BS6 vs BS4: Key Differences in Emission Standards, EATS Technology, and Pollution Control

 BS6 vs BS4: Key Differences in the Emission After-Treatment System (EATS)

With the implementation of BS6 (Bharat Stage VI) emission norms, India has taken a giant leap towards reducing vehicular pollution. However, the shift from BS4 to BS6 has not been just about setting new emission limits—it also introduced a range of advanced technologies like the Emission After-Treatment System (EATS). In this blog, we’ll dive into the key differences between BS6 and BS4 emission norms with a special focus on how EATS has transformed between the two standards.

Introduction: The Need for BS6 Over BS4

BS4 emission norms were introduced in India in 2017 to regulate the amount of harmful gases emitted by vehicles. While it was a step in the right direction, increasing pollution levels and climate concerns required stricter standards. That’s where BS6 comes in, introduced in April 2020, which sets far more stringent limits on pollutants like nitrogen oxides (NOx), hydrocarbons (HC), particulate matter (PM), and carbon monoxide (CO).

The Emission After-Treatment System (EATS) is a critical technology ensuring that vehicles meet these stricter BS6 emission norms, particularly in diesel engines, which are typically used in commercial vehicles like trucks and buses.

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What is BS4?

Before we discuss BS6, let's first understand what BS4 (Bharat Stage IV) norms were. BS4 was an emission standard implemented to reduce pollutants, mainly focusing on:

Nitrogen oxides (NOx)

Carbon monoxide (CO)

Hydrocarbons (HC)

Particulate matter (PM)

While BS4 norms required some basic emission control systems like the catalytic converter and exhaust gas recirculation (EGR), it lacked the advanced after-treatment systems seen in BS6 vehicles.

Emission Control in BS4 Vehicles

In BS4 vehicles, emissions were managed using simpler techniques compared to BS6. These included:

Catalytic Converters: Used to reduce CO, HC, and NOx emissions.

Exhaust Gas Recirculation (EGR): A technology that recirculates a portion of the exhaust gas back into the engine cylinders to reduce NOx emissions.

However, the absence of sophisticated systems like the Diesel Particulate Filter (DPF) and Selective Catalytic Reduction (SCR) meant that BS4 vehicles emitted higher levels of harmful gases compared to BS6 vehicles.

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What is BS6?

BS6, or Bharat Stage VI, represents a significant upgrade in terms of emission control. The focus shifted from merely reducing emissions to eliminating key pollutants almost entirely. BS6 norms are similar to the Euro 6 standards implemented in Europe and focus on reducing:

Nitrogen Oxides (NOx) by over 70% for diesel engines.

Particulate Matter (PM) by 80% in diesel vehicles.

Hydrocarbons (HC) and Carbon Monoxide (CO) to significantly lower levels.

To achieve these reductions, BS6 vehicles, especially diesel-powered commercial vehicles, require a more advanced Emission After-Treatment System (EATS).

Advanced EATS in BS6 Vehicles

Here are the advanced EATS technologies that differentiate BS6 vehicles from their BS4 counterparts:

1. Diesel Particulate Filter (DPF): A DPF captures and stores particulate matter (PM) from diesel engine exhaust. This filter reduces harmful black soot emissions by more than 80% compared to BS4 vehicles.

2. Selective Catalytic Reduction (SCR): One of the most critical additions in BS6 vehicles is the SCR system. SCR uses a urea solution called AdBlue to convert nitrogen oxides (NOx) into harmless nitrogen and water. This drastically reduces NOx emissions.

3. Ammonia Slip Catalyst (ASC): The ASC ensures that no unreacted ammonia escapes into the environment. It works in conjunction with the SCR system to ensure a complete reduction of pollutants.

4. Low-Sulfur Fuel Requirement: BS6 vehicles also require ultra-low sulfur diesel (ULSD), which contains sulfur content of only 10 ppm (parts per million), compared to 50 ppm in BS4. This cleaner fuel ensures better compatibility with EATS and reduces emissions.

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Key Differences Between BS6 and BS4 Emission Standards

1. NOx Emissions Reduction

BS4: The NOx emission limit for diesel vehicles was 250 mg/km.

