Headline : The problem with diesel
- Automakers in India in the recent times have started moving away from diesel cars value chain.
- The proportion of diesel cars in the total passenger vehicles sales has decreased from 48% in 2012-13 to 22% in 2018-19.
Decrease in price differential
- The price differential between petrol and diesel has reduced substantially after the deregulation of diesel prices in 2014.
Introduction of BS VI norms
- India is leapfrogging from BSIV to BSVI with 13 cities adopting BS VI norms starting this year and the entire country switching to BS VI fuel by April 2020.
- The technological changes needed in a diesel engine are more complicated when compared to petrol engines.
- As a result diesel cars will be prohibitively expensive.
Constraint on Oil Makers
- The transition to BS IV took 7 years for oil refiners to start producing better fuel.
- Thus the ability of oil refiners to produce enough quantity of high-grade dieselin accordance with BS VI standards is questioned.
Design constraints for Indian roads
- The new-gen vehicles to meet the BS VI standards require the following technology upgrades:
- Diesel particulate filter
- Selective catalytic reduction system
- Lean NOx trap
- However the slow speeds on Indian roads makes it difficult for carrying out design changes with these critical components.
- For instance the diesel particulate filter has a system to burn soot produced in the emissions.
- This requires temperatures of around 600 degrees Celsius which is difficult to achieve at low speed driving on Indian roads.
In brief: BS VI Norms
- Bharat Stage VI (BS VI) is an emission standard that will induce technology in the vehicles to reduce pollutant emissions.
- The vehicles will mandatorily include OBD (On-board diagnostics) which will monitor the pollution caused by the vehicle in real time.
- The BS-VI vehicles use selective catalytic reduction technology which substantially reduces particulate matter emission.
Specification of BS-VI norms for diesel engines
- BS-VI grade fuel contains 10 parts per million (ppm) of sulphur as against 50 ppm in BS-IV fuels.
- 10-20% reduction in particulate emission when used in BS-IV or lesser grade engines.
- The Octane number for petrol engines – 91 under BS-VI emission norms. (BS II – 88)
- The PM emission in diesel engines – 80% reduction
- NOx emission in diesel engines – 68% reduction.
Diesel Engine Emissions
- Incomplete combustion of diesel results in carbon monoxide, hydrocarbons and aldehydes.
- The characteristic smell of the diesel is due to hydrocarbons and aldehydes.
- High temperature and pressure inside the engine gives rise to Nitrogen oxides including nitric oxide (NO) and traces of nitrogen dioxide (NO2).
- Sulphur present in diesel gives rise to Sulfur dioxide (SO2) upon combustion.
- Particulate matter includes soot, aromatic hydrocarbons, and hydrated sulfuric acid.
Selective catalytic reduction system
- SCR systems are emissions control system that injects a fluid through a special catalyst into the exhaust stream of a diesel engine.
- The fluid used is usually a reducing agent like urea that converts nitrogen oxides into nitrogen and water.
- Thus SCR technology is used to reduce NOx emissions in diesel engine.
Diesel particulate filter
- Diesel particulate filter is a filter that captures and stores exhaust soot to reduce particulate matter emissions from diesel engines.
- If the soot is trapped inside the filter it gets clogged.
- As a result the filter is regenerated by burning the soot particles at the exhaust pipe.
- The soot is burnt at high temperatures of around 600 degree Celsius which is obtained by the temperature of the exhaust gas itself.
- This regeneration process burns off the excess soot deposited in the filter, reducing the harmful exhaust emission and thus reduces the black smoke seen in diesel vehicles.