1D-3D CFD Investigations to Improve the Performance of Two-Stroke Camless Engine 2024-01-2686

The transportation sector still depends on conventional engines in many countries as the alternative technologies are not mature enough to reduce carbon footprints in society. The four-stroke diesel engines, primarily used for heavy-duty applications, need either high intake boosting or a large bore to produce higher torque and power output. There is an alternative where a four-stroke engine operated in two-stroke mode with the help of a fully flexible variable valve actuation (VVA) system can achieve similar power density without raising the intake boosting or engine size. A fully flexible VVA is required to control the valve events (lift, timing, and durations) independently so that the four-stroke events can be completed in one cycle. In this study, 1D-3D CFD coupled simulations were performed to develop a gas exchange process for better air entrapment in the cylinder and evacuate the exhaust products simultaneously. The intake and exhaust valve closing timings were optimized based on the engine torque. The in-cylinder fresh charge mostly leaves the cylinder through exhaust ports during the gas exchange process even if the valve timings were optimized. Hence, a new design was proposed in which different deflectors (rectangular and semi-circular) were placed near the intake valve seats with the hope of achieving better air entrapment in the cylinder. The deflectors prevented the intake charge particles from being shot-circuited through the exhaust port and helped the charge particles to trap in the cylinder. The semi-circular deflector showed a more promising technique than the rectangular deflector and achieved a 45% higher torque improvement than the baseline design without a deflector.