Technologies that improve fuel efficiency and emissions performance of these systems can positively impact the environment earlier than alternative systems and for decades to come.
Continuous Improvements Since the 1970s
The evolution of cleaner fuels began in the 1970s with reductions in the amount of lead which was added to gasoline to reduce engine knocking. Lead was eliminated from gasoline sold in the United States by the 1970s. Europe followed soon after, with ExxonMobil being the first to sell unleaded petrol in the U.K. in 1987. We were among the first to eliminate lead from gasoline sold in Africa, and we’re working with others to remove lead from gasoline worldwide.
There have been many other improvements in motor fuels including the introduction in the 1990s of fuel detergents to clean fuel injectors, valves and combustion chambers. Also during this time came further improvements to gasoline in the U.S. that reduced emissions of ozone-forming chemicals and air toxics. This reformulated gasoline (RFG) was specially designed to meet the needs of areas with the most serious ozone levels.
Perhaps the most noteworthy improvement in motor fuel quality is the significant reduction in the amount of sulfur. Recent engine improvements designed to reduce air pollution work best with very-low-sulfur fuel. That’s why many countries have adopted rules requiring major reductions in the amount of sulfur in motor fuels.
A key tool in reducing sulfur levels in fuels has been the use of an ExxonMobil technology called SCANfining. This technology not only removes sulfur, but also preserves valuable molecules needed to maintain octane levels for smooth engine performance. ExxonMobil is making this technology available to other fuel producers around the world, and it’s being implemented in refineries in Asia, Europe, the Middle East, North America, and the Caribbean.
We are now working to further upgrade ExxonMobil refineries to make fuel that is virtually sulfur-free.
The Ethanol Option
One potential alternative fuel is ethanol, produced from corn or other crops. Cultivation of crops for use as fuel requires substantial amounts of land that would otherwise be available for food production, forests or other uses. Unless subsidized by government, ethanol is more expensive than gasoline. Moreover, producing ethanol requires the use of fossil fuels to produce the crops and convert them into fuel.
Optimizing The Current System
As part of a global community of scientists and engineers, we continue to explore new internal combustion engine (ICE) technologies. The goal is to design fuel/engine systems for higher efficiency and lower emissions. Gasoline and diesel fuels are blends of various molecules, and each fuel behaves slightly differently during combustion. Working with Toyota, we are investigating in detail what happens when different blends of molecules are burned in an ICE. The knowledge gained may lead to new fuel and vehicle systems that use less fuel and produce less pollution than today's vehicles.
The Promise of Hydrogen
In the longer term (beyond 2020), hydrogen often is cited as a potential alternative fuel. Hydrogen is appealing because it is the most abundant element in the universe. Combined with oxygen, hydrogen can power fuel cells – an advanced technology under development for automobiles and other applications. In a fuel cell, hydrogen produces only water – and no emissions. And compared to a gasoline vehicle, a hydrogen vehicle offers the promise of doubling the miles driven for each unit of fuel energy.
If hydrogen is to become a widely used transportation fuel, several challenges must be overcome.
Although common in many compounds, such as water, pure hydrogen is rare. Like electricity, it is a clean energy carrier, but it must be made from another energy source. One possibility is to produce hydrogen from hydrocarbon fuels such as natural gas.
An alternative process called electrolysis can extract hydrogen from water, but only by using lots of electricity, which is typically generated by fossil or nuclear fuels. The electricity required could also come from renewables, but the CO2 benefits would be larger if renewables were used to displace coal in power generation.
All known ways of producing hydrogen today require significant energy input and are costly, making hydrogen much more expensive than gasoline. Additionally, depending on the source of the energy, hydrogen can be less efficient and generate greater emissions when the complete cycle of fuel production, distribution, and end-use is considered.
Second, where can hydrogen be produced? The industry could make it in large central facilities and then move it to consumers. That would require new infrastructure of high-pressure pipelines, storage facilities, and retail station pumps because hydrogen’s properties preclude the use of existing facilities. Or it may be possible to produce and store hydrogen in a smaller installation at a modified retail station.
Another option could be to make hydrogen on the vehicle itself. ExxonMobil is investigating breakthrough technology to produce hydrogen from gasoline on board a fuel-cell automobile as the hydrogen is needed, thereby using the existing gasoline infrastructure. The technology could also be used to produce hydrogen on a larger scale if the challenges around onboard storage of hydrogen are overcome. While fuel cells are now competitive with internal combustion engines in size and weight, fuel cells are still about 10 times more costly.
Hydrogen is 20 times more explosive than gasoline and has a higher propensity to leak than other fuels, raising a range of safety concerns relating to its distribution and use. ExxonMobil is actively addressing these concerns through sponsorship of studies looking into safety issues of hydrogen.
Hydrogen deserves a chance to earn its place and could become important in several decades if the formidable challenges it poses can be resolved.
ExxonMobil is actively engaged, both internally and through industry groups, in a range of activities to address the many challenges associated with hydrogen.
Since we sold our first gallon of gasoline, we’ve been at the forefront of fuels technology. As we go forward, the fuels will almost certainly change. But our commitment to improving them won’t.