassing rates than in-vacuum baked chambers, suggesting that the surface oxide acts as a further barrier for H2 outgassing. However, the main effect may be attributed to the removal of mobile hydrogen through diffusion. The results showed that the ultralow outgassing rate can be reproducibly achieved for stainless steel chambers with the established heat treatment procedure. The study also showed that the ultralow outgassing property of a treated chamber can be restored by a low temperature (>150 °C) postbakeout, after exposure to ambient air.
Ferroelectric properties of Bi3.25La0.75Ti3O12 films using HfO2 as buffer layers for nonvolatile-memory field-effect transistors
Authors: Kim Kyoung-Tae , Kim Gwan-Ha , Woo Jong-Chang , Kim Chang-II
Published: September 2008

The ferroelectric Bi3.25La0.75Ti3O12 (BLT) thin film and HfO2 layer were fabricated using both metal-organic decomposition and atomic-layer deposition methods. The HfO2 thin film was deposited as a buffer layer between Si substrate and BLT thin films. The electrical and structural properties of the metal-ferroelectric-insulator-semiconductor (MFIS) structure were investigated by varying the HfO2 layer thickness. Transmission electron microscopy showed no interdiffusion and reaction occurring when the HfO2 film is used as a buffer layer. The width of the memory window in the capacitance-voltage curves for the MFIS structure was decreased with increasing thickness of the HfO2 buffer layer. The experimental results showed that the BLT-based MFIS structure is suitable for nonvolatile-memory field-effect transistors with a large memory window.
Cyclic, cryogenic, highly anisotropic plasma etching of silicon using SF6∕O2
Authors: Isakovic A. F. , Evans-Lutterodt K. , Elliott D. , Stein A. , Warren J. B.
Published: September 2008

The authors report on the development and characterization of a plasma etching method that utilizes process steps common to both the well-known Bosch and the cryogenic deep reactive ion etching methods for silicon. This hybrid process uses cyclical etch steps that alternate between etching and passivating chemistries as in the Bosch process, while still maintaining sample temperatures at −100°C on a cryogenically cooled stage. The advantages of this process are superior control of wall profiles for isolated features, minimization of grass formation, and the elimination of an expensive gas, c-C4F8, required in the Bosch passivation step. The authors show examples of x-ray optic elements deep etched to 100μm depth with the cyclic cryogenic process.
Influence of N2 gas pressure and negative bias voltage on the microstructure and properties of Cr–Si–N films by a hybrid coating system
Authors: Wang Qimin , Park In-Wook , Kim Kwangho
Published: September 2008

Cr–Si–N films were deposited using a hybrid coating system combining arc ion plating and magnetron sputtering. The authors investigated the influence of N2 flux rate and negative bias voltage on the microstructure and properties of Cr–Si–N films, e.g., chemical composition, film morphology, phase structure, residual stress, and microhardness. The results showed that all the Cr–Si–N films were close to stoichiometry. The N2 flux rate had no important influence on the microstructure and properties of the Cr–Si–N films. Applying a negative bias voltage resulted in significant decrease in macroparticle densities and smoother film surface. Also the film microstructure transformed from apparent columnar to nanocomposite microstructure. The maximum microhardness obtained ranged from 45to50GPa at a bias voltage ranging from −50to−100V. The microhardness enhancement could be ascribed to the mixed effect of grain size diminishment and residual compressive stress.