bluuebunny/crossref_metadata_2025 huggingface dataset:
Defining ecological restoration of peatlands in Central Kalimantan, Indonesia
Authors: Puspitaloka Dyah , Kim Yeon‐Su , Purnomo Herry , Fulé Peter Z.
Published: December 2019

Indonesia declared an ambitious plan to restore its degraded and fire‐prone peatlands, which have been a source of significant greenhouse gas and haze. However, the progress has been slow and the plan cannot succeed without sustained social supports and political will. Although many previous studies argued for the need to see ecological restoration in socio‐economic contexts, empirical assessments have been lacking for how restoration is operationalized on the ground. We interviewed 47 key informants involved in four different projects in Central Kalimantan, Indonesia, and assessed their definitions, goals, and practices of peatland restoration. Most of the actors we interviewed defined peatland restoration primarily in an ecological context following the global concept of ecological restoration. However, all four restoration projects were designed without determining reference and trajectory conditions. Their intermediate goals and practices were more focused on engaging local communities and developing sustainable livelihood options than improving the ecological conditions of peatlands. To be internally consistent, peatland restoration needs to recognize a social dimension in its process, as well as in its goal. Setting clear trajectory conditions is also important to clarify achievable goals and measurable intermediate outcomes. We propose the following definition of peatland restoration: a process of assisting the recovery of degraded peatland ecosystems to achieve the appropriate trajectories defined through multi‐stakeholder collaboration within social‐ecological contexts. We hope to generate healthy debates to further refine the definition that encompasses both social and ecological dimensions to generate broader support for sustaining and expanding peatland restoration projects in Indonesia.
“Dental Stem Cells”: Awareness, knowledge, and attitude of dental professionals—A cross‐sectional study
Authors: Goswami Mridula , Kumar Gyanendra , Sharma Sadhna
Published: December 2019

Aim

The present study was conducted with an aim to assess the awareness about existence of dental stem cells among dental professionals.

Materials and Methods

A total sample size of 100 dental professionals in the age group of 22‐32 years, comprising of 28 interns, 46 postgraduate students, and 26 senior residents from various specialties was selected. A self‐administered, hand‐delivered, 10‐point questionnaire was used to assess the awareness, knowledge, and attitude of dental professionals towards dental stem cells. Results were documented and statistically analyzed using chi‐square test.

Results

A total of 72% dental professionals were aware about dental stem cells with dental curriculum books being the main source of information. Note that 81% of positive respondents were aware about the different types and a total of 28% were aware about the procedure to procure dental stem cells. Only 33.3% of positive respondents were aware about existence of dental stem cell banks in India.

Conclusion

A high level of awareness about dental stem cells and its applications was noted during the course of this study. A significant association of age and type of practice with awareness of dental stem cells and knowledge regarding their use in developing nondental tissues was observed. A positive attitude towards recommending dental stem cell banking was seen.
Young immigrants in Norway: The role of national and ethnic identity in immigrants’ integration
Authors: Martiny Sarah E. , Froehlich Laura , Soltanpanah Jilwan , Haugen Maria S.
Published: December 2019

The present work investigates the endorsement, antecedents, relationships, and consequences of young immigrants’ social identities in Norway. Despite increasing numbers of refugees and immigrants entering Norway in recent years, little is known about the relationship between immigrants’ different social identities and their feeling of integration into Norwegian society. The main goal of the present research is to fill this gap by investigating whether relationships found in other European countries replicate in the Norwegian context. In line with theoretical considerations and earlier international findings, results from two studies with different immigrant groups (Study 1: high school students; N = 97; Study 2: university students; N = 93) show that the more young immigrants in Norway endorse their national (i.e., Norwegian) identity, the less they endorse their ethnic identity (e.g., Kurdish). We further show that perceived conflict between the two cultures cannot explain the negative relationship between national and ethnic identity. In addition, immigrants’ national identity endorsement is positively related to their dual identity endorsement (e.g., Kurdish‐Norwegian). Positive contact with members of the receiving society predicts young immigrants’ feeling of being integrated in Norwegian society and this relationship is mediated by national identity. Results are discussed in terms of the crucial role social identities play in immigrants’ feeling of integration into European societies.
Laparoscopic repositioning of an obstructed ventriculoperitoneal shunt catheter with laparoscopy‐assisted partial omentectomy and omentopexy
Authors: Brückner Michael
Published: December 2019

Objective

To describe the use of laparoscopy for repositioning of a ventriculoperitoneal shunt (VPS) catheter.

Study design

Case report.

Animal

One 11‐month‐old male cairn terrier weighing 5.5 kg.

Methods

The dog had placement of a VPS system for primary hydrocephalus at 4 months of age. Poor functioning of the shunt system was suspected because of deteriorating neurological signs. A contrast study of the VPS system provided evidence of a distal shunt obstruction, and repeated brain computed tomography (CT) was consistent with persistent hydrocephalus.

