Miller-Late Inlet Valve Closing with Boost Intake Pressure for the Performance Improvement of a Biogas-Fuelled SI Engine: A Modelling and Optimization Approach

Abstract

In order to reduce emissions and dependency on fossil fuels, biogas has been recognized as a good substitute fuel for SI engines. However, its low heating value reduces power output, requiring costly engine modifications. To resolve this, this study proposes a novel approach to enhance the power and efficiency of an SI engine by incorporating the Miller cycle with late inlet valve closing and boosted intake pressure at a 12:1 geometric compression ratio. A quasi-dimensional thermodynamic model was employed to simulate engine performance under various operating conditions. The simulation was validated using experimental data from the literature and then used to predict engine performance for operating parameters, including an equivalence ratio of 0.7–1.0, late inlet valve closing timing of 60–85° aBDC, start of ignition at 15–30° bTDC, and intake pressure of 1.0–2.5 bar. The optimal operating conditions were then determined using response surface methodology to balance energy utilization, emissions reduction, and fuel consumption minimization. The optimized parameters were determined to be an equivalence ratio of 0.782, late inlet valve closing timing of 72.84° aBDC, start of ignition timing at 28.80° bTDC, and an intake pressure of 2.49 bar. Correspondingly, the optimal results included 4.02 kW indicated power, 3.70 kW brake power, 28.39% indicated thermal efficiency, 26.22% brake thermal efficiency, 13,614.5 kJ/kWh brake-specific energy consumption, and emissions of 0.0191 vol% CO and 1167.03 ppm NO emissions at Exhaust valve opening. © The Author(s), under exclusive licence to Springer Nature Singapore Pte Ltd. 2025.