Context: In a major step toward adopting alternative clean fuel for transportation, the Ministry of Road Transport and Highways has allowed use of H-CNG (18% mix of hydrogen) in CNG engines. A notification for amendments to the Central Motor Vehicles Rules 1989, for inclusion of H-CNG as an automotive fuel has been published.
What is Hydrogen-CNG?

• HCNG is a vehicle fuel which is a blend of compressed natural gas and hydrogen, typically 8-50% hydrogen by volume.
• Existing natural gas engines can be used with HCNG, although higher hydrogen blends require re-tuning of the engines for optimal performance. Studies indicate that HCNG mixtures with 20- 30% hydrogen by volume are optimal for vehicle performance and emissions reduction.
• Delhi has become India’s first city to launch hydrogen-enriched CNG (HCNG) buses in 2019. 

Advantages 

• No retrofitting required: It does not need any modification of the engine or retrofitting. Only some calibration is required thus allowing governments and agencies to promote the use of hydrogen to greater number of people at less cost. It is usable with the existing CNG infrastructure. It requires only small hydrogen storage and a column for the mixing of hydrogen with natural gas. Safety properties are similar to CNG.
• Lower pollutant emissions: Global HCNG testing to date has demonstrated the fuel’s potential to reduce nitrous oxide (NOx), carbon dioxide (CO2), carbon monoxide (approximately 70%) and hydrocarbon emissions (approximately 15%) vehicle emissions compared to traditional CNG. Hydrogen addition to natural gas can decrease engine’s unburned hydrocarbons and speed up the combustion process.
• Improves fuel economy: It improves the engine efficiency, lowers fuel consumption upto 5 per cent as compared to a CNG bus.
• The thermal efficiency of both Natural gas and HCNG increases with increase in load which makes it an ideal fuel for high load applications and heavy-duty vehicles. 

Issues involved 

• Determining the most optimised hydrogen/compressed natural gas ratio: If the hydrogen faction increases above a certain limit, it will result in abnormal combustion such as pre-ignition, knock and backfire occur.
• Ensure safe infrastructure: Probably most evident challenge for wide-spread use of the new fuel is the current lack of infrastructure. Similar to other gaseous fuels, natural gas and hydrogen are both lighter than air, therefore if there is a leak it will quickly disperse into air with adequate ventilation.
• Cost and continuous availability: The cost of Hydrogen is higher than cost of Natural gas resulting in HCNG being costlier than CNG. Further, continuous availability of HCNG needs to be assured before embarking on its major use in IC engines.
• Continued engine performance, emissions and durability testing in variety of engine types and sizes need to be developed to increase consumer and manufacturer confidence.