Future alternative transportation fuels: A synthesis report from literature reviews on fuel properties, combustion engine performance and environmental effects

Report, 2015

According to EU, all transport related greenhouse gas emissions must be reduced by 60% by 2050, compared to 1990. The ambitions of the Swedish Government is an energy system without net emissions of greenhouse gases by 2050 as well as a vehicle fleet that is independent of fossil fuels by 2030. The aim of this study is, through literature review, to reach a better understanding of the complexity around the transition from conventional oil‐based fuels to future alternative transportation fuels and how to identify fuel candidates with excellent combustion properties that also are better than conventional fuels from an environmental perspective. There are multiple challenges connected to a globally large‐scale expansion of biofuel production. These may, however, not necessarily apply to an increased biofuel production in Sweden. Advantages for Swedish biofuel production are the availability of forestry residues, a well‐established infrastructure for handling large volumes of biomass (from a long tradition of pulp and paper industry), a built out refueling infrastructure for E85 as well as Sweden being a sparsely populated country implying no immediate land scarcity. In a short term perspective reviewed literature shows that SI engines work even better on alcohols than on gasoline. Negative aspects are cold start performance, corrosion issues and increased volumetric fuel consumption. A mix of molecules with different ignition properties in the fuel is beneficial for cold starting issues. Ternary blends of gasoline, ethanol and methanol are such mix of molecules that would improve cold start issues. On the DICI engine side HVO as well as alcohol mixtures seem the most relevant ones to investigate further in the short term perspective. In a longer term perspective there is an opportunity to adapt both fuels and engines to each other. The emerging combustion concepts HCCI, RCCI and PPC demonstrate both higher efficiency and lower emissions than conventional SI or DICI. These concepts do also provide emission benefits when operated on alternative fuels, where fuels with combustion properties somewhere in‐between gasoline and diesel seems promising. For DICI engines POMDME and its derivatives are candidates that at least theoretically could be good for clean DICI operation. From a production cost perspective it is beneficial if the fuel either (1) is a small molecule that can be synthesized from syngas or similar processes or (2) a molecule that is similar to molecules in biomass or (3) already is a large scale produced chemical. From the systems studies perspective no single fuel is identified as winning alternative. Fuels that can be blended into conventional fuels are generally seen advantageous, as well as fuels that can be produced from waste streams or locally available bioenergy sources. The insecurity regarding which fuel has a future and which are facing major challenges need to be better understood. This implies that there is a need for interdisciplinary and iterative system and engine research.