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Progress in Developing SOFC APUs for Heavy-Duty Trucks

Sofc1
Projected system efficiency of the Delphi prototype SOFC APU compared to that of a conventional diesel APU. Click to enlarge. Source: Delphi

Two US DOE (Department of Energy)-funded projects to develop a SOFC (solid oxide fuel cell)-based APU (auxiliary power unit) system for heavy-duty trucks reported on their progress this week during the DOE’s Hydrogen Program annual merit review in Washington, DC.

One team is led by Cummins Power Generation and includes Protonex LLC and International Truck and Engine. The other is led by Delphi—which is leveraging its SOFC work in the Solid State Energy Conversion Alliance (SECA) (earlier post)—and includes OEMs PACCAR Incorporated (producer of Kenworth, Peterbilt, DAF and Foden Trucks) and Volvo Trucks North America.

Sofc
Diagram of a solid oxide fuel cell. Click to enlarge.

The goal of each project is to build and demonstrate a diesel-fueled SOFC truck APU. APUs are increasingly being turned to as a solution to reduce the fuel consumption drain of idling and hotel loads on heavy-duty long-haul diesels. While current APUs can use a small diesel-fueled genset, a diesel-fueled SOFC APU would ideally deliver improved efficiency and thus lower fuel consumption.

SOFCs use a hard, ceramic compound of metal oxides as an electrolyte, rather than the thin, permeable polymer electrolyte sheet in a PEM. In a PEM fuel cell, hydrogen ions cross the membrane; in an SOFC, oxygen ions cross the electrolyte. SOFCs operate well on hydrogen and mixtures of hydrogen and carbon monoxide, among other fuels.

Benefits of a SOFC APU for a truck application include:

  • Hydrocarbon fuel reformation requirements for SOFCs are greatly simplified (they are thermally matched, the CO output is a fuel constituent, and there is some sulfur tolerance);

  • There is no internal water management issue;

  • SOFCs are a lower cost fuel cell option with no or low requirements for precious metals;

  • No external cooling is required; and

  • There is a high quality, high temperature single waste heat stream that can be used in the fuel reforming process as well as for vehicle heating.

On the other hand, there are thermal management issues, as well as issues with startup time, stack degradation, and the OEM requirement for zero net water diesel fuel reforming.

Sofc2
The Cummins SOFC APU system. Click to enlarge. Source: Cummins

Cummins Power Generation. The Cummins program began in 2004, but was placed on hold due to budget issues, before being restarted in 2007 (the Delphi project has a similar history.) DOE’s share of the project is $3,225,611, with the industry partners providing $1,732,938.

The Cummins system delivers 2 kW of steady state power from the Protonex SOFC stacks, and about 3 kW of intermittent power from a battery bank. A bi-directional inverter and control (which Cummins leveraged from its work in the recreational vehicle industry) provides up to 5 kW of intermittent power or 2 kW of continuous power to the truck systems.

The stack consists of 4 modules, each comprising 66 tubular fuel cells, which are currently delivering 12.8 W each. The initial target was 10 W each. Each module will include a CPOX (catalytic partial oxidation) reformer, fuel cells, recuperator, tail-gas combustor, and insulation. Cummins says that the SOFC system fuel to electric efficiency is 21% gross, 17% net.

The partners have demonstrated both atomization and vaporization of the fuel. They will use vaporization for the initial units, but will move, in the longer-term, to the atomizer, which requires less start-up energy and has extended maintenance intervals.

Protonex has screened four catalysts and selected one that is capable of more than 93% carbon and H2 selectivity. The team has demonstrated steady-state operation of the tubes for more than 500 hours with the selected catalyst, without carbon formation.

Later this year, the team will build single modules and 4-module sets, and begin testing. Performance optimization is targeting for Q4 2008, along with fuel feed system improvements.

Road testing of the units is due to begin in 2009.

