Survey on Advanced Fuels for Advanced Engines

The literature study “Survey on Advanced Fuels for Advanced Engines” has been set up as a reviewlike compilation and consolidation of relevant information concerning recent and upcoming advanced engine fuels for road vehicles with special focus on biomass-based liquid fuels. It is provided as a selfcontained report, but at the same time serves as an updated and complementary resource to IEAAMF’s online fuel information portal (http://www.iea-amf.org). An attempt is made to describe the status quo and perspectives of advanced fuels and to give a broad overview on parameters, tools and experimental approaches necessary for fuel characterization and evaluation. The focus of literature coverage, especially concerning fuel properties and exhaust emission research results, is from recent to approximately five or ten years back, but if appropriate, older resources were considered too in the general discussion of relevant effects and mechanisms.

Introductory Chapter 2 summarizes framework conditions for advanced fuel applications in terms of regulatory measures and incentives for sustainable and fair-trade action, climate change prevention and energy-efficient vehicle operation. Following these non-technical topics, Chapters 3 and 4 gives information about fuel standards and fuel properties, which should be considered when introducing new fuels. Chapter 5 provides tabulated information on feedstock, production schemes, costs and market issues for the main types of advanced biofuels considered in this study, i.e. hydrotreated vegetable oils (HVO/HEFA), biomass-to-liquid (BTL) fuels (i.e. paraffinic Fischer-Tropsch (FT)), methanol, dimethyl ether (DME), oxymethylene dimethyl ether (OME), lignocellulosic ethanol and liquefied biomethane. Also fuel properties and emission trends are shown in this chapter. Accordingly, biodiesel is explicitly included in subsequent discussions and complemented by an excursus on metathesis biodiesel.

Chapter 6 refers to reactivity and stability of fuels with regard to interactions among different fuel components and between fuel and engine oil. Deterioration of fuel and engine oil quality will affect long-term fuel storage and vehicle functionality by formation of deposits and sludge and is manifested by laboratory parameters not necessarily detectable macroscopically. Influencing factors like molecular structure, temperature, oxidizing agents, additives, impurities and metal catalysis are discussed according to published research results.

Chapter 7 deals with health effects of engine exhaust and to this end describes important gaseous and particulate constituents, their characterization and measurement. As specific exhaust species, regulated parameters CO, HC, NOX and unregulated components polycyclic aromatic hydrocarbons (PAH) and carbonylics are considered, and particular aspects of particle size, number and composition are discussed. Reference is made to formation of ozone and ambient aerosol as secondary impacts of engine exhaust. Short keynotes on research and review articles on issues of toxicology, mutagenicity and other adverse effects of engine exhaust are provided. A thorough introduction to dedicated engine emission testing and a literature survey on published emission measurement results using various engine types and fuels are given.

As a conclusion of the study, the diversity of fuels will increase in the future. New advanced fuels will be introduced in the market (e.g. HVO) or will become the focus of research activities (e.g. OME). One criterion for successful introduction of a new fuel in the market is that the new fuel can be used as a drop-in fuel. These fuels have the advantage that small amount of the fuel can be tested using existing infrastructure and engine techniques. In this phase of market introduction, reactions among fuel components and material interactions can also be detected. At the moment, most research activity deals with the behavior of aging products of biodiesel in non-polar fuels like HVO/HEFA or X-to-liquid (XTL, FT fuels).

Introducing new fuels needing an adaption of the engine technique or a new engine concept in the market requires much more effort. Next to the new fuel, also a new infrastructure and new engines have to be developed and launched. This is only possible if fuel and automotive industries, politics and broad public support the new development.

Another key factor for advanced fuel is the raw material base. The production of advanced fuels should be independent of fossil resources. Therefore, biomass or renewable electrical power (e.g. wind power or solar energy) must be the source of advanced fuels. Biomass is intensively used by first generation biofuels, but there is a potential to raise the share of renewable fuel with the introduction of advanced fuels having a broader base of biomass. Electric power as an energy source for advanced fuels also will become interesting, if the share of renewable electricity in the grid will increase. Nevertheless, already today research is necessary to have the technique(s) ready in time.

Last but not least, for further development of engine technique, advanced fuels can be use as construction or design element. If it is possible to optimize the burning process and to minimize emissions by the use of advanced fuels, new vehicles can have a better performance at the same price.

In summary, advantages and disadvantages of the considered advanced fuels are listed in Table 1. From today’s point of view, no advanced fuel has the potential to fully replace fossil fuel use in the near or middle future, but all advanced fuel options have the potential reduce fossil fuels usage significantly.