Assessing the capability of conventional in-cylinder insulation materials in achieving temperature swing engine performance benefits

[EN] Materials that enable wall temperature swing to follow the gas temperature throughout a reciprocating internal combustion engine cycle promise the greatest benefits from in-cylinder insulation without detriments to volumetric efficiency or fuel autoignition behavior. An anisotropic barium-neodymium-titanate insulation was selected as a promising off-the-shelf material to begin investigating temperature swing characteristics while maintaining adequate strength and adherence to the aluminum components it was applied to. Experimental analysis showed that permeable porosity within the barium-neodymium-titanate coating resulted in increased heat losses despite thermal insulation, fuel absorption losses, and a reduction in compression ratio. Additionally, the thickest coating suffered severe degradation throughout testing. Any potential benefits of temperature swing insulation were dominated by these losses, emphasizing the need to maintain a sealed coating surface.Andruskiewicz, P.; Najt, P.; Durrett, R.; Payri, R. (2018). Assessing the capability of conventional in-cylinder insulation materials in achieving temperature swing engine performance benefits. International Journal of Engine Research. 19(6):599-612. https://doi.org/10.1177/1468087417729254S59961219

An experimental study of gasoline effects on injection rate, momentum flux and spray characteristics using a common rail diesel injection system

A comparative study using diesel fuel and gasoline has been conducted focusing on the injection process. In this paper an experimental study has been carried out comparing the effects of the different fuels on the mass flow rate, momentum flux and spray visualization in non-reactive conditions with a conventional common rail system with a multi-hole injector and two different nozzle designs. Analysis of the results for both fuels show no significant variations of the momentum flux between fuels while mass flow appears to be higher for diesel with respect to gasoline when the injector needle is fully open. The use of gasoline in these injectors seems relevant in the opening and closing phases of the injector. The high-speed imaging under non-evaporative conditions revealed that both diesel and gasoline spray penetration are "quite" similar and the statistical analysis of the results shows good agreement with the literature, furthermore new parametric correlation for gasoline is presented in this work. No major differences in the spray cone angle have been found either, showing consistency with the momentum flux measurements.The authors wish to acknowledge General Motors for supporting this research.Payri, R.; García Martínez, A.; Doménech Llopis, V.; Durrett, R.; Plazas, AH. (2012). An experimental study of gasoline effects on injection rate, momentum flux and spray characteristics using a common rail diesel injection system. Fuel. 97:390-399. doi:10.1016/j.fuel.2011.11.0653903999

Analysis of the effects of wall temperature swing on reciprocating internal combustion engine processes

[EN] A thermal wall temperature swing model was built to capture the transient effects of various material properties and coating layers on the intra-cycle wall temperature of an internal combustion engine. This model was used with a thermodynamic engine simulation to predict and analyze the effects of different types of in-cylinder insulation on engine performance. Coatings that allow the surface temperature to swing in response to the gas' cyclical heat flux enable approximately 1/3 of the energy that was prevented from leaving the gas during expansion to be recovered while improving volumetric efficiency. Reductions in compression work due to better volumetric efficiency and less heat transfer from the walls to the gas accounted for half of the improvements, while additional work extraction during combustion and expansion accounted for the other half. As load increases, the temperature swing and benefits derived from it also increase. NSFC improvements of 0.5% to 1% were seen with a highly swinging coating in the throttled regime for a realistic engine geometry and coating area, up to 2.5% at high loadsAndruskiewicz, P.; Najt, P.; Durrett, R.; Biesboer, S.; Schaedler, T.; Payri, R. (2018). Analysis of the effects of wall temperature swing on reciprocating internal combustion engine processes. International Journal of Engine Research. 19(4):461-473. https://doi.org/10.1177/1468087417717903S461473194Ramesh Kumar, C., & Nagarajan, G. (2012). Performance and emission characteristics of a low heat rejection spark ignited engine fuelled with E20. Journal of Mechanical Science and Technology, 26(4), 1241-1250. doi:10.1007/s12206-012-0206-0Hoffman, M. A., Lawler, B. J., Güralp, O. A., Najt, P. M., & Filipi, Z. S. (2014). The impact of a magnesium zirconate thermal barrier coating on homogeneous charge compression ignition operational variability and the formation of combustion chamber deposits. International Journal of Engine Research, 16(8), 968-981. doi:10.1177/146808741456127

Performance and engine-out emissions evaluation of the double injection strategy applied to the gasoline partially premixed compression ignition spark assisted combustion concept

Spark assistance has been found to improve combustion control when combined with both single and double injection operation applied to compression ignition (CI) engines using gasoline as the fuel. Previous work has verified the potential of a double injection strategy when applied to the gasoline spark assisted partially premixed compression ignition combustion (PPC) concept. The current research presents performance and engine-out emissions results using a double injection strategy with the spark assisted PPC concept and shows its benefits compared to a single injection strategy. For this purpose, a parametric study was carried out using gasoline in a high-speed single-cylinder diesel engine equipped with a modified cylinder head, which included a spark plug. The parameters that were varied during the double injection testing included: injection timing, dwell, fuel mass split between the injections and intake oxygen concentration. A detailed analysis of the air/fuel mixing process was also conducted by means of a 1-D in-house spray model (DICOM)The authors would like to thank General Motors for supporting this research.Benajes Calvo, JV.; Molina Alcaide, SA.; García Martínez, A.; Monsalve Serrano, J.; Durrett, R. (2014). Performance and engine-out emissions evaluation of the double injection strategy applied to the gasoline partially premixed compression ignition spark assisted combustion concept. Applied Energy. 134:90-101. doi:10.1016/j.apenergy.2014.08.008S9010113

