Optical Arrangements for Time-Gated Ballistic Imaging

We report on a comparison of two optical setups used in time-gated ballistic imaging simulating monodisperse scattering environments with polystyrene spheres in different sizes and concentrations suspended in water

Forecasting Auxiliary Energy Consumption for Electric Heavy-Duty Vehicles

Accurate energy consumption prediction is crucial for optimizing the operation of electric commercial heavy-duty vehicles, e.g., route planning for charging. Moreover, understanding why certain predictions are cast is paramount for such a predictive model to gain user trust and be deployed in practice. Since commercial vehicles operate differently as transportation tasks, ambient, and drivers vary, a heterogeneous population is expected when building an AI system for forecasting energy consumption. The dependencies between the input features and the target values are expected to also differ across sub-populations. One well-known example of such a statistical phenomenon is the Simpson paradox. In this paper, we illustrate that such a setting poses a challenge for existing XAI methods that produce global feature statistics, e.g. LIME or SHAP, causing them to yield misleading results. We demonstrate a potential solution by training multiple regression models on subsets of data. It not only leads to superior regression performance but also more relevant and consistent LIME explanations. Given that the employed groupings correspond to relevant sub-populations, the associations between the input features and the target values are consistent within each cluster but different across clusters. Experiments on both synthetic and real-world datasets show that such splitting of a complex problem into simpler ones yields better regression performance and interpretability

Thin reaction zone and distributed reaction zone regimes in turbulent premixed methane/air flames : Scalar distributions and correlations

A series of premixed turbulent methane/air jet flames in the thin reaction zone (TRZ) and distributed reaction zone (DRZ) regimes were studied using simultaneous three-scalar high-resolution imaging measurements, including HCO/OH/CH2O, CH/OH/CH2O, T/OH/CH2O and T/CH/OH/. These scalar fields offer a possibility of revisiting the structures of turbulent premixed flames in different combustion regimes. In particular, CH2O provides a measure of the preheat zone, CH/HCO a measure of the inner layer of the reaction zone, and OH a measure of the oxidation zone. Scalar correlations are analyzed on both single-shot and statistical basis, and resolvable correlated structures of ∼100 µm between scalars are captured. With increasing turbulence intensity, it is shown that the preheat zone and the inner layer of the reaction zone become gradually broadened/distributed, and the correlation between HCO and [OH]LIF×[CH2O]LIF decreases. A transition from the TRZ regime to the DRZ regime is found around Karlovitz number of 70–100. The physical and chemical effects on the broadening of the flame are investigated. In the TRZ regime the inner layer marker CH and HCO remains thin in general although occasional local broadening of CH/HCO could be observed. Furthermore, there is a significant probability of finding CH and HCO at rather low temperatures even in the TRZ regime. In the DRZ regime, the broadening of CH and HCO are shown to be mainly a result of local reactions facilitated by rapid turbulent transport of radicals and intermediate reactants in the upstream of the reaction paths. Differential diffusion is expected to have an important effect in the DRZ regime, as H radicals seemingly play a more important role than OH radicals

Multi-species PLIF study of the structures of turbulent premixed methane/air jet flames in the flamelet and thin-reaction zones regimes

Simultaneously planar laser-induced fluorescence (PLIF) measurements of OH, CH, CH2O and toluene are carried out to investigate the structures of turbulent premixed methane/air jet flames in the flamelet regime and the thin-reaction zones regime. A premixed flame jet burner of an inner diameter of 1.5 mm is employed. Stoichiometric methane/air mixtures introduced as a jet are ignited and stabilized in a hot co-flow generated by a coaxial porous plug pilot flame surrounding the jet. The Reynolds number for the studied jet ranges from 960 to 11,500 with the characteristic Karlovitz number ranging from 1 to 60. The focus of this study is on the characterization of the structures and turbulent burning velocity of premixed flames in the flamelet and the thin-reaction zones regimes. The preheat zone is analyzed using the CH2O and toluene PLIF fields, whereas the reaction zone is analyzed using the CH and OH PLIF fields. Laser Doppler Anemometer (LDA) measurements are performed to characterize the turbulence field and it is noted that when the Reynolds/Karlovitz number increases a successive thickening of the preheat zone is observed, whereas the reaction zone, characterized by the CH layer maintains nearly the same thickness. The heat release zone, characterized by the combination of the OH and CH2O PLIF fields, is shown to nearly maintain the same thickness under the present experimental conditions. The flame surface wrinkle ratio is shown to be Reynolds number and Karlovitz number independent when the Reynolds number is high enough such that the smallest wrinkle scales reach to the length scales of the thin reaction layers. The global fuel consumption speed of the jet flame is analyzed using the toluene PLIF field and the OH PLIF field. A discrepancy in the two consumption velocities is found as the Karlovitz number increases. This is found to be a result of the broadening of the oxidation zone. These findings provide experimental support to the flamelet and thin-reaction zone regime hypotheses of turbulent premixed combustion

Influence of spatial and temporal distribution of Turbulent Kinetic Energy on heat transfer coefficient in a light duty CI engine operating with Partially Premixed Combustion

[EN] Emission regulations together with the need of more fuel-efficient engines have driven the development of promising combustion concepts in compression ignition (CI) engines. Most of these combustion concepts, lead towards a lean and low temperature combustion potentially suitable to achieve lower emission and fuel consumption levels compared to conventional diesel combustion. In this framework, Partially Premixed Combustion (PPC) using gasoline as fuel is one of the most accepted concepts. There are numerous studies focused on studying concepts such as PPC from the emissions point of view. Nonetheless, there is a lack of knowledge regarding changes in heat transfer introduced by the use of these combustion concepts. It is worth noting that heat transfer can be considered as a key aspect behind possible engine performance improvements. Thus, the reliable estimation of this parameter is of considerable importance. Additionally, a better understanding of how events such as injection and combustion might affect heat transfer is also relevant. To gain insight into gasoline PPC heat transfer coefficient, its evolution during late compression and early expansion were studied. In particular, this work aims to analyze Turbulent Kinetic Energy (TKE) spatial and temporal evolution influence on heat transfer coefficient. The analysis is based on experimental TKE maps derived from Particle Image Velocimetry (PIV) data. For the heat transfer coefficient estimation a modified Woschni correlation has been used. Results from several injection strategies and a reference motored case have been analyzed. It has been found that injection strategy has a considerable influence on the TKE field and hence on heat transfer coefficient evolution. (C) 2017 Elsevier Ltd. All rights reserved.The authors gratefully acknowledge the Swedish Energy Agency and the Competence Center for Combustion Processes KCFP. The authors also would like to acknowledge that part of the work has been partially funded by the Spanish Government under the grant "Jose Castillejo" (JC2015/0036). Research leading to this work has also receive funding from Universitat Politecnica de Valencia through the FPI program.Tanov, S.; Pachano-Prieto, LM.; Andersson, Ö.; Wang, Z.; Richter, M.; Pastor, JV.; García-Oliver, JM.... (2018). Influence of spatial and temporal distribution of Turbulent Kinetic Energy on heat transfer coefficient in a light duty CI engine operating with Partially Premixed Combustion. Applied Thermal Engineering. 129:31-40. https://doi.org/10.1016/j.applthermaleng.2017.10.006S314012

Development and application of laser diagnostics - from laboratory devices towards practical combustion engines

For many decades, research work on combustion has been focused on improving combustion efficiency and reducing harmful emissions. Laser diagnostics is one of the best ways to investigate the combustion process and emission formation as it is non-intrusive and it has high spatiotemporal resolution. In this thesis work, many laser diagnostics have been developed and employed for combustion research. The laser-based optical methods cover ballistic imaging (BI), multi-scaler laser introduced fluorescence (LIF) imaging, particle imaging velocimetry (PIV), laser Doppler anemometry (LDA), and high speed LIF measurement (up to 140 kHz). Two BI systems were developed and compared, together with ultrafast shadow imaging (USI) for better imaging through a high optical depth (OD) substance, e.g. a spray. In addition, multi-scaler planar laser introduced fluorescence (PLIF) measurements were developed in Lund University Piloted Jet (LUPJ) burners including simultaneous measurement of temperature, CH radicals and OH radicals distribution, and simultaneous measurement of CH2O radicals, CH radicals and OH radicals distribution. Key parameters, such as Damköhler number, Karlovitz number, and Kolmogorov time scale, were calculated and are listed in this thesis based on LDA measurements. Moreover, high speed PLIF measurements were developed in an LUPJ burner including simultaneous OH/CH2O PLIF at 50 kHz, OH PLIF at 100 kHz and CH2O PLIF at 140 kHz, with more than 100 consecutive images for the first ever time. That was achieved by using a burst-mode laser pumped optical parametric oscillator (OPO) system synchronised with high speed cameras and high speed intensifiers. The diagnostics approaches were capable of following the temporal evolution of the reacting flow down to the Kolmogorov scale for better understanding of the transient behaviour of the eddy/flame interaction in highly turbulent premixed flames.The developed laser diagnostics have also been applied in a diesel spray in a high temperature high pressure (HTHP) constant volume vessel, in a pulsed plasma discharge and in practical combustion devices, e.g. internal combustion engines with elevated pressure and temperature (>90 bar and >1000 ºC). The developed 2f-BI system has been successfully employed for investigation of the spray formation region of a diesel spray, i.e. engine combustion network (ECN) Spray A, and the supercritical phenomenon has been observed with cellular structures of the spray for the first time. It’s also the first time that a burst-mode laser system has been applied for high-speed OH PLIF imaging in pulsed plasma discharges at tens of kHz repetition rate. The changing of OH radical distribution during post discharge was captured at 27 kHz, e.g. the deformation of the OH PLIF intensity from toroidal shape to a filled circle was observed. In addition, the decay rate of OH distribution at the outer layer of the plasma column and the increasing rate of that in the plasma column were calculated. The mixing process of gasoline/diesel and air in homogeneous charge compression ignition (HCCI) and partially premixed combustion (PPC) engines was visualised and investigated by 10 Hz fuel-tracer PLIF measurements and, also, the developed high-speed PLIF techniques with the burst-mode laser system. In addition, the mixture formation and evolution of low temperature combustion, i.e. CH2O distribution, together with the auto-ignition, i.e. high temperature combustion, were captured and followed for more than ten crank angle degrees (CADs) in one engine cycle at 36 kHz. To the best of my knowledge, no one has ever achieved this before. The results are also of significant value for computational fluid dynamics of internal combustion engines. An extended conceptual model for gasoline PPC mode with exhaust gas recirculation (EGR)-dilution and single-injection strategy is proposed. Furthermore, cycle-resolved PIV measurement was performed in a light-duty optical diesel engine with single, double and triple injection strategies. Last but not least, the experimental equipment and setups are introduced in this thesis, together with some practical experience and hands-on advice not mentioned in the attached papers

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Simultaneous OH and CH2O PLIF imaging at 50kHz for case 1(Ujet=66 m/s, PHIjet=1, Ucoflow=0.3 m/s)

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Simultaneous OH and CH2O PLIF imaging at 50kHz for case 2 (Ujet=66 m/s, PHIjet=0.3, Ucoflow=0.1 m/s)

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Simultaneous OH and CH2O PLIF imaging at 50kHz for case 2 (Ujet=66 m/s, PHIjet=0.3, Ucoflow=0.1 m/s)