Evaluation of the Thermal NO formation mechanism under low-temperature diesel combustion conditions

Over the past two decades, the amount of exhaust gas pollutants emissions has been significantly reduced due to the severe emission legislation imposed in most countries worldwide. Initial strategies simply required the employment of simple after-treatment and engine control devices; however, as the restrictions become more stringent, these strategies are evolving in the development of different combustion modes, specially characterized by having low-temperature combustion characteristics. These new working conditions demand the need to check the suitability of the current NO predictive models that coexist nowadays under standard diesel combustion characteristics, paying closer attention to the Thermal mechanism. In order to do so, a common chemical-kinetic software was employed to simulate, for n-heptane and methane fuels, fixed local conditions (standard diesel and low-temperature combustion) described by constant pressure, relative mixture fraction, oxygen mass fraction and initial and final reaction temperature. The study reflects a common trend between all the studied cases, independently of the considered local conditions, making it applicable to more complex situations such as real NO formation processes in diesel sprays. This relationship was characterized by a fourth-degree polynomial equation capable of substantially improving the NO prediction by just using the Thermal NO predictive model.The authors thank the Ministerio de Ciencia e Innovacion of the Spanish government for contributing to this work with the grant BES-2009-021897.Desantes Fernández, JM.; López, JJ.; Redón Lurbe, P.; Arregle, JJP. (2012). Evaluation of the Thermal NO formation mechanism under low-temperature diesel combustion conditions. International Journal of Engine Research. 13(6):531-539. https://doi.org/10.1177/1468087411429638S53153913

Optical study on characteristics of non-reacting and reacting diesel spray with different strategies of split injection