Results

Laparoscopy was used to free the abdominal catheter of the shunt system and perform a partial omentectomy and omentopexy of the remaining omentum. Concurrently, the dog was sterilized. Recovery was routine, and follow‐up CT 1 year after repositioning revealed that the hydrocephalus had substantially improved. Results of a contrast study of the VPS system also provided evidence that it was functional.

Conclusion

Ventriculoperitoneal shunt systems are placed in dogs with primary and secondary hydrocephalus, and complications are quite common, including obstruction, bleeding, infection, and overshunting or undershunting. This is the first published clinical case report in which the repositioning of a VPS catheter with partial omentectomy and omentopexy in a dog are described.

Clinical significance

Future studies may be performed to determine whether laparoscopy can be considered as a treatment to assist with safe placement of VPS systems, avoiding misplacement of the shunt system and iatrogenic damage to the viscera and vessels.
Fibrin supports subcutaneous neonatal porcine islet transplantation without the need for pre‐vascularization
Authors: Salama Bassem F. , Seeberger Karen L. , Korbutt Gregory S.
Published: December 2019

Background

Neonatal porcine islets (NPIs) are a promising tissue source for clinical islet xenotransplantation. To facilitate graft monitoring and recovery if needed, an extra‐hepatic transplant site would be optimal. In addition, islet transplantation into the portal vein has been associated with life‐threatening intraperitoneal bleeding, portal vein thrombosis, hepatic steatosis, and loss of islet graft function. Although it is hypoxic, the subcutaneous space is a potential extra‐hepatic location for clinical islet transplantation. In this study, we explore the benefits of fibrin scaffolds in enhancing the engraftment and long‐term function of NPI grafts in this ectopic site.

Methods

Diabetic immune‐compromised mice were transplanted with 5000 NPIs under the kidney capsule (KC), and subcutaneously with or without fibrin (SC + F, SC, respectively). All mice were monitored for reversal of hyperglycemia and long‐term metabolic function.

Results

All mice transplanted with NPI under the KC or SC + F (12/12 and 17/17, respectively) achieved normal fasting blood glucose levels between 5 and 22 weeks post‐transplantation and displayed normal glucose tolerance during an intraperitoneal glucose tolerance test. In contrast, NPIs transplanted SC with no fibrin (n = 7) failed to obtain normoglycemia.

Conclusion

Fibrin matrix facilitates engraftment of NPIs in the subcutaneous site of diabetic mice. These data support further investigation of the subcutaneous site for clinical islet xenotransplantation.
Technical Report Writing in Engineering Studies
Authors: Mohd. Raus Teh Zanariah , Yusoff Mariana , Subatira B.
Published: December 2019

Technical reports are very important in engineering domain, as they are the main genre in reporting and communicating information among members in an engineering community. In addition, the engineering students need to be competent in writing technical report because an effective technical report will determine them in being hired and being promoted in their future career. A set of questionnaires was distributed to sixty undergraduates from the Faculty of Electronics and Computer Engineering, Universiti Teknikal Malaysia Melaka (UTeM) to seek the engineering students’ knowledge on technical report writing. Additionally, samples of students’ technical report writing were analysed by using the Genre Analysis approach for technical report writing (Cheung & Lai, 1997) to identify the Move Structure involved in writing technical report. The findings indicated that the students have already obtained the knowledge of generic structure in report genre and five Move Structure were identified in technical report writing. This study has recommended the ESP practitioners to use the genre-based approach in teaching technical report writing to the students as it allows them to have better understanding on how the technical reports were structured and organised.
The Energy of Cayley Graphs for a Generating Subset of the Dihedral Groups
Authors: Ahmad Fadzil Amira Fadina , Sarmin Nor Haniza , Erfanian Ahmad
Published: December 2019

Let G be a finite group and S be a subset of G where S does not include the identity of G and is inverse closed. A Cayley graph of a group G with respect to the subset S is a graph where its vertices are the elements of G and two vertices a and b are connected if ab^(−1) is in the subset S. The energy of a Cayley graph is the sum of all absolute values of the eigenvalues of its adjacency matrix. In this paper, we consider a specific subset S = {b, ab, . . . , a^(n−1)b} for dihedral group of order 2n, where n is greater or equal to 3 and find the Cayley graph with respect to the set. We also calculate the eigenvalues and compute the energy of the respected Cayley graphs. Finally, the generalization of the energy of the respected Cayley graphs is found.
Co-prime Probability for Nonabelian Metabelian Groups of Order Less than 24 and Their Related Graphs
Authors: Zulkifli Nurfarah , Mohd Ali Nor Muhainiah
Published: December 2019

Let G be a finite group. The probability of a random pair of elements in G are said to be co-prime when the greatest common divisor of order x and y, where x and y in G, is equal to one. Meanwhile the co-prime graph of a group is defined as a graph whose vertices are elements of G and two distinct vertices are adjacent if and only if the greatest common divisor of order x and y is equal to one. In this paper, the co-prime probability and its graph such as the type and the properties of the graph are determined.
Multiscale Boundary Element Method for Acoustic Wave Model
Authors: Zulkefli Nor Afifah Hanim , Hoe Yeak Su , Ismail Munira
Published: December 2019

