Marine diesel engines power a vast fleet – from small fishing boats and pleasure craft to inland waterway vessels (tugboats, ferries, barges) and large ocean-going ships. International and regional regulations have become increasingly stringent: IMO Tier III (2016+, NOx control in Emission Control Areas), EPA Tier 4 (2014+, US waterways), and EU Stage V (2019+, inland waterway). Marine engines face unique challenges: high-sulfur fuel (up to 3.5% globally, 0.1% in ECAs), saltwater corrosion, wet exhaust systems, and very long service lives (20,000-50,000+ hours). We provide complete, validated aftertreatment solutions for marine diesel engines from 100 kW to 10+ MW.
Marine engines operate in corrosive saltwater environments with high fuel sulfur. Exhaust may be wet for cooling or spark arresting, requiring corrosion-resistant materials. Vibration and motion (pitch, roll) demand ruggedized packaging. Systems use sulfur-tolerant vanadia SCR, high-grade stainless (316L, duplex), and seawater-resistant components.
Application | Configuration |
IMO Tier III / EPA Tier 4 (low-sulfur ECA, 0.1% S) | Engine → DOC (optional) → SCR → ASC → Tailpipe |
Global / high-sulfur fuel (3.5% S, non-ECA) | Engine → SCR (vanadia) → Tailpipe |
Small marine / pleasure craft (50–500 kW) | Engine → DOC → SCR → ASC → Tailpipe |
Vanadia-based (V₂O₅/WO₃/TiO₂), sulfur-tolerant, 300–450°C. Honeycomb or plate catalyst. NOx reduction: 80–95% (IMO Tier III). Service life: 10,000–25,000 hrs.
For smaller engines (<1 MW) with low-sulfur fuel. Converts CO/HC, generates NO₂ for SCR. Optional on large engines to avoid fouling.
Pt on alumina. Reduces NH₃ slip <10 ppm in enclosed engine rooms.
Marine-grade DEF or aqueous ammonia. Corrosion-resistant injectors, heated lines, redundant pumps for reliability, automatic purge to prevent crystallization.
SCR mounted upstream of water injection. Corrosion-resistant housing (316L, duplex, Inconel). Condensate drains prevent acid pooling.
Engine Type | Fuel Sulfur | Aftertreatment | NOx Outlet | IMO Tier III Limit |
Medium-speed (ferry, tug) | 0.1% (ECA) | SCR (vanadia) | 2.5–3.0 g/kWh | 3.4 g/kWh |
Medium-speed (global) | 3.5% | SCR (vanadia) | 3.0–3.4 g/kWh | N/A |
High-speed (yacht, fishing) | 0.1% | DOC + SCR | 2.0–2.5 g/kWh | 3.4 g/kWh |
Low-speed (ocean-going) | 3.5% | SCR (plate) | 3.0–3.5 g/kWh | N/A |
Vessel Type | Power Range | Fuel | Aftertreatment | Key Requirements |
Ferry (inland/coastal, ECA) | 500 kW–5 MW | 0.1% S diesel | SCR + ASC | Continuous duty, enclosed engine room |
Tugboat / workboat | 1–5 MW | 0.1–3.5% S | Vanadia SCR | High load, extreme vibration, salt spray |
Cruise ship auxiliary | 2–10+ MW | 0.1% S | SCR (or EGR + SCR) | Hotel load, NH₃ slip control |
Fishing vessel | 200–2,000 kW | 0.1–3.5% S | DOC + SCR | Unattended operation, remote monitoring |
Pleasure yacht | 500–5 MW | 0.1% S | DOC + SCR + ASC | Silent operation, zero odor |
Inland barge / tanker | 300–2,000 kW | 0.1% S | SCR + ASC | Limited engine room space, low-load idle |
Passenger HSC | 1–10+ MW | 0.1% S | SCR (plate) | High exhaust flow, compact packaging |
Naval / coast guard | 1–20+ MW | 0.1–3.5% S | SCR (redundant) | Shock resistance, silent mode |
Maintains >80% NOx reduction with 3.5% fuel S. Operates globally (low- or high-sulfur). Service life 10,000–25,000 hrs.
316L stainless, duplex 2205, Inconel. Salt-spray tested >2,000 hrs. Condensate drains.
ISO 10816 compliant, reinforced catalyst supports, braided stainless urea lines, sealed connectors (IP67).
SCR upstream of water injection, thermal shock protection, backflow prevention.
Electric pre-heater for SCR, exhaust bypass for cold start, insulated catalyst housing.
Marine-grade injectors, heated lines, redundant pumps, automatic purge, fail-safe derate mode.
Onboard monitoring (NOx, NH₃ slip, exhaust flow, temperature), data logging, remote telematics.
Hundreds of marine SCR systems in operation, validated to IMO Tier III, EPA Tier 4, EU Stage V.
Works globally with 0.1–3.5% sulfur fuel. Maintains Tier III compliance in ECAs.
2,000+ hour salt-spray certified, wet exhaust integration, condensate-free designs.
Marine service engineers at major ports, emergency response, remote telematics.
From a 200 kW fishing vessel in the North Sea to a 10 MW ferry in US ECAs or a superyacht in the Mediterranean, our marine aftertreatment solutions deliver IMO Tier III compliance, corrosion resistance, and operational reliability in the harshest saltwater environments.