[EN] Even though studies on split-injection strategies have been published in recent years, there are still many remaining questions about how the first injection affects the mixing and combustion processes of the second one by changing the dwell time between both injection events or by the first injection quantity. In this article, split-injection diesel sprays with different injection strategies are investigated. Visualization of n-dodecane sprays was carried out under both non-reacting and reacting operating conditions in an optically accessible two-stroke engine equipped with a single-hole diesel injector. High-speed Schlieren imaging was applied to visualize the spray geometry development, while diffused backgroundillumination extinction imaging was applied to quantify the instantaneous soot production (net result of soot formation and oxidation). For non-reacting conditions, it was found that the vapor phase of second injection penetrates faster with a shorter dwell time and independently of the duration of the first injection. This could be explained in terms of onedimensional spray model results, which provided information on the local mixing and momentum state within the flow. Under reacting conditions, interaction between the second injection and combustion recession of the first injection is observed, resulting in shorter ignition delay and lift-off compared to the first injection. However, soot production behaves differently with different injection strategies. The maximum instantaneous soot mass produced by the second injection increases with a shorter dwell time and with longer first injection duration.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was partially funded by the Spanish Ministry of Economy and Competitiveness in the frame of the advanced spray combustion models for efficient powertrains (COMEFF) (TRA2014-59483-R) project. Funding for Tiemin Xuan's PhD studies was granted by Universitat Politecnica de Valencia through the Programa de Apoyo para la Investigacion y Desarrollo (PAID) (grant reference FPI-2015-S2-1068)Desantes, J.; García-Oliver, JM.; García Martínez, A.; Xuan, T. (2019). Optical study on characteristics of non-reacting and reacting diesel spray with different strategies of split injection. International Journal of Engine Research. 20(6):606-623. https://doi.org/10.1177/1468087418773012S606623206Arrègle, J., Pastor, J. V., López, J. J., & García, A. (2008). Insights on postinjection-associated soot emissions in direct injection diesel engines. Combustion and Flame, 154(3), 448-461. doi:10.1016/j.combustflame.2008.04.021Mendez, S., & Thirouard, B. (2008). Using Multiple Injection Strategies in Diesel Combustion: Potential to Improve Emissions, Noise and Fuel Economy Trade-Off in Low CR Engines. SAE International Journal of Fuels and Lubricants, 1(1), 662-674. doi:10.4271/2008-01-1329He, Z., Xuan, T., Jiang, Z., & Yan, Y. (2013). Study on effect of fuel injection strategy on combustion noise and exhaust emission of diesel engine. Thermal Science, 17(1), 81-90. doi:10.2298/tsci120603159hKook, S., Pickett, L. M., & Musculus, M. P. B. (2009). Influence of Diesel Injection Parameters on End-of-Injection Liquid Length Recession. SAE International Journal of Engines, 2(1), 1194-1210. doi:10.4271/2009-01-1356Musculus, M. P. B., & Kattke, K. (2009). Entrainment Waves in Diesel Jets. SAE International Journal of Engines, 2(1), 1170-1193. doi:10.4271/2009-01-1355O’Connor, J., Musculus, M. P. B., & Pickett, L. M. (2016). Effect of post injections on mixture preparation and unburned hydrocarbon emissions in a heavy-duty diesel engine. Combustion and Flame, 170, 111-123. doi:10.1016/j.combustflame.2016.03.031O’Connor, J., & Musculus, M. (2013). Post Injections for Soot Reduction in Diesel Engines: A Review of Current Understanding. SAE International Journal of Engines, 6(1), 400-421. doi:10.4271/2013-01-0917O’Connor, J., & Musculus, M. (2014). In-Cylinder Mechanisms of Soot Reduction by Close-Coupled Post-Injections as Revealed by Imaging of Soot Luminosity and Planar Laser-Induced Soot Incandescence in a Heavy-Duty Diesel Engine. SAE International Journal of Engines, 7(2), 673-693. doi:10.4271/2014-01-1255Bruneaux, G., & Maligne, D. (2009). Study of the Mixing and Combustion Processes of Consecutive Short Double Diesel Injections. SAE International Journal of Engines, 2(1), 1151-1169. doi:10.4271/2009-01-1352Pickett, L. M., Kook, S., & Williams, T. C. (2009). Transient Liquid Penetration of Early-Injection Diesel Sprays. SAE International Journal of Engines, 2(1), 785-804. doi:10.4271/2009-01-0839Skeen, S., Manin, J., & Pickett, L. M. (2015). Visualization of Ignition Processes in High-Pressure Sprays with Multiple Injections of n-Dodecane. SAE International Journal of Engines, 8(2), 696-715. doi:10.4271/2015-01-0799Bolla, M., Chishty, M. A., Hawkes, E. R., & Kook, S. (2017). Modeling combustion under engine combustion network Spray A conditions with multiple injections using the transported probability density function method. International Journal of Engine Research, 18(1-2), 6-14. doi:10.1177/1468087416689174Blomberg, C. K., Zeugin, L., Pandurangi, S. S., Bolla, M., Boulouchos, K., & Wright, Y. M. (2016). Modeling Split Injections of ECN «Spray A» Using a Conditional Moment Closure Combustion Model with RANS and LES. SAE International Journal of Engines, 9(4), 2107-2119. doi:10.4271/2016-01-2237Cung, K., Moiz, A., Johnson, J., Lee, S.