It is a technology that melds a diesel engine's high efficiency and massive torque with a gasoline engine's low emissions and smooth running. And it could be the next big evolution of the internal combustion engine.
It's called HCCI, or homogeneous charge compression ignition. Major automakers in North America, Europe and Asia are spending millions to bring it to production.
General Motors expects to have a test vehicle with an HCCI engine running by next year. If it works as well as engineers expect, the next step will be to decide whether the technology is ready for prime time, says Uwe Grebe, GM Powertrain's executive director of advanced engineering.
Though HCCI uses proven technologies already in production, such as direct injection of fuel into the cylinders and variable valve timing, the combustion process is complex, and controlling it requires a massive increase in computer power.
Fuel economy quest
The rush to HCCI is being spurred by the quest to increase fuel economy without huge investments in new technologies. Engineers expect HCCI engines to deliver about 80 percent of the efficiency of