A new model of particle entrapment during continuous casting of steel is presented, which includes the effects of multiphase flow from argon gas injection and thermal buoyancy from superheat in the strand. The model simulates three different capture mechanisms, including capture by solidified hooks at the meniscus, entrapment between dendrites, and engulfment by the surrounding of large particles. The fluid flow and bubble capture results are validated with plant measurements, including nail board dipping tests and ultrasonic tests, respectively, and good agreement is seen. Results suggest that the superheat has a negligible effect on the flow in the mold region. However, higher (30 K) superheat causes a more complex flow in the lower strand by creating multiple recirculation zones due to the thermal buoyancy effects. This causes less penetration deep into the strand, which leads to fewer and shallower particle captures. Lower (10 K) superheat may enable significant top surface freezing, leading to very large internal defect clusters. Lower superheat also leads to deeper meniscus hooks, which sometimes (0.003%) capture large (1 mm) bubbles. Capture bands occur near the transition line from vertical to curved, due to the downward fluid velocity balancing the particle terminal velocity, enabling capture in the relative stagnation region beneath the longitudinal recirculation zone. These findings agree with plant observations.

Hydrogen direct-injection engines offer a promising pathway for decarbonizing heavy-duty transportation, but accurate prediction of mixture formation and NO $$_x$$ emissions remains challenging due to complex injector dynamics and strong cycle-to-cycle variability. This work presents a comprehensive computational and experimental investigation of supersonic H $$_2$$ direct injection, mixing, combustion, and NO formation in a single-cylinder heavy-duty hydrogen engine operated at 1100 rpm and $$\lambda $$ = 2.6. A detailed three-dimensional CFD model is developed, coupling a pressure-based injection boundary condition with a realistic Bosch F2 prototype injector needle-lift profile to capture valve-bounce effects. The model is validated against measured in-cylinder pressure, fuel and air mass, and NO emission data. Multi-cycle combustion behavior and NO emission variability are analyzed using the concurrent perturbation method (CPM), with 20 statistically independent realizations at reduced computational cost. Results show that near-spark mixtures with higher fuel concentration accelerate flame propagation and increase peak NO by a factor of two (76 ppm vs. 32 ppm). Simulations reveal that NO forms predominantly in local pockets of high fuel concentration, with turbulent flame speeds of 11–22 m/s during the early combustion phase. Predicted exhaust-port NO levels agree qualitatively with experiments, though unsteady RANS tends to overpredict NO due to limited small-scale mixing. The study demonstrates that resolving the injector flow rather than approximating boundary conditions, combined with CPM can effectively capture hydrogen combustion dynamics and emission variability.

A model of turbulent multiphase flow, heat transfer, and particle entrapment during continuous casting of steel is presented. The model includes the top 7m of the vertical and curved strand, and considers the effects of argon gas injection and thermal buoyancy. RANS model flow results are compared with LES. Lagrangian particle transport through the Eulerian-Eulerian multiphase flow field from the k-ɛ RANS model is based on random walk and features advanced particle capture criteria, improved from previous work by including anisotropic turbulent velocity fluctuations near the walls. Particle capture via 3 mechanisms is included: capture by solidified hooks at the meniscus, entrapment between dendrites, and engulfment by surrounding large particles. The fluid flow and bubble/inclusion capture results are validated with plant measurements, including nail board dipping tests and ultrasonic tests of particle locations, and good agreement is seen. The superheat has negligible effect on flow in the mold region but causes complex flow in the lower strand by creating multiple recirculation zones due to the thermal buoyancy. With high (30 K) superheat, this leads to less penetration, and slightly fewer and shallower capture of particles. Lower (10 K) superheat may enable significant top surface freezing, leading to very large internal defect clusters. Lower superheat also leads to deeper meniscus hooks, and more surface capture. Capture bands occur near the transition from vertical to curved, where downward liquid flow velocity balances the particle terminal velocity.