Before we start understanding the difference between the Bharat Stage 4 vs Bharat Stage 6 emission standards let us first try to see what are the different pollutants an internal combustion engine generates when it burns fuel. So the typical pollutants that are generated by an IC engine are – Carbon Dioxide (CO2), Carbon Monoxide (CO), Hydrocarbons (HC), Nitrous Oxides (NOx). Particulate matter (PM) gets generated in diesel engines and direct injection gasoline engines. Now we all know the adverse effects these pollutants have on our air that we breathe and hence on our bodies as well. Hence the step taken by our government and the auto industry to switch to Bharat Stage 6 norms. As a result of this transition, the pollutants emitted by IC engines conforming to these new norms will be significantly lower compared to those conforming to BS4 norms.
So how much cleaner will the BS6 IC engines be compared to their BS4 counterparts?
The Diesel engines are going to see a drastic reduction in emissions with the switch to BS6 norms. The particulate matter emitting from a BS6 diesel engine should see a reduction of more than 80% compared to BS4 levels. A BS6 diesel engine needs to adhere to the limit of 4.5 mg/km of PM emission compared to 25 mg/km in case of BS4 diesel engine. This on its own is going to significantly help in improving the Air Quality Index (AQI) in most of our urban areas. Additionally NOx should see a reduction from 250 mg/km to 80 mg/km, which is a reduction of 68% with the introduction of BS6 norms. Hydrocarbons (HC) will see a comparatively modest reduction of 43% going from 300 mg/km to 170 mg/km with the introduction of BS6 norms conforming diesel engines.
In case of gasoline (petrol) engines we aren’t going to witness a huge reduction something like the diesels but still it is going to be a cleaner engine compared to the BS4 one. So we shall see a 25% reduction in NOx going from 80 mg/km to 60 mg/km while HC emission targets are going to stay the same. It will be the first time that PM will be regulated, but applicable only to direct injection gasoline engines and the limit will be set at 4.5 mg/km.
Now such significant reduction in pollutants being emitted from exhausts of IC engines is definitely going to help curb the air pollution, especially in our country as diesel engine vehicles are still preferred over gasoline engine ones when the mileage done is significant and many times also because diesel engines provide bucket loads of torque compared to gasoline engines. This is true for our SUV loving population who want their SUVs to have loads of torque and hence the default choice of engine being diesel. So this is definitely a step in the right direction of improving the quality of the air that we breathe.
What are the changes happening on engines to achieve these BS6 norm targets?
In case of Diesel engines, to control the PM emission, a Diesel Particulate Filter (DPF) is being introduced as an exhaust gas after treatment. NOx is being controlled by using two different technologies – one is by using a Lean NOx Trap (LNT) which is a filtration method filtering nitrous oxides from the exhaust. And second by using Selective Catalytic Reduction (SCR) system which uses water based urea solution to reduce the nitrous oxides to inert nitrogen and water. This urea solution is injected into exhaust stream while passing through the SCR. Reduction in hydrocarbons is being achieved by better controlling the combustion using modern injectors and fuel injection systems.
It’s not only the engines that are going through a significant design change but the fuels that will be used are also changing and will have to prescribe to the new norms. Hence going forward from April 1st 2020 our fuel stations will have to sell BS6 compliant Diesel and Petrol. Now BS6 grade fuels will have significantly lower sulphur content – 10 mg/kg compared to 50 mg/kg allowed in BS4 grade fuels. Although the availability of BS6 conforming fuels might make us apprehensive especially in rural areas and on highways out of major city limits, the government and authorities will be making sure that such fuels are available throughout India.
Following the availability of fuels, comes the anxious question of – Whether a BS4 fuel can be used in BS6 engines? The answer to this is – in case of gasoline engines the impact of using BS4 grade fuel in a BS6 engine will not be catastrophic. While in a Diesel engine a BS4 grade fuel may cause significant damage to the catalysts used in emission equipment like the DPF, LNT or SCR system. So it’s important to use the right grade of fuel in the new BS6 diesel engines otherwise the maintenance cost of such engine would shoot up significantly due to the damages done to the exhaust after treatment systems. Now, for existing BS4 engines if they use BS6 grade fuels, it will cause no harm at all and in fact, the low sulphur content in the BS6 fuel would help in reducing to a very small extent the emissions from BS4 engines.
Will there be any penalty on the performance of our cars like drivability issue, low pickup or low fuel mileage?
In order to get the emissions from the engines boxed to lower limits as specified in the BS6 norms, it is imperative that there will be an impact on the power/torque and fuel economy of the engine. But it is something which most of the car users will not agree on. Knowing this very well, all the car manufacturers have made sure that the BS6 engines are at least on par if not better when compared to their BS4 counterparts in terms of driveability, acceleration and fuel efficiency. They have made the necessary design tweaks to the engine components to overcome whatever penalty the stricter emission norms would have imposed on the performance of the engine. So there won’t be any detrimental effect on the performance of the BS6 compliant car.
What will be the impact on the vehicle purchase price?
Finally with all the design changes and the engineering effort that auto companies would have gone through to make the IC engines meet the stricter BS6 emission standards, there ought to be a price increase which will be passed on to the consumer. It is expected that this price increase would be in the range of 10k to 30k for a Gasoline engine car and about 50k to 80k for a Diesel engine car. Although the exact price differential would be known only when the car companies debut the BS6 engine models, it is safe to assume that the intent to improve the quality of the air will come at some price in terms of hitting our pockets, but it would be a small price to pay if it is going to have a positive impact on our health!
