GM's driveable fuel-cell lab

GM in May demonstrated a Chevrolet S-10 powered by a fuel cell that uses an onboard reformer to extract hydrogen from gasoline to produce electricity.

General Motors Corp. wants everyone to know it takes fuel cells seriously. "Make no mistake about it, we are on the path to commercialization of fuel cells," said Byron McCormick, Co-Director of GM's Global Alternative Propulsion Center, just about two and a half years ago.

At the time, McCormick was talking about a new catalyst that GM had developed for its next-generation fuel processor. The fuel-cell catalyst helps convert fuel into electricity, and needed to be designed so it would not break down from vibration during driving. Engineers designed the catalyst to be held in place by a honeycomb-like device. The company planned to install the catalyst in a fuel-cell-powered Chevrolet S-10 that the company intended "to demonstrate in early 2002." In May 2002, GM did it.

The S-10 extracts hydrogen from gasoline. It is equipped with a fuel processor, which currently takes up the better part of the bed, that reforms low-sulfur gasoline via a series of chemical reactions. The fuel is mixed with air and water and then passed over a series of catalysts to remove the hydrogen from the carbon. The hydrogen is then sent to the fuel-cell stack, where it is combined with oxygen from the air to produce electricity.

GM claims that linking the reformer technology in the vehicle to a fuel-cell stack could result in an overall efficiency gain of up to 40%, a 50% improvement over a conventional internal-combustion engine. With the onboard gasoline reformer, carbon dioxide emissions would be cut by up to 50%—even more if the reformer was placed at the gas station.

According to Larry Burns, Vice President of Research and Development, and Planning, the gasoline can also be reformed at personal residences or businesses. "In most cases you already have natural gas, water, and electricity coming into your home or place of business," he said. "To create hydrogen, all that is missing is a natural gas reformer or an electrolyzer. Bottom line, the (fuel-cell) transition will happen faster (than previously thought) because there will be so many competing ways to refuel without replacing the existing infrastructure."

While oil companies, natural gas companies, electric utilities, and other energy providers are in a race to provide the fuel to power viable fuel-cell vehicles, just as OEMs and suppliers are in a race to provide the fuel-cell technology, Burns believes that right now "gasoline remains a very viable alternative, especially given the existing fuel-distribution infrastructure." The end goal, according to GM, is to use whatever combination of feedstocks necessary to produce hydrogen, be it crude oil, natural gas, or renewable forms of energy.

In the mean time, engineers at GM will continue to put the S-10 fuel-cell pickup through a variety of tests to more clearly determine the vehicle's range, efficiency, emissions, and fuel-reforming characteristics. Burns expects GM to put "affordable, profitable fuel-cell vehicles on the road" by the end of the decade.

- Jean L. Broge

Direct injection for the Audi A2

Externally, only the badge differentiates the Audi FSI front-wheel-drive A2, which is poweres by a 1.6-L engine, from other A2 models.

The application of gasoline-direct-injection technology is steadily gaining momentum in production cars, and the first Audi to receive it is the aluminum-bodied, spaceframe A2. Designated FSI (Audi says the initials do not stand for anything specific), its possible arrival in a production car was signaled in 1997 when the A12 concept was shown at the Frankfurt Motor Show with a three-cylinder direct-injection gasoline engine. Also, direct injection was used for Audi's 2001 Le Mans-winning R8 racecar.

One of the benefits the technology brings to long-distance competition cars is improved fuel consumption, and hence, fewer refueling stops. Audi cites potential fuel consumption reduction of up to 15% in production cars. The company lists the core elements of the technology as a common-rail fuel-injection system with high-pressure injection pump; a four-valve cylinder head with laterally located injector and intake port divided by a tumble plate; two-position tumble control; an external exhaust gas recirculation (EGR) system; optimized emissions treatment system with NOx-storage catalytic converter and NOx sensor; and two-line exhaust gas cooling with radiation cooler.

According to Audi, the greatest challenge apart from exhaust gas treatment was the implementation of the necessary software in the engine control unit (ECU) because of the many maps and the transitions between the operating states, calling for a computing capacity more than twice the norm. Advanced computer simulation techniques were applied to achieve a match of the 3-D maps. Injection pressures are up to 11,000 kPa (1600 psi).

