BS 6 vs BS 4 emission norms: Key Differences explained
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BS 6 vs BS 4 emission norms: Key Differences explained

BS 4 emission norms came into effect in India in 2017, but from april 2020 the Indian automobile industry has adopted stricter BS 6 emission standards and while completely skipping the BS 5 emission norms.

What is BS4 (BSIV)?

Before we understand about BS6 emission or BS6 compliant engine, let’s understand the current BS4 (BSIV) emission norms, engine, performance, and its significance. 

The BSES, which is the governing organization for emissions from all types of vehicles in the country, introduced the first emission norms with the name ‘India 2000’ in the year 2000. BS2 and BS3 were introduced in 2005 and 2010, while BS4 norms came into effect in 2017 with stricter emission standards or norms.

Among the regulations set by the governing body, emission-related changes included tailpipe emissions, Electronic Control Unit (ECU), ignition control, etc. The most visible change was the AHO (Automatic Headlamp On), this is one of the norms under the BS4 which catered to the safety aspect of the new emission standards.

What is BS6 (BSVI)?

The governing body, Bharat Stage Emission Standards (BSES), regulates the output of pollutants from vehicles plying in the country. The Central Pollution Control Board which falls under the Ministry of Environment, Forest and Climate Change sets the standards to regulate emissions from vehicles in India.

The first emission standard or norm, introduced in the year 2000, was known as ‘India 2000’ and later, BS2 and BS3 were introduced in 2005 and 2010, respectively. While the first three emission norms were introduced at regular intervals, BS4 was introduced in 2017, after a gap of seven years.

The BS6 emission standard is the sixth iteration of the emission norm and comparatively, it’s a substantial leap in terms of reducing pollution compared to the outgoing BS4. This is also because the BS5 (BSV) has been skipped in an effort to move to better emission norms.

Difference Between BS4 (BSIV) and BS6 (BSVI):

Both BSIV and BSVI are emission norms that set the maximum permissible levels for pollutants emitting from a car or a two-wheeler exhaust. Compared to the BS4, BS6 emission standards are stricter. While manufacturers use this change to update their vehicles with new features and safety standards, the biggest or the significant change comes in the form of stricter permissible emission norms.

The below table offers an insight into the change in the permissible emission levels of BS6 vehicles compared to BS4 vehicles:

source: google

How does BS6 emission norms differ from BS4?

The following are the key differences between BS4 and BS6 emission norms:

● Diesel Particulate Filter (DPF) and Selective Catalytic Reduction (SCR) are being introduced with the roll-out of Bharat Stage VI norms, which were not a part of Bharat Stage IV.
● Real Driving Emission (RDE) will be introduced in India for the first time with the implementation of Bharat Stage VI emission norms. It will measure a vehicle’s emission in real-time conditions against laboratory conditions.
● Another change that is being introduced with the implementation of Bharat Stage VI emission norms is that Onboard Diagnostics (OD) has been made mandatory for all vehicles.
● Change in the fuel used in vehicles is the major upgrade that is being brought about with the roll-out of Bharat Stage VI emission norms. A vehicle with BS6 compliant engine will require BS6 fuel. If a BS6 vehicle uses BS4-grade fuel, it won’t be able to adhere to the BS6 emission norms. Similarly, if a BS4 vehicle uses BS6-grade fuel, its engine will take a hit and increase emissions.
● The most crucial difference between BS6-grade fuel and BS4-grade fuel will be in terms of Sulphur and Nitrogen Oxide content. The sulphur traces in BS6 fuel is five times lower (10 ppm) as compared to sulphur traces in BS4 fuel (50 ppm). Further, nitrogen oxide level for BS6-grade diesel engines and petrol engines will be brought down by 70% and 25%, respectively.

Will BS4 vehicles be able to run on BS6-grade fuel?

If you own a Bharat Stage IV car that is powered by petrol, you can relax as you do not have to worry about Bharat Stage VI compliance. The reason being, BS6-grade petrol and BS4-grade petrol have very similar chemical composition. However, if you are an owner of a diesel-powered car of Bharat Stage IV generation, you might have to face some problems.

As discussed earlier, BS4-grade diesel has sulphur traces of 50 ppm, whereas BS6-grade diesel has only 10 ppm sulphur traces. Although this low sulphur content is forgiving for the environment, it can be harmful for BS4 engines. A diesel engine depends on its injector to ionise the fuel and make it combustible, and the sulphur in diesel acts as a lubricant for the injector.

If you use BS6-grade diesel in a BS4 vehicle, low sulphur content will lead to less lubrication and hence can cause frictional issues. This in turn will wear out the injector prematurely, cause disruptions in the flow pattern of the fuel and increase emissions. As a result, the ultimate motive of decreasing air pollution will be compromised.

Will BS6 vehicles be able to run on BS4-grade fuel?

Again, petrol powered car owners don’t have to worry as the chemical composition of BS4-grade petrol and BS6-grade petrol is almost similar. However, if you use BS4-grade diesel in a car that is compliant to BS6 norms, it will undergo serious damage.

BS6 diesel engines are designed with very sophisticated electronics like a re-developed exhaust system, Diesel Particulate Filter (DPF) and Selective Catalytic Reduction (SCR). The high sulphur content in BS4 diesel will increase the emission drastically and cause serious damage to the fuel delivery system.

The high amount of sulphur will also clog the fuel filter and catalytic converter, which will affect the fuel economy of diesel cars. Thus, it will be prudent not to use BS4-grade fuel in BS6 compliant vehicles.

Will BS4 vehicles be banned after the introduction of BS6 vehicles?

As per the mandate ruled out by the Supreme Court of India in October 2018, the sale and purchase of Bharat Stage IV vehicles will be banned after April 2020. The court has asked all car manufacturers to clear their stock of BS4 vehicles before the deadline. The court has also made it clear that it will not provide any extension to car manufacturers for the stock clearance of BS4 vehicles.

However, the Finance Minister of India, Smt. Nirmala Sitharaman has stated that BS4 vehicles purchased till March 2020 will remain operational throughout the period of registration. So, if you own a BS4 compliant car, you don’t need to worry about selling it immediately and buy a BS6 compliant car.

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