In numerical methods, boundary element method has been widely used to solve acoustic problems. However, it suffers from certain drawbacks in terms of computational efficiency. This prevents the boundary element method from being applied to large-scale problems. This paper presents proposal of a new multiscale technique, coupled with boundary element method to speed up numerical calculations. Numerical example is given to illustrate the efficiency of the proposed method. The solution of the proposed method has been validated with conventional boundary element method and the proposed method is indeed faster in computation.
INVESTIGATING THE EFFECT OF SAMPLING POINT DISTANCE ON IKPOBA RIVER WATER QUALITY USING LEAST SQUARE REGRESSION MODEL
Authors: Okonofua Ehizonomhen Solomon , Nwadialo Ifeanyi Benjamin , Lasisi Kayode Hassan
Published: December 2019

In this study, the sampling point distance as it affects Ikpoba River water quality was examined in order to ascertain the quality of the river before and after waste discharge. Water samples were taken from eight (8) different locations (at distance 750 m, at 150 m interval); covering the locations of wastewater release, upstream and downstream points. Samples were taken from the river for analysis twice every month in March, May and July, 2014. Samples were analyzed for pH, Electrical conductivity, Ca, colour, turbidity etc; using WHO standard methods for water quality tests. Results obtained showed that the Water Quality Index of the river water was poor at discharge point but improved as the sampling distance increased. The month of March had the worst Water Quality Index value of   -5429792.89 at STN1, distance 0 m while the best WQI was in May (-457153.58) STN8 at 750 m. The model equations explaining the correlation between the computed WQI and sampling station distance are: Y = -4.112E6 + 1836.272X (March), Y = -1.848E6 + 2184.649X (May) and Y =-2.185E6 + 678.695X (July) respectively. One-way analysis of variance result (ANOVA) at 95% confidence interval revealed that there is a strong relationship between sampling distance and WQI for months of May and July except March. The study revealed that there is a correlation between sampling distance and water quality and hence recommends adequate effluent treatment before disposal. Also, waste disposal into the stream should be done at considerable distance from downstream users.
DEVELOPMENT OF PROGRAM IN C++ FOR ANALYSIS OF NSV SURVEY DATA BY PCI METHOD FOR FLEXIBLE PAVEMENT
Authors: Bagui Soumadeep , Bagui Swapan Kumar , Saxena Anukul
Published: December 2019

This paper presents the development of software in C++ Language for the determination of Pavement Condition Index (PCI) based on the design procedure mentioned in ASTM D 4433 and future requirement of maintenance of existing road /road network. Presently in India, Manual Pavement Condition survey has been replaced by automated Network Survey Vehicle (NSV). PCI procedure mentioned in ASTM D 4433 which needs uses of several curves and same curves have been converted in regression equations. These equations are used to prepare a Program in C++ Language. This will be useful for Pavement Engineer to determine PCI and maintenance strategy.
Approximate Limit Cycles for Vortex-Induced Vibration of a Sprung Cylinder
Authors: Zhang Guoqi , Wu Zhiqiang , Wang Yuancen
Published: December 2019

The homotopy analysis method (HAM) is an analytical approximate method to solve nonlinear problems, which is employed to give series solutions of a sprung cylinder's vortex-induced vibration. The wake flow is modeled by a classical van der Pol oscillation coupled with a cylinder by an acceleration term. The frequency and initial conditions of all possible limit cycles are obtained as Maclaurin series of an embedding parameter. A series of algebraic equations for eliminating secular terms are derived and solved to obtain the priori unknown coefficients, such as the initial conditions and frequency. The validity and efficiency of the HAM are conducted by numerical integration solutions and the harmonic balance method (HBM). The influence of fluid velocity on the frequencies and amplitudes of the limit cycles are obtained very accurately compared with numerical ones.
Investigating Mode Localization at Lower- and Higher-Order Modes in Mechanically Coupled MEMS Resonators
Authors: Ouakad Hassen M. , Ilyas Saad , Younis Mohammad I.
Published: December 2019

Mode localization is investigated in a weakly mechanically coupled system. The system comprises of two doubly clamped microbeams mechanically linked with a coupling beam close to the anchors. The phenomenon is explored among the first three vibration modes pairs, each consisting of an in-phase and out-of-phase mode. A distributed-parameter model accounting for the two mechanically coupled resonators, the coupling beam, and their geometric and electric nonlinearities are derived using the extended Hamilton's principle. A reduced-order model is then derived from the Lagrangian of the equations. An eigenvalue analysis is performed under different side electrode bias scenarios. The voltage bias impact on the natural frequencies of the pairs of modes is investigated. Veering among the various modes is observed and studied as varying the bias conditions. It is demonstrated that the veering zones can be greatly affected, tuned, and shifted by the biasing voltages. Finally, forced vibration analysis is performed. It is observed that the choice of the resonator to be excited, perturbed, and its response to be monitored is very important to fully understand and utilize the localization phenomenon for practical applications. Further, it is observed that very weak coupling is required to activate mode localization in higher-order modes. The reported selective localization and activation and deactivation of higher-order modes can be potentially useful for various applications, such as parallel mechanical computing, and for ultra-sensitive in high-frequency environments.
The Effect of Metal Foam Thickness on Jet Array Impingement Heat Transfer in High-Porosity Aluminum Foams
Authors: Singh Prashant , Nithyanandam Karthik , Zhang Mingyang , Mahajan Roop L.
Published: December 2019