Delphi. DOE is contributing $3,000,000 to the Delphi project—which is now 50% complete—while Delphi is contributing $1,750,000. Delphi’s system has a rated net power output of 3.5 kW, with a target fuel to electric efficiency at rated power of 25%.

The Delphi system is designed with a cycle life—i.e., to go from ambient temperature to the operating temperature of around 750°C and back down to ambient—of 250 cycles. Delphi anticipate one cycle/week, 50 weeks per year, for a 5 year lifetime. (In other words, Delphi sees the system powering up at the beginning of the truck work week and staying on until the end of the week.)

Life the Cummins system, the Delphi system is packaged into the form factor of an existing diesel APU unit.

Delphi is developing reforming technology for diesel/JP-8 SOFC applications by modifying its existing natural gas reformer. Two main designs are being developed:

  • A CPOX reformer; and

  • A recycle based (endothermic) reformer.

The CPOX reformer offers moderate efficiency and simplicity of design. The endothermic reformer offers higher efficiencies through anode tail-gas recycling. With an SOFC, water is created on the anode side of the fuel cell. Delphi is looking at taking that water and bringing it back into the reforming process to accommodate autothermal or steam reforming capability.

The current version of the platform only uses CPOX; the next generation will use the endothermic capability.

Through the rest of this year, the Delphi team will complete the SOFC APU hardware design and build and begin subsystem testing and development iterations. The following year will see complete system module testing and the beginning of full SOFC APU testing, with road tests scheduled for 2010.

Delphi sees the mobile SOFC market expanding beyond heavy-duty diesel trucks to recreational vehicles (diesel and LPG), truck and trailer refrigeration (diesel), and military (JP-8) applications.

Comments

Rikiki

Stas is the SAGE! Vote for Stas. You have a real understanding of the independent long haul trucker's life. I have one minor point from my experieces.... I have never seen a trucker leave his loaded rig running unattended while he checked into a motel (unless he has a mean guard dog tethered). Load pilfering still occurs and may be a bigger fear than not being able to restart the engine.

Having Power available at stops is the simple answer. Most truckers, I think, really just need enough power for a small heat pump for heat/cool, his A/V and Fridge and maybe a laptop. I know that when I go to a KOA with RV, I am very happy to have power, water and sewer hookups available. In most of Texas and indeed in the south, the summer nightime temps remain in the mid 70s with high humidity. I don't fault the truckers for wanting a cool living space in back, especially if there is no motel next door.

POWER TO THE NIGHT STOPS! Even a lowly 115v/20A circuit may do the trick.

In northern climes, maybe a 30A will be required to power the additional engine heater (I have one on my Mercedes diesel from when we lived in the Cascades of WA).

To another poster... Refrigerated trailors generally have their own (IR or other) unit with its own engine/gen/compressor keeping the load cool(or frozen) . I rarely see these carriers in stops. The load remains cooled even if the tractor is removed because the trailer is self-contained. Perishable loads in refrigerated units might be able to take advantage of modernized stops. However, that would require at least a 220v/50A hookup and a switch over from fuel to electric.

Rikiki

Rikiki

Stas is the SAGE! Vote for Stas. You have a real understanding of the independent long haul trucker's life. I have one minor point from my experieces.... I have never seen a trucker leave his loaded rig running unattended while he checked into a motel (unless he has a mean guard dog tethered). Load pilfering still occurs and may be a bigger fear than not being able to restart the engine.

Having Power available at stops is the simple answer. Most truckers, I think, really just need enough power for a small heat pump for heat/cool, his A/V and Fridge and maybe a laptop. I know that when I go to a KOA with RV, I am very happy to have power, water and sewer hookups available. In most of Texas and indeed in the south, the summer nightime temps remain in the mid 70s with high humidity. I don't fault the truckers for wanting a cool living space in back, especially if there is no motel next door.

POWER TO THE NIGHT STOPS! Even a lowly 115v/20A circuit may do the trick.

