Technical background on India BS VI fuel specifications

Published: 2016.04.22
The proposed Bharat Stage (BS) VI regulation for on-road vehicles in India includes contains both emission standards for new vehicles as well as specifications for reference and commercial gasoline and diesel fuels. These specifications define requirements for physical properties and chemical composition of the fuels, and are meant to ensure that commercial fuels are of sufficient quality and compatible with engine and emission control technologies that will be required to meet BS VI emission standards.
From an emissions and air quality perspective, the most important parameter defined in the fuel quality specifications is the maximum sulfur content of gasoline and diesel fuels. In both cases, sulfur content is limited to a maximum of 10 ppm in the proposed BS VI regulation, which matches global best practices. Low sulfur fuels enable the use of advanced aftertreatment control technologies, which greatly reduce emission rates of pollutants that have a signi cant human health burden, such as particulate matter (PM) and nitrogen oxides (NOX). While proposed BS VI fuel specifications largely follow European regulations, proposed limits for several commercial gasoline and diesel fuel parameters in India differ from EU values. These parameters include octane number and olefin content for regular grade gasoline; and density, 95% distillation boiling point (T95), and polycyclic aromatic hydrocarbon (PAH) content for diesel. This working paper details these differences in fuel specifications for commercial gasoline and diesel fuels in India and the EU, and assesses potential air pollutant emission impacts of these differences.
A common insight for each of these fuel parameters is that the magnitude of fuel effects on emissions of regulated air pollutants has decreased as engine and aftertreatment control technologies have advanced in design and efficiency. Modern engines incorporating advanced combustion control and exhaust aftertreatment systems have largely reduced or eliminated the e ects of small changes in these fuel parameters on emissions. These modern engine designs require low sulfur fuels to maintain robust emissions performance throughout their useful lifetimes. It is due to this fact that the single most important fuel parameter specified in the proposed BS VI regulation is the 10 ppm limit on sulfur content of gasoline and diesel fuels. Access to ultra-low sulfur fuels enables the introduction of modern, low-emitting BS VI vehicles that incorporate best available technologies for the control of air pollutant emissions.
Relative to the exceedingly large emissions benefits that will result from the implementation of proposed BS VI emission standards in 2020, any change in air pollutant emissions resulting from differences between BS VI and Euro 6/VI fuel specifications is likely to be minimal. By 2023-2025 timeframe, India should try to match, or even improve upon, Euro 6/VI fuel specifications. However, current differences in fuel quality specifications should not delay the full implementation of BS VI emission standards in 2020.