-Y., Kweon, C.-B., & Montanaro, A. (2015). Spray–combustion interaction mechanism of multiple-injection under diesel engine conditions. Proceedings of the Combustion Institute, 35(3), 3061-3068. doi:10.1016/j.proci.2014.07.054Moiz, A. A., Cung, K. D., & Lee, S.-Y. (2017). Simultaneous Schlieren–PLIF Studies for Ignition and Soot Luminosity Visualization With Close-Coupled High-Pressure Double Injections of n-Dodecane. Journal of Energy Resources Technology, 139(1). doi:10.1115/1.4035071Maes, N., Bakker, P. C., Dam, N., & Somers, B. (2017). Transient Flame Development in a Constant-Volume Vessel Using a Split-Scheme Injection Strategy. SAE International Journal of Fuels and Lubricants, 10(2), 318-327. doi:10.4271/2017-01-0815Moiz, A. A., Ameen, M. M., Lee, S.-Y., & Som, S. (2016). Study of soot production for double injections of n-dodecane in CI engine-like conditions. Combustion and Flame, 173, 123-131. doi:10.1016/j.combustflame.2016.08.005PASTOR, J., JAVIERLOPEZ, J., GARCIA, J., & PASTOR, J. (2008). A 1D model for the description of mixing-controlled inert diesel sprays. Fuel, 87(13-14), 2871-2885. doi:10.1016/j.fuel.2008.04.017Desantes, J. M., Pastor, J. V., García-Oliver, J. M., & Pastor, J. M. (2009). A 1D model for the description of mixing-controlled reacting diesel sprays. Combustion and Flame, 156(1), 234-249. doi:10.1016/j.combustflame.2008.10.008Pastor, J., Garcia-Oliver, J. M., Garcia, A., Zhong, W., Micó, C., & Xuan, T. (2017). An Experimental Study on Diesel Spray Injection into a Non-Quiescent Chamber. SAE International Journal of Fuels and Lubricants, 10(2), 394-406. doi:10.4271/2017-01-0850Settles, G. S. (2001). Schlieren and Shadowgraph Techniques. doi:10.1007/978-3-642-56640-0Pastor, J. V., Payri, R., Garcia-Oliver, J. M., & Briceño, F. J. (2013). Schlieren Methodology for the Analysis of Transient Diesel Flame Evolution. SAE International Journal of Engines, 6(3), 1661-1676. doi:10.4271/2013-24-0041Pastor, J. V., Garcia-Oliver, J. M., Novella, R., & Xuan, T. (2015). Soot Quantification of Single-Hole Diesel Sprays by Means of Extinction Imaging. SAE International Journal of Engines, 8(5), 2068-2077. doi:10.4271/2015-24-2417Pickett, L. M., & Siebers, D. L. (2004). Soot in diesel fuel jets: effects of ambient temperature, ambient density, and injection pressure. Combustion and Flame, 138(1-2), 114-135. doi:10.1016/j.combustflame.2004.04.006Ko¨ylu¨, U. O., & Faeth, G. M. (1994). Optical Properties of Overfire Soot in Buoyant Turbulent Diffusion Flames at Long Residence Times. Journal of Heat Transfer, 116(1), 152-159. doi:10.1115/1.2910849Manin, J., Pickett, L. M., & Skeen, S. A. (2013). Two-Color Diffused Back-Illumination Imaging as a Diagnostic for Time-Resolved Soot Measurements in Reacting Sprays. SAE International Journal of Engines, 6(4), 1908-1921. doi:10.4271/2013-01-2548Choi, M. Y., Mulholland, G. W., Hamins, A., & Kashiwagi, T. (1995). Comparisons of the soot volume fraction using gravimetric and light extinction techniques. Combustion and Flame, 102(1-2), 161-169. doi:10.1016/0010-2180(94)00282-wKnox, B. W., & Genzale, C. L. (2015). Reduced-order numerical model for transient reacting diesel sprays with detailed kinetics. International Journal of Engine Research, 17(3), 261-279. doi:10.1177/1468087415570765Burke, S. P., & Schumann, T. E. W. (1928). Diffusion Flames. Industrial & Engineering Chemistry, 20(10), 998-1004. doi:10.1021/ie50226a005Desantes, J. M., García-Oliver, J. M., Xuan, T., & Vera-Tudela, W. (2017). A study on tip penetration velocity and radial expansion of reacting diesel sprays with different fuels. Fuel, 207, 323-335. doi:10.1016/j.fuel.2017.06.108Nerva, J.-G. (s. f.). An Assessment of fuel physical and chemical properties in the combustion of a Diesel spray. doi:10.4995/thesis/10251/29767Payri, R., Salvador, F. J., Gimeno, J., & Bracho, G. (2008). A NEW METHODOLOGY FOR CORRECTING THE SIGNAL CUMULATIVE PHENOMENON ON INJECTION RATE MEASUREMENTS. Experimental Techniques, 32(1), 46-49. doi:10.1111/j.1747-1567.2007.00188.xPayri, R., Gimeno, J., Novella, R., & Bracho, G. (2016). On the rate of injection modeling applied to direct injection compression ignition engines. International Journal of Engine Research, 17(10), 1015-1030. doi:10.1177/1468087416636281Malbec, L.-M., Eagle, W. E., Musculus, M. P. B., & Schihl, P. (2015). Influence of Injection Duration and Ambient Temperature on the Ignition Delay in a 2.34L Optical Diesel Engine. SAE International Journal of Engines, 9(1), 47-70. doi:10.4271/2015-01-1830Payri, R., García-Oliver, J. M., Xuan, T., & Bardi, M. (2015). A study on diesel spray tip penetration and radial expansion under reacting conditions. Applied Thermal Engineering, 90, 619-629. doi:10.1016/j.applthermaleng.2015.07.042Knox, B. W., & Genzale, C. L. (2017). Scaling combustion recession after end of injection in diesel sprays. Combustion and Flame, 177, 24-36. doi:10.1016/j.combustflame.2016.11.021García-Oliver, J. M., Malbec, L.-M., Toda, H. B., & Bruneaux, G. (2017). A study on the interaction between local flow and flame structure for mixing-controlled Diesel sprays. Combustion and Flame, 179, 157-171. doi:10.1016/j.combustflame.2017.01.02

