In an article in the September issue of Car & Driver, Csaba Csere takes an interesting look at the current status and near-term future outlook of the major alternatives to gasoline.
Here are his thoughts on each of the possible gasoline alternatives:
Modern turbo-diesels get about 30 percent better fuel economy than their gasoline counterparts, have gutsy low-rpm torque, and work well in vehicles with automatics and for towing; they’re a seemingly perfect solution for the U.S.
Unfortunately, diesel emissions are far dirtier than gas emissions. Removing diesel’s pollutants requires costly pieces of emissions equipment. Diesel also requires approximately 30,000-psi fuel-injection systems. These costs make diesels more pricey than even turbocharged, direct-injection gasoline engines, and those gas engines have the potential to achieve about two-thirds of diesel’s fuel-economy advantage.
While diesel costs about the same as gas today, it has run as much as 30 percent higher—and it is taxed at a higher rate than gas. There’s no easy fix to keep diesel prices low, relative to gas, because American refineries, in general, produce about 19.5 gallons of gasoline and 10.3 gallons of diesel from each barrel of oil. That means a gas-powered vehicle getting 20 mpg can drive about 390 miles on a barrel of oil, while a diesel, at 26 mpg, can go only 270 miles.
Since a barrel of oil doesn’t go as far in a diesel car, a wholesale conversion to diesels is unlikely in America unless we suddenly figure out how to make diesel fuel from something other than petroleum. European refineries produce more diesel and less gasoline from each barrel of oil, but making that switch would essentially require building brand-new refineries. Don’t hold your breath.
One approach is to transform animal fat or vegetable oil, via a transesterification process, into what is called “biodiesel.” The resulting fuel doesn’t contain sulfur and can be used in pure form, though many vehicle manufacturers recommend that it be blended with petroleum diesel in proportions between 5 and 20 percent. Biodiesel contains about 9 percent less energy than petroleum diesel, but it has a higher cetane rating (which promotes more-efficient combustion) and better lubrication properties.
Despite America’s appetite for french fries, there isn’t enough used cooking oil to make very much biodiesel. In fact, it has been suggested that to replace all of our petroleum needs with biodiesel would require the planting of soybeans on all of the arable land in the United States. New approaches for making biodiesel from algae are being explored, but they are likely decades away from mass production. Until then, biodiesel’s limited availability and higher cost will keep it a bit player.
Another diesel alternative is synthetic diesel, made by a variety of chemical conversion processes that transform natural gas, methanol, or coal into diesel. The resulting fuel is usually sulfur-free and has a higher energy content than petroleum diesel, plus cleaner exhaust emissions. Converting natural gas to diesel fuel, also known as “gas-to-liquid,” makes it easier to transport because it requires no refrigeration or compression.
The cost of synthetic diesel is also reasonable, although the environmental and energy-independence benefits are minimal. Converting coal to diesel creates much more carbon-dioxide emissions than simply using petroleum diesel. In fact, this is a problem, in varying degrees, with any of the synthetic-fuel processes. However, North America has plentiful natural-gas reserves, and this could be a simple way to convert it into an easy-to-use motor fuel.
The use of E85, which mixes 85 percent corn-based ethanol with 15 percent gasoline, has stalled due to the fuel’s limited availability, high price (no thanks to our government’s tariff on E85 imports), the roughly 30 percent fewer miles to the gallon it gets, and the understanding that its use provides little in the way of carbon reduction if the energy required to grow the corn and turn it into ethanol is factored in.
Brazil, a country that achieved energy independence by using home-grown ethanol, makes the fuel from sugar. Starting with corn is a much more complex and energy-intensive process. In the U.S., sugar-based ethanol would be challenging because most of our land is unsuitable for sugar production.
If we could produce ethanol efficiently from easier-to-grow plants, ethanol would be a good solution. Dubbed “grassoline,” this ethanol is produced from tall prairie grass or even algae. Several projects to develop a workable process are under way, but commercial quantities won’t appear before 2020.
A more readily available alternative fuel is compressed natural gas (CNG). Converting a gasoline engine to run on the same stuff most of us use to heat our homes is an easy, low-cost approach. Natural gas is also cheap, and America has a lot of it. And natural gas contains far less carbon than gasoline. In fact, a normal engine running on CNG almost matches a plug-in hybrid for its carbon-dioxide emissions. The price of CNG for the energy equivalent of a gallon of gasoline is less than a dollar (before taxes).
Still, automakers are reluctant to embrace CNG because it emits some pollutants, while a hydrogen car or an electric vehicle does not. Also, since it must be compressed to 3500 psi to get enough of it into a tank to provide a decent range, CNG requires cylindrical Kevlar tanks that are heavier, more expensive, and harder to package than normal gas tanks.
Hydrogen is the holy grail of synthetic alternative fuels. Whether burned in an internal-combustion engine or used to power a fuel cell, its primary byproduct is water. And with that emitted water, you can produce more hydrogen. Of course, it’s not as easy as it sounds.
Most commercial hydrogen produced today is made by stripping carbon atoms from natural gas—a fossil fuel. The removed carbon atoms then hook up with oxygen to release carbon dioxide into the atmosphere. If you work through the losses in the process, it would be cleaner, easier, and cheaper to simply burn natural gas in an internal-combustion engine.
Hydrogen, in its gaseous or liquid form, isn’t easy to store or transport. The network of pipelines that currently moves natural gas around the country is too porous to keep the tiny hydrogen molecules from escaping. In automobiles, hydrogen has to be stored in stout cylindrical tanks and compressed to between 5000 and 10,000 psi.
Creating hydrogen using solar, hydroelectric, or wind power are pollution-free solutions, but solar cells, wind turbines, and hydroelectric dams aren’t free. Until we come up with a cheap, large-scale, and pollution-free method of generating electricity so that we can produce hydrogen from water, the widespread use of hydrogen as a fuel seems unlikely.
Thanks to Car & Driver for offering to let us repost this article on our blog.