Combustion-to-Work Conversion: A Cross-Platform Review of Thermo‑Chemical Pathways, Cycles, and Emerging Low‑Carbon Directions

Abstract

Combustion-to-work systems convert fuel chemical energy into mechanical power through coupled thermo‑chemical processes and heat‑engine cycles. This review synthesizes the pathway across reciprocating internal combustion engines, gas turbines, and combined cycles, emphasizing how irreversibilities accumulate from mixing and finite‑rate chemistry to component aerodynamics, heat transfer, friction, and auxiliary loads. A loss‑based framework is used to compare platforms on a consistent lower-heating-value basis and, where informative, through exergy destruction localization. The synthesis highlights that efficiency gains increasingly require coordinated improvements—heat‑release shaping, effective expansion, minimized pressure drops, and recovery of high‑quality exhaust exergy—rather than isolated component upgrades. Emissions are treated as intrinsic constraints that reshape the achievable optimum, with NOx, soot/PM, CO, and unburned hydrocarbons responding differently to temperature–mixture distributions, dilution, and residence time. Emerging directions are reviewed, including lean and staged combustors, low-temperature compression‑ignition modes, hybridized operation, supercritical CO₂ bottoming cycles, and pressure‑gain combustion. Finally, the review discusses fuel transitions (hydrogen, ammonia, sustainable and synthetic fuels) and the implications for stability, materials, and net climate benefit.