The initiation and development of combustion under cold idling conditions using a glow plug in diesel engines

Factors determining the success or failure of combustion initiation using a glow plug have been investigated through experimental work on a single cylinder, common rail diesel engine with a geometric compression ratio of 15.5, and a quiescent combustion bomb with optical access. A glow plug was required to avoid engine misfires when bulk gas temperature at the start of injection was less than 413 C. The distance between the glow plug and the spray edge, the glow plug temperature, and the bulk gas temperature were important factors in meeting two requirements for successful ignition: a minimum local temperature of 413 C and a minimum air/fuel vapour equivalence ratio of 0.15–0.35

Optimisation of the vehicle transmission and the gear-shifting strategy for the minimum fuel consumption and the minimum nitrogen oxide emissions

The paper outlines a computationally efficient analytical method for evaluating the fuel consumption and the nitrogen oxide emissions during manoeuvres pertaining to the New European Driving Cycle. An integrated optimisation procedure is also included in the analyses with minimisation of the brake specific fuel consumption and minimisation of the nitrogen oxide emissions as objective functions. A set of optimum gear ratios are determined for a four-speed transmission, a five-speed transmission and six-speed transmission as the governing parameters in the optimisation process. The analysis highlights the determination of gear-shifting objective-driven strategies based on the minimisation of either of the declared objective functions. A reduction of 7.5% in the brake specific fuel consumption and a reduction of 6.75% in nitrogen oxide emissions are attainable in the best-case scenario for a six-speed transmission and a gear-shifting strategy based on the lowest brake specific fuel consumption for the case of an engine. The novel integrated analytical simulations and multi-objective optimisation have not been hitherto reported in literature. It provides the opportunity for an objective intelligent-based approach to the use of gear shift indicator technology. The results of this study also show that transmission optimisation can act as an effective and inexpensive mean to enhance the fuel efficiency and to reduce the emissions

Cycle-to-cycle combustion variability modelling in spark ignited engines for control purposes

