A mass-redistributed compression-decoupled cycle for high power-density engines

Increasingly stringent emissions and energy-efficiency regulations are driving the innovation of engine concepts with higher thermal efficiency and power density. To better utilize the high-boost technology commonly adopted in high power-density diesel engines, a mass-redistributed compression-decoupled cycle (MRDC) is proposed. In this cycle, the fresh charge introduced during a single intake process is redistributed to two combustion stages. A thermodynamic framework is first established for the MRDC, and a zero-dimensional cycle model is developed to evaluate its theoretical potential. Under peak-pressure conditions matched to the conventional diesel cycle, the MRDC increases thermal efficiency by 3.60 percentage points. The cycle is then implemented in a six-stroke engine architecture featuring a gas storage chamber, and its performance is assessed using a calibrated one-dimensional GT-Power model. The results show that mass redistribution during first-stage compression governs the trade-off between compression work and second-stage air availability, whereas valve events during the coupling stroke influence the trapped charge through both pressure differentials and gas dynamic interactions. Appropriate coordination of these valve events and gas-dynamic effects can further improve redistributed-charge utilization in the practical six-stroke engine system. Under the investigated full-load simulation condition, the finalized MRDC-based six-stroke implementation increases thermal efficiency by 2.57 percentage points and power output by 6.27% relative to the calibrated baseline four-stroke engine, while decreasing specific fuel consumption by 4.97%. These results demonstrate that the MRDC provides a feasible pathway for exploiting high-boost benefits and for simultaneously improving diesel engine efficiency and power density.