Blockchain Consensus Mechanisms: A Comprehensive Review of Principles, Protocols, and Future Directions

Blockchain consensus mechanisms are the foundation of decentralized trust, enabling
autonomous agreement among distributed nodes without relying on a central authority. This
review presents a comprehensive analysis of classical, advanced, and emerging consensus
protocols, including Proof of Work (PoW), Proof of Stake (PoS), Delegated PoS (DPoS),
Practical Byzantine Fault Tolerance (PBFT), Proof of Authority (PoA), and next-generation
models such as Directed Acyclic Graph (DAG)-based systems, Proof of Space and Time
(PoST), AI-augmented consensus, and quantum-resilient protocols. Each mechanism is
evaluated in terms of scalability, energy efficiency, security, decentralization, and applicability.
The study also discusses major challenges such as the blockchain trilemma, centralization risks,
Sybil attacks, energy concerns, and interoperability limitations. Finally, the paper outlines
future research directions that emphasize hybrid architectures, sustainability, and cryptographic
resilience. This review serves as a valuable resource for researchers, developers, and architects
seeking to optimize consensus strategies in varied blockchain ecosystems.