Diesel Generator Exhaust System Components: Silencer, SCR, Pipework

In Short

A diesel generator exhaust system takes hot gas from the turbocharger to the stack. Along the way it controls noise and heat, keeps resistance low enough for the engine to breathe and, where the permit requires, cleans the gas before release. It combines pipework, silencing and emission treatment into one route.

The exhaust of a diesel generator leaves the turbocharger very hot and in large volume, carrying noise, heat, soot and nitrogen oxides. The exhaust system takes it from the engine to a point where it can be released - quietly enough for the neighbours, clean enough for the permit, and with a resistance low enough for the engine to breathe. This guide names the parts between the turbocharger and the stack and what each is for.

From the Turbocharger: Flexible, Pipework, Insulation

The first part is a flexible connection - a stainless steel bellows - that takes the engine's vibration and thermal growth so that the pipework does not load the turbocharger. The pipework itself is steel, laid out to stay within the engine maker's back pressure limit, with gentle bends, expansion joints on long runs and supports that let it grow with the heat. Inside an enclosure the pipe is insulated and clad to keep the heat out of the room and the surfaces safe to touch; outside, insulation also prevents condensation inside the pipe.

A condensate drain at the lowest point and a drain on the silencer let the water that condenses in a cold exhaust leave before it reaches the engine. Every joint is gas-tight; an exhaust leak in an enclosure is a carbon monoxide hazard.

The Silencer and Its Grades

The exhaust silencer is where the noise goes. Reactive silencers use chambers and tubes to take out the low rumble of the engine; absorptive silencers line a straight path with sound-absorbing material for the hiss; combined silencers do both. They are specified by grade - industrial, residential, critical and hospital are the common names - which stands for how quiet the exhaust becomes, rising from industrial to hospital grade. The grade is chosen for the sound limit together with the enclosure, and the silencer's resistance is checked against the back pressure limit.

Spark arrestor silencers add a particle trap for sites with fire risk; the silencer can stand inside the enclosure, on its roof or on the stack, and its weight and its surface temperature decide the supports and the guards.

SCR, Catalysts and Particulate Filters

Where emissions rules limit nitrogen oxides - data centers in many jurisdictions, urban sites, plants with many running hours - a selective catalytic reduction system is added: a urea solution is injected into the exhaust, decomposes to ammonia and reacts with the NOx on a catalyst to nitrogen and water, removing most of it. The SCR needs a dosing system, a urea tank, enough exhaust heat and a control that follows the engine load. A diesel oxidation catalyst in front of it burns carbon monoxide and hydrocarbons, and a particulate filter catches soot where the rules ask for it.

All of these add back pressure, and the whole chain - flexible, pipework, silencer, catalysts, stack - is looked at together against the engine maker's limit; exceeding it raises exhaust temperatures, costs power and shortens the turbocharger's life.

The Stack, the Rain Cap and the Permit

The stack carries the gas above the roof and away from air inlets, windows and neighbours; its height is set by the local rules and by what the permit requires, and it ends with a rain cap or a flap that keeps water out when the engine stands. Guards protect people from the hot surfaces, and the whole system is supported so that no load reaches the engine.

AXON supplies exhaust systems for generator sets of any make - silencers of every grade, SCR and catalyst systems, pipework, stacks and chimneys - designed as one system against the engine maker's back pressure limit and the site's sound and emissions requirements, alone or as part of a container. Send the engine model, the sound limit and the emissions requirement, and the proposal shows the system.

The parts of the system

Flexible connection at the turbocharger
Pipework with bends, expansion joints, supports, insulation and drains
Exhaust silencer: reactive, absorptive or combined, by grade
SCR with urea dosing, oxidation catalyst, particulate filter where required
Stack or chimney with rain cap, guards and supports
Back pressure of the whole chain checked against the engine maker's limit

What to send with an enquiry

Engine model, exhaust flow, temperature and the back pressure limit
Sound limit and distance, or the silencer grade required
Emissions requirement: NOx, CO, particulates, and the running hours
Routing: length, bends, inside or outside the enclosure, stack height
Site ambient and corrosion class
Fire-risk sites: spark arrestor requirement

Send an enquiry Send us files

Questions we are often asked

What is exhaust back pressure?

The resistance the exhaust system presents to the engine, measured at the turbocharger outlet. Every part adds some; the engine maker gives a limit, and the system has to stay under it.

Which silencer grade do I need?

The one that, together with the enclosure, meets the sound limit at the stated distance. Industrial grade for open industrial sites, residential for neighbours nearby, critical and hospital for sensitive sites - the sound limit decides.

When is an SCR system required?

When the emissions rules of the site or the permit limit NOx below what the engine achieves on its own - common for data centers, urban sites and plants with many running hours. The rules are local; the enquiry states them.

Can the silencer be inside the container?

Yes, insulated and guarded, which keeps the sound inside; or on the roof, which saves length inside. The back pressure and the heat into the room are checked either way.

Why is the exhaust pipe insulated?

To keep the heat out of the enclosure, to protect people from a very hot surface, and outdoors to keep condensate and corrosion from forming in the pipe.