cleaner fuel (clean fuel)

The label cleaner fuel, applied to compressed biogas in contrast with diesel and petrol, is a relative comparison of point-of-use combustion emissions per unit of useful energy delivered. It is not an absolute claim that CBG is emission-free, and the comparison is most meaningful when the full lifecycle from feedstock to wheel is examined.

At the tailpipe, CBG combustion produces 20-30% lower CO₂ per kilometre than diesel because methane has a higher hydrogen-to-carbon ratio and burns more completely. Particulate matter is essentially zero — typically below 0.001 g/km versus 0.02-0.04 g/km for BS-VI diesel — because there is no carbon-soot pathway in gaseous-fuel combustion. NOₓ is 50-80% lower than uncontrolled diesel, though Bharat Stage VI diesel with SCR closes much of this gap. SOₓ is below detection limits because the IS 16087:2016 limit of 20 mg/Nm³ H₂S leaves virtually no sulphur to oxidise.

On a lifecycle basis CBG's case strengthens further. Biogenic CO₂ released from combustion is offset by the CO₂ that the feedstock absorbed during plant growth, giving a near-zero net carbon footprint when the feedstock is agricultural residue or food waste. Captured methane that would otherwise have escaped from open dumps (with a global warming potential 28-34 times that of CO₂ over 100 years) yields additional avoided-emission credit. India's CBG lifecycle GHG intensity is estimated at 10-25 g CO₂-eq/MJ against 90-100 g CO₂-eq/MJ for diesel.

The caveats matter. Methane slip from the engine (1-3% of fuel uncombusted) erodes the climate benefit because of methane's high GWP. Open digestate lagoons leak both methane and ammonia. Feedstock collected from distant rural sources can incur transport emissions that consume 20-30% of the lifecycle benefit. The cleaner-fuel label is therefore conditional on closed digestate handling, methane-leak monitoring, and short feedstock supply chains — not a property of the molecule alone.