When a facility operates multiple diesel generators, sharing infrastructure can appear to be an efficient way to reduce installation space, exhaust piping, and equipment costs. This often leads to an important question: can two diesel generators share a single Retrofit Emission Control Device (RECD)? Although a common exhaust arrangement may look practical, the answer depends on engine configuration, exhaust routing, operating conditions, back-pressure, and compliance requirements.

CPCB's RECD compliance procedureAn RECD is designed to control emissions from a specific diesel generator engine. The device must be properly matched to the engine's exhaust characteristics and approved application range. The Central Pollution Control Board (CPCB) has established a specific testing and compliance procedure for RECDs used with diesel power generating set engines, making correct system selection and installation important. The provides the technical framework for emission-compliance testing of retrofit devices.

Why Sharing One RECD Can Be Complicated

Two generators do not necessarily produce identical exhaust flow, temperature, pressure, or operating patterns. Even if both machines have similar ratings, their actual operating conditions can vary depending on load demand, engine condition, maintenance, and running hours.

If the exhausts from two generators are connected to a common line before a single RECD, the device may experience changing exhaust conditions depending on which generator is running. If both generators operate simultaneously, the combined exhaust flow can also be substantially different from the condition for which the RECD was designed and evaluated.

This makes capacity and operating compatibility major considerations. A device selected for one engine cannot automatically be assumed to be suitable for two engines simply because its physical size appears sufficient.

Back-Pressure Is a Major Concern

One of the most important technical issues in a shared arrangement is exhaust back-pressure. Every diesel engine has a permissible exhaust back-pressure limit specified by its manufacturer. Adding common piping, bends, junctions, and an emission-control device can increase resistance in the exhaust system.

With two generators connected to one RECD, back-pressure can change according to the number of operating engines and the exhaust flow at a particular moment. An incorrectly designed arrangement could therefore affect engine performance or create operating problems.

For this reason, exhaust calculations should consider actual flow rates, pipe dimensions, bends, silencers, the RECD pressure drop, and the operating combination of the generators rather than relying only on nominal generator capacity.

What Happens When One Generator Is Off?

A shared exhaust system also introduces another concern: the interaction between running and stopped generators. If two engines are connected to a common exhaust arrangement, exhaust from the running generator may potentially travel toward the branch connected to the stopped generator.

This is why common headers require careful engineering, isolation arrangements, and consideration of exhaust flow direction. A system that works when both generators operate together may behave differently when only one generator is running.

The issue becomes particularly important for standby installations, where generators may operate independently rather than continuously together.

Aceget guide on whether two diesel generators can share one RECDFor a detailed discussion of the engineering factors involved, the provides additional practical context.

Compliance and Device Certification Matter

Another important point is that an RECD is not simply a generic exhaust filter. The applicability of a device depends on factors such as engine power range and the certified configuration. CPCB's published list of certified RECD manufacturers shows that devices are associated with specific diesel genset capacity ranges and certification details. Therefore, combining two engines into one treatment arrangement should not be treated as equivalent to installing one device on one engine.

BIS Know Your Standard portalThe safest approach is to verify the proposed configuration with the RECD manufacturer, engine manufacturer, and relevant compliance authority before installation. The can also help users identify and review applicable Indian Standards when evaluating equipment and technical requirements.

Separate RECDs Are Usually Easier to Manage

For installations with two independent diesel generators, providing a separate RECD for each engine generally makes the exhaust arrangement easier to design, monitor, maintain, and troubleshoot.

Each device can be selected according to its generator's rated output and exhaust characteristics. Back-pressure can be measured independently, maintenance records can be associated with a particular engine, and emission-control performance can be evaluated without uncertainty about which engine is contributing to the exhaust stream.

This approach can also make future maintenance simpler. If one generator requires servicing, the other generator's emission-control system remains independently configured rather than being tied to a common treatment device.

Consider the Complete Exhaust Layout

Before deciding on a shared RECD, engineers should examine the complete exhaust arrangement rather than looking at the RECD alone. Important factors include:

Generator rating and engine configuration
Exhaust gas flow and temperature
Maximum allowable engine back-pressure
Pipe diameter and total exhaust length
Number of bends, reducers, and junctions
Whether one or both generators operate simultaneously
Possibility of exhaust backflow toward an idle engine
RECD capacity and certified application range
Sampling and testing arrangements
Maintenance and access requirements

Central Electricity Authority's safety and electric-supply regulationsElectrical installation and operating safety should also be considered alongside emission-control design. The provide an official reference point for broader generating-installation safety requirements.

A Better Way to Approach Multiple-Generator Sites

Facilities planning multiple generators should decide the exhaust strategy during the initial system-design stage. Retrofitting a common header later can introduce space, pressure, access, and testing complications.

Where generators are synchronised or used for load sharing, the operating sequence should also be considered. Different generators may carry different loads at different times, meaning their exhaust conditions can change considerably. A design that accounts for these operating scenarios is more reliable than selecting one large RECD simply because it appears capable of handling the combined output.

Conclusion

Can two diesel generators share one RECD? In some specially engineered exhaust configurations, a shared arrangement may be technically considered, but it should never be assumed to be suitable simply because the combined capacity appears manageable. Exhaust flow, back-pressure, operating combinations, isolation, certification, and compliance requirements all need to be evaluated.

one appropriately selected RECD for each generator is the clearer and more manageable approachFor most installations with independent generators, . Proper engineering at the planning stage can help avoid exhaust-flow problems, maintenance complications, and compliance uncertainties later.

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