Diesel particulate and hydrocarbon emissions from marine propulsion engines are under increasing scrutiny in ports, coastal zones and emission control areas. We designed a DOC + DPF aftertreatment system specifically for 800 kW-class marine main engines — a package that is sized from the engine's real operating data, not from a generic catalogue.

This article covers what the system is, the engine it was engineered around, the four constraints that shaped the design, and how it fits into a low-sulphur fuel compliance strategy.

A DOC + DPF combination performs two distinct jobs in one exhaust line:

Together they turn a visibly smoking exhaust into a clean, compliant one — without touching the engine's own performance map.

The system was engineered around a 6-cylinder, inline, four-stroke marine propulsion engine, turbocharged and intercooled, with the following specification used as the sizing baseline:

1. Fuel quality gates the entire architecture. DOC and DPF chemistry requires low-sulphur fuel — MGO/MDO at or below 0.10% S in emission control areas. On high-sulphur HFO, sulphate formation poisons the catalysts and damages the DPF substrate. The system is therefore specified for engines running on low-sulphur distillate; HFO installations require a different architecture (e.g. scrubber-based or alternative strategies).

2. Exhaust temperature is both the problem and the solution. At cruise power, a propulsion engine's exhaust temperature sits in the passive regeneration window (roughly 250–450°C), allowing continuous soot oxidation with minimal active intervention. But at full load, temperature can exceed the DPF substrate's safe limit, and during slow steaming or harbour operation it falls below the window. The regeneration strategy is mapped against the engine's actual voyage profile to protect both the filter and the canister.

3. Backpressure is an engine-performance number. On a turbocharged engine, added exhaust restriction degrades turbocharger performance and increases specific fuel consumption. The canisters are sized so total DOC+DPF restriction stays within the engine's allowance across the full operating map, with the worst case verified at full load.

4. The engine room is not a test bench. Salt air, vibration, cramped installation and surveyor inspection all shaped material and layout choices: corrosion-resistant shells, flanged bolted connections, and a footprint that fits the space available on the vessel.

This DOC+DPF package is a particulate and gaseous (CO/HC) emission control solution, aligned with tightening requirements on visible smoke and particulate emissions in ports and coastal waters under the MARPOL framework and regional port rules. Where NOx compliance (e.g. IMO Tier III in NOx emission control areas) is also required, the system can be combined with SCR or EGR solutions in the same project scope.

Every installation begins with your engine's data sheet and operating profile. We offer:

Q: Which engines is this DOC+DPF system compatible with?A: The system is currently engineered for 800 kW-class marine propulsion engines (e.g. 734 kW @ 1,900 r/min continuous rating). The same design methodology applies from ~200 kW to 2 MW, and we custom-size the canisters for each engine data sheet.

Q: What fuel does the system require? A: Low-sulphur distillate — MGO/MDO at or below 0.10% S in emission control areas. The system is not suitable for high-sulphur heavy fuel oil (HFO) without a different pre-treatment architecture.

Q: Will the system reduce engine performance? A: Backpressure is treated as an engine-performance constraint. Canister sizing is verified against the engine's full operating map so the impact on power and fuel consumption stays within the engine's allowance.

Q: Does DOC+DPF reduce NOx? A: No — DOC+DPF addresses particulate matter, CO and HC. NOx reduction requires SCR or EGR. We can supply a combined DOC+DPF+SCR package where Tier III compliance is required.

Q: Can you design a system for our specific engine? A: Yes. Send us your engine data sheet and duty profile and we will size a package to match — including retrofit layouts for vessels in service.

[CTA] Need a DOC+DPF package sized for your engine? Send us your engine data sheet and we'll respond with a technical proposal.