ABSTRACT
For engineers and scientists who are new to the field of biofuel production for aviation, it can be bewildering to come to terms with the conflicting conclusions drawn in the literature or evaluate the claims found in a casual Web search. It is a multidisciplinary field that spans chemical, petroleum, environmental, mechanical, aerospace, materials, and industrial engineering. The field is also overlaid by a web of geographically varying public policies that profoundly impact economic feasibility and the pace and directions in technology development. It is a field that has grown rapidly in all of these areas, so that there is a vast, rich literature base to peruse. Finally, there are passionate and articulate advocates for every conceivable viewpoint. This can make the leap across the interdisciplinary aspects rather challenging. Some of the most embedded sources of confusion arise from the following:
Terminology may be conflicting or otherwise difficult to understand. For example, the naming of the same set of hydrocarbon compounds in petroleum engineering differs from the conventions in organic chemistry.
The standard units in which values are reported vary widely. Often this is because conventions had already been established in various disciplines and geographical regions.
There may be no clear standards or protocols for measurements, which leads to difficulty in comparing values; for example, the manner in which to quantify biomass yield from algae.
Some studies do not clearly state their assumptions or identify their uncertainties, which are critical to evaluating its conclusions.
In order to create assessments for global applications, the numbers used to describe the physics may be derived from laboratory results; thus, the uncertainties/error present in the small- scale data (e.g., producing 500 mL of crude algal oil over a few days in a laboratory) become grossly magnified when the process is scaled up (e.g., producing millions of barrels per hectare per year (MMbbl/ha-y) of biodiesel).
