Automakers seek higher fuel vapour emission limit under BS VII citing E20 petrol

Automakers are seeking a fuel-vapour limit of at least 2 grams per test. The government’s draft BS VII rules set the limit at 1.5 grams. This matters because vapours from petrol can escape during testing and contribute to air pollution.

The industry points to India’s E20 petrol, containing 20% ethanol, compared with Europe’s E10 or E5 fuels. It argues that higher ethanol blends can raise fuel volatility, measured by Reid Vapour Pressure, and increase evaporation. However, ethanol manufacturers say E20 is not automatically more volatile than E10; fuel composition and vehicle controls also matter.

BS VII is proposed from 2029, covering cars, light trucks, and heavy commercial vehicles in three phases. SIAM’s request would therefore allow 0.5 grams more vapour per test than the government’s proposal. The final limit may depend on testing under Indian E20 conditions, while tighter monitoring will also cover tyre wear emissions.

Evaporative emissions are fuel vapours that escape from a vehicle rather than leaving through its exhaust. They matter because these vapours can add to air pollution, especially when fuel evaporates easily. Unlike exhaust emissions, this measure focuses on fuel escaping during a prescribed vehicle test.

The escaping vapour is measured by weight during a prescribed test. The proposed limit is 1.5 grams per test, meaning the vehicle must stay at or below that amount. SIAM seeks at least two grams, arguing India’s E20 petrol may evaporate differently from Europe’s E10 or E5.

India’s standard E20 fuel makes this debate especially important. Experts link higher ethanol blends with higher vapour pressure, but fuel composition and vehicle controls also matter. BS VII is proposed from 2029, with limits intended to reduce pollution from vehicles. Testing will show whether 1.5 grams is practical under Indian fuel and driving conditions.

The gap is 0.5 grams of fuel vapour per test. Automakers’ requested limit is one-third higher than the government’s proposed 1.5-gram cap. This matters because the limit sets how much vapour a vehicle may release during testing.

For example, the draft BS VII notification allows no more than 1.5 grams during the prescribed evaporative-emissions test. SIAM, the automakers’ association, has asked for at least 2 grams, citing India’s E20 petrol. Ethanol blends can affect fuel evaporation, making vapour controls and fuel composition important. The article also notes E20 does not automatically have higher vapour pressure than E10.

Thus, the requested allowance is 0.5 grams larger, or about 33% above the proposal. India is moving to BS VII from 2029, while E20 is the standard petrol blend from 2025. Testing will help determine whether the stricter limit is practical under Indian fuel and driving conditions. Until then, 1.5 grams remains the proposed benchmark, not a final result.

The concern is fuel volatility: how easily petrol turns into vapor. More vapor can escape from a vehicle and add to pollution, so automakers want the limit to reflect India’s standard fuel.

The draft BS VII rule sets a 1.5-gram limit for vapors during each test. SIAM reportedly proposed at least 2 grams, citing E20’s higher Reid Vapour Pressure, a measure of evaporation, compared with E10’s. The proposed allowance would recognize the blend’s possible effect on testing, rather than treating all petrol as equally volatile.

Europe commonly uses E10, or sometimes E5, while India made E20 standard for petrol vehicles from 2025. Automakers say this difference could make the European-style limit harder to meet in India. However, C.K. Jain of Gema cautioned that E20 does not automatically have higher vapour pressure; fuel composition and vehicle controls also matter. Testing will therefore determine whether a higher limit is justified.

Fuel vapour escapes as petrol evaporates and adds pollutants to the air. Higher vapour emissions could therefore worsen air quality, while vehicles may fail stricter evaporative-emission tests.

India’s draft BS VII rules set a 1.5-gram fuel-vapour limit during each prescribed test. SIAM proposes at least 2 grams, arguing E20’s evaporation rate exceeds E10’s. If testing confirms higher emissions, manufacturers could need better vapour controls or a concession.

However, E20 does not automatically create higher vapour pressure; fuel composition and vehicle controls also matter. Europe’s Euro 7 baseline generally uses E10, or E5 in some cases. The government plans BS VII from 2029, while E20 became standard fuel from 2025. Until testing settles the difference, a higher limit could ease compliance but potentially allow more vapour pollution.

E20 does not automatically create more vapour than E10. The result depends on the complete fuel recipe, the vehicle’s vapour controls, and the test conditions.

India’s E20 fuel may have higher Reid Vapour Pressure, meaning it evaporates more readily, according to SIAM’s draft representation. However, Gema president C.K. Jain said composition matters, and E20 does not necessarily have higher pressure than E10. The draft BS VII limit is 1.5 grams per test, while SIAM seeks at least 2 grams for E20.

A tightly sealed fuel system can capture vapour, while test temperature or procedure changes measured emissions. Therefore, comparisons need identical fuels, temperatures, vehicles, and procedures. Testing should establish whether India’s E20 conditions justify a different limit before BS VII begins in 2029.

Ethanol is an alcohol fuel, while petrol is a petroleum-based liquid fuel. Blending ethanol into petrol changes how the fuel burns, evaporates, performs, and is produced. It matters because it can support farmers and energy security, while affecting drivers and air-quality rules.

India made E20—petrol containing 20% ethanol—the standard fuel for petrol vehicles from 2025. Ethanol carries less energy per litre, so the government acknowledges mileage may fall 3–5%; motorists also reported engine problems. Ethanol can raise or alter vapour pressure, increasing evaporation, but fuel composition and vehicle vapour controls matter.

More evaporation means more fuel-vapour emissions, which contribute to air pollution. India’s draft BS VII limit is 1.5 grams per test, while SIAM seeks at least 2 grams. Although ethanol supports farmers and energy security, ethanol-blended petrol costs more to produce, so it cannot simply be sold cheaper.