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In this study, the crash performances of square and cylindrical crash boxes with tetra-chiral and reentrant unit cell structures were explored and optimized. First, tensile tests were conducted to determine the mechanical properties of the Al 6061-T6. These mechanical properties were then incorporated in the finite element (FE) models generated using LS-DYNA. To validate the FE models, tetra-chiral and reentrant crash plates were produced, and the FE analysis results were compared with the test results. Subsequent to this validation, for each crash box design type (i.e., tetra-chiral cylindrical, tetra-chiral square, reentrant cylindrical, and reentrant square), Kriging surrogate models were constructed using MATLAB for two crash metrics: specific energy absorption (SEA) and crash load efficiency (CLE). Finally, a multi-objective optimization problem was formulated for each crash box design type, the generated Kriging models are integrated into genetic algorithm available in MATLAB, and the Pareto optimal crash box designs were obtained. It was found that the SEA and CLE of reentrant crash boxes were better than those of the tetra-chiral crash boxes. In addition, the reentrant cylindrical crash box displayed better performance than the reentrant square, as well as the tetra-chiral cylindrical and square crash boxes.

Strict measures in emission regulations constantly lead researchers to technologies that are cleaner, renewable, and energy conversion efficient. Reactivity controlled compression ignition (RCCI), which is a low-temperature combustion (LTC) mode, is a promising technology providing simultaneously low nitrogen oxides (NOx) and soot emissions without reduction in engine thermal efficiency. However, the fact that the operating range is still not wide enough compared to conventional engines is one of the most challenging obstacles to RCCI engines. In this study the effects of the premixed ratio (PR) on engine operating range and emissions were investigated experimentally. A compression ignition (CI) engine was modified to be run in RCCI mode. Gasoline and diesel fuels were used as fuel pair in the experiments. The engine was operated at three different PRs of PR25, PR50, and PR75. It was found that the widest operating ranges and minimum brake specific fuel consumption (BSFC) values were obtained with PR50. The minimum BSFC was 162.5 g/kWh. It was determined that HC emissions increased as the PR increased due to the decreasing reactivity of the mixture. It was also found that CO emissions are more sensitive to engine load compared to the PR. © 2023 SAE International.