The European Automobile Manufacturers Association (ACEA) has offered, and the European Commission (EC) has accepted, a voluntary commitment to reduce the CO2 emissions from new light-duty passenger vehicles, with firm fleetwide targets of 140 g CO2 /km (B41 mpg for gasoline) by 2008, measured under the new European test cycle (Directives 93/116/EC and 99/100/EC). This represents approximately a 25% reduction from the 1995 average of 187 g/km (B30 mpg) on this cycle. The European cycle is likely to produce lower fuel economy ratings than the U.S. combined urban/ highway cycle, so the ‘‘U.S. equivalent’’ miles per gallon ratings of the year 2008 European fleet will likely be higher than 41 mpg if the targets are met. (more…)

Economists have overwhelmingly favored fuel taxes over fuel economy standards as a means to reduce fuel or gasoline consumption because taxes give maximum flexibility to both vehicle manufacturers and purchasers and because they influence fuel consumption through both fuel demand and vehicle supply by making travel more expensive (thereby reducing vehicle miles traveled) and by creating an economic incentive for manufacturers to build efficient vehicles and for consumers to purchase them. (more…)

To date, most discussion and research relating to the various of biomass role in mitigating CO2 emissions has been focused around its use as a fuel or as a sink. However, full utilization of the potential of biomass products, particularly from woody biomass, may provide significant opportunities. (more…)

Analysis of future light-duty transportation energy use require estimates of the impact of fuel prices on travel and fleet fuel economy, estimates of the fuel price elasticity of travel, fuel economy, and fuel consumption are ubiquitous in the literature. However, there is substantial disagreement about the magnitude of these elasticities because travel volumes, fuel economy, and fuel consumption are dependent on several variables other than fuel price and because fuel prices have tended to be volatile during the past few decades, thereby complicating attempts to estimate long-run elasticities. Thus, the magnitude of the effect of changes in fuel taxes in US on fleet fuel economy and on travel volumes and fuel consumption is also subject to considerable disagreement. (more…)

Establishing the impact of climate change on energy demand requires a measure of heating and cooling requirements. In the United States, this measure is a degree day, which is defined in terms of an absolute difference between average daily temperature and 651F, which is an arbitrary benchmark for household comfort. Commercial heating degree days are incurred when outside temperatures are below 651F, generally during the winter heating season from October through March. (more…)

Here, the sensitivity of energy demand to climate is measured two ways. The first method uses elasticities that provide simple summary measures of how departures from normal temperatures affect energy consumption. The second approach, reported in the following section, uses econometric simulation to estimate how climate changes affect energy demand. (more…)

The gradual change in the energy consumption pattern of the United States from 1860 to 1990. In the mid-1800s, biomass, principally woody biomass, supplied over 90% of U.S. energy and fuel needs, after which energy biomass consumption began to decrease as fossil fuels became the preferred energy resources. For many years, a safe illuminant had been sought as a less expensive substitute for whale oils. (more…)

The growth in air transportation volume has important global energy sustainable development
associated with the potential for greenhouse gases sources. On local to regional scales, noise, decreased air quality related primarily to ozone production and particulate levels, and other issues, such as roadway congestion related to airport services and local water quality, are all recognized as important impacts. (more…)

In these regenerators the heat energy transfer between primary and secondary fluid is primarily by radiation and its installation is always done in a vertical stack.This type of exchange is strongly favoured by temperature, so that these retrievers are especially suitable in the following cases: (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.