Exhaust Gas Recirculation
Abbreviation: EGR
NOx-reduction technique that recirculates a portion of exhaust gas back into the engine intake, lowering combustion peak temperature.
In practice
Engine builder-controlled; the duty engineer verifies EGR valve position and exhaust-gas cooling. EGR raises piston-ring fouling; oil-sample analysis tracks soot increase. Generally engine OEM (MAN ES, WinGD) handles repairs.
Regulatory detail & full definition
Alternative to SCR for IMO Tier III compliance. Works by displacing oxygen and adding inert (already-burned) gas to the cylinder, lowering peak combustion temperature and thus thermal-NOx formation. Typical recirculation rate 30-40% on slow-speed two-strokes. Uses scrubber + cooler in the EGR line because exhaust is wet/sooty.
Authoritative source: MARPOL Annex VI (Air pollution) ↗
Related
Source: MARPOL Annex VI Reg. 13; MAN B&W EGR Tier III Guide
High confidence
Editorial confidence: how we grade.