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Introduction
Society in the early 21st century appears to be undergoing an unprecedented transition with respect to the fundamental source of its materials and energy. Petroleum, the fuel that has been driving modern society for one century, is showing signs of scarcity (Grant, 2005). Demand for petroleum is increasing, but discoveries of fresh deposits are dwindling. The complex hydrocarbon mixtures found in crude oil deposits were formed under conditions of low heat and pressure over millions of years (Berner, 2003). Conventional petroleum is essentially non‐renewable. Intertwined with this practical impediment, there is an apparent moral dilemma arising from petroleum usage. It has become widely accepted that the combustion of long‐sequestered petroleum carbon is strongly contributing to the observed increase in atmospheric carbon dioxide, with concomitant global warming effects. The convergence of market pressure and concern for the environment is driving a headlong rush to new fuels that are largely bio‐based. But are biofuels really new?
History and needs
For millennia, human societies depended on biological materials for energy and materials. Plant material was combusted for heat, used for building materials and clothing; animal power was harnessed for transportation. A little more than a century ago, society underwent another transition: from horse to automobile, from whale oil to crude oil. The 1890s was similar to today in that many fuel sources were being tested, production was in flux, and the industry was not yet integrated and consolidated. A similar situation exists today with the transitioning to a renewable energy society.
Not all of the technology is new; for example, humans have been purposely making ethanol and fatty acid derivatives for millenia. But current molecular biological tools are opening new doors for old technology, and making radical new technologies seem possible. The biology of today is vastly different from that of decades ago and most of the new technology is microbially based. So it is not surprising that microbial metabolic activities are coming into focus for solutions to our fuel needs for the 21st century.
One of the important questions as we enter this stage of transition is, ‘What constitutes a good motor fuel?’ The answer is partly engine dependent but there are certain rules of thumb that span across different engine types....