This is the author's version of a work that was accepted for publication in International Journal of Engine Research. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published as https://doi.org/10.1177/1468087419885754.[EN] A control-oriented model of spark ignition combustion is presented. The model makes use of avaliable signals, such as spark advance, air mass, intake pressure, and lambda, to characterize not only the average combustion evolution but also the cycle-to-cycle variability. The conventional turbulent flame propagation model with two states, namely entrained mass and burnt mass, is improved by look-up tables at some parameters, and the cycle-to-cycle variability is estimated by propagation of an exogenous noise with a normal probabilistic distribution at the turbulent and laminar flame speed, which intends to simulate the unknowns at turbulent flow, temperature distribution, or initial kernel distribution. The model is able to estimate which is the expected variability during the combustion evolution and might be used online for characterizing the time response of closed-loop control actions or it can be used offline to improve the control strategies without large experimental test campaigns. Experimental data from a four-stroke commercial engine was used for calibration and validation purposes, demonstrating the capabilities of the model in steady and transient conditions.The authors appreciate the technical support and the clues given by J. Israel Sanchez for the model development and also acknowledge the support of Spanish Ministerio de Economia, Industria y Competitividad through project TRA2016-78717-R.Pla Moreno, B.; De La Morena, J.; Bares-Moreno, P.; Jimenez, IA. (2020). Cycle-to-cycle combustion variability modelling in spark ignited engines for control purposes. International Journal of Engine Research. 21(8):1398-1411. https://doi.org/10.1177/1468087419885754S13981411218Wang, S., Prucka, R., Zhu, Q., Prucka, M., & Dourra, H. (2016). A Real-Time Model for Spark Ignition Engine Combustion Phasing Prediction. SAE International Journal of Engines, 9(2), 1180-1190. doi:10.4271/2016-01-0819Kim, N., Ko, I., & Min, K. (2018). Development of a zero-dimensional turbulence model for a spark ignition engine. International Journal of Engine Research, 20(4), 441-451. doi:10.1177/1468087418760406Wang, S., Zhu, Q., Prucka, R., Prucka, M., & Dourra, H. (2015). Input Adaptation for Control Oriented Physics-Based SI Engine Combustion Models Based on Cylinder Pressure Feedback. SAE International Journal of Engines, 8(4), 1463-1471. doi:10.4271/2015-01-0877Zhen, X., Wang, Y., Xu, S., Zhu, Y., Tao, C., Xu, T., & Song, M. (2012). The engine knock analysis – An overview. Applied Energy, 92, 628-636. doi:10.1016/j.apenergy.2011.11.079Bares, P., Selmanaj, D., Guardiola, C., & Onder, C. (2018). Knock probability estimation through an in-cylinder temperature model with exogenous noise. Mechanical Systems and Signal Processing, 98, 756-769. doi:10.1016/j.ymssp.2017.05.033Zhang, Y., Shen, X., Wu, Y., & Shen, T. (2019). On-board knock probability map learning–based spark advance control for combustion engines. International Journal of Engine Research, 20(10), 1073-1088. doi:10.1177/1468087419858026Spelina, J. M., Peyton Jones, J. C., & Frey, J. (2014). Stochastic simulation and analysis of a classical knock controller. International Journal of Engine Research, 16(3), 461-473. doi:10.1177/1468087414551073Neumann, D., Jörg, C., Peschke, N., Schaub, J., & Schnorbus, T. (2017). Real-time capable simulation of diesel combustion processes for HiL applications. International Journal of Engine Research, 19(2), 214-229. doi:10.1177/1468087417726226Pipitone, E. (2008). A Comparison Between Combustion Phase Indicators for Optimal Spark Timing. Journal of Engineering for Gas Turbines and Power, 130(5). doi:10.1115/1.2939012Bares, P., Selmanaj, D., Guardiola, C., & Onder, C. (2018). A new knock event definition for knock detection and control optimization. Applied Thermal Engineering, 131, 80-88. doi:10.1016/j.applthermaleng.2017.11.138Peyton Jones, J. C., Spelina, J. M., & Frey, J. (2013). Optimizing knock thresholds for improved knock control. International Journal of Engine Research, 15(1), 123-132. doi:10.1177/1468087413482321Emiliano, P. (2014). Spark Ignition Feedback Control by Means of Combustion Phase Indicators on Steady and Transient Operation. Journal of Dynamic Systems, Measurement, and Control, 136(5). doi:10.1115/1.4026966Zhu, Q., Prucka, R., Wang, S., Prucka, M., & Dourra, H. (2016). Model-Based Optimal Combustion Phasing Control Strategy for Spark Ignition Engines. SAE International Journal of Engines, 9(2), 1170-1179. doi:10.4271/2016-01-0818Zhang, Y., & Shen, T. (2017). Cylinder pressure based combustion phase optimization and control in spark-ignited engines. Control Theory and Technology, 15(2), 83-91. doi:10.1007/s11768-017-6175-1Zhang, Y., Shen, X., & Shen, T. (2018). A survey on