<![CDATA[The energy transition places internal combustion engines in a paradoxical position: they remain dominant in heavy-duty transport, marine propulsion, mobile power generation, and industrial applications, yet they are major sources of NOx, particulate matter, hydrocarbons, CO, and greenhouse gases. This article reviews Scopus-indexed literature from 2022 to 2026 available in the author's extraction dataset to synthesize recent progress in low-temperature combustion, low-carbon fuels, injection strategies, EGR, turbocharging, after-treatment, nano-additives, and artificial intelligence for emission prediction and optimization. A narrative-systematic approach was applied by clustering the literature into advanced combustion modes, fuel formulation, air-injection control, residual pollutant mitigation, and sensing-prediction-control models. The synthesis shows that HCCI, PCCI/PPCI, GCI, RCCI, CAI, and dual-mode dual-fuel concepts expand opportunities for high efficiency and soot/PM reduction, but they remain constrained by combustion phasing control, narrow operating range, pressure rise, knocking, and CO/HC/NOx trade-offs. Hydrogen, biohydrogen, ammonia, oxygenated biofuels, HVO, water-diesel emulsions, H2O2, and CeO2 offer strong emission-reduction potential, but their benefits depend on blend ratio, injection timing, EGR, and combustion chamber design. This review concludes that the most promising research direction is an integrated fuel-combustion-control-after-treatment-intelligence framework for adaptive and measurable low-emission engines aligned with net-zero targets.]]>
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