Thermoeconomic and environmental co-optimization of diesel combined heat and power systems via compression ratio tuning: Parametric study for residential application

Abstract

This study addresses key research gaps in diesel engine-based combined heat and power (CHP) systems by presenting the very first overall Energy, Exergy, Economic, and Environmental (4E) investigation of compression ratio optimization. Unlike previous research, this research uniquely demonstrates that optimization of the in-built compression ratio in diesel-CHP systems can alone result in significant efficiency, economic, and environmental improvements. This novel 4E analysis and optimization approach opens up a new design pathway via quantification of multi-objective trade-offs of compression ratio modulation, thereby advancing CHP system design beyond peripheral retrofits. It has been demonstrated that raising the compression ratio (14:25) elevates engine power output by 44% and recoverable heat, to as much as 89.5% CHP efficiency. These advantages are realized, however, at severe costs: 6.8% more exergy destruction and 10.3% less carbon emission savings (CDER). To mitigate these trade-offs, a novel multi-objective genetic algorithm framework was developed with normalized objectives. Optimization returns cr = 20.11 as the Pareto-optimal solution, trading off 89.13% CHP efficiency, 0.2469 $/kWh energy cost, moderated exergy destruction (44.7 kJ/kg), and sustainable CDER (0.2389). Above all, the Pareto frontier delineates actionable design regimes: sustainability-focused applications favor cr = 14–18.89 (high emission reduction), while efficiency-focused systems operate at cr = 20.11–25 (peak η_CHP).