online learning and optimization for spark advance control of SI engines. Science China Information Sciences, 61(7). doi:10.1007/s11432-017-9377-7Corti, E., Forte, C., Mancini, G., & Moro, D. (2014). Automatic Combustion Phase Calibration With Extremum Seeking Approach. Journal of Engineering for Gas Turbines and Power, 136(9). doi:10.1115/1.4027188Corti, E., Cerofolini, A., Cavina, N., Forte, C., Mancini, G., Moro, D., … Ravaglioli, V. (2014). Automatic Calibration of Control Parameters based on Merit Function Spectral Analysis. Energy Procedia, 45, 919-928. doi:10.1016/j.egypro.2014.01.097Popovic, D., Jankovic, M., Magner, S., & Teel, A. R. (2006). Extremum seeking methods for optimization of variable cam timing engine operation. IEEE Transactions on Control Systems Technology, 14(3), 398-407. doi:10.1109/tcst.2005.863660Hellstrom, E., Lee, D., Jiang, L., Stefanopoulou, A. G., & Yilmaz, H. (2013). On-Board Calibration of Spark Timing by Extremum Seeking for Flex-Fuel Engines. IEEE Transactions on Control Systems Technology, 21(6), 2273-2279. doi:10.1109/tcst.2012.2236093Pera, C., Chevillard, S., & Reveillon, J. (2013). Effects of residual burnt gas heterogeneity on early flame propagation and on cyclic variability in spark-ignited engines. Combustion and Flame, 160(6), 1020-1032. doi:10.1016/j.combustflame.2013.01.009Zhao, L., Moiz, A. A., Som, S., Fogla, N., Bybee, M., Wahiduzzaman, S., … Kodavasal, J. (2017). Examining the role of flame topologies and in-cylinder flow fields on cyclic variability in spark-ignited engines using large-eddy simulation. International Journal of Engine Research, 19(8), 886-904. doi:10.1177/1468087417732447Pera, C., Knop, V., & Reveillon, J. (2015). Influence of flow and ignition fluctuations on cycle-to-cycle variations in early flame kernel growth. Proceedings of the Combustion Institute, 35(3), 2897-2905. doi:10.1016/j.proci.2014.07.037Schiffmann, P., Reuss, D. L., & Sick, V. (2017). Empirical investigation of spark-ignited flame-initiation cycle-to-cycle variability in a homogeneous charge reciprocating engine. International Journal of Engine Research, 19(5), 491-508. doi:10.1177/1468087417720558Galloni, E. (2009). Analyses about parameters that affect cyclic variation in a spark ignition engine. Applied Thermal Engineering, 29(5-6), 1131-1137. doi:10.1016/j.applthermaleng.2008.06.001Tamaki, S., Sakayanagi, Y., Sekiguchi, K., Ibuki, T., Tahara, K., & Sampei, M. (2014). On-line Feedforward Map Generation for Engine Ignition Timing Control. IFAC Proceedings Volumes, 47(3), 5691-5696. doi:10.3182/20140824-6-za-1003.01886Zhang, Y., & Shen, T. (2018). Combustion Variation Feedback Control Approach for Multi-cylinder Spark Ignition Engines. IFAC-PapersOnLine, 51(31), 105-110. doi:10.1016/j.ifacol.2018.10.020Corti, E., & Forte, C. (2011). Spark Advance Real-Time Optimization Based on Combustion Analysis. Journal of Engineering for Gas Turbines and Power, 133(9). doi:10.1115/1.4002919Gao, J., Wu, Y., & Shen, T. (2016). Experimental comparisons of hypothesis test and moving average based combustion phase controllers. ISA Transactions, 65, 504-515. doi:10.1016/j.isatra.2016.09.003Gao, J., Wu, Y., & Shen, T. (2017). A statistical combustion phase control approach of SI engines. Mechanical Systems and Signal Processing, 85, 218-235. doi:10.1016/j.ymssp.2016.08.007Lee, D., Jiang, L., Yilmaz, H., & Stefanopoulou, A. G. (2010). Preliminary Results on Optimal Variable Valve Timing and Spark Timing Control via Extremum Seeking. IFAC Proceedings Volumes, 43(18), 377-384. doi:10.3182/20100913-3-us-2015.00038Di Mauro, A., Chen, H., & Sick, V. (2019). Neural network prediction of cycle-to-cycle power variability in a spark-ignited internal combustion engine. Proceedings of the Combustion Institute, 37(4), 4937-4944. doi:10.1016/j.proci.2018.08.058Lapuerta, M., Armas, O., & Hernández, J. J. (1999). Diagnosis of DI Diesel combustion from in-cylinder pressure signal by estimation of mean thermodynamic properties of the gas. Applied Thermal Engineering, 19(5), 513-529. doi:10.1016/s1359-4311(98)00075-1Ceviz, M. A., & Kaymaz, İ. (2005). Temperature and air–fuel ratio dependent specific heat ratio functions for lean burned and unburned mixture. Energy Conversion and Management, 46(15-16), 2387-2404. doi:10.1016/j.enconman.2004.12.009Guardiola, C., Triantopoulos, V., Bares, P., Bohac, S., & Stefanopoulou, A. (2016). Simultaneous Estimation of Intake and Residual Mass Using In-Cylinder Pressure in an Engine with Negative Valve Overlap. IFAC-PapersOnLine, 49(11), 461-468. doi:10.1016/j.ifacol.2016.08.068Wang, S., Prucka, R., Prucka, M., & Dourra, H. (2014). Control-oriented residual gas mass prediction for spark ignition engines. International Journal of Engine Research, 16(7), 897-907. doi:10.1177/1468087414555732Keck, J. C. (1982). Turbulent flame structure and speed in spark-ignition engines. Symposium (International) on Combustion, 19(1), 1451-1466. doi:10.1016/s0082-0784(82)80322-