High-porosity metal foam (MF) is a popular option for high-performance heat exchangers as it offers significantly higher heat transfer participation area per unit volume compared to other convection enhancement cooling methods. Further, metal foams provide highly tortuous flow paths resulting in thermal dispersion assisted by enhanced mixing. This paper presents experimental and numerical studies and the detailed underlying physics of jet array impingement onto high-porosity (ε∼0.95) thin aluminum foams. The jet and foam configurations were designed for the maximum utilization of the foam area for heat transfer and reduced penalty on the pumping power requirement. Three different pore density foams were tested with three different array-jet impingement configurations. The minimum possible thickness for each pore density was tested, viz., 5 pores-per-inch (PPI): 19 mm, 10 PPI: 12.7 mm, and 20 PPI: 6.35 mm. The baseline case for these foam-based jet impingement configurations was the corresponding configuration of orthogonal jet impingement onto a smooth heated surface, where the distance between the jet-issuing plane and the heated surface was maintained at the foam thickness level. In general, thinner foams facilitated greater jet penetration and increased foam volume usage, resulting in higher heat transfer rates for a given pore density, especially when combined with jet configurations with larger open areas. Finally, we evaluated the thermal hydraulic performance for different foam configurations and the optimum value of a given PPI was found to be at an intermediate rather than the lowest foam thickness.
Study of Magnetic Field Effects on the Oxygen Transfer in Liquid Lead Cavity Flow Using the Lattice Boltzmann Method
Authors: Pouryazdanpanah Kermani Emad , Chen Yitung
Published: December 2019

Natural convection and oxygen transfer characteristics in square cavity subjected to the magnetic field are studied numerically. Oxygen transfer in liquid metals has attracted much attention because it can decrease the corrosion rate of steel in contact with liquid metals. In advanced reactors, liquid lead has been utilized as an effective coolant. As indicated by many research reports that corrosion could be decreased by controlling the proper level of oxygen in the liquid lead. In this method, oxygen needs to mix in liquid lead homogenously and rapidly to produce a protective oxide layer. In this study, the impact of the magnetic force on oxygen transfer in a rectangular container is studied using the lattice Boltzmann method (LBM). Three different Schmidt numbers (Sc) and Hartmann numbers (Ha) have been simulated in this study. Some useful results are obtained such as an adverse effect was found that heat/mass transfer rates are decreased when Ha number is increased. In addition, the existence of an applied magnetic field has caused a significant increase in the required time to reach desired oxygen concentration and needs to be controlled in operation to have a faster distribution of the oxygen in the domain.
Application of Tabulated Detailed Chemistry to LES Model of Diesel ICE Combustion
Authors: Vitek Oldrich , Dolecek Vit , Goryntsev Dmitry , Tap Ferry , Pavlovic Zoran , Priesching Peter
Published: December 2019

The use of 3-D CFD combustion models based on tabulated chemistry is becoming increasingly popular. Especially the runtime benefit is attractive, as the tabulated chemistry method allows including state-of-the-art chemical reaction schemes in CFD simulations without significant penalties in terms of computational time. In this work, the Tabkin FGM combustion model in AVL FIRE is used to perform LES simulations of a diesel ICE (AVL SCRE). Four load conditions are investigated with three different fuel surrogates. Predicted data are compared with reference ones (measurements or data from calibrated 0-D/1-D model) while discussing differences between them. CPU benefits are quantified. The main conclusion is that such CFD model has high predictive ability while requiring low calibration effort and being relatively fast, hence it is an interesting alternative to RANS-based industrial applications.
Investigation Into Reactivity Separation Between Direct Injected and Premixed Fuels in RCCI Combustion Mode
Authors: Yan Ziming , Gainey Brian , Hariharan Deivanayagam , Lawler Benjamin
Published: December 2019

This experimental study focuses on the effects of the reactivity separation between the port injected fuel and the direct injection fuel, the amount of external-cooled exhaust gas recirculation (EGR), and the direct injection timing of the high reactivity fuel on Reactivity Controlled Compression Ignition (RCCI) combustion. The experiments were conducted on a light-duty, single-cylinder diesel engine with a production GM/Isuzu engine head and piston and a retrofitted port fuel injection system. The global charge-mass equivalence ratio, ϕ′, was fixed at 0.32 throughout all of the experiments. To investigate the effects of the fuel reactivity separation, different Primary Reference Fuels (PRF) were port injected, with the PRF number varying from 50 to 90. To investigate the effects of EGR, an EGR range of 0 to 55% was used. To investigate the effects of the injection timing, an injection timing window of −65 to −45 degrees ATDC was chosen.

