Propane Rolls on as Reliable Fleet Fuel

 

 

 

Winter 2014/2015

A growing number of fleets are choosing propane

It might seem that multi-billion dollar companies and local school districts share few business interests, but orga­nizations large and small are faced with the challenges of stretching budgets and making their fleets “greener.” Now, more and more are finding that propane helps them accomplish both goals.
Also known as liquefied petroleum gas (LPG), propane as a transporta­tion fuel has roots that go back nearly a century. In recent years, however, its reputation as a top fuel pick for fleets has gained traction. This is largely because of fuel injection system ad­vancements and more vehicle options available in the marketplace.
Adams 12 School District in Thornton, Colorado, is just one of hundreds of school districts taking advantage of propane-powered buses. After arriv­ing in 2005, Transportation Director David Anderson began developing the district’s alternative fuels program, which would include a pilot project with 12 Blue Bird Vision propane buses equipped with Ford 6.8L V10 engines and Roush CleanTech fuel systems.

“In my previous position as the fleet manager for Cherry Creek Schools, also in Colorado, we developed an alternative fuels program for our buses as a way to save money and clean up the air and environment for our students. When I arrived at Adams 12, we wanted to start a similar project,” Anderson said. “Our first purchase was a diesel hybrid bus, and it was very successful. So, when Blue Bird came out with a propane-powered bus, everyone agreed that it was something we should try.”
Anderson said the final decision for choosing propane came down to the infrastructure costs.
“We evaluated costs and found that we could install our entire propane station infrastructure, including a card reader system, for less than $50,000.”

In 2011, Anderson secured three buses and in 2012, nine more. As of August 2014, the buses have traveled 191,000 miles, averaging about five miles per gallon. Although propane buses typi­cally experience about a 10% decrease in fuel economy compared to con­ventional buses, Anderson found that propane’s lower fuel cost easily offset the fuel economy loss. In addition to these savings, Anderson notes that the buses have had lower maintenance costs and have become a favorite among bus drivers and the district alike. Spurred by the success of the pilot project, An­derson wants to secure funding for an additional 10 propane buses this year.
The fact that hundreds of school bus fleets have chosen propane is a testa­ment to how successful it’s been in this particular niche. A case study recently released by Argonne National Laboratory examined five fleets (a total of 110 buses) and found that some of the school districts saved nearly 50% on fuel and maintenance and recouped the incremental costs of the vehicles and infrastructure within three to eight years (afdc.energy.gov/uploads/publication/case-study-propane-school-bus-fleets.pdf).

One added benefit that all fleet man­agers and drivers can appreciate is propane’s cold-weather performance. Because the fuel is more easily vaporized at low temperatures, pro­pane-fueled vehicles are able to avoid the cold-start problems inherent with traditional liquid fuels.

Adams 12 School District in Thornton, Colorado, has successfully added 12 Blue Bird Vision propane buses to their fleet.

Photo by Dennis Schroeder, NREL 31349

The “Red Jammer” buses at Glacier National Park have been running on propane for more than a decade. Photo from Glacier National Park, NREL 27574Clean Cities Now • Vol. 18, No. 2 • Page 6

source : the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy

Clean Cities Now

 

Winter 2014/2015
Program News

One Year—One Billion and Beyond

In 2013, Clean Cities hit a major milestone. For the first time, the program and its stakeholders reduced U.S. petroleum consumption by more than 1 billion gallons in a single year.

Clean Cities’ efforts in 2013 also prevented the production of 7.5 mil­lion tons of greenhouse gas emissions, which is equivalent to removing 1.5 million cars from American roads.
In addition to minimizing America’s oil dependency and our transporta­tion system’s environmental footprint, these numbers demonstrate that Clean Cities coalitions are building on their strengths and expanding their reach. With their 14,000 stakeholders, coali­tions inventoried 475,000 alternative fuel vehicles in 2013. These vehicles and the fuel they used accounted for 39% of 2013’s petroleum displacement. While the largest number were flex fuel ve­hicles (FFVs), compressed natural gas vehicles displaced the most petroleum.
Electric drive vehicles also experienced substantial growth in 2013. While hybrid electric, plug-in hybrid electric, and all-electric vehicles only accounted for 7% of petroleum displacement, they displaced 39% more petroleum than in 2012. With more coalitions improving community readiness for plug-in elec­tric vehicles, we expect these numbers to continue to rise.

Coalitions kept up the pace when it came to educating their stakeholders and the public. Coordinators conducted more than 2,000 outreach, education, and training activities that reached about 120 million people. Fleet managers were a major focus of these efforts, with coalitions reaching out to private, government, transit, and utility fleets.
While these accomplishments are im­pressive, they are just one step towards Clean Cities’ major goal of reducing 2.5 billion gallons of petroleum annually by 2020. The 2013 petroleum reduction was 13% higher than 2012 efforts, put­ting the Clean Cities program ahead of schedule for reaching that goal.
From 15 million gallons in its first year to a cumulative 6.4 billion now, Clean Cities is shifting transportation away from petroleum one vehicle, fleet, and community at a time. 
Clean Cities’ 2013 petroleum-reduction milestone puts the program ahead of schedule for meeting its goal of reducing U.S. petroleum consumption by 2.5 billion gallons per year by 2020. Source: Clean Cities 2013 Annual Metrics Report Compressed Natural Gas: 56% Biodiesel: 15% Ethanol: 12% Propane: 7% Liquefied Natural Gas: 5% Plug-In Hybrid & Electric: 5% Hydrogen: 0.1%

Petroleum displacement by fuel type in 2013. Source: Clean Cities 2013 Annual Metrics Report

 

Morphable surfaces cut air resistance: Golf ball-like dimples on cars may improve fuel efficiency

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Researchers made this sphere to test their concept of morphable surfaces. Made of soft polymer with a hollow center, and a thin coating of a stiffer polymer, the sphere becomes dimpled when the air is pumped out of the hollow center, causing it to shrink.

