Speed-Resolved experimental and CFD evaluation of a Low-Power Intake-Air ionization retrofit for diesel combustion and emission control

A low-power intake-air ionization attachment was experimentally and numerically evaluated as a retrofit strategy for diesel-engine performance and emission control without fuel reformulation or engine modification. A single-cylinder compression-ignition engine was tested under baseline and staged ionized-air conditions at 300–1500 rpm, with five repeated measurements at each operating point. Each negative-ion module operated at a fixed 12 V DC input (<1 W per module) with device-rated values of approximately −9.5 kV DC high-voltage output, 1.2 x 10 13 ions s −1 negative-ion production, and 1.9 x 10 12 ions cm −3 at a 2.9-cm reference distance. The staged strategy activated one to five modules as speed increased. At the fully load-matched 1500-rpm condition, brake power and torque remained 1.94072 kW and 12.35 N m in both modes, while fuel mass-flow rate decreased from 2.34 x 10 -4 to 2.25 x 10 -4 kg s −1 . Using an LHV of 42.5 MJ kg −1 , BSFC decreased from 0.4341 to 0.4174 kg kW -1 h −1 and brake thermal efficiency increased from 19.51 % to 20.30 %. Across the speed range, mean exhaust-gas temperature decreased by 6.8–19.8 °C and CO, HC, and NO x analyzer concentrations were lower under the staged ionization-ON condition. Crank-angle-resolved in-cylinder pressure and ion-current signals were measured, and apparent net and cumulative heat release were derived from the pressure trace. A steady three-dimensional RANS model used displacement-consistent inlet conditions based on the 0.363-L swept volume and eta_v = 0.82. Grid refinement at 1500 rpm used approximately 1.6, 3.2, 6.3, 12.6, and 25.2 million cells; the 6.3-million-cell grid was selected as the production mesh after the monitored solution changed by less than 1 % with further refinement. Residual reduction, monitored-variable stability, and inlet–outlet mass conservation were verified before post-processing. The CFD results include velocity, pressure, recirculation, residence-time, turbulence/mixing, outlet-flow redistribution, and normalized scalar-transport fields for the solved operating points.