Hydromethane: A bridge towards the hydrogen economy or an unsustainable promise?

Last decade enthusiasm about hydrogen-based economy on FC has partially been lost and spotlight is now back on using pure hydrogen or hydrogen mixtures in ICE. Pure hydrogen use in spark ignition (SI) ICE requires a dedicated engine design to optimize the high speed flame and the high pressure and temperature inside the combustion chamber. But, on the other end, may lead to high exhaust emissions of nitrogen oxides NOx. Moreover, hydrogen fueled vehicles also suffer of a very low mileage due to the very low energy density of the fuel, since hydrogen as a compressed gas at 200 atmospheres and ambient temperature has around 5% of the energy of gasoline of the same volume.All these motivations, together with the now capillary diffusion of natural gas (NG) distribution for residential and transportation purposes (especially in Europe) is making more and more interesting the option of H2 using as an additive to natural gas: NG powered vehicles, in fact, reached a very high maturity with high reliability and environmental performances. In recent years experimentations were conducted in many laboratories and research centers to verify the positive effects of hydrogen when blended with natural gas. The maturity achieved by H2–NG mixtures is also stated by commercialized gas which is available in USA with the registered trademark of Hythane® (a mixture of 20% H2–80% NG in volume).In this paper the hydro-methane option is fully outlined, a complete energy analysis and environmental sustainability is realized, considering all the main possible options available in mixture production and final use.

► Hydromethane showed good results in energy and CO2 emission reduction. ► On-road tests have emphasized these effects. ► Emissions and energy consumption reduction not-linearly depend on H2 content in the mixture. ► Energy saving is good and fairly constant with mixtures between 15% and 25%: lower for 5% and 10% mixtures. ► The CO2 reduction showed on-road is halved if CO2 emissions due to hydrogen production are taken into account.