In northern climes, maybe a 30A will be required to power the additional engine heater (I have one on my Mercedes diesel from when we lived in the Cascades of WA).

To another poster... Refrigerated trailors generally have their own (IR or other) unit with its own engine/gen/compressor keeping the load cool(or frozen) . I rarely see these carriers in stops. The load remains cooled even if the tractor is removed because the trailer is self-contained. Perishable loads in refrigerated units might be able to take advantage of modernized stops. However, that would require at least a 220v/50A hookup and a switch over from fuel to electric.

Rikiki

Henrik

@EP

Dual mode trucks may work. I would like to see some estimates of how much it would cost to equip highways with rails and how they could be maintained without causing too much traffic jams. I fear it will be too expensive. However, it does look like a doable way to in increase the vehicle range of an EV long-haul heavy duty truck. I don’t believe in equipping highways with electric wires. It is very costly to build and maintain and accidents will jam traffic too often. Plus it will make the trucks more costly and increase the air drag to have electric connectors on the roof of the trucks. All highway bridges in the world can handle about 4 meter high trucks. If you need electric wires as well the electric truck need to be max 3.5 meters high to make space for electric connectors or all bridges need to be rebuilt. None is practically possible.

We need to build a quick chare infrastructure anyway to support private EV transportation. It should be one infrastructure that can support all vehicle categories for private cars to long-haul 80000 lbs truck. It will be inexpensive and fast to build. The viability of the business case depends critically on the $500 / kWh battery price and a durability of 2000 cycles. This is possible today and it may improve many folds in just 5-10 years from now making alternative solutions redundant.

Engineer-Poet
I would like to see some estimates of how much it would cost to equip highways with rails and how they could be maintained without causing too much traffic jams.
We've got two trends working here:
  1. The amount of road traffic will decrease as freight moves to rail and people drive less.  This will lead to underutilized traffic lanes.
  2. As road construction costs increase, it will pay to replace high-maintenance pavement with low-maintenance rail.
Removing heavy trucks and possibly buses from the remaining traffic lanes will let them go faster, and further cut the load on the remaining paved lanes.
I don’t believe in equipping highways with electric wires. It is very costly to build and maintain and accidents will jam traffic too often.
It wouldn't be any more costly than putting wires over dedicated rail right of way, and the effect of accidents could be reduced by putting rail in the median a la the Chicago "El" with the inner shoulder or barriers between the rails and road vehicles.  If something does block the rails, the solution is for trucks to get off and drive around on battery power.  These obstacles have to be weighed against having rights-of-way which already go just about everywhere we need them to.
All highway bridges in the world can handle about 4 meter high trucks. If you need electric wires as well the electric truck need to be max 3.5 meters high to make space for electric connectors or all bridges need to be rebuilt.
If the contacts can retract below the top of the vehicle, the solution is to break the wires at bridges and go under on battery power.  This is not overly difficult.

Sure, pantographs and such add drag.  But steel wheels on rail cut rolling friction, and electricity is so cheap the cost savings would be massive despite additional losses.

Henrik

@EP
You have convinced me I need to keep my eyes and ears open for news on this kind of solutions. I think I read somewhere that the wheel to road friction on a conventional truck with rubber wheels was much more important than air drag and that this roll friction is almost nothing on rails. So the efficiency bounty should be worth pursuing.

Tim

I own and operate a class 8 vehicle that moves freight from place to place on the lower 48 states. Adding power to truck stops would not help at this point. The HVAC systems on most trucks is driven off the engine. You would be just powering the onboard electronics. We are moving to electric HVAC systems but they have not been reliable.

Perhaps a bigger problem is that we do not have enough truck stops and we spend most nights parked wherever we can find a spot. We prefer this freedom as the truck stops are not a desireable place for us.

You want to solve the problem? start with figuring out how to recapture the kinetic energy that is lost when you slow the vehicle down. The energy spent getting the vehicle up a hill is a total loss when comming back down the hill ...

... tim

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