Development of a micro-cogeneration model for a small air-cooled spark-ignition internal combustion engine-based system

• Micro-cogeneration internal combustion engine-based system that provides mechanical power and hot air as main products. • Parametric modelling of a micro-cogeneration system for a wide range of usable engine rotational speeds and loads. • Detailed presentation of system mapping and model topology, fitting and validation. This work presents the development and empirical calibration of a micro-cogeneration model specifically tailored to a system based on a single-cylinder air-cooled spark-ignition internal combustion engine, as its prime mover. The engine is assessed as a micro-cogeneration system that simultaneously delivers mechanical power and useful heated air output. The model structure builds upon the framework of the International Energy Agency Annex 42 parametric equations but introduces a novel formulation in which engine rotational speed and throttle valve opening serve as primary inputs—enabling accurate prediction of system behaviour over a wide range of operating conditions. The model equations are empirically obtained through extensive experimentation and data fitting. Energy balances are applied to the energy conversion control volume, engine block, cooling air flow, and a potential heated space. The model parameters are calibrated using experimental data collected across engine speeds of 1500–4600 min⁻¹ and throttle openings of 25–100 %. Compared to the original Annex 42 equations (also adjusted here for comparison), the proposed model achieves superior accuracy (R² > 0.78). Validation tests show prediction errors below 13 % for net power outputs above 0.8 kW and below 9.1 % for air temperature. The resulting model provides a practical and effective tool for predicting, simulating, and controlling the performance of this specific micro-cogeneration system across a broad operating envelope.