Nearly 16 years after Delhi’s entire bus fleet started to run on CNG to reduce air pollution, authorities are now pitching for an even cleaner alternative, hydrogen-CNG (H-CNG). The Environment Pollution Prevention and Control Authority (EPCA) recently recommended to the Supreme Court that Delhi’s buses switch to H-CNG within the next two or three years. Days earlier, the Ministry of Petroleum & Natural Gas had issued a draft notification, following a NITI Aayog proposal, for H-CNG as an automotive fuel.
CNG & H-CNG
CNG is compressed natural gas. With natural gas mainly composed of methane, CNG emits less air pollutants — carbon dioxide, carbon monoxide, nitrogen oxides and particulate matter — than petrol or diesel.
H-CNG is a blend of hydrogen and CNG, the ideal hydrogen concentration being 18%. Compared to conventional CNG, use of H-CNG can reduce emission of carbon monoxide up to 70%, besides enabling up to 5% savings in fuel, tests by the Automotive Research Association of India and Indian Oil Corporation Ltd (IOCL) have found.
H-CNG has not yet gained worldwide currency. Trials have been held in countries such as the US, Canada, Brazil and South Korea.
In its report to the Supreme Court, the EPCA has estimated that to fuel Delhi’s 5,500 buses, about 400 tonnes H-CNG would be needed per day. Setting up four fuel-dispensing facilities would cost Rs 330 crore, which can be funded from the Environment Compensation Charge (ECC) fund made up of cess on commercial vehicles entering Delhi, it said. For consumers who pay Rs 42 per kg for CNG, the cost of H-CNG would not be more than Rs 43 per kg. “Clearly, the costs are not prohibitive and if further work can be done to reduce NOx (oxides of nitrogen) then this approach can be scaled up and implemented across the full bus fleet in the city within 2-3 years,” the report says.
Easy for buses
The EPCA report says Delhi is well placed for a transition to H-CNG for its buses as its public transport system already runs on CNG. “The most promising aspect of this technology is that it will allow for the utilisation of the existing infrastructure of CNG — buses as well as the piping network and dispensing station.”
The engines of CNG-fuelled buses “will be able to process hythane or H-CNG considering the ratio at which hydrogen is being mixed”, said Anumita Roychowdhury, executive director (research & advocacy), Centre for Science and Environment. However, the gas storage system may be impacted if the hydrogen concentration goes up. She added some “minor engine optimisation” is needed to make existing buses H-CNG-ready as it will involve “high temperature combustion”. Existing buses need not be replaced.
Not yet for autos
Delhi’s public transport includes autos, which too run on CNG, but researchers believe that these are not yet ready for a switch. The tests so far have been conducted in heavy-duty engines. Anumita Roychowdhury said cars and autos would not be able to use H-CNG with the prevailing technology, mainly because hydrogen is “highly volatile” and the possibility of a rise in combustion temperature.
While recommending the use of H-CNG as an alternative fuel, the NITI Aayog-CII Action Plan for Clean Fuel notes that physical blending of CNG and hydrogen involves a series of energy-intensive steps that would make H-CNG more expensive than CNG.
IOCL’s research & development wing has developed a technology that does away with the need for physical blending. Its ‘Compact Reforming Process’ directly produces a hydrogen-CNG mixture from natural gas, using a single step. The cost of production is significantly lower than physical blending, the EPCA report says.