Audi's new gasoline-direct-injection engine for the A2 1.6 FSI features an external exhaust gas recirculation system and a common-rail injection system with a high-pressure injection pump.

The Audi engine has a two-position tumble flap in the intake port. When open it allows air unobstructed ingress. In its second position it moves against a tumble plate shielding the lower part of the intake port to channel intake air via a controlled path into the combustion chamber. Audi claims that this feature makes two operating modes possible, which are the fundamental requirements for the versatility of the FSI principle: homogeneous- and stratified-charge operation. Depending on load status and accelerator position, the engine electronics always switch to the optimum mode without the driver noticing. The FSI engine has a 12.1:1 compression ratio.

A problem with direct-injection-gasoline technology has traditionally concerned NOx emissions, with excess air in the combustion process making it difficult to reduce NOx to nitrogen gas completely by using a conventional catalytic converter. Audi says it has used a "series of measures" to solve this problem. EGR is one of these measures, resulting in untreated NOx emissions being reduced by some 70% during stratified lean-burn operation.

The debut of the 1.6 FSI broadens Audi's A2 range to four, which includes two 1.4-L versions (one gasoline, one diesel) and a 1.2-L diesel.

Another measure is the engine being equipped with two catalytic converters, one of the regular three-way type positioned behind the manifold, and the other a NOx "storage-type" converter located beneath the floorpan and specifically developed for a direct-injection-gasoline engine. It has a barium coating with which the oxides of nitrogen combine and is controlled via mapping and temperature. When the converter is saturated, the engine's mixture is briefly made richer, raising the temperature of the slightly rich exhaust gas. The barium molecules in the converter release the oxides of nitrogen, which are then reduced to nitrogen, explains Audi. A NOx sensor is positioned at the discharge end. NOx-storage converters operate most efficiently between 250 and 500°C (482 and 932°F), therefore this range is the prerequisite for the lean-burn operation of the gasoline-direct-injection engine since NOx emissions are particularly high in this mode. To ensure that exhaust gas temperatures remain within this range, the A2's exhaust system is fitted with an exhaust gas cooler positioned ahead of the NOx-storage converter. To improve cooling efficiency particularly when exhaust gas temperatures are high, the heat sink is designed as a radiation cooler.

The A2 1.6-L FSI engine has an output of 81 kW (109 hp) at 5800 rpm and a maximum torque of 155 N•m (114 lb•ft) at 4500 rpm. Engine management is via a Bosch Motronic MED7. The engine is mated to a five-speed manual transmission. Suspension is similar to that of other A2 versions, with MacPherson struts and lower wishbones at the front, torsion beam at the rear. Performance includes 0-100 km/h (62 mph) acceleration in 9.8 s, top speed of 202 km/h (125 mph), and fuel consumption of 5.9 L/100 km (40 mpg). Unladen mass of the car is 992 kg (2187 lb). The fuel-tank capacity on all A2s has been upped from 34 to 42 L (9 to 11 gal).

- Stuart Birch

VW's fuel cell chills out

Operating fuel-cell vehicles in extreme conditions is an area of continuing development for many companies. Volkswagen took its Bora-based Hy.Power over the 2005-m (6578-ft) Simplon Pass between Switzerland and Italy in January through conditions that included sub-zero Celsius temperatures and steep grades. VW has worked with the Paul Scherrer Institute in Zurich to develop what it terms a "low-cost" hydrogen fuel cell with extra-high-performance capacitors called "supercaps" to provide additional energy storage. The 75-kW (100-hp) fuel-cell Bora was accompanied on the Simplon test by a Bora TDI (turbo-diesel) using synthetic SunFuel. Within VW's fuel strategy, the Bora SunFuel represents one of the first steps toward the introduction of the fuel cell, says the company. One of the targets for the Simplon Pass test was to allow the Bora Hy.Power to demonstrate a comparable performance to that of a similar internal-combustion-powered car.

The Hy.Power's supercaps provide a 30-kW (40-hp) power boost for short periods, including acceleration when climbing steep grades. The car also has a new type of membrane between the fuel cell's anode and cathode. Developed by the Paul Scherrer Institute, VW says this technology is "much cheaper" than the type used in most fuel-cell systems.

- Stuart Birch