Investigating in-service failures of water pipes from a multiaxial notch fatigue point of view: A conceptual study

Many mechanisms and processes can cause deterioration and ultimately failure of water distribution pipes during in-service operation, amongst these is damage caused by metal fatigue. This paper summarises an attempt at formalising a novel methodology suitable for estimating the number of years taken for a through thickness fatigue crack to form in this complex scenario. The devised method is based on the so-called modified Wo¨hler curve method and can be applied to estimate fatigue damage of water pipes independently from the degree of multiaxiality and non-proportionality of the load history. The computational approach of the proposed fatigue life estimation technique makes full use of an incremental procedure: fatigue damage is evaluated year by year by assuming that all variable involved in the process can change over time. The detrimental effect of corrosion pits is directly accounted for by treating them as conventional notches whose size increases with time. Finally, by taking as reference information the number of years for a blowout hole to form, the proposed approach is used to show how the lifetime of grey cast iron pipes can be remarkably shortened by fatigue

Effects of advanced injection strategies on the in-cylinder air-fuel homogeneity of diesel engines

This document is an Accepted Manuscript. The final, definitive version of this paper has been published in Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, Vol. 228 (3), February 2015, published by SAGE Publishing, All rights reserved.The air–fuel mixing quality in the combustion chamber of a diesel engine is very critical for controlling the ignition and the combustion quality of direct-injection diesel engines. With a view to understanding the air–fuel mixing behaviour and the effect of the mixture quality on the emissions formation, an innovative approach with a new quantitative factor of the in-cylinder air–fuel homogeneity, called the homogeneity factor, was used, and its characteristics under various injection conditions were analysed with computational fluid dynamics simulations. By investigating the effect of advanced injection strategies on the homogeneity of the mixture and the emissions production, the study suggested that the homogeneity factor is greatly affected by the pulse number of injections, the injection timing and the dwell angle between two injections. The more advanced the injection taking place in the cylinder, the earlier the air–fuel mixing quality reaches a high level. Although the homogeneity factor is not sufficiently precise by itself to reflect the emissions formation, the results demonstrated that most often, the higher the homogeneity available in the cylinder, the more nitrogen oxides and the less soot were formedPeer reviewe