BS6: BS6 norms reduced the NOx emissions by over 70%, capping it at 80 mg/km.

This drastic reduction in NOx emissions has been possible due to the introduction of the Selective Catalytic Reduction (SCR) technology in BS6 vehicles.

2. Particulate Matter (PM) Emissions

BS4: Particulate matter (PM) emission limits in BS4 vehicles were higher due to the absence of filters like DPF.

BS6: BS6 norms enforce the use of Diesel Particulate Filters (DPF), which reduce particulate matter emissions by more than 80%.

This is particularly significant for diesel-powered commercial vehicles, as particulate matter is one of the leading causes of air pollution and respiratory problems.

3. Introduction of Advanced EATS Technologies

BS4: Vehicles mainly used simpler technologies like catalytic converters and EGR for emission control. These systems were effective for reducing CO, HC, and some NOx emissions but did not address particulate matter or achieve the stringent NOx reductions required in BS6.

BS6: BS6 vehicles come equipped with more complex and effective EATS components, including SCR, DPF, and ASC, to meet the much stricter emission standards.

4. Fuel Requirements

BS4: BS4 engines were compatible with diesel that had a sulfur content of 50 ppm (parts per million).

BS6: BS6 engines require ultra-low sulfur diesel (ULSD) with a sulfur content of only 10 ppm. This cleaner fuel is essential for preventing clogging and ensuring the proper functioning of EATS components like the DPF.

5. Onboard Diagnostics (OBD)

BS4: OBD systems in BS4 vehicles were basic and did not monitor many emissions-related parameters.

BS6: BS6 vehicles feature advanced Onboard Diagnostics (OBD II), which monitor the performance of all emission control systems, including the SCR and DPF. If any issue is detected, the OBD system alerts the driver, ensuring that vehicles maintain emission compliance over time.

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Impact of EATS on Commercial Vehicles in BS6 vs BS4

Fuel Efficiency

One of the concerns with the introduction of BS6 was that the advanced EATS systems could negatively impact fuel efficiency. However, while BS6 vehicles have seen a slight decrease in fuel efficiency due to the SCR system, the impact is minimal. The use of AdBlue in SCR also ensures that engine performance remains optimal, reducing fuel wastage.

Cost Implications

BS6 vehicles, especially commercial ones, are more expensive than BS4 vehicles due to the advanced EATS technologies. The cost of maintaining systems like the DPF and SCR can also be higher, particularly if issues like DPF clogging arise. However, the long-term benefits of reduced emissions, cleaner engines, and compliance with global emission standards outweigh these costs.

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Challenges and Maintenance of BS6 EATS

While BS6 emission norms have brought significant environmental benefits, they also present some challenges for vehicle owners and operators:

1. DPF Clogging

The Diesel Particulate Filter (DPF) can get clogged over time with soot and ash. Regular DPF regeneration is required to burn off the accumulated particles and keep the filter functioning properly.

2. AdBlue Refilling

The Selective Catalytic Reduction (SCR) system relies on AdBlue, a urea-based solution. Running out of AdBlue can result in increased NOx emissions and lower performance, so vehicle operators must ensure regular refilling.

3. EGR Valve Issues

The Exhaust Gas Recirculation (EGR) system can suffer from valve clogging due to carbon build-up, which can reduce performance and increase emissions if not regularly serviced.

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Conclusion: BS6 vs BS4 – A Major Leap in Emission Control

The transition from BS4 to BS6 norms has marked a significant improvement in reducing harmful vehicle emissions, particularly in commercial vehicles. With the introduction of advanced Emission After-Treatment Systems (EATS), BS6 vehicles can achieve far lower levels of pollutants like NOx and particulate matter.

While the shift to BS6 has increased vehicle costs and maintenance requirements, the environmental and health benefits make it a necessary and worthwhile change. For workshop owners, truck operators, and fleet managers, understanding the key differences between BS4 and BS6, especially in the context of EATS, is crucial for ensuring compliance and maintaining optimal vehicle performance.