Compressed Natural Gas (Compressed Natural Gas)

Compressed Natural Gas (CNG) is natural gas — predominantly methane (CH4) at 88-96% purity, with smaller fractions of ethane, propane, and inert nitrogen — that has been compressed to 200-250 bar (roughly 1% of its atmospheric volume) and stored in high-pressure cylinders for use as a gaseous transportation fuel. In India, CNG is the technical and regulatory benchmark against which compressed biogas (CBG) is measured, since both fuels are interchangeable in the same vehicles, dispensers, and pipeline infrastructure provided they meet the same composition standards.

Indian CNG specifications are governed by IS 15958:2009 (CNG for automotive purposes), which sets minimum methane content at 89%, maximum H2S at 5 mg/Nm3, maximum water dew point at 5 degC below the lowest expected ambient, and maximum oil content at 5 mg/Nm3. CNG distribution infrastructure in India serves over 6,500 stations as of 2025, operated primarily by city gas distribution (CGD) companies including IGL (Delhi-NCR), MGL (Mumbai), Adani Total Gas, and Gujarat Gas, under PNGRB (Petroleum and Natural Gas Regulatory Board) authorisations.

Key technical characteristics of CNG include:

• Lower Heating Value (LHV): 47-50 MJ/kg, or 35-38 MJ/Nm3 at standard conditions.
• Storage density: about 230 kg/m3 at 250 bar and 15 degC.
• Auto-ignition temperature: 540 degC (much higher than diesel at 220 degC), conferring inherent safety against fuel-tank fires.
• Volume reduction: 1 m3 of natural gas at atmospheric pressure becomes about 4 litres at 250 bar.

The CBG-CNG relationship under India's SATAT initiative is direct: bio-CNG produced from agricultural waste must meet IS 16087:2016 (CBG quality standard), which is materially aligned with IS 15958 except for trace siloxane limits. CBG is then injected into the CNG distribution network or sold through dedicated dispensers at parity prices. The trade-off in CNG versus diesel for fleet operators is favourable on fuel cost (CNG typically 25-40% cheaper per km) and pollution (60-90% lower NOx and PM emissions), but limited by refuelling infrastructure outside major metros and 8-12% reduction in payload capacity due to heavier high-pressure cylinders.