What happens when we put BS4 fuel in a BS6 car or vice-versa?

The Government of India has skipped Bharat Stage 5 and instead is transitioning towards stringent BS6-emission norms that will be kicking-in from April 1, 2020. While all the original equipment manufacturers have already updated or are updating their portfolio to comply with the newer emission norms, but people have a lot of questions in mind regarding Bharat Stage 6. In this article, we will be addressing all those questions and will also answer you that what happens when we put BS4 fuel in a BS6 car or vice-versa?

The BS6 norms will come into effect from the new financial year of 2020, however, car manufacturers have been launching BS6-compliant vehicles since a real long time when BS6 fuel was not readily available across India, except Delhi-NCR (BS6 fuel is available in NCR area since April 1, 2019). There is no major hazard with petrol-powered engines but diesel-powered ones might have some problems in a long course of time and so the company's used to provide AdBlue too. An AdBlue is a fluid made up of a mix of urea and deionized water which is squirted into the exhaust system, helping to reduce nitrous oxide emissions produced by diesel engines.

Getting back to our main question, what happens when we put BS4 fuel in a BS6 car or a BS6 fuel in a BS4 car? There are two sides to this question: using BS6 fuel in a BS4 car, and using BS4 fuel in a BS6 car. While there are no major problems associated with the former one, but with the latter there might be some problems, especially with the oil-burners.

Using BS6 fuel in a BS4 car:
While petrol moving from BS4 to BS6 will not be very different in terms of its chemical properties, the real difference will actually be in the diesel. The new diesel will have an even lower rating of Sulphur as compared to the diesel available now. While normal diesel which was available in earlier carried 500 PPM (parts per million) of Sulphur, the current fuel that is termed as 'Low Sulphur Diesel' is rated at just 50 PPM. The BS6 fuel, in turn, will actually carry just 10 PPM of Sulphur, which is much cleaner and better for the environment. While the engine will run cleaner, the long term effects of using BS6 fuel on BS4 engines exist too (more in the oil-burners).

 Sulphur in the fuel helps with the chemical lubrication of the injectors in a diesel engine. Diesel engines rely on their injectors to turn diesel from a liquid to a mist which then combusts in the cylinder. If we have a low level of Sulphur in your diesel, the injectors (in the long run) will showcase signs of internal wear and scoring. This might result in flow patterns being disrupted which in turn will cause incorrect and incomplete combustion and can also increase emissions. However, these are only long term implications on the engine. Point to be noted is that such effects were noticed every time when India has moved from one emission norm to the other in the past too.

Using BS4 fuel in BS6 cars:

On the other hand, BS6 cars will be having updated electronics and hardware (injectors) that can run on BS6 fuel, and also they have additional components in the exhaust stream. For example, the exhaust system has the likes of the diesel particulate filter and even Urea injection in some cases. Using older fuel with a higher rating of sulphur in a modern engine will mean higher particulate matter (as compared to using BS6 fuel in a BS6 engine) which in turn will result in the diesel particulate filters clogging and needing replacements faster than an average life cycle. This might also cause the engine to run in a slightly under efficient manner affecting fuel economy and overall emissions. While the earlier combination is the issue of a more long term, the problems caused by using BS4 fuel in a BS6 car can be seen immediately.