Testing a Retrofit Emission Control Device (RECD) is not simply a matter of measuring emissions before and after installation. The condition of the diesel generator and the fuel being used can have a significant influence on the final results. If these factors change between tests, the measured emission reduction may not represent the actual performance of the RECD alone.
A reliable testing programme therefore starts with preparing the engine, documenting its condition and controlling fuel-related variables before measurements begin.
Why Engine Condition Matters
An RECD performance comparison generally depends on the difference between emissions measured before and after installation. If the engine itself changes during this period, some of the change in emissions may be incorrectly attributed to the emission control device.
For example, if a DG set has dirty injectors during the baseline test and those injectors are serviced before the post-RECD test, the second test may show lower engine-out emissions even without considering the RECD's contribution.
This is why the engine should ideally be brought to a stable and documented operating condition before testing.
For a more detailed discussion, see Aceget's guide on fuel and engine conditions that can affect RECD performance tests.
Check Fuel Quality and Consistency
Fuel is one of the first variables that should be controlled.
Changes in fuel quality, supplier, batch or blend can affect combustion and particulate formation. When two tests use different fuel conditions, it becomes harder to determine whether a difference in emissions came from the RECD or from the fuel itself.
Before testing, record:
Fuel supplier
Delivery date
Fuel batch, where available
Relevant fuel certificate
Fuel type and blend
Condition of the storage tank
Fuel-filter condition
Where practical, using fuel from the same batch for baseline and post-installation testing can reduce one source of variability.
The Bureau of Indian Standards (BIS) provides standards and specifications relevant to petroleum products and fuels, making it a useful reference when documenting fuel requirements. BIS – Official Website
Inspect the Fuel Injectors
Injectors have a direct role in combustion quality. Worn, dirty or leaking injectors can produce an abnormal fuel spray pattern and increase smoke or particulate emissions.
Before an RECD test, review the injector service history and investigate visible signs of poor combustion.
If injectors have recently been serviced, this should be documented. Ideally, major engine maintenance should be completed before establishing the baseline so that the baseline represents a reasonably healthy operating condition.
Check the Air Filter and Intake System
A restricted air filter can reduce the amount of air available for combustion. This can increase soot formation, particularly when the generator is operating under significant load.
Record the air-filter replacement date and inspect the intake system before testing. If an air filter is replaced between baseline and post-RECD measurements, that change should be documented because it can influence the comparison.
Review Turbocharger and Lubricating-Oil Condition
The turbocharger should also be inspected, particularly on engines where boost pressure is important for normal combustion.
Unusual oil consumption can be another warning sign. Oil entering the combustion process may contribute to particulate formation and can also affect the loading behaviour of the emission-control system.
Useful records include recent oil top-ups, maintenance history and observations such as excessive blue smoke or unusual turbocharger behaviour.
Keep Engine Settings Consistent
Fuel-pump settings, injection timing and governor adjustments can influence engine emissions.
If any of these parameters are changed between the baseline and post-RECD tests, the results may no longer represent a controlled comparison.
Therefore, document relevant service work and avoid unnecessary engine adjustments between measurements. If an adjustment becomes necessary, it should be recorded and its potential effect on the test should be considered.
Record Operating Conditions
The engine should be tested under clearly documented operating conditions.
Important parameters can include:
DG set load in kW
Power factor
Engine speed
Coolant temperature
Lubricating-oil temperature
Exhaust temperature
Engine back-pressure
Running hours
Recent maintenance history
Maintaining comparable operating conditions makes the before-and-after comparison much more meaningful.
The Central Pollution Control Board (CPCB) publishes specific procedures for emission-compliance testing of RECDs for diesel power-generating-set engines. Reviewing the applicable CPCB procedure can help testing teams understand the required testing framework and documentation. CPCB – RECD Emission Compliance Testing Procedure Central Pollution Control Board
Check Exhaust Back-Pressure After Installation
An RECD becomes part of the exhaust system, so back-pressure should not be ignored.
Excessive back-pressure can influence engine operation and potentially affect emissions. Therefore, back-pressure should be recorded during the relevant test conditions and compared with the engine manufacturer's permissible limits.
This is particularly important when evaluating whether an apparently lower emission-reduction result is related to the device itself or to an installation issue.
Consider Ambient Conditions
Engine testing can also be influenced by the surrounding environment.
Temperature, humidity and atmospheric pressure can affect the air entering the engine and therefore combustion behaviour. For sequential tests performed on different days, recording these conditions can provide useful context.
For the most controlled comparison, testing arrangements that minimise changes in environmental and engine conditions are preferable.
Use an Accredited Testing Laboratory
The laboratory itself is another important consideration. Before testing, confirm the laboratory's relevant scope, measurement capabilities and calibration arrangements.
NABL provides accreditation for testing and calibration laboratories under applicable requirements, including ISO/IEC 17025 for testing and calibration activities. NABL – Official Website NABL
Create a Pre-Test Checklist
Before beginning an RECD test, the project team should verify:
Engine maintenance is up to date.
Injectors and air filters are in suitable condition.
Fuel source and batch are documented.
No unplanned engine adjustments are made between tests.
Load and operating conditions are recorded.
Exhaust back-pressure is checked.
Ambient conditions are documented.
Instruments and calibration records are available.
Test procedures are agreed in advance.
Final Thoughts
Reliable RECD testing starts with controlling the variables that can influence the result. Fuel quality, injector condition, air supply, turbocharger health, oil consumption, engine settings, load and operating temperature can all affect emissions independently of the RECD.
Preparing the DG set properly before testing and keeping important conditions consistent between measurements can make the final results much easier to interpret. A well-documented test also provides greater confidence that the reported emission reduction represents the performance of the RECD rather than an unrelated change in engine or fuel condition.