In order to reduce exhaust gas emissions, multiple computations must be completed to carry out engine design optimisations.
In this application, our customer was keen to deliver equivalent engine performance in a medium duty diesel engine whilst reducing corresponding exhaust gas emissions by redesigning the piston bowl geometry.
THE CHALLENGE
Diesel combustion occurs with high amounts of fuel stratification, conventionally in order to account for these inhomogeneities, 3D CFD software codes are adopted. In this application, to solve for combustion and emissions, one month of computational time was required on a single processor.
These timescales are not appropriate for engine design optimisation hence the combustion and emissions models are usually simplified with loss of model robustness and predictive capability.
Hence, the features of a 3D CFD simulation with detailed chemistry must be obtained over shorter timescales.
THE SOLUTION
The temperature-equivalence ratio statistics obtained 3D CFD were mapped into the srm suite code to study the impact of combustion chamber design (open bowl, vertical side wall bowl and re-entry bowl) combustion and emissions.
THE RESULTS
Equivalent 3D CFD model performance in reduced timescales
Firstly, the results obtained from the 3D CFD model and those obtained from the 3D CFD/srm suite model were almost identical, however the computational times were around one month and eight hours respectively. Both computations agreed well with those observed experimentally.
Insight into combustion chamber design
Three alternative piston geometries were simulated, in this case making little impact on the pressure profiles. However these subtle changes in the in-cylinder flow field resulted in differing exhaust emissions. By considering these computations, subtle improvements to the piston geometry were obtained.
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