The results indicate that there are several tradeoffs. First, decreasing the port injected fuel reactivity (increasing the PRF number) delays combustion phasing, decreases the combustion efficiency by up to 9%, increases the gross indicated thermal efficiency up to 22%, enhances the combustion sensitivity to the direct injection timing, and slightly increases the UHC, CO, and NOx emissions. Second, increasing the EGR percentage delays combustion phasing, lowers the peak heat release rate, and lowers the NOx emissions. The combustion efficiency first increases and then decreases with EGR percentage for high reactivity fuels (low PRF number), but only decreases for low reactivity fuels. Finally, delaying the injection timing advances combustion phasing and increases the combustion efficiency, but decreases the gross indicated thermal efficiency and increases the NOx emissions. Across all of the experiments, delays in CA50 increase the gross indicated thermal efficiency and decrease the combustion efficiency, which represents an inherent tradeoff for RCCI combustion on a light-duty engine.
A Novel Air and EGR Emulation Facility for the Optimisation of the Powertrain Architecture
Authors: Orchard Simon , Ozturk Umud , Evans Nick , Duda Tomasz , Chappell Ed , Burke Richard
Published: December 2019

In this work, an external air and EGR emulation facility has been designed that can replicate a wide range of boosting and EGR delivery systems to a multi-cylinder engine platform. The facility works by removing the incumbent air path and replacing it with externally boosted fresh air that is conditioned using a transient flow and temperature controller. The facility also recycles the actual exhaust gases from the engine whilst removing the constraints of required pressure differences to drive this flow. The resulting system is able to control the boundary conditions of intake air flow - pressure and temperature, engine back-pressure and EGR flow rate independently.

Three testing approaches have been described that allow to obtain valuable data across a wide range of the engine map (based on an example of a 1.0L direct injection gasoline engine) also beyond its typical hardware related limits.

The facility is designed to be used as part of an engine design optimisation process. The facility generates data of the engine combustion system independently of the associated air path subsystems and excites the boundary conditions beyond those that would be expected from a specific air path design. The data is then used to populate 1D engine models which can be confidently used to predict the performance of a specific air path hardware combination and control strategy.
High Efficiency Diesel Engine Concept With Variable Valve Train and Cylinder Deactivation for Integration Into a Tractor
Authors: Thees Matthias , Buitkamp Thomas , Guenthner Michael , Pickel Peter
Published: December 2019

The objective of current research on internal combustion engines is to further reduce exhaust emissions while simultaneously reducing fuel consumption. The resulting measures often mean an increase in complexity of internal combustion engines, which on one hand increases production cost and on the other hand increases the susceptibility of the overall system to defects. It is therefore necessary to develop technologies which can generate an advantage for the consumer despite increasing complexity. Within the scope of the project “High Efficiency Diesel Engine Concept” (“Hocheffizientes Diesel-Motoren-Konzept” HDMK), funded by the Federal Ministry of Economic Affairs and Energy with TÜV Rheinland as project management organization (funding code: 19U15003A), two engine concepts were investigated and combined on a John Deere four-cylinder inline engine.

On the one hand, a new cylinder activation concept (“3/4-cylinder concept”) was implemented with the aim of reducing fuel consumption. On the other hand, a fully variable valve train was developed for this engine, which both improves the functionality of the 3/4-cylinder concept and can have a positive influence on exhaust emissions through internal exhaust gas recirculation.

A comparison of this engine concept with its series reference based on measurement data showed a fuel economy advantage of up to 5.2% in the low load field cycles of the DLG PowerMix. The maximum fuel consumption benefit in the low load engine regime exceeded 15% in some of the operating points.

As a final step, the engine was modified for the integration into an existing and working tractor, maintaining the available installation space of the powertrain.
Needle Displacement Visualization With Simultaneous Measurement of Injection Rate for CR Diesel Injector: A Novel Experimental Technique
Authors: Chiatti Giancarlo , Chiavola Ornella , Palmieri Fulvio
Published: December 2019

The control of combustion is a key topic for diesel engine development in terms of performance and pollutant emissions. The combustion process is piloted through the proper injection strategy, which depends on the features of the injection system. Mechanical-hydraulic models of high-pressure injection systems often support the accurate tuning of the injection strategy.

The higher is the accuracy in the modeling of the electro-injector behavior, the deeper is the role of the simulation. Under such a viewpoint, the validation of the models is undoubtedly fundamental.

One of the most crucial information characterizing the injector relies on the measurement of the needle displacement. Needle displacement affects rate, timing and quantity of injected fuel; it also influences the flow features within the nozzle, which are then reflected by the primary atomization process.

