Transportation is another sector that has increased its relative share of primary energy use. This sector has serious concerns as it is a significant source of CO2 emissions and other airborne pollutants, and it is almost totally based on oil as its energy source. An important aspect of future changes in transportation depends on what happens to the available oil resources, production and prices. At present, 95% of all energy for transportation comes from oil. (more…)

We know of no studies that have examined vehicle taxation incentives programs elsewhere in the world, but it seems likely that there are a number of tax regimes that affect vehicle fuel economy, albeit indirectly.

Aside from new car tax credit for new car aimed specifically at fuel economy or associated vehicle characteristics, (more…)

Fuel efficiency gains due to technological and operational change can mitigate the influence of growth on total emissions. Increased demand has historically outpaced these gains, resulting in an overall increase in emissions over the history of commercial aviation. The figure of merit relative to total energy use and emissions in aviation is the energy intensity (EI).

When discussing energy intensity, the most convenient unit of technology is the system represented by a complete aircraft. In this section, trends in energy use and energy intensity are elaborated. In the following section, the discussion focuses on the relation of energy intensity to the technological and operational characteristics of an aircraft.

Reviews of trends in technology and aircraft operations undertaken by Lee et al. and Babikian et al. indicate that continuation of historical precedents would result in a future decline in energy intensity for the large commercial aircraft fleet of 1.2–2.2%/year when averaged over the next 25 years, and perhaps an increase in energy intensity for regional aircraft, because regional jets use larger engines and replace turbo- props in the regional fleet. When compared with trends in traffic growth, expected improvements in aircraft technologies and operational measures alone are not likely to offset more than one-third of total emissions growth. Therefore, effects on the global atmosphere are expected to increase in the future in the absence of additional measures. Industry and government projections, which are based on more sophisticated technology and operations forecasting, are in general agreement with the historical trend.

Compared with the early 1990s, global aviation fuel consumption and subsequent CO2 emissions level could increase three-to sevenfold by 2050, equivalent to a 1.8–3.2% annual rate of change. In addition to the different demand growth projections entailed in such forecasts, variability in projected emissions also originates from different assumptions about aircraft technology, fleet mix, and operational evolution in air traffic management and scheduling.

We shows historical trends in energy intensity for the U.S. large commercial and regional fleets. Year-to-year variations in energy intensity for each aircraft type, due to different operating conditions, such as load factor, flight speed, altitude, and routing, controlled by different operators, can be 730%, as represented by the vertical extent of the data symbols. For large commercial aircraft, a combination of technological and operational improvements led to a reduction in energy intensity of the entire U.S. fleet of more than 60% between 1971 and 1998, averaging about 3.3%/year. In contrast, total RPK has grown by 330%, or 5.5%/year over the same period.

Long- range aircraft are B5% more fuel efficient than are short-range aircraft because they carry more passengers over a flight spent primarily at the cruise condition. Regional aircraft are 40–60% less fuel efficient than are their larger narrow- and wide-body counterparts, and regional jets are 10–60% less fuel efficient compared to turboprops. Importantly, fuel efficiency differences between large and regional aircraft can be explained mostly by differences in aircraft operations, not technology.

Reductions in energy intensity do not always directly imply lower environmental impact. For example, the prevalence of contrails is enhanced by greater engine efficiency. NOx emissions also become increasingly difficult to limit as engine temperatures and pressures are increased—a common method for improving engine efficiency. These conflicting influences make it difficult to translate the expected changes in overall system performance into air quality impacts. Historical trends suggest that feet-averaged NOx emissions per unit thrust during landing and takeoff (LTO) cycles have seen little improvement, and total NOx emissions have slightly increased. However, HC and CO emissions have been reduced drastically since the 1950s.

The development and blending of gasoline additives and petroleum additivies are undertaken for the most part by the petroleum refining industry. Additives are essential to the economic well-being of the industry because they tend to boost sales for gasoline fuel and diesel fuel. In most cases, gasoline additives do not differ in price by more than three to four cents a gallon. The recently developed additives do not necessarily sacrifice fuel efficiency and fuel savings for higher octane numbers. They are multifunctional. In addition to boosting octane ratings they may also clean the engine, which, in turn, leads to greater fuel efficiency. (more…)