There is a story about how the modern golf ball, with its dimpled surface, came to be: In the mid-1800s, it is said, new golf balls were smooth, but became dimpled over time as impacts left permanent dents. Smooth new balls were typically used for tournament play, but in one match, a player ran short, had to use an old, dented one, and realized that he could drive this dimpled ball much further than a smooth one.

Whether that story is true or not, testing over the years has proved that a golf ball's irregular surface really does dramatically increase the distance it travels, because it can cut the drag caused by air resistance in half. Now researchers at MIT are aiming to harness that same effect to reduce drag on a variety of surfaces -- including domes that sometimes crumple in high winds, or perhaps even vehicles.

Detailed studies of aerodynamics have shown that while a ball with a dimpled surface has half the drag of a smooth one at lower speeds, at higher speeds that advantage reverses. So the ideal would be a surface whose smoothness can be altered, literally, on the fly -- and that's what the MIT team has developed.

The new work is described in a paper in the journal Advanced Materials by MIT's Pedro Reis and former MIT postdocs Denis Terwagne (now at the Université Libre de Bruxelles in Belgium) and Miha Brojan (now at the University of Ljubljana in Slovenia).

Shrinking leads to wrinkling

The ability to change the surface in real time comes from the use of a multilayer material with a stiff skin and a soft interior -- the same basic configuration that causes smooth plums to dry into wrinkly prunes. To mimic that process, Reis and his team made a hollow ball of soft material with a stiff skin -- with both layers made of rubberlike materials -- then extracted air from the hollow interior to make the ball shrink and its surface wrinkle.

"Numerous studies of wrinkling have been done on flat surfaces," says Reis, an assistant professor of mechanical engineering and civil and environmental engineering. "Less is known about what happens when you curve the surface. How does that affect the whole wrinkling process?"

The answer, it turns out, is that at a certain degree of shrinkage, the surface can produce a dimpled pattern that's very similar to that of a golf ball -- and with the same aerodynamic properties.

The aerodynamic properties of dimpled balls can be a bit counterintuitive: One might expect that a ball with a smooth surface would sail through the air more easily than one with an irregular surface. The reason for the opposite result has to do with the nature of a small layer of the air next to the surface of the ball. The irregular surface, it turns out, holds the airflow close to the ball's surface longer, delaying the separation of this boundary layer. This reduces the size of the wake -- the zone of turbulence behind the ball -- which is the primary cause of drag for blunt objects.

When the researchers saw the wrinkled outcomes of their initial tests with their multilayer spheres, "We realized that these samples look just like golf balls," Reis says. "We systematically tested them in a wind tunnel, and we saw a reduction in drag very similar to that of golf balls."

Now you see it, now you don't

Because the surface texture can be controlled by adjusting the balls' interior pressure, the degree of drag reduction can be controlled at will. "We can generate that surface topography, or erase it," Reis says. "That reversibility is why this is pretty interesting; you can switch the drag-reducing effect on and off, and tune it."

As a result of that variability, the team refers to these as "smart morphable surfaces" -- or "smorphs," for short. The pun is intentional, Reis says: The paper's lead author -- Terwagne, a Belgian comics fan -- pointed out that one characteristic of Smurfs cartoon characters is that no matter how old they get, they never develop wrinkles.

Terwagne says that making the morphable surfaces for lab testing required a great deal of trial-and-error -- work that ultimately yielded a simple and efficient fabrication process. "This beautiful simplicity to achieve a complex functionality is often used by nature," he says, "and really inspired me to investigate further."

Many researchers have studied various kinds of wrinkled surfaces, with possible applications in areas such as adhesion, or even unusual optical properties. "But we are the first to use wrinkling for aerodynamic properties," Reis says.

The drag reduction of a textured surface has already expanded beyond golf balls: The soccer ball being used at this year's World Cup, for example, uses a similar effect; so do some track suits worn by competitive runners. For many purposes, such as in golf and soccer, constant dimpling is adequate, Reis says.

But in other uses, the ability to alter a surface could prove useful: For example, many radar antennas are housed in spherical domes, which can collapse catastrophically in very high winds. A dome that could alter its surface to reduce drag when strong winds are expected might avert such failures, Reis suggests. Another application could be the exterior of automobiles, where the ability to adjust the texture of panels to minimize drag at different speeds could increase fuel efficiency, he says.

John Rogers, a professor of materials research and engineering at the University of Illinois at Urbana-Champaign who was not involved in this work, says, "It represents a delightful example of how controlled processes of mechanical buckling can be used to create three-dimensional structures with interesting aerodynamic properties. The type of dynamic tuning of sophisticated surface morphologies made possible by this approach would be difficult or impossible to achieve in any other way."

Video: http://www.youtube.com/watch?v=_86mIMPbcDg

The research was supported by the National Science Foundation, MIT's Charles E. Reed Faculty Initiatives Fund, the Wallonie-Bruxelles International, the Belgian American Education Foundation, and the Fulbright Foundation.