Valorization of Agricultural Residue-Derived Syngas for Decentralized Electricity Generation: A Gasification-Informed HCCI Combustion and Techno-Economic Assessment

The depletion of fossil fuels and the need to valorize agricultural residues motivate biomass-to-electricity pathways coupling gasification with an efficient, low-emission prime mover. This study evaluates four residues—olive pomace (Fuel A), olive tree pruning (Fuel B), date palm seeds (Fuel C), and date pits (Fuel D)—converted into H2-rich syngas and supplied to a homogeneous charge compression ignition (HCCI) engine. A three-dimensional CFD model with GRI-Mech 3.0 detailed chemical kinetics resolves the in-cylinder combustion of each syngas, supported by a qualitative cross-study physical-consistency comparison against published syngas-HCCI pressure data. Intake temperature, equivalence ratio, and EGR are varied at both fixed equivalence ratio and fixed fuel-energy input per cycle. At fixed ϕ=0.40, CA50 remains nearly uniform across the four fuels despite the more-than-twofold variation in H2/CO, whereas peak pressure differs substantially: steam-gasified date-seed syngases (Fuels C and D; H2/CO = 1.21–2.00) reach 93–97 bar, compared with 79–83 bar for air-blown olive-residue syngases (Fuels A and B; H2/CO = 0.76–0.89), though the baseline maximum pressure-rise rate exceeds the adopted engine-damage threshold for all four fuels. Indicated thermal efficiency ranges from 43.2 to 44.4% across the four fuels. CO and UHC emissions are generally lower in the more hydrogen-rich cases, whereas NOx varies non-monotonically with fuel composition and operating condition. Combining literature-derived gasification cold-gas efficiencies with the engine results gives an estimated upper-bound biomass-to-electricity efficiency of approximately 26–28% and a base-case LCOE of 0.071 USD/kWh, with combined scenario bounds of 0.025–0.150 USD/kWh, based on adopted techno-economic assumptions and a baseline operating point that would require further mitigation to meet the adopted pressure-rise-rate limit. The results provide a feedstock-resolved basis for assessing agro-industrial residue-to-electricity pathways in decentralized, off-grid applications.