engine modification (no engine modification)

Engine modification, in the CBG context, refers to a property — not a process. Because compressed biogas at 90%+ methane content is chemically near-identical to fossil-derived CNG (typically 88-92% methane), any vehicle already certified for CNG by ARAI under CMVR (Central Motor Vehicles Rules) can run on bio-CNG without hardware, electronic control unit, or fuel-line changes. The fuel injectors, throttle body, oxygen sensor calibration, catalytic converter, ignition timing maps and high-pressure cylinder rating all operate within the same envelope.

This drop-in compatibility is a deliberate design outcome of IS 16087:2016 and the parallel IS 15958 specification for CNG. Both standards constrain Wobbe Index, calorific value, sulphur, moisture and inert content to overlapping windows, so a vehicle calibrated for one cannot tell it is running on the other. In practice an Indian OEM warranty on a Maruti WagonR S-CNG, Tata Magic Iris, Ashok Leyland or Tata bus remains valid when refuelled with SATAT-supplied CBG at any retail outlet.

The failure modes that would require modification are precisely the ones the standards prevent. If hydrogen sulphide were left above 20 mg/Nm³, valve seats and exhaust catalysts would degrade within months. If moisture passed through, fuel rails and pressure regulators would corrode. If methane content fell below 90%, the air-fuel ratio sensor would chronically run lean, triggering check-engine codes and torque cut-back. The discipline upstream at the upgrading plant is therefore what keeps the no-modification promise true for the end user.

The commercial implication is significant: a CBG producer is not selling into a niche modified-vehicle market but into the full installed CNG fleet — over 7.5 million CNG vehicles in India as of 2024. For investors this addressable demand is the single largest argument for SATAT bankability, since offtake risk is anchored to a regulated, growing fleet rather than to a fuel-switching campaign.