What is BS6 Phase 2: Complete Guide to the Latest Emission Norms

Table of Contents

• Introduction to the Bharat Stage (BS) Standards
• What are BS6 Norms?
• What is Bharat Stage 6 (BS6) Phase 1?
• What is BS6 Phase 2?
  • Real Driving Emission (RDE) Testing
  • On-Board Diagnostics (OBD-II)
• What is the Impact of BS6 Phase 2 Norms?
  • Cleaner Emissions
  • Mileage Performance
  • Prevents Major Vehicle Failures
  • Complex Exhaust System
  • DPF Regeneration
  • City Use Challenges
  • Requires High-Quality Fuel
  • Maintenance Challenges
  • Higher Upfront Cost
• What Future Holds: Bharat Stage 7 (BS7) Norms

Introduction to the Bharat Stage (BS) Standards

India faces a significant challenge in combating air pollution to protect public health and the environment. Given that vehicle emissions are a major contributor, the Indian government began implementing Bharat Stage (BS) emission standards on the lines of the Euro norms. These BS norms offer an appropriate balance between environmental protection and the adoption of cleaner technologies. Diesel engines undergo greater changes due to their higher emission levels. Thus, these BS norms have also led to higher vehicle prices and maintenance costs for customers. Currently, BS6 Phase 2 is operational in India. There are also emission standards for Construction Equipment Vehicles (CEVs) and agricultural/farm machinery (TREM). For instance, Trem IV emission norms regulate tractors above 50 HP. Along with its positives and challenges, BS emission standards play a critical role in ensuring better air quality for the entire population.   

What are BS6 Norms?

BS6 (Bharat Stage 6) emission norms are strict guidelines outlined by the Indian government to limit emissions like particulate matter and nitrogen oxides from vehicles. The goal is to reduce pollutants from vehicle exhaust and improve the currently struggling air quality. BS6 norms promote the use of advanced engine and exhaust technologies to cut down on harmful pollutants. At par with the European Euro 6 standards, BS6 norms also contribute to better fuel efficiency, longer engine life and real-time monitoring.

The Indian government skipped BS-5 entirely and moved directly from the former BS4 norms to the Bharat Stage 6 standards. BS6 emission standards were rolled out in two phases in India. BS6 Phase 1 norms came into effect on 1^st April 2020, mainly to lower permissible emission levels significantly. For diesel vehicles, Selective Catalytic Reduction (SCR) and Diesel Particulate Filters (DPF) were some technologies introduced in Phase 1. BS6 Phase 2 was enforced from April 2023 to bring in stricter emission standards with a focus on On-Board Diagnostics (OBD) and Real Driving Emissions (RDE). It prioritizes meeting emission standards in real-world driving conditions.

What is Bharat Stage 6 (BS6) Phase 1?

BS6 Phase 1 was a big move towards setting a stricter limit for pollutants emitted from a vehicle’s exhaust. This phase came out with more stringent emission standards than its BS4 counterpart. Previously, the per-km limit for nitrogen oxide (NOx) for petrol and diesel vehicles was 80 mg and 250 mg, respectively. With the BS6 Phase 1, the NOx limit has been substantially lowered to 60 mg (petrol) and 80 mg (diesel). The norms are stricter for diesel vehicles as particulate emissions have been lowered from 25 mg to 4.5 mg. Also, HC+NOx emissions are now limited to 170 mg, a sharp decline from the 300 mg limit set by BS4.   

BS6 Phase 1 also enforced the use of cleaner, low-sulphur BS6 fuel. The sulphur content of the BS4 fuel was 50 ppm, while the BS6 fuel has 10 ppm. To benefit from the BS6 norms, it is necessary for vehicles to use BS6 fuel only. In addition, after-treatment technologies like SCR and DPF have been adopted by manufacturers to comply with BS6 norms and reduce harmful emissions.

What is BS6 Phase 2?

The BS6 Phase 2 launch date was 1^st April 2023. Under its norms, it is mandatory for vehicles to meet the emission standards in real-world driving conditions. This phase also introduced an advanced On-Board Diagnostics (OBD-II) system for real-time monitoring of any issue related to emissions.

