Topology Optimization of an Engine Piston to Reduce Particulate Emissions during Cold Start Operation

The majority of engine out particulate emissions are released in the first several minutes of cold start operation, in large part due to cold piston surface temperatures which fall well below the boiling point of the injected fuel. Use of topology optimization methods to increase piston surface temperatures is a promising approach to solve this challenge, but existing applications have focused largely on basic small-scale canonical scenarios in the steady-state. In this work an algorithm was developed and demonstrated which is aimed at optimizing the internal structure of an engine piston to increase piston surface temperatures during the early phases of engine cold start, while subjected to a peak temperature limit during hot steady-state conditions. Finite difference heat transfer models of a light duty aluminum engine piston were created and an evolutionary optimization algorithm in conjunction with the Lagrange Multiplier Method were used to develop optimal piston topologies. Overall the methods developed represent a unique successful application of topology optimization techniques to an unsteady thermal system at a practical scale. Various optimal designs were generated and common geometric traits between them were identified, providing insight for future piston designs. The relationship between mean piston surface temperature after one minute of cold operation and maximum piston temperature during hot steady-state operation was quantified, defining optimal design limits and quantifying the trade-off between the two temperatures.