A review of novel energy options for clean rail applications

• Natural gas appears as a key potential option for clean railway applications.
• Environmental impingement work is calculated based on the chemical exergy.
• Well-to-wheel environmental impingement of natural gas fuelled locomotive.
• Environmental impact of NG railway is 15% inferior to SCR-equipped diesel.

In this review paper, some novel energy options for clean rail applications are discussed and evaluated. Rail transportation is of strategic importance and therefore a reliable, clean, sufficiently abundant and cost expensive fuel is required. It has been found that integration of selective catalytic reducer and increase of bio-diesel used (including blending with petrochemical diesel) may be an immediate solution which bring some benefits such as up to 50% reduction on environmental impact. However, accounting for the technical feasibility of the solution, the worldwide existence of a well-established infrastructure, high efficiency and lower emissions, the natural gas appears as a key potential option for the railway. Other reviewed technologies include the CNG, LNG-LPG, methanol, ammonia and hydrogen as fuels. Electrical railways represent a solution where large investment is available. Hydrogen, is most likely a solution for the far future, when an infrastructure could be set-up. The life cycle assessment shows high ecological advantages of NG with respect to the baseline diesel with average 15% decrease of environmental impact categories. A novel criterion has been used here to assess the environmental impact which is suitable for pollutant emitting applications such as railway transportation. This criterion is denoted as environmental impingement work of the polluting effluent which is calculated based on the chemical exergy of the polluting species. Chemical exergy is a true measure of the impingement (change, modification) produced by the pollutant on the environment. It is shown that the well-to-wheel environmental impingement of natural gas fuelled locomotive is inferior with at least 15% to diesel-electric locomotive equipped with a selective catalytic reducer. The environmental impact in terms of work impingement on the environment and environmental pollution cost are slightly similar for natural gas, ammonia, methanol and biodiesel fuels. The life cycle environmental impact categories of natural gas locomotive are overall 15% lower than for the conventional diesel-electric locomotive. According to our conclusion, liquefied natural gas is indicated as a prime potential option for clean rail transportation.