TransForum Vol. 6, No. 1

Argonne Engineers See into the Future of Hydrogen Internal Combustion Engines

This full-combustion image of OH* shows the number of H + O = OH* reactions that occur inside a direct-injection hydrogen engine. It provides a qualitative assessment of where (areas in white, red, and green) and how rapidly those combustion reactions occur. The image was taken at 3,000 RPM and with 6 bar indicated mean effective pressure (IMEP), which is about 75% load. The engine was fueled by gaseous hydrogen using a port fuel injector.

Images of hydrogen combustion have been captured for the first time in an internal combustion engine operating at real-world speeds and loads by engineers at the U.S. Department of Energy's (DOE) Argonne National Laboratory. This window into the inner workings of a hydrogen-powered engine is helping to optimize the engines for use on the streets.

"Hydrogen-powered internal combustion engines (ICEs) are a low-cost, near-term technology," explains mechanical engineer Steve Ciatti, who is the project's principal investigator. "They can be the catalyst to building a hydrogen infrastructure for fuel cells."

Some automakers are already viewing hydrogen ICEs as a near-term bridge to the use of fuel cells in vehicles, according to Ciatti. Both Ford and BMW already have demonstration fleets gathering data. "Hydrogen ICEs can ease the transition to fuel-cell powered cars," Ciatti says. "We're envisioning a two-step conversion to hydrogen. Using hydrogen ICEs as a stop gap will give consumers a chance to adapt to a new hydrogen economy in steps as the new infrastructure is phased in. With these engines, they will still pump fuel into their cars."

By using imaging tools and other standard engine measurement devices on a Ford Motor Co. single-cylinder, direct-injection hydrogen engine, Argonne mechanical engineers Ciatti, Henning Lohse-Busch, and Thomas Wallner are optimizing engine operation and identifying the root causes of combustion anomalies, such as pre-ignition and knock. These problems are more pronounced at high speeds and high loads. Argonne researchers observe 50 performance measurements during each engine test.

Researchers use ultraviolet imaging to capture images inside the running engine. "Hydrogen's visible radiation signature is barely discernible, so we focused on the chemical reactions of hydrogen and oxygen, called OH* chemiluminescence, in the engine," Ciatti says. These reactions emit photons in the ultraviolet energy range, and that light is captured and analyzed with specialized optics.

"Hydrogen ICEs are a lot like gasoline engines, except the fuel is gaseous instead of liquid," Ciatti adds. Hydrogen has wide flammability limits, so the engine does not need a throttle, a device that chokes the air/fuel mixture to control the engine power and hampers efficiency (a standard car today is 25 percent efficient; a hydrogen car will be close to 45 percent efficient), nor do they require exhaust after-treatment when operating correctly.

"The unique properties of hydrogen fuel (wide flammability limits and ignition characteristics) are exciting because you can do things with hydrogen that you can’t do with hydrocarbons," Ciatti says. "For example, you can use direct injection (spraying the fuel directly into the combustion chamber), so the efficiency goes up and the power density goes up, but unfortunately, the complexity goes up as well."

DOE EERE Assistant Secretary Andy Karsner experiences "driving" a vehicle on Argonne's four-wheel-drive dynamometer in August 2006. This unique DOE facility can test a wide variety of advanced vehicles, including those with hydrogen engines and fuel cell vehicles.

EERE's Andy Karsner (r- center) and Steve Chuslo (r) learn about hydrogen engines with Argonne's Larry Johnson (l-center) and Don Hillebrand (l).

Researchers are also determining the most efficient and cleanest way to run the engine without knock or pre-ignition, another technical challenge. Because of its nature, hydrogen easily combusts, so researchers are experimenting with a multiple-injection approach. They are injecting hydrogen directly into the cylinder once or twice during each combustion cycle, depending upon operating conditions. The goal is to determine the optimum timing and amount of hydrogen injected during each cycle. The wrong mixture of hydrogen causes engine operation and emission problems. The researchers are also experimenting with prototype injectors. Making them is a materials science and engineering challenge because the operating atmosphere is unusually hot and under high pressure. Sealing and cooling the injector become critical tasks.

"Working with a single cylinder allows us to isolate problems so we don't have four cylinders to track through to see where and how problems started," explains Ciatti. "We plan to solve problems in the single cylinder and then try them out in a four cylinder," says Ciatti. The mechanical engineering team has installed and is commissioning a 2.3-liter four-cylinder Ford hydrogen engine. Eventually, the team will integrate the four-cylinder engine into a flexible hybrid vehicle to test how the engine operates as part of a vehicle in Argonne's Advanced Powertrain Research Facility.

This research is funded by the DOE's Office of Energy Efficiency and Renewable Energy, FreedomCAR and Vehicle Technologies Program. Argonne researchers are collaborating with Sandia National Laboratories, Ford, BMW, and the European Hydrogen Internal Combustion Engine (HyICE) initiative.

September 9, 2006