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What will power tomorrow's vehicles?

What will power tomorrow's vehicles?

Charles D. Wood III, Vice President,
Engine, Fuel, and Vehicle Research Division, Southwest Research Institute, San Antonio, TX

Wood has spent most of his professional career in the field of engine-vehicle systems research and development. He joined SWRI in 1962 as a senior research engineer in the automotive research department, served as its section manager until 1966, then held the post of director of the department of engine and vehicle research until 1983, when he was named to his present position. Before joining SWRI, Wood served as a test engineer at Ling-Temco-Vought. He and some co-inventors hold 21 U.S. patents, one of which received an IR 100 award.

Technological advances have reduced emissions from internal combustion (IC) engines by up to 90%, but the demand for lower emissions continues, says SWRI's Charles Wood.

Design News: When, if ever, are we likely to see the dominance of IC engines recede?

Wood: The pressure is on vehicle manufacturers to develop power sources with reduced emissions that can also satisfy customer demands for reliable, affordable, functional transportation. To resolve these often conflicting needs, design engineers are vigorously examining alternative fuels and power sources.

Q: What types of alternatives show the most promise?

A: Natural gas and hydrogen are two alternative fuels being considered. Natural gas, consisting primarily of methane, is superior to conventional liquid HC fuels in that its combustion produces very small amounts of soot in the useful range of fuel-air ratios. It also has a high octane number and low chemical reactivity. When substituted for diesel fuel by incorporating substantial changes to the diesel's combustion system, the problem of soot emissions is eliminated. However, this approach reduces engine efficiency.

Q: What about the hydrogen alternative?

A: Hydrogen contains no carbon and produces no carbon monoxide (CO), carbon dioxide (CO2), or hydrocarbon (HC) in the exhaust. Although nitrogen (NOx) is produced, it can presumably be controlled more easily because hydrogen can be burned at low fuel-air ratios. While natural gas is economically available in many parts of the world, economical methods for hydrogen production and distribution are not established.

The main disadvantage with gas and hydrogen is that they have lower energy densities than gasoline or diesel fuel. Liquified natural gas approaches gasoline's energy density, but requires cryogenic storage. The low energy density of hydrogen in either state poses serious storage difficulties.

Q: Are there alternatives?

A: Other fuel candidates are alcohols and liquified petroleum gas. The energy density of these fuels is superior to that of natural gas, but the latter seems a better choice in terms of emissions, as well as supply and economics. In any case, no alternative fuel is a panacea.

Q: If alternative fuels are not the solution, what about alternative powerplants?

A: Electric vehicles using battery-stored energy are being promoted on the basis that such vehicles are, in themselves, emission-free. Emissions from the electrical energy source, a central power-generating station, are more easily regulated, so total emissions from transportation could be decreased, especially in areas where much of the power is generated by nuclear or hydroelectric plants. Unfortunately, the energy density of available batteries is low, limiting vehicle range. Batteries with higher energy densities are being studied, but may pose safety and environmental problems.

Q: Can't these shortcomings be overcome?

A: The range of battery-powered electric vehicles can be extended by using an onboard engine-driven generator for battery recharge or sharing wheel-power needs, or a combination of the two. The advantages of this "hybrid" vehicle are a smaller IC engine and the possibility of running the generator engine at speed-load conditions more favorable for fuel economy and emission control. Yet to be addressed is whether there are sufficiently reduced emissions in the hybrid to make its use a rational proposition.

Q: Given all these possibilities, just how will vehicles be powered in the future?

A: Gasoline and diesel fuels in IC engines will dominate for another 40 years, with increasing competition from alternative fuels during the first 20 years, and electric and hybrid powerplants during the second. Gradually, the consumer will become resigned to higher transportation costs, reduced vehicle range, and more dependence on public transportation. Private ownership of vehicles will decrease on a per capita basis. Alternative fuels and electric hybrids will be used only briefly due to environmental concerns and increasing fuel costs, opening up the market for electric vehicles, which will eventually dominate as personal vehicles.

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