Hydrogen and HCCI

  • 24-Jun-2008 07:54 EDT
HCCI engine.jpg
General Motor's prototype HCCI multi-cylinder engine undergoes combustion and controls system development at GM Research and Development.

Automotive research labs are harbingers of things to come. Peer inside these environments and the common denominators are technologies aimed at improving fuel economy and reducing vehicle emissions.

Hydrogen-fueled engines are one of the many fuel- and emissions-smart programs under development in the industry. BMW had its first liquid hydrogen vehicle in 1979, and in 2007 the Hydrogen 7 entered the scene. "It's the sixth generation of hydrogen cars and the first of our hydrogen cars going through a serial development process," Andreas Obieglo, Manager of the Liaison Office South Carolina for the BMW Group, said during May's Advanced Powertrain Technologies session at the 2008 SAE Government/Industry Meeting in Washington D.C.

Select customers in Europe and the U.S. are driving BMW Hydrogen 7 cars and that fleet of 100 sedans is only one of the automaker's ongoing hydrogen-related projects. "We have two different hydrogen-fueled engines on the test bench. One engine is using direct-injection technology and the other engine is using cryogenic port-injection technology," said Obieglo.

Today's hydrogen port-injection engines insert a large volume of gas into the intake manifold to displace the air, but that essentially reduces the power potential by 20% in comparison to liquid fuels, according to Obieglo. "In the cryogenic port injection process, the low-pressure range of a liquid hydrogen tank is sufficient. This concept takes advantage of the external mixture formation of hydrogen and air by making use of the resulting coldness. By mixing cryogenic hydrogen gas—at -240°C (-400°F)—with the aspirated air, the mixture can be cooled down, and thus the energy content inside the combustion chamber increases," said Obieglo.

Injecting hydrogen directly into the combustion chamber after the full amount of air has been aspirated and the intake valves have closed is essentially the same technique as seen in direct-injection diesel and gasoline engines. With high-pressure injection, the injection timing can be varied within a wide range, which means controlled fuel stratification can be realized, according to Obieglo.

"The reason that we're pursuing cryogenic port and direct injection is because in the beginning of this hydrogen research project we didn't know which version would make it to the 100 kW per liter mark, but both versions have reached the 100 kW per liter mark," Obieglo said. "The two new approaches promise the potential to outperform conventional fuels."

General Motors' engineers continue development work on the homogeneous charge compression ignition (HCCI) engine. Among the technical issues still being addressed is refinement of the switching between spark-ignition to HCCI modes.

"The gas remnants of a previous cycle that are left in the existing cycle needs to be handled in such a way that the mode transition occurs without a loss in power delivery. Another issue that's being addressed involves making sure that the transition from spark ignition to HCCI mode or vice-versa is imperceptible in terms of noise," said Ken Patton, an engineering group manager in GM Powertrain Advanced Engineering.

For several months now, engineers have been driving vehicles equipped with an HCCI engine. "We're definitely still in the zone where we're making progress. The next steps are to understand how this technology earns its way into our portfolio from a cost-effectiveness, durability, and serviceability standpoints as well as from a perspective that addresses the key attributes that our customers care about. It really needs to earn its way in because this technology definitely brings a significant amount of added content to the engine," Patton said.­

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