Decoupled multi-fuel combustion control in CI engines: A staged hydrogen-assisted framework for resolving emission-efficiency trade-offs

Hydrogen-assisted biodiesel–alcohol combustion can improve compression ignition engine performance, but premixed fuels may suffer from phase instability and prevent independent fuel control. This study investigates a staged CIME–ethanol–hydrogen strategy in a single-cylinder direct-injection engine operated at 1500 rpm. B20 CIME was supplied through the original diesel system, whereas ethanol was port-injected using a dedicated NYRA-controlled injector. Independently controlled fuel delivery enabled sequential comparison of the ethanol baseline and hydrogen-assisted response without storing a premixed alcohol–diesel/biodiesel fuel. Ethanol fractions of 5–20% were first evaluated, and B20E10 was subsequently enriched with 5–25 L/min hydrogen through manifold induction. Hydrogen contributed 5.65–64.64% of the total LHV-based fuel energy across the load–flow matrix and 24.34% at full load with 20 L/min. At this condition (BMEP = 6.29 bar), peak cylinder pressure, heat-release rate, and brake thermal efficiency reached 105.3 bar, 125 J/deg, and 35.2%, respectively, while NOx increased to 1100 ppm. A weighted desirability analysis combining BTE, BSFC, CO, HC, NOx, and smoke identified 20 L/min as the thermo-performance optimum; 25 L/min represented only a conditional NOx-weighted compromise. The staged approach therefore clarifies the efficiency–emission trade-off and hydrogen's load-dependent energy contribution.