Methane Purity Standards Explained: What “Vehicle Grade” Bio-CNG Actually Means

Blog
June 29, 2026

Raw Biogas Isn't Fuel Yet

Straight out of a digester, biogas runs roughly 55 to 60% methane, with the rest mostly carbon dioxide plus traces of hydrogen sulphide. That composition won’t power an engine reliably, and the hydrogen sulphide content actively corrodes cylinders and pipelines over time.

Getting to usable fuel means stripping out everything that isn’t methane, which is a distinct engineering stage, not an afterthought.

Compliant vs. Clean: The Purity Gap

Under IS 16087:2016, gas needs a minimum of 90% methane and 250 bar compression to legally qualify as bio-CNG. But 90% is just the entry point, not the target. Basic scrubbing or PSA systems typically settle in the high 90s, while amine based systems can push past 99% with barely any methane lost in the process.

The standard tells you what’s legal. The purity above it tells you how well the fuel actually treats the engine, less corrosion, less wear, more consistent performance over time.

Purity Bar Keeps Climbing

Vehicle grade bio-CNG is no longer the ceiling. Newer applications, liquefied biomethane among them, now call for methane above 98.5%, sometimes 99%, with contaminant levels measured in single digit parts per million.

At the same time, India’s gas grid is phasing in a mandatory bio-CNG blending requirement, moving the whole sector from a voluntary scheme into a compliance driven one. Purity is shifting from a nice to have into the baseline expectation.

Brajdham's Engineering Depth Beyond the Standard

Hitting 90% once in a lab test is one thing. Holding a plant well above it every day, across shifting feedstock, is a different problem entirely.

Brajdham’s bio-CNG systems are certified for 99% methane purity with sulphur levels held below 10 ppm, well inside the IS 16087 threshold and closer to the standards newer applications like liquefied biomethane now demand.

That gap between the legal compliant and a certified result is exactly where engineering discipline shows up