Needle is considered hardly-accessible due to the injector architecture itself, making difficult the measurement of displacement. Nevertheless, the problem has been handled in different ways and three measurement techniques have been proposed. On one side, there is the measurement based on eddy-current transducers; on the other side, there are two alternative procedures, based on the use of optical sensors. However, in all cases, the needle is traced indirectly, since the position of the control plunger of the needle is observed.

The current contribution presents a novel experimental technique for the measurement of needle displacement.

The method is based on the direct visualization of the needle, allowing for the detailed definition of its law of motion through digital imaging, when the injector is characterized on a test-rig under transient conditions.

The paper describes the details of the diagnostic scheme, the experimental facility and the digital imaging set-up. The main features and the capabilities of the method are discussed, in comparison with the other available techniques.
Two-Stage Lean-Burn Combustion Inside a Natural-Gas Spark-Ignition Engine With a Bowl-in-Piston Chamber
Authors: Liu Jinlong , Dumitrescu Cosmin E.
Published: December 2019

The conversion of existing diesel engines to spark ignition (SI) operation by adding a low-pressure injector in the intake manifold for fuel delivery and replacing the original high-pressure fuel injector with a spark plug to initiate and control the combustion process can reduce U.S. dependence on petroleum imports and increase natural gas (NG) applications in heavy-duty transportation sectors. Since the conventional diesel combustion chamber (i.e., flat-head-and-bowl-in-piston-chamber) creates high turbulence, the converted NG SI engine can operate leaner with stable and repeatable combustion process. However, existing literatures point to a long late-combustion duration and increased unburned hydrocarbon emissions in such retrofitted engines that maintained the original combustion chamber. Consequently, the main objective of this paper was to report recent findings of NG combustion characteristics inside a bowl-in-piston combustion chamber that will add to the general understanding of the phenomena. The new results indicated that the premixed NG burn inside the bowl-in-piston combustion chamber will separate into a bowl-burn and a squish-burn processes in terms of burning location and timing. The slow burning event in the squish region explains the low slope of the burn rate towards the end of combustion in existing studies (hence the longer late-combustion period). In addition, the less-favorable conditions for the combustion in the squish region explained the increased carbon monoxide and unburned hydrocarbon emissions.
Effect of Fuel Injection Parameters on Performance and Emissions for High Efficiency Engines
Authors: Kumar Raj , Wang Yan , Vojtech Ryan , Cigler James
Published: December 2019

Future diesel engine legislations are focused on further improvements in green-house gas emissions, such as carbon dioxide while additionally pushing for lower NOx emissions levels. These are being achieved with a combination of base-engine, fuel-injection system, air-system and after-treatment system improvements. In this paper, the effect of one injection system characteristics, namely injector flow-rate was investigated on engine performance and emissions using both numerical and experimental techniques. The phenomenon of increasing injector flow was first numerically investigated using commercial code Converge. Two approaches to increasing injector flow-rate were investigated. The first approach was by increasing the injector nozzle hole size while keeping the number of holes constant. The second approach was to change the number of the holes while keeping the injector nozzle size fixed. These simulations led to procurement of injectors to validate the simulation trends. Engine tests were performed with Navistar’s 12.4 L multi-cylinder heavy-duty diesel engine. The identified nozzle flow rates included a 66% increase from that of the baseline case. All the engine tests were performed at the typical cruising condition for this engine, at a series of injection timing and injection pressure values. It was observed that the crank angle for 50% of the integrated total calculated heat release (CA50) for the fuel burned was the most important factor that influenced the brake-thermal efficiency (BTE) and different injectors had similar BTE at constant CA50. With regards to emission, at higher nozzle flow rates, the combustion showed a slightly higher propensity for soot and increased levels of carbon monoxide.
Investigation of the Electrical-to-Thermal Energy Transfer Efficiency of Different Discharge Strategies Through Electrical and Calorimetry Measurement
Authors: Zhu Hua , Yu Xiao , Yang Zhenyi , Liang Li , Zheng Ming
Published: December 2019

In this paper, the electrical-to-thermal energy transfer efficiency of the transistor coil ignition system for spark-ignition engines is investigated using both electrical and calorimetry measurements. The gap voltage and discharge current are measured to determine the electrical energy supplied to the spark gap. A pressure-rise calorimeter is used to estimate the thermal energy transferred from the plasma channel to the gas. Firstly, this paper studies the influences of spark gap size, electrode geometry and background pressure on the energy transfer efficiency. To further investigate the effectiveness of increasing breakdown energy on the energy transfer process, a direct-capacitor is paralleled to the spark gap to redistribute the spark energy in both breakdown and glow phases. The varying of the capacitance enables the investigation of the energy transfer efficiency under different breakdown energy level. Results show that the electrical-to-thermal energy transfer efficiency is strongly dependent on gap size, electrode geometry and background pressure. Increasing the breakdown discharge energy is beneficial for the electrical to thermal energy transfer process.
Optimization of Engine Efficiency for Diesel Engine Equipped With EGR-VGT and Aftertreatment Systems
Authors: Yang Kuo , Chen Pingen
Published: December 2019

