In short. A retrofitted emission control device is an aftertreatment system fitted to the exhaust of an existing diesel generator to cut particulate matter and other pollutants. Results depend on the engine, fuel, load profile and correct integration, and approval requirements should be confirmed.
What it is
Engine exhaust → oxidation catalyst → particulate filter → (optionally SCR) → stack. The same ideas used on newer engines are applied to older ones.
| Element | Job |
|---|---|
| Diesel oxidation catalyst (DOC) | Oxidises CO and hydrocarbons; helps filter regeneration |
| Diesel particulate filter (DPF) | Traps soot; must be regenerated or cleaned |
| SCR with urea | Reduces NOx using a reagent |
| Sensors and controller | Temperature, back-pressure, status |
Limits
- Back-pressure from the filter must stay within the engine’s limit.
- Filters need exhaust temperature high enough to regenerate; low-load standby duty can be a problem.
- Fuel and lube oil quality affect catalysts and ash build-up.
- Performance claims should be supported by test data for your engine.
Next steps
See selection and compatibility, installation and operation and maintenance.
Illustrative example
A set that runs a few hours per month rarely reaches filter regeneration temperature. The retrofit design includes an active regeneration strategy or a different device choice, rather than a filter that clogs between outages.
How each stage works
Oxidation catalyst. A honeycomb coated with precious-metal catalyst converts CO and unburned hydrocarbons into carbon dioxide and water. It also oxidises part of the NO to NO2, which helps burn soot in the filter at lower temperature.
Particulate filter. Exhaust passes through porous walls that trap soot. As soot accumulates, back-pressure rises. The filter is cleaned either passively, by burning soot continuously when exhaust is hot enough, or actively, by raising exhaust temperature periodically, or by removing and cleaning the filter off-site. Incombustible ash from lubricating oil stays behind and needs periodic cleaning.
SCR. Urea solution is injected into hot exhaust, breaks down into ammonia, and reacts over a catalyst with NOx to form nitrogen and water. Dosing must match NOx: too little leaves NOx, too much releases ammonia slip.
Back-pressure and why it matters
Total back-pressure = silencer + piping + catalyst + filter losses
Engine makers specify a maximum back-pressure. A clean filter adds a modest amount; a loaded filter adds much more. Design for the loaded condition, with margin, and alarm before the limit.
Duty cycle and regeneration
| Duty | Regeneration concern | Mitigation |
|---|---|---|
| Steady load, high temperature | Passive regeneration works | Monitor only |
| Variable load | Intermittent regeneration | Active control |
| Standby, short test runs | Exhaust rarely hot enough | Scheduled on-load runs or off-site cleaning |
What to ask a supplier
- Test results on an engine like yours, from a recognised laboratory.
- Back-pressure at rated load, clean and loaded.
- Regeneration strategy for your duty.
- Warranty on the device and the effect on engine warranty.
- Approvals or acceptance in your jurisdiction.
- Service plan and consumables.
Warning signs after installation
- Rising back-pressure over weeks.
- Visible smoke.
- Engine derate or alarm.
- Higher fuel consumption.
Any of these means inspection, not waiting.
The master engineering question
Will this engine, at its real load and temperature, let the device work as designed?
What to send us
Send engine data, load profile and exhaust layout. Send your application details.
Questions engineers ask
Does RECD make an old set equal to a new one?
Not necessarily; results vary and need verification.
Does it affect engine performance?
Back-pressure and heat must be controlled.
Is approval needed?
Confirm with the relevant authority for your location.
Is maintenance heavy?
Filters and sensors need regular attention.
General guidance only. Confirm approvals and test data.