TRANSPORT: IS LESS MORE?

GM’S fuel cell design “defies cliché”, according to one
expert.

The history of fuel cell vehicles at General Motors goes back nearly four decades. The OEM has achieved steadily-improving technology benchmarks in its stack and system design, and has been willing to make drastic course changes – notably a shift away from using an onboard gasoline fuel processor. Vicki McConnell reports.

GM’s latest hydrogen (H2) fuelled PEM fuel cell system has been significantly downsized so as to achieve a cross-platform fit in multiple GM models. The automaker has also rolled out
two new FCVs and launched a 100+ vehicle on-road test program.

When asked the most challenging aspect of fuel cell vehicle development, Matthew Fronk, chief engineer for Fuel Cell Systems at General Motors’ Fuel Cell Activities Center in Honeoye Falls, upstate New York, answers“making sure the three-legged stool is sturdy.”

What he means by that is ensuring that GM commercialises a fuel cell propulsion system that meets the few but critical automotive fuel cell requirements: cost, lifetime and performance. A tour of this centre in October revealed new milestones achieved, and progress along the path toward these priorities. Rick Wagoner, GM’s chairman and CEO, has tasked his fuel cell team with accomplishing these goals at affordable, scale volumes comparable to internal combustion
engines (ICEs) by 2010.

In fact, GM’s next-generation fuel cell system is already in development, one significantly more compact even from
the system to be used in its latest fuel cell vehicles. This system could achieve a footprint and weight comparable to that of a four-cylinder internal combustion engine, such as GM’s Ecotec 2.2L, which is 658 mm high, 627 mm wide, 633 mm
long, and weighs 122 kg; the 2005 model Saturn Ion and Chevy Cobalt subcompacts feature this engine. The importance of this downsized design cannot be underestimated– it is crucial to GM’s plan to integrate more compact, configurable fuel cell propulsion systems into multiple
vehicle platforms. This linkage extends to production line installation and commercial volumes of FCVs.

Other differences in the new system include weight and part-count reduction, in part by use of more composite and moulded materials. The air inlet has been reduced by 50%, for example. On the other hand, air/anode and fuel filtration elements may be added. All wiring and connections will come from Tier 1 automotive suppliers, and overall, the system is designed to significantly reduce manual swages during assembly. So this system architecture is designed to demonstrate the effectiveness of ‘less is more’ in materials, mass, assembly, and cost.

Sequel hits the road

A permanent inspiration for the engineers working at the Fuel Cell Activities Center might be to park the behemoth of the
Electrovan – GM’s first drivable FCV, tested in 1968, with its entire cargo space full of fuel cell equipment – next to the 2006 drivable Sequel sport utility vehicle (SUV) concept FCV. Built from the tyres up, the premium, five-passenger crossover Sequel features its main propulsion, braking and chassis components packaged inside GM’s innovative ‘skateboard’ chassis (only 11 inches/28 cm thick). In addition, the Sequel
is outfitted with steer- and brake-by-wire controls, rear wheel hub motors, lithiumion batteries, and a lightweight aluminium
structure. Since the largest market segment for GM is its internal combustion engine SUVs and trucks, it makes only good business sense to configure the Sequel FCV in the medium-sized sector of this category.

Other important Sequel capabilities:

• 480 km range between H2 fill-ups using a 73 kW PEMFC, 65 kW lithium-ion battery pack, and three 10,000 psi or 700 bar composite hydrogen storage tanks;
• Quick acceleration to 60 mph (100 kph) in 10 seconds, due to 70% more torque (3950 Nm at the wheels).
• Shorter braking distances;
• Unequalled control on snow and ice, or on uneven terrain.

Proof of the latter will be verified through on-road testing of several Sequel prototypes in cold-weather climates. Cold-start performance in the HydroGen3 FCV, based on GM’s Opel division Zafira minivan and holder of most of the automaker’s FCV records, has reached–25°C. Mark Mathias, staff technical fellow at the Fuel Cell Activities Center, reports the ultimate
cold-start goal for GM stacks is –40°C. Larry Burns, GM’s vice president of R&D/Strategic Planning and sometimes called Mr
Hydrogen because of his passion for the potential of a hydrogen economy, believes the Sequel design is a crucial part of the answer to Waggoner’s 2010 vision. He believes it “proves a new DNA for vehicles, that is viable for the future.” Burns also believes FCVs will stimulate auto industry growth, allow automakers to create fundamentally better vehicles, and
increase energy independence in the US.