Engine efficiency improvement is very critical for medium to heavy-duty vehicles to reduce Diesel fuel consumption and enhance U.S. energy security. The tradeoff between engine efficiency and NOx emissions is an intrinsic property that prevents modern Diesel engines, which are generally equipped with exhaust gas recirculation (EGR) and variable geometry turbocharger (VGT), from achieving the optimal engine efficiency while meeting the stringent NOx emission standards. The addition of urea-based selective catalytic reduction (SCR) systems to modern Diesel engine aftertreatment systems alleviate the burden of NOx emission control on Diesel engines, which in return creates extra freedom for optimizing Diesel engine efficiency. This paper proposes two model-based approaches to locate the optimal operating point of EGR and VGT in the air-path loop to maximize the indicated efficiency of turbocharged diesel engine. Simulation results demonstrated that the engine brake specific fuel consumption (BSFC) can be reduced by up to 1.6% through optimization of EGR and VGT, compared to a baseline EGR-VGT control which considers both NOx emissions and engine efficiency on engine side. The overall equivalent BSFCs are 1.8% higher with optimized EGR and VGT control than with the baseline control. In addition, the influence of reducing EGR valve opening on the non-minimum phase behavior of the air path loop is also analyzed. Simulation results showed slightly stronger non-minimum phase behaviors when EGR is fully closed.
Numerical Investigation of Fuel Property Effects on Mixed-Mode Combustion in a Spark-Ignition Engine
Authors: Xu Chao , Pal Pinaki , Ren Xiao , Som Sibendu , Sjöberg Magnus , Van Dam Noah , Wu Yunchao , Lu Tianfeng , McNenly Matthew
Published: December 2019

In the present study, mixed-mode combustion of an E30 fuel in a direct-injection spark-ignition engine is numerically investigated at a fuel-lean operating condition using multidimensional computational fluid dynamics (CFD). A fuel surrogate matching Research Octane Number (RON) and Motor Octane Number (MON) of E30 is first developed using neural network based non-linear regression model. To enable efficient 3D engine simulations, a 164-species skeletal reaction mechanism incorporating NOx chemistry is reduced from a detailed chemical kinetic model. A hybrid approach that incorporates the G-equation model for tracking turbulent flame front, and the multi-zone well-stirred reactor model for predicting auto-ignition in the end gas, is employed to account for turbulent combustion interactions in the engine cylinder. Predicted in-cylinder pressure and heat release rate traces agree well with experimental measurements. The proposed modelling approach also captures moderated cyclic variability. Two different types of combustion cycles, corresponding to purely deflagrative and mixed-mode combustion, are observed. In contrast to the purely deflagrative cycles, mixed-mode combustion cycles feature early flame propagation followed by end-gas auto-ignition, leading to two distinctive peaks in heat release rate traces. The positive correlation between mixed-mode combustion cycles and early flame propagation is well captured by simulations. With the validated numerical setup, effects of NOx chemistry on mixed-mode combustion predictions are investigated. NOx chemistry is found to promote auto-ignition through residual gas recirculation, while the deflagrative flame propagation phase remains largely unaffected. Local sensitivity analysis is then performed to understand effects of physical and chemical properties of the fuel, i.e., heat of evaporation (HoV) and laminar flame speed (SL). An increased HoV tends to suppress end-gas auto-ignition due to increased vaporization cooling, while the impact of HoV on flame propagation is insignificant. In contrast, an increased SL is found to significantly promote both flame propagation and auto-ignition. The promoting effect of SL on auto-ignition is not a direct chemical effect; it is rather caused by an advancement of the combustion phasing, which increases compression heating of the end gas.
Effect of Fuel Chemical and Physical Properties on Spray and Ignition Characteristics Under Heavy-Duty Diesel Engine Conditions
Authors: Tang Meng , Pei Yuanjiang , Zhang Yu , Traver Michael , Naber Jeffrey
Published: December 2019

Spray combustion in compression ignition (CI) engines is a complex physical-chemical phenomenon. The differences in key fuel properties between gasoline range fuels and diesel, including the distillation temperature ranges and fuel reactivity, affect spray formation and combustion. To understand the impact of these fuel effects, this study aims at a thorough computational investigation involving variations in both the fuel physical and chemical properties. Physical properties include latent heat of vaporization, specific heat capacity, density, vapor pressure, viscosity, and surface tension. These properties were individually perturbed between gasoline and diesel. Chemical properties were represented by different fuel reactivity, including PRF0 and PRF60. The model was validated against diesel and RON60 gasoline spray experiments performed in a constant-volume combustion chamber. The physical and chemical properties were modeled separately to isolate the effect of a single parameter that is often difficult to single out in experimental investigations. Sprays under non-reacting and reacting conditions were then simulated to understand the physical processes that lead to ignition and thus the fuel reactivity effects on the subsequent processes. The investigation covered low to high temperature combustion and different exhaust gas recirculation (EGR) levels. Simulation results suggested that the chemical property dominated the ignition process, whereas the physical properties had more influence on the atomization and vaporization process. Also, there was a complex interaction between physical and chemical parameters on spray ignition depending on the operating conditions, which provide insights on tailoring fuel properties for different CI applications.
Assessing Fuel Property Effects on Cavitation and Erosion Propensity Using a Computational Fuel Screening Tool
Authors: Magnotti Gina M. , Som Sibendu
Published: December 2019

