Hydrogen enrichment of natural gas: thermoeconomic production analysis and effects on internal combustion engines performance

Hydrogen can be a valid alternative to gasoline in the next future, both in terms of environmental impact and as energy source. Hydrogen will be, most likely, employed in the next future in power plant applications as well as for terrestrial vehicles. Anyway, hydrogen cannot be considered a fuel but rather an energy carrier. In fact, H2 cannot be found in the atmosphere and it should be obtained by any of the many ways to produce it. All the methods to produce hydrogen are energy consuming, such as the fuel-reforming and the electrolysis; some of them are industrially developed, some others, such as the biological production or the photodissociation are not (1,2). The environmental impact of the hydrogen production depends on the way it is obtained. Thus, it is not a zero-environmental impact fuel, since during its life cycle there is always generation of pollutants because of energy requirements (3). The start-up of the so-called "Hydrogen Economy" can be achieved by introducing hydrogen to a small extent in the first phase of everyday life. This is the key idea on which this paper is based on. In fact, the present study investigates both the thermodynamic and economical aspects of the hydrogen production to be used for gaseous mixtures in terrestrial vehicles, by considering the production via water electrolysis. The hydrogen is employed to obtain a fuel mixture with natural gas employed for internal combustion engines and energetic, economic and environmental aspects are taken into account. Both energy and exergy analyses are carried out in the present investigation to evaluate the efficiency of the process. The cost analysis is carried out to evaluate the economic aspects of the project for localized small to medium quantity hydrogen production plants. These findings are essential to investors who need indication about the cost of production per kg of hydrogen, which should be sold in the natural gas-hydrogen mixture at an affordable market price. An investigation on the effects of CNG - H2 mixtures on internal combustion engines is carried out; in particular, the impact on vehicle range and CO2 emissions on a passenger car is evaluated.