Of course, hydrogen for these FCVs needs to be generated, distributed, and stored to be practical for automotive applications. Here again, Burns sees part of the answer for that H2 infrastructure already in place, derivable from many
energy pathways. These include the existing gasoline and natural gas infrastructure, with H2 reformed on-site. He points out that 95% of the H2 produced in the US – and 50% of the
H2 produced in the world – is already reformed from natural gas at large, central plants.

Renewable H2 feedstock sources cited by Burns include ethanol, biomass, and organic waste. Further, he suggests the versatility of electrolysis for deriving H2 from clean coal, nuclear, solar, hydro, wind, wave, and geothermal resources. According to Burns, 10 million fuel cell vehicles would increase the natural gas demand by less than 2%. “As the cost of fuel cell technology continues to decrease, so will the cost of electrolyser technology,” Burns concludes. GM currently holds intellectual property assets in high-pressure electrolysis
methodology.

Project Driveway

In its latest significant FCV milestone, GM will test a fleet of 100 new FCVs starting next year, with its fourth-generation fuel cell system configured to fit into the space of an existing, commercial SUV platform, the Equinox. This deployment plan is called Project Driveway, and is designed to gain comprehensive data on all aspects of the customer experience with an FCV. Initially, US drivers in California, New York and
Washington DC will subject the FCVs to widely differing driving environments.

Badged under GM’s global volume brand, Chevrolet, the Equinox FCV is engineered for a 50,000 mile lifetime. Gregory Cesiel, program director of Fuel Cell Propulsion Systems for GM in Warren, Michigan, says that accelerated testing will prove out that lifetime next year (at 3,500 hours), before the Equinox begins road testing.

The PEMFC for the Equinox FCV provides 93 kW, and the nickel metal hydride battery pack operates at 35 kW. Acceleration from 0 to 60 mph (100 kph) is 12 seconds, and torque is 320 Nm. Its operating range is expected to reach 200 miles (320 km). Cesiel adds that the Equinox propulsion system is expected to meet all 2007 US Federal motor vehicle safety standards. Part of the vehicle’s architecture directly related
to safety is the positioning of the three 700 bar H2 storage tanks well forward of the crush space between the rear bumper and the storage tanks. Holding a total of 4.2 kg of compressed H2 onboard, the carbon fibre storage tanks from Quantum Fuel Cell Technologies Worldwide of Irvine, California also add to safety by virtue of advanced burst strength and durability properties. GM has worked with Quantum Technologies to design these tanks for crashworthiness.

Mathias tells FC Focus that GM is still considering both fluorinated and non-fluorinated membranes for commercial vehicle application, with fluorinated materials currently viewed as more likely for first-generation automotive applications. Current membrane-electrode assemblies feature a 25 micron thin membrane in a multilayer membrane-electrode assembly (MEA).

GM’s partner, Giner Electrochemical in Newton, Massachusetts, provides in-depth fuel cell materials characterisation data with
an emphasis on membranes.

Testing and manufacturing

Each Equinox FCV will use two PEMFC stacks, comparable to the performance of a four-cylinder ICE. David Waters, staff engineer for Process and Manufacturing Development at the Honeoye Falls Center, is in charge of setting up an assembly area for these stacks. Assembly functions that could be automated are under analysis. Leading up to the Equinox system installations, complete build tests are being performed on every stack “to establish the right protocols and test procedures that will help with diagnostics,” explains Waters. He says it takes several days to run a full diagnostic engineering test. Over the past year and a half, some 20 to 30 stack iterations have been built and tested to establish the protocols and test procedures for the fourth-generation fuel cell architecture that will be used in the Equinox FCVs.

Thermal management, and control of the water flow produced during a fuel cell’s electrochemistry (and used as a cooling agent in some fuel cell systems), are two of the most competitive areas of fuel cell design among OEMs, according to Andrew Bosco, staff engineer, GM Fuel Cell Advanced Product
Engineering. In single-cell, short stack and full-scale hardware testing under Bosco’s purview at the centre, he reports that GM has determined that the thermal management parameters of automotive fuel cell stacks are wider than first thought.

“Such tests also help us understand where we can stretch the
unit,” Bosco says, “and help us characterise drive cycle performance, especially compared to internal combustion engines.” The number of heat-exchangers in the GM FCVs
remains an engineering challenge: the Sequel has five, and the Equinox three. Mathias comments that “this will require the further development of membranes and electrodes that operate at higher temperature, which is the subject of worldwide research efforts.”

Other testing in Bosco’s area includes drive schedules, air optimisation, fuel control, and stack calibration. Each stack also goes through the header area, where air and H2 delivery into
the intake manifold is analysed. This is equivalent to a high rpm dynamometer test. Water control in a fuel cell system affects acceleration, idle, and cold-start performance.

