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[FAQ]

There are three main types of simulations, regardless of engine type, that one may use to check the input data and the quality of the results prior to running the entire simulation and prior to doing any kind of parameter study. The types of simulation are:
•No-hydro: Checks the quality of the mesh over the crank angle range of interest. In addition, it can be used as a quick check of the geometric engine compression ratio.
•Motored: This type of simulation only involves the compression of air with heat transfer and turbulent flow, i.e. no spray and no combustion. This type of simulation can also be used to check the observed compression ratio by comparing to a measured motored pressure trace. It can also be used to help detect errors in the boundary and initial conditions
. •Fired: This is the final simulation type and will generate the results to compare with the experimental data of interest.

The motored pressure trace is a very important step as it can be used to identify any adjustments that may need to be made to match the motored pressure curve by adjusting the squish (clearance) height and also to identify phasing issues with the pressure measurement (i.e., align peak pressure with TDC). The adjustment of the squish height will adjust the compression ratio of the engine. The compression ratio provided, in many cases, is the geometric compression ratio. In CFD simulations, some crevice volumes are neglected which requires an adjustment of the squish height or crevice volume to account for these neglected volumes. In general, the “simulated” compression ratio may be up to 1.5 smaller than the geometric compression ratio, e.g. if the geometric compression ratio is 15, the simulated compression ratio may be 13.5 in order to match the motored pressure curve. If a motored pressure trace is not available, use a case with the latest injection timing possible (ideally after TDC) to check how well the predicted pressure trace compares to the experimental data during the compression stroke. To compare the data for a motored case, plot log(P) vs. log(V).