Real Driving Emission (RDE) Testing

One of the most important directives of Phase 2 was Real Driving Emissions (RDE) testing. It aims to provide a more precise outlook than the lab testing approach on the emission levels of the vehicle. For RDE testing, manufacturers use Portable Emission Measurement Systems (PEMS) to test emission levels and fuel efficiency of the vehicle. This device offers more accurate results than traditional lab testing. Also, the vehicle is tested on different route settings, including slopes, steep inclines, highways and traffic. With RDE testing, OEMs can develop engines and after-treatment systems with better performance in varied driving conditions. All vehicles need to have the RDE certification

On-Board Diagnostics (OBD-II)

OBD systems are required to monitor the vehicular emissions and ensure emission standards are met. OBD ports are installed to get real-time information on any malfunctions in vehicles. This preventive measure helps in taking immediate action to remedy the detected problem. An advanced OBD-II system keeps a check on the emission level of the vehicle and alerts when any potential issues arise. This system goes a long way in not only enhancing fuel efficiency but also complying with BS6 standards. Under the BS6 Phase 2, the government has also made OBD2 mandatory for two-wheelers.

What is the Impact of BS6 Phase 2 Norms?

BS6 Phase 2 has resulted in major technological upgrades in both diesel and petrol engines to reduce emissions significantly. This has impacted the Indian automobile industry by influencing refinements in vehicle engines and exhaust systems. There is a bigger impact on diesel engines as they have higher NOx and particulate matter (PM) emissions, due to which after-treatment systems are required. Also, BS6 norms mandated a 70% reduction in NOx emissions and an 80% reduction in PM. Diesel engines have to undergo substantial and expensive upgrades to achieve these reductions.

Cleaner Emissions

BS6 Phase 2 ensures cleaner emissions in diesel engines by mandating RDE testing, OBD-II and advanced after-treatment systems. These measures keep emissions within limits and notify drivers in case of any malfunction. DPF and SCR systems are in place for preventing the release of exhaust soot, PM and harmful nitrogen oxides into the atmosphere.

Mileage Performance 

Vehicles are likely to improve their mileage due to optimized engine calibration. Bike manufacturers are implementing an advanced fuel management system, resulting in lower fuel consumption. For instance, manufacturers are providing enhanced fuel injection systems in their BS6 petrol engines for better combustion efficiency and improved fuel efficiency. Also, petrol vehicles may experience better cold starts due to precise fuel delivery. However, mileage depends on many factors, including driving habits and conditions, so mileage performance in BS6 vehicles may not be the same for all.

Prevents Major Vehicle Failures

The OBD-II system helps to take proactive steps by detecting issues early. It diagnoses faults and monitors emissions by using sensors for different components, including the engine and transmission. As soon as any issue is observed, it stores a Diagnostic Trouble Code (DTC) and the ‘Check Engine’ light turns on. An OBD II scanner can be used to read this code and determine which component or system needs fixing. Regular monitoring of the real-time and historical data from the OBD II system can help prevent issues like engine misfire and a faulty oxygen sensor. Minor issues can be easily detected and addressed early on before they escalate into risky and costly issues. Also, BS6 CNG vehicles come with enhanced protection with features like leak-detection systems and sensors.

Complex Exhaust System

With the implementation of BS6 norms, exhaust systems have become more complex, especially in diesel engines. It is mainly due to the strict monitoring of real-time emissions and the use of advanced after-treatment technologies. BS6 vehicles use components like Diesel Particulate Filter and Selective Catalytic Reduction, which have not only made potential repairs expensive but also led to maintenance challenges. AdBlue is an important fluid used in the SCR system for NOx reduction. The driver needs to properly maintain AdBlue in BS6 vehicles by refuelling it regularly. This also adds up to vehicle maintenance tasks and costs.   

