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DOE Pulse - Science and Technology Highlights from the DOE National Laboratories
LLNL's Salvador AcevesLLNL's Salvador Aceves
If the car or truck you're driving 10 years from now is more efficient, pollutes less, and is less dependent on foreign energy sources than today's vehicles, you may have the analytical skills of Salvador Aceves
to thank. Aceves
, associate program leader for energy efficiency and renewable energy in Lawrence Livermore National Laboratory 's Energy and Environment Directorate, heads up several research programs aimed at improving vehicle engine design and fuel storage technology.
"The energy system as it is now is very nice," Aceves
, who has worked on hydrogen technologies for many years, is now focused on overcoming one of the major barriers to practical hydrogen-fueled vehicles: onboard storage.Aceves
team have developed and are testing a safe, compact hydrogen storage tank that combines the around-town energy efficiency of conventional compressed hydrogen gas with the long-distance driving range of cryogenic (low-temperature) compressed gaseous and liquid hydrogen. Aceves, who was born in the United States but raised in Mexico, received his undergraduate degree from the University of Guanajuato.He returned to the United States in 1984 to attend graduate school at Oregon State University, where he earned master's degrees in mechanical engineering and physics and a Ph.D. in mechanical engineering.He came to LLNL as a Post-Doctoral researcher to work on thermal systems analysis in 1993, and was elected a fellow of the American Society of Mechanical Engineering in 2000.
Fill'er Up -- With Hydrogen
Five kg of liquid hydrogen would give a high-efficiency hydrogen fuel cell or internal combustion engine vehicle a 600-km driving range, according to Salvador Aceves, an ASME member and associate program leader for transportation at Lawrence Livermore National Laboratory in Livermore, Calif. Aceves is a past chairman of ASME's Advanced Energy Systems division.
However, drawbacks of cryogenic storage are the high electrical consumption required to liquefy the hydrogen, and the evaporative losses that can occur when the low-pressure tanks are filled and when the car is parked."It would take about 65 kilowatt-hours of electricity to liquefy the 5-kg target for vehicular hydrogen," said Aceves
The loss of cryogenic hydrogen by evaporation is caused by heat transfer between the tank and environment.
"If the car was driven 5 km or more per day, there was virtually no evaporative loss," said Aceves
An insulated cylinder, designed to contain hydrogen chilled to 20 K, has to hold up in a bonfire at Authorized Testing Inc.
before the tank is deemed worthy of testing on automobiles.
"These tanks would require 16 percent less energy when running on compressed fuel than when using cryogenic hydrogen, and would experience less evaporative losses when charged with subzero (20 K) hydrogen by virtue of their insulation," noted Aceves
colleagues built openings in the outer jackets for thermocouples, strain gauges, and a capacitive level sensor to measure pressure, temperature, and level within the tanks.They also equipped the tanks with safety devices to prevent catastrophic failure in case hydrogen leaked into the vacuum.These were relief valves that would open if the pressure limits were exceeded, and rupture discs if the relief valves failed.
The researchers then subjected the tanks to a variety of Department of Transportation
and Society of Automotive Engineers tests at Lawrence Livermore's High Pressure Laboratory.
For example, the outer jacket did not leak after being subjected to the stresses of 1,000 vacuum cycles.
"We stayed in a safety bunker while the tanks were tested in the open," said Aceves
The laboratory subjected the tanks to a variety of certification tests to meet the standards of the U.S. Department of Transportation
.These included cycling the tanks, at ambient temperatures, 10,000 times from less than 10 percent of the service pressure to full service pressure.
In a series of environmental cycling tests, the tanks were filled with gaseous hydrogen to determine their performance in extreme climates.First, the tanks were cycled 5,000 times from zero to full service pressure, with an internal tank temperature of 140°F and external ambient air temperatures in 95 percent humidity.Then, the tanks were cycled 5,000 times from zero to service pressure at -60°F tank temperature.
"After we pass the SAE tests, we want to install the insulated cryogenic tanks on vehicles for field testing," Aceves
"One, a Ford F 250, will carry liquefied natural gas, and the other, a Ford Ranger, will hold liquid hydrogen," Aceves
The project is funded by the Department of Energy's
hydrogen program and the South Coast Air Quality Management District.
Hydrides on a Diet
Compressed gas tanks store hydrogen as a gas, and their cryogenic counterparts store it as a liquid.A less familiar method of storing hydrogen is as a solid in metal hydrides, alloys of rare earth, transition metal, and magnesium.These granulated materials absorb hydrogen.Because the hydrogen is chemically bonded to the alloys, heat is required to release it.
UC Merced - Merced
Professor Gerardo Diaz and Joel Martinez-Frias, Ph. D., of the University of California, Merced, School of Engineering are collaborating with a group of scientists at Lawrence Livermore National Laboratory (LLNL) directed by Salvador Aceves, Ph.D., on the development of advanced computational tools for analysis of alternative fuel engines.
Work like this can get complicated - fuels like gasoline and diesel are chemically complex, and models have to take into account how each component of the fuel behaves as it ignites in an engine, Aceves
...Aceves leads the Engineering Directorate' s Energy Conversion and Storage Group at LLNL and is sponsoring the project and developing the chemical models used in the analysis.
Lawrence Livermore National Laboratory
ARES-ARICE Symposium on Gas Fired Reciprocating Engines
Salvador M. Aceves - Lawrence Livermore National Laboratory