GM’s current fuel cell stack is liquid-cooled. Bosco explains that the Fuel Cell Activities Center “has been able to use current production controllers from GM’s powertrain organisation to reduce the cost of the system and establish common control toolsets with the rest of GM. In addition, several novel control
algorithms have been developed that improve the fuel cell’s efficiency, performance, durability, and reliability. These algorithms represent a significant amount of intellectual property for the corporation, and are the foundation of our
future systems.”

Bosco estimates that over the lifetime of a fuel cell vehicle, some 30,000 startups and shutdowns will occur. Sensors embedded in the test stacks and balance-of-plant (BOP) components monitor the movement of water, and identify when water excess may occur, and the best means for removing it.

Overall, Bosco concludes that one of the most positive aspects of fuel cells “is scalability, depending on power demand and
physical configuration, with fewer total parts in the system.” And he adds that the Equinox fleet test input will be invaluable
in further refinement of testing protocols, providing good early reliability and durability data from sensors and actuators; this will also allow the opportunity to try control enhancements with the customer/drivers.

“There’s no substitute for that kind of direct experience,” he believes. Another aspect of fuel cell technology progress comes in reducing the total part count and keeping the BOP system’s componentry moving parts to a minimum. The impact of fewer parts and fewer moving parts will ultimately reduce the engineering and validation time for propulsion enhancements; get such enhancements to market faster than the more complicated ICEs; and reduce total cost. Burns maintains that fuel cell systems will provide better reliability,
durability, and higher-quality propulsion.

In terms of vehicle architecture, the smaller fuel cell propulsion footprint – eliminating the existing large and heavy powertrain attached to the chassis in an ICE system – will also have the ability to self-test; use distributed smaller subsystems that accommodate assembly; and be reconfigurable, programmable and fieldupgradeable.

Mechanical all-wheel drive will be replaced by an independent, software-controlled system with internal traction, stability and ride control. Warranties will shift from mechanical wear-out to electrochemical degradation.

Global, multi-option effort

The transition from a petroleum economy to a hydrogen economy for GM will encompass interim vehicle technologies including hybrid, plug-in electric and plug-in hybrid propulsion, along with clean diesel, flex-fuel and natural gas fuelled vehicles. In other words, no single alternative fuel vehicle
technology answers all the needs of different regions of the world in the short and midterm, although GM is committed to hydrogen as the long-term energy solution for itsportfolio of vehicle brands. Along the way, improved fuel efficiency and reduced emissions will result from technology improvements
in these interim technologies, as well as from fuel cell technology.

In November 2006, Wagoner announced that GM will introduce a new hybrid vehicle technology annually over the next several years. The OEM’s first gasoline/electric hybrid, the Saturn Vue, came out in September 2006, and in 2007 the Saturn Aura Green Line and Chevy Malibu will expand the hybrid integrated
starter/alternator technology.

Although not yet ready to reveal details, GM has been
assessing home H2 refuelling systems, and may join with
Honda in this effort. Honda has already developed a thirdgeneration home refuelling unit with fuel cell system OEM, Plug Power, which uses reformed natural gas as the H2 source.

Matt Fronk is a direct and optimistic engineer. When asked about a plethora of GM’s resources – such as participation with
Hydrogenics and General Hydrogen in demonstrating fuel cell systems for battery replacement in forklift trucks; establishing
a collaborative research laboratory at the University of Michigan to study electronic smart materials (mechatronics); and GM’s application of multiple automotive stacks to stationary power generation at a Dow Chemical plant in Texas, – he smiles and says, “we will pull technology from any place on the planet to help us move this to a commercial product.” He adds that GM’s fuel cell technology development is a global
effort, including cultivating materials, subsystems, and component suppliers, which he calls “crucial to our success, suppliers to support progress in prototype builds and determining what it really takes to create a commercial product, including quality of parts, materials requirements, and scaling up speciality materials like membranes and diffusion media.”

Which brings us back to the ‘three-legged stool’ of commercial FCV priorities: cost, lifetime, and performance. “It’s my job to worry about these priorities,” Fronk says, “and we have made some good progress in the next designs for FCVs as described here. There is still more work to do to get full automotive
competitive materials, components, designs, and suppliers.

We’ve come a long way, and there’s clearly a path to get there, on all‘legs’. There is no substitute for learning by doing, and my team is actively engaged in the next level of fuel cell
development, working with our key suppliers and partners. It will be a matter of time to put all in practice simultaneously.’

About the Author

Vicki McConnell has been writing about plastics and composites in multiple application areas for more than 30 years, and is based in Denver, Colorado, USA.