To advance compression ignition combustion strategies, researchers have evaluated fuel property effects and their impact on achieving higher efficiencies and lower emissions levels relative to current capabilities. Within the Department of Energy’s Co-Optima initiative, there has been a recent focus on understanding the influence of fuel properties on fuel injection performance. To help identify candidate fuels that can meet desired injector performance metrics, a computational fuel screening tool is under development that can link fuel properties with the tendency of a given fuel to cavitate and lead to cavitation-induced erosion. In the initial development of this tool, five liquid fuel properties were selected to represent candidate fuels, namely density, viscosity, vapor pressure, surface tension, and heat of vaporization. A design of experiments methodology was employed to generate a set of pseudo-fuel cases, which can represent the main effects and interactions among the fuel properties and be related to cavitation erosion predictions. Large eddy simulations were performed using a mixture modeling approach to predict the cavitation and erosion propensity of these pseudo-fuels in terms of the mean fuel vapor mole fraction and stored impact energy from repeated cloud collapse events. The low order regression models generated from this study revealed the importance of liquid fuel density on cavitation formation, whereas liquid viscosity was found to have a strong negative correlation with erosion severity. The surrogate models were then used in the fuel screening tool to rank the cavitation and erosion tendency of four candidate single-component fuels: methyl decanoate, iso-octane, ethanol and n-dodecane. While the fuel screening tool was not able to quantitatively predict the cavitation and erosion response metrics, the tool was able to accurately rank the relative cavitation and erosion propensity of the four fuels. Overall, ethanol and iso-octane were observed to produce the highest levels of cavitation and erosion, respectively.
Experimental Investigation and Thermodynamic Modelling of an RCCI Engine With Gasoline and Ethanol As Pilot Fuels
Authors: Mishra Chinmaya , Subbarao P. M. V.
Published: December 2019

Reactivity controlled compression ignition (RCCI) is an emerging premix low temperature combustion philosophy. Contemporary understanding suggests that RCCI concept with a premix high octane (low reactivity) fuel and direct injected high cetane (high reactivity) fuel ensures in-cylinder stratification of equivalence ratio as well as fuel reactivity. This stratification of reactivity coupled with partial premixing ensures simultaneous reduction of oxides of nitrogen and smoke. Furthermore, the induced delay in combustion phasing and high compression ratio ensures diffusive flames away from piston surface resulting in higher thermal efficiency. In the present work, an experimental investigation was carried out using port injected gasoline and anhydrous ethanol as low reactivity pilot fuels and direct injected diesel as high reactivity main fuel under various energy share. A comparative study of both the pilot fuels were carried out in terms of engine performance, emission and in-cylinder behavior in both representative and statistical perspective.
Overcoming Turbocharger Limitations for Low BMEP Two-Stroke Large Bore Gas Engines: A Technical Analysis and Case Study
Authors: Toema Mohamed , Watts Paul , Mathews Hans , Beshouri Greg
Published: December 2019

This paper reviews the unique challenges of implementing emissions upgrade on low Brake Mean Effective Pressure (BMEP) natural gas engines. A large population of the low BMEP gas engines are still utilized in natural gas compressor stations nationwide. Reducing NOx emissions of these engines requires leaner air-to-fuel ratio operation. The typical engine upgrade utilizing a “pure” turbocharged approach is a challenge for low BMEP engines due to poor overall efficiencies of turbochargers at relatively low pressure ratios needed. Previous papers have reported on the use of pure turbocharging and noted performance deficiencies. Other papers have dealt with turbocharging in series with the reciprocating scavenger. Neither approach proved successful, as the units either had a very limited turn down, or suffered fuel efficiency penalties that can no longer be tolerated, given today concerns for Green House Gas emissions.

Current strict emission regulations and the need of pipeline companies to utilize their low BMEP engine fleet, necessitates revisiting of the low BMEP upgrade challenge. One of the main merits of these low BMEP units is the operation flexibility. They provide pipeline companies the ability to accommodate wide range of gas demand.

This paper first offers a thermodynamic analysis to demonstrate that the exhaust energy of the low BMEP engine is not sufficient to properly match the required compression energy of the turbocharger compressor wheel for a broad operating range. This means the required boost pressure can’t be achieved with a self-sustaining Turbo across a “normal” operating range. The paper then offers a technical analysis of the various viable options to upgrade low BMEP engines. Using a Cooper GMV-TF, a very common engine type in this class as a benchmark, several options are investigated, starting from a series turbocharging with the exiting on engine blower/piston scavenger to supercharging with electrical motor driven blower. It also investigates the option of using an external gas burner in the exhaust stream. The paper closes with a successful case study using electric driven blower in two different compressor station sites.