Conceptual model description of the double injection strategy applied to the gasoline partially premixed compression ignition combustion concept with spark assistance

New combustion concepts applied to Compression Ignition engines are focused on achieve low temperature combustion together with a lean mixture distribution by allowing extra time from the end of injection to the start of combustion. Recently, the use of gasoline in a Compression Ignition engine under PPC conditions has been demonstrated as a suitable technique to achieve this extra mixing time, however the concept has also demonstrated difficulties under low load conditions using gasoline with octane number up to 95. The use of spark assistance with single injection operation has been found to be an appropriate way to improve the combustion control, providing both temporal and spatial control over the combustion process. The current paper details the influence of the double injection strategy on the Spark Assisted Partially Premixed Combustion concept compared with the single injection strategy. For this purpose, a reference combustion cycle for both injection strategies is compared in terms of the main parameters derived from the in-cylinder pressure signal as well as OH* and natural luminosity images acquired from the single-cylinder transparent engine. The cylinder head used along the research has been modified including a spark plug. In addition, a detailed analysis of the air/fuel mixing process has been developed by means of a 1-D in-house spray model.The authors would like to thank General Motors for supporting this research.Benajes Calvo, JV.; Molina Alcaide, SA.; García Martínez, A.; Monsalve Serrano, J.; Durrett, R. (2014). Conceptual model description of the double injection strategy applied to the gasoline partially premixed compression ignition combustion concept with spark assistance. Applied Energy. 129:1-9. doi:10.1016/j.apenergy.2014.04.093S1912

An investigation of partially premixed compression ignition combustion using gasoline and spark assistance

Nowadays the automotive scientific community and companies are focusing part of their efforts on the investigation of new combustion modes in Compression Ignition (Cl) engines, mainly based on the use of locally lean air fuel mixtures. This characteristic, combined with exhaust gas recirculation, provides low combustion temperatures that reduce pollutant formation. However these combustion concepts have some shortcomings, related to combustion phasing control and combustion stability under the light load engine operating range which must be overcome. The aim of this work is focused on the study of the integration of phasing and cycle-to-cycle repeatability control by means of an ignition spark plug system in a CI engine working under partially premixed charge (PPC) in order to overcome the lack of combustion stability in light load conditions when very low fuel reactivity is used. To achieve this objective, experimental tests have been carried out in a single cylinder optical engine combining broadband luminosity images with cylinder pressure derived heat release rate analysis. Research results reveals the spark assistance as a proper methodology to provide temporal and spatial control over the combustion process solving the lack of cycle to cycle control on the highly premixed compression ignition modes overall in light loads with high octane number (ON) fuels. Additionally, different stages have been identified in the combustion mode. The process starts with the spark discharge, which produces a flame kernel around the spark plug that later evolves to a premixed flame front. This premixed flame front heats unburned mixture and progresses into an auto-ignition combustion that burns out the rest of the charge with higher light intensity and finally an extinction of combustion process. Finally, the effect of injected fuel mass on the combustion mode has been also tested. An increase in the injected fuel mass has a positive effect on the assistance of the spark in the combustion process for both, combustion stability and cycle to cycle control. (C) 2013 Elsevier Ltd. All rights reserved.The authors would like to thank General Motors for supporting this research.Benajes Calvo, JV.; García Martínez, A.; Doménech Llopis, V.; Durret, R. (2013). An investigation of partially premixed compression ignition combustion using gasoline and spark assistance. Applied Thermal Engineering. 52(2):468-477. doi:10.1016/j.applthermaleng.2012.12.025S46847752

Plasma cell output from germinal centers is regulated by signals from Tfh and stromal cells

Germinal centers (GCs) are the sites where B cells undergo affinity maturation. The regulation of cellular output from the GC is not well understood. Here, we show that from the earliest stages of the GC response, plasmablasts emerge at the GC-T zone interface (GTI). We define two main factors that regulate this process: Tfh-derived IL-21, which supports production of plasmablasts from the GC, and TNFSF13 (APRIL), which is produced by a population of podoplanin+CD157highfibroblastic reticular cells located in the GTI that are also rich in message for IL-6 and chemokines CXCL12, CCL19, and CCL21. Plasmablasts in the GTI express the APRIL receptor TNFRSF13B (TACI), and blocking TACI interactions specifically reduces the numbers of plasmablasts appearing in the GTI. Plasma cells generated in the GTI may provide an early source of affinity-matured antibodies that may neutralize pathogens or provide feedback regulating GC B cell selection

Phase Transitions on Nonamenable Graphs

We survey known results about phase transitions in various models of statistical physics when the underlying space is a nonamenable graph. Most attention is devoted to transitive graphs and trees

Evolutionary games on graphs

Game theory is one of the key paradigms behind many scientific disciplines from biology to behavioral sciences to economics. In its evolutionary form and especially when the interacting agents are linked in a specific social network the underlying solution concepts and methods are very similar to those applied in non-equilibrium statistical physics. This review gives a tutorial-type overview of the field for physicists. The first three sections introduce the necessary background in classical and evolutionary game theory from the basic definitions to the most important results. The fourth section surveys the topological complications implied by non-mean-field-type social network structures in general. The last three sections discuss in detail the dynamic behavior of three prominent classes of models: the Prisoner's Dilemma, the Rock-Scissors-Paper game, and Competing Associations. The major theme of the review is in what sense and how the graph structure of interactions can modify and enrich the picture of long term behavioral patterns emerging in evolutionary games.Comment: Review, final version, 133 pages, 65 figure