An integrative review of dual-fuel strategies, Nano-additives, and emission control in compression ignition engines fueled by renewable energy sources

This review aims to establish an integrated understanding of alternative fuel performance and combustion strategies in compression ignition engines by synthesizing high-impact studies from 2020 to 2025. Key findings include thermal efficiency gains of up to 42 % for ammonia‑hydrogen blends, 15 % for biodiesel with elliptical injectors, and 12 % for methanol dual-fuel systems. Biodiesel reduces CO and PM emissions by 30–40 % but raises NOx by 10–15 %. Hydrogen and ammonia yield near-zero CO₂ emissions yet require EGR and water injection to control high NOx. Alcohols improve combustion homogeneity but need pilot injection due to long ignition delays. Nano-additives like Al₂O₃ and CeO₂ reduce CO and HC by over 20 %, improve atomization, and boost brake thermal efficiency. By integrating combustion strategies, spray characteristics, and emission trade-offs, this review develops a unified framework for optimizing alternative fuels in CI engines. The novelty lies in its comprehensive synthesis of multi-fuel blending, nano-additive application, and advanced combustion technologies (e.g., RCCI and LTC), which prior reviews have addressed only in isolation. A comprehensive literature check revealed that, to date, no single review has concurrently synthesized dual-fuel strategies, nano-additive applications, and advanced combustion technologies specifically for compression ignition engines fueled by multiple renewable sources, as conducted in the present work. Existing reviews typically isolate individual fuels or technologies, lacking the integrated framework developed here. This study fills a crucial gap by offering a unified benchmark framework to guide future design and implementation of low-emission, high-efficiency CI engine systems.