DPF Regeneration

This process involves burning off the trapped soot and ash to clean the DPF. A clogged DPF filter can lead to higher emissions, reduced engine performance and efficiency. So, DPF regeneration uses high exhaust temperatures to burn away the soot from the filter. For passive regeneration, the vehicle needs to run at sustained high (>2000) RPM levels for 15-30+ minutes continuously. This is usually only possible during long highway runs. In case passive regeneration is not enough due to high soot levels, the ECU signals to send more fuel to increase exhaust temperature and burn off the accumulated soot.

DPF regeneration has also become a concern for drivers, especially with short runs. If you interrupt automatic DPF regeneration repeatedly, the engine will trigger warnings and enter limp mode. This mode restricts engine power and limits speed, resulting in extremely poor acceleration. So, you need to perform manual or parked regeneration where the vehicles need to be parked in a safe area for around 30 minutes. This is a major hassle for drivers while operating on highways.

City Use Challenges

As mentioned above, DPF regeneration requires the diesel vehicle to run at higher RPMs for about 30 minutes continuously. However, this is not possible in city driving due to low speeds and frequent stops due to traffic. If ignored, it may result in a clogged DPF and other engine issues. The driver needs to perform manual regeneration in such situations or visit a service centre. The best approach is to balance between city and highway drives.

Requires High-Quality Fuel

BS6 vehicles must only use BS6 fuel with lower sulphur content. Any impurity in the fuel can cause severe damage to the vehicle's advanced emissions control systems and engine components. It can result in performance issues or breakdowns. Also, only quality additives must be used for proper cleaning of fuel systems. BS6 diesel vehicles are highly sensitive to fuel quality; thus, only high-quality BS6-grade fuel must be used for reliable performance.

Maintenance Challenges

With complex emission systems and technologies, maintaining BS6 vehicles can be slightly tricky. Drivers can face key issues related to DPF clogging, oil dilution and ADBlue on a regular basis. Some of the best practices include highway driving, the use of quality fuel, monitoring warning lights, and regular servicing. With BS6 norms, vehicle servicing requires skilled technicians who follow manufacturer guidelines. Also, maintenance costs for BS6 vehicles have increased due to the use of modern components and the need for skilled expertise.

In addition, BS6 vehicles come equipped with an advanced emission control system that uses a wide range of sensors, including exhaust temperature and oxygen (O₂) sensors. It makes them highly sensitive to sensor-related issues, as more sensors increase the likelihood of failures. Proper monitoring and maintenance are needed to ensure all sensors function as intended.

Higher Upfront Cost

Compared with BS4 vehicles, BS6-compliant vehicles are more expensive. It is mainly due to R&D, advanced components, and technologies used by OEMs to meet stricter emission standards. These costs are passed on to the customers. This is also why several car manufacturers have discontinued many diesel models from their affordable (lower-end) segment due to the high cost of complying with BS6 norms. Also, higher prices mean lower customer demand. This is why diesel trims are being limited to the higher-end segment, offering larger SUVs and MPVs.

What Future Holds: Bharat Stage 7 (BS7) Norms

India is struggling with a severe air pollution crisis, which is why the government is taking proactive steps to keep up with the global emission standards and improve air quality. This was one of the reasons why BS5 norms were skipped. Similarly, the government is aiming to launch BS7 norms to align with the upcoming Euro 7 emission norms. It would prevent sudden disruption and technological upgrade for manufacturers, which was observed when transitioning from BS4 to BS6 norms. As of now, there has been no official announcement regarding the launch or the specifics of BS7 norms. However, it is expected to roll out around 2026-2027 in India.

BS7 norms are assumed to enforce stricter pollutant limits on NOx, CO, etc. Also, these emission limits may become uniform across all vehicles, regardless of fuel type. BS7 is expected to introduce specific rules for electric vehicles (EVs) for the first time. Till now, the focus has been only on tailpipe emissions. But now non-exhaust emissions can also be regulated. It may include microplastic emissions from tyres and particulate matter (PM) emissions from brakes. Testing for overall safety, charge capacity, and battery longevity of EVs and hybrids may become stricter under BS7 norms. It is only a matter of time before the exact details of BS7 norms are out in public. One thing is certain: the next iteration of emission standards will be a transformative step toward a cleaner automotive ecosystem in India.