Topic 4: Panel Discussions 1 April 5, 2014 EFC Panelist-inspired Open Discussion 1.Assessment of 4.1Dave Reuss 2.Assessment of 4.2 Dan Haworth 3.Assessment of 4.3 & 4.4 Tommaso Lucchini 4.Path for Spray G into an engine Scott Parrish 5.Diesel Needs Oivind Andersson EFC Priorities and Needs for ECN 3.x Action Item: Choose most important and universal problems inhibiting progress that would inspirer non-competitive unfunded effort?

Topic 4: Panel Discussions 2 April 5, 2014 ECN 3.X Topic 4.1 Measurements for Simulation benchmarking Experimental efforts require more than simulation benchmarking. Experiments provide observations beyond 5 senses. Contributions of simulation to experimental results Steady-state operation is not adequate for assessing LES effectiveness. Compute n cycles perturb cycle n+1 initial/boundary conditions compute next cycle(s) Compare with equivalent perturbation in the experiment Interpret Interpolate & extrapolate design Archive

Topic 4: Panel Discussions 3 April 5, 2014 ECN 3.X Topic 4.2 Simulation-to-simulation benchmarking (LES, RANS) - Haworth How do we know when (if) our physical models/numerical methods/mesh resolution/boundary condition specification/etc. are sufficient for the task at hand? – Engine simulations are expensive - especially multiple-cycle LES Should we require/suggest submission of results using reference models? – e.g., turbulence, ignition, flame propagation... – To what extent do results from different codes vary, even with nominally the same physical models? Should we require/suggest submission of results for one or more reference configurations? – Back to decaying homogeneous isotropic turbulence in a period box? Should we require/suggest submission of quantitative resolution metrics for LES results? – Several metrics have been proposed, e.g., xx% of TKE resolved Should we require/suggest submission of convergence metrics for LES? – e.g., resolved + residual (subfilter-scale) contributions to specified quantities independent of mesh size in appropriate limits

Topic 4: Panel Discussions 4 April 5, 2014 ECN 3.X Topics 4.3 Benchmarking: comparisons, analysis, and validation 4.4 CCV origins and abatement - Lucchini Simulations vs exp. data: How to validate a CFD code for engine simulations? 1)Identification of a common engine geometry which will be used for cold-flow validation and a single operating point. TCC is a good candidate. 2)How many cycles to simulate (RANS)? How many cycles to measure to properly get average quantities for RANS comparison? 3)Which are the proper boundary conditions to be set at boundaries: Total variable pressure? Mass flow? How do boundary conditions affect the predicted volumetric efficiency? How to evaluate this? 4)Effects of mesh structure (even more than grid size) to be absolutely evaluated. Is a coarse, flow-oriented grid much better than a refined non-oriented one?

Topic 4: Panel Discussions 5 April 5, 2014 Is the Spray G injector suitable for engine experiments? EFC – Pathway for Spray G into and engine YES! early injection, homogenous late injection, stratified late injection, HCCI, dilute combustion, etc. Central mount position required (no bend angle) What could be learned by putting Spray G into an engine? What problems should be pursued? MUCH TO BE LEARNED! Cylinder flow / spray interaction - stochastics Ignition and combustion Spray / wall interactions... Need to be careful to maintain focus

Topic 4: Panel Discussions 6 April 5, 2014 ECN 3.X Diesel Engine Needs for Spray B - Oivind Andersson Which important spray phenomena are not accounted for in spray vessels? Spray-swirl interaction Spray-spray interaction – Entrainment of hot products – Effects on flow between jets Spray-wall interaction – Processes downstream of impingement point Late cycle mixing (?) – How do sprays affect processes occurring after EOI? Multiple injections – Why does a post injection reduce soot, etc? – Combustion system effects!

Topic 4: Panel Discussions 7 April 5, 2014

Topic 4: Panel Discussions 8 April 5, Measurement and instrumentation standards Required engine and system geometry In-cylinder & extra-cylinder instrumentation needs EnsAve, crank-resolved volume-ave Gas temperature measurements Wall temperatures Sensors: location, type, BC Engine operation, test-to-test repeatability criteria Metrics and criteria Run-time control Post-run analysis & charting Motored flow characterization Motored spray characterization Combustion characterization Global analysis Product gas Identification, 2-D/ 3-D Resolved homogeneous-Flame Front Error Analysis Compression ratio, TDC, valve events, & pegging Pressure measurements Temperature measurements PIV: u & dx dynamic range, u &du/dx accuracy Spray measurements 4.1. Measurements for Simulation benchmarking

Topic 4: Panel Discussions 9 April 5, Simulation-to-simulation benchmarking (LES, RANS) Engine simulation methodology Complete test-bench coupled with 1D simulation Type of boundary conditions Consecutive vs. Perturbed engine cycles Meshing strategy and resolution Immersed boundary, auto mesh movement Spatial resolution Resolved-flow measures for sub-grid efficacy Modeling issues Numerical method (spatial and temporal) Which models capture relevant physics & chemistry? Robust CPU doable computations

Topic 4: Panel Discussions 10 April 5, Benchmarking: comparisons, analysis, and validation Global engine metrics In-cylinder Global & 0-D Metrics Intake & Exhaust Systems 1-D quantities In-cylinder flow characterization Statistical Methods phase-average and standard deviation CCV vs. turbulence vs. noise Required Number of sampled cycles Conditional sampling on flow events POD: phase dependent, phase invariant Intra-cycle vs. inter-cycle comparison Qualitative comparison of velocity fields, 2-D vs. 3-D Sub-grid model efficacy from resolved-scale measures Simulation efficacy of scalar mixing Combustion modeling validation Global Heat Release Ignition and early flame development Fully-developed turbulent flame

Topic 4: Panel Discussions 11 April 5, CCV Origins and abatement Exploring CCV origin Flow motion influence Geometry of intake manifold and ducts Flow around valve or exiting valve curtain In-cylinder flow motion Flow motion near spark plug at spark timing Influence of the previous engine cycle Influence of the engine scavenging process Cylinder charging variation Local mixture heterogeneity Role of the spark-ignition period Combustion process in CCVs Early flame kernel propagation? Occurrence of partial combustion & quenching Heat transfer influence Factors that increase CCVs Engine geometry Engine operating points Mixture preparation Flow motion pattern