Diesel generator (DG) sets are essential for maintaining an uninterrupted power supply in factories, hospitals, commercial buildings, offices, and industrial facilities. However, diesel combustion produces exhaust emissions that can contribute to air pollution, making emission control an important consideration for businesses operating backup power systems.

Two commonly discussed approaches for managing DG set emissions are Retrofit Emission Control Devices (RECDs) and dual fuel kits. Both can play a role in reducing the environmental impact of generator operation, but they work through different mechanisms.

An RECD treats exhaust gases after combustion, while a dual fuel kit enables a compatible diesel engine to operate using diesel along with an alternative fuel, such as natural gas, under an appropriately designed system.

Understanding the difference between these technologies helps facility managers, plant operators, and business owners evaluate the most suitable solution for their equipment, operating requirements, and applicable environmental regulations.

RECD vs dual fuel kit for diesel generatorsFor a more detailed comparison, explore this guide on.

What Is a RECD?

A Retrofit Emission Control Device is an emission-control system installed on an existing diesel generator to reduce specified exhaust pollutants. Depending on its design, an RECD may use filtration, catalytic treatment, or a combination of technologies.

Many RECD systems designed for diesel generator applications focus on reducing particulate matter (PM), including fine particles produced during diesel combustion.

How Does an RECD Work?

In a filtration-based system, exhaust gases pass through a specially designed filter that captures particulate matter. The treated gases then move through the remaining exhaust system.

Depending on the device design, accumulated particles may need to be removed through a manufacturer-specified regeneration, cleaning, or servicing process.

The performance of an RECD depends on several factors, including:

Compatibility with the DG set's engine and exhaust flow.
The technology used in the emission-control device.
Correct installation and commissioning.
Exhaust temperature and generator operating conditions.
Maintenance history and the condition of the filter.
Compliance with the applicable certification and testing requirements.

A properly selected and maintained RECD can help reduce particulate emissions without requiring the generator to be converted to a different fuel system.

What Is a Dual Fuel Kit?

A dual fuel kit allows a compatible diesel engine to operate using a combination of diesel and another fuel, commonly natural gas. In many retrofit applications, gas is introduced into the engine's intake system while diesel continues to provide the ignition source.

The exact design depends on the engine, fuel type, control system, and retrofit configuration.

How Does a Dual Fuel Kit Work?

In a typical diesel-natural gas retrofit, the kit manages gas delivery and operating parameters so that the engine can use a portion of its energy from natural gas while continuing to consume diesel.

The proportion of gas and diesel varies according to engine load, system calibration, gas availability, and equipment design. A stated substitution percentage should therefore not be treated as a guaranteed result for every generator.

Dual fuel operation can reduce diesel consumption when the system operates effectively. It may also change the quantity and composition of exhaust emissions. However, the result depends on the engine, gas substitution rate, combustion conditions, and the pollutants being measured.

Important Components of a Dual Fuel System

A typical system may include:

Gas supply and pressure regulation equipment.
Gas metering and delivery components.
An electronic controller or fuel management system.
Sensors and safety interlocks.
Engine-specific installation and calibration arrangements.

Gas detection, ventilation, automatic isolation, and other safeguards should be designed according to the applicable fuel system and site safety requirements.

RECD vs Dual Fuel Kit: Key Differences

The most important difference is that an RECD treats exhaust emissions, whereas a dual fuel kit changes how the engine receives and uses fuel.

Comparison factor	RECD	Dual fuel kit
Main purpose	Treat specified pollutants in exhaust	Enable operation on diesel and an alternative fuel
Operating principle	Filtration, catalytic treatment, or a combination	Alternative-fuel introduction and engine control
Diesel consumption	Does not inherently replace diesel with another fuel	Can reduce diesel consumption through fuel substitution
Particulate matter	Designed to reduce PM where covered by the device's approved performance	PM emissions may change, depending on engine operation and calibration
Gaseous emissions	Depends on the treatment technology and pollutants addressed	Depends on fuel composition, substitution rate, and combustion conditions
Fuel infrastructure	Generally does not require an alternative-fuel supply	Requires a suitable alternative-fuel supply and associated equipment
Maintenance	Device inspection, cleaning, regeneration, or other specified servicing	Fuel-system checks, sensor checks, calibration, and safety-system maintenance
Installation considerations	Exhaust flow, pressure drop, temperature, and engine compatibility	Fuel delivery, engine compatibility, combustion control, and safety
Operating cost	Includes device purchase, installation, maintenance, and operating requirements	Includes retrofit cost, gas supply, diesel consumption, and maintenance
Compliance	Depends on device certification, applicability, and local requirements	Depends on system approval, applicable emission requirements, and local regulations

Neither solution is automatically superior in every situation. The correct choice depends on the generator's specifications, operating pattern, available infrastructure, and regulatory obligations.

Environmental Benefits of RECD and Dual Fuel Systems

Benefits of an RECD

An appropriately certified and compatible RECD can reduce the particulate matter released by a diesel generator. This can be particularly important at sites where DG sets operate regularly and particulate emissions are a major concern.

The actual reduction depends on the device's approved performance, installation quality, operating conditions, and maintenance.

An RECD should not be assumed to eliminate every pollutant. Its ability to control PM, nitrogen oxides, carbon monoxide, hydrocarbons, or other emissions depends on the specific technology and its demonstrated performance.

Benefits of a Dual Fuel Kit

A dual fuel kit can reduce the quantity of diesel required to generate a given amount of electricity when alternative-fuel substitution is achieved efficiently.

Replacing part of the diesel energy input with natural gas may change particulate and other exhaust emissions. Nevertheless, emissions of nitrogen oxides, carbon monoxide, methane, and other pollutants can vary with the engine and operating conditions.

Consequently, a dual fuel conversion should be evaluated using appropriate technical evidence rather than assuming that lower diesel consumption automatically means every pollutant will decrease.

Which Solution Is More Suitable for Your DG Set?

Choosing between an RECD and a dual fuel kit requires a practical assessment of the installation.

Consider an RECD When:

The existing diesel generator needs a retrofit emission-control solution.
Reducing particulate emissions is a key objective.
A compatible, appropriately certified device is available.
The site can accommodate the device and its maintenance requirements.
The applicable regulatory framework permits or requires this approach.

Consider a Dual Fuel Kit When:

A suitable natural gas or other approved alternative-fuel supply is available.
Reducing diesel consumption is an important operating objective.
The engine can safely and effectively support dual fuel operation.
The site can install the required fuel handling and safety equipment.
The conversion meets the relevant regulatory and technical requirements.

Evaluate Both Options Before Investing

Before choosing either technology, businesses should review their generator rating, engine model, annual operating hours, average load, fuel expenditure, maintenance resources, and local compliance requirements.

A cost comparison should include more than the purchase price. Installation, fuel infrastructure, servicing, downtime, energy consumption, and ongoing compliance costs can all influence the final decision.

Understanding DG Set Emission Regulations in India

Emission-control requirements in India depend on factors such as generator capacity, engine category, location, applicable notifications, and the current directions of the relevant authorities.

The Central Pollution Control Board (CPCB) has published a specific procedure for emission compliance testing of retrofit emission-control devices used with diesel generator engines up to 800 kW gross mechanical power.

CPCB RECD Emission Compliance Testing ProcedureOfficial reference:.

In the National Capital Region, the Commission for Air Quality Management (CAQM) has issued directions governing DG set operation and emission-control measures. Depending on the applicable requirements, different capacity ranges may be subject to different compliance routes.

Press Information BureauAn official government summary of DG set measures is available through the.

Businesses should not assume that the same compliance option applies to every generator or every location. They should verify the latest applicable CAQM directions, CPCB requirements, state pollution control board rules, and any relevant site-specific conditions before purchasing or installing equipment.

A dual fuel kit and an RECD should not be considered interchangeable simply because both can support emission-control objectives. Their regulatory acceptance depends on the specific rules and conditions that apply.

Can an RECD and Dual Fuel Kit Be Used Together?

In some technical configurations, an RECD and a dual fuel system may be capable of operating on the same generator. However, compatibility must be established before combining them.

The dual fuel conversion can change exhaust temperature, combustion characteristics, particulate loading, and the composition of the exhaust gases. These changes may affect how an RECD performs.

The combined system should therefore be assessed for:

Engine compatibility and approved operating conditions.
Total exhaust back pressure.
Exhaust temperature and flow requirements.
Compatibility between the fuel control system and emission-control equipment.
Applicable safety requirements.
Manufacturer approval, warranty conditions, and regulatory acceptance.

Where the combination is being considered, the RECD supplier, dual fuel system supplier, and qualified technical personnel should evaluate the complete installation. Any required testing and documentation should be completed before routine operation.

Maintenance Requirements for Reliable Operation

Both technologies need appropriate maintenance, although the specific procedures differ.

RECD Maintenance

Routine checks may include inspecting the device, reviewing pressure and temperature readings where applicable, checking for exhaust leaks, and carrying out manufacturer-specified cleaning or regeneration procedures.

Increasing pressure drop, abnormal temperatures, or a change in measured performance may indicate that further investigation is required.

Dual Fuel Kit Maintenance

A dual fuel system may require inspection of gas lines, pressure regulators, valves, sensors, electrical connections, safety interlocks, and control settings.

Gas supply interruptions, unusual engine behaviour, or recurring fault alarms should be investigated by qualified personnel. Fuel-system adjustments should follow the manufacturer's instructions.

Maintaining accurate service records can help businesses identify recurring problems, assess operating costs, and support compliance documentation.

Conclusion

RECDs and dual fuel kits provide two different approaches to managing the environmental impact of diesel generator operation. An RECD treats specified pollutants in the exhaust, while a dual fuel kit enables a compatible engine to use diesel alongside an alternative fuel.

An RECD may be appropriate where particulate emission reduction is the primary objective and the device is suitable for the generator. A dual fuel kit may be attractive where alternative-fuel infrastructure is available and reducing diesel consumption is a priority.

The final decision should be based on technical compatibility, operating costs, maintenance requirements, safety, and the applicable regulatory framework.

By evaluating these factors carefully, facility managers and industrial operators can select a practical solution that supports reliable power generation and responsible emission management.

RECD vs Dual Fuel Kit: Which Is the Right Emission Control Solution for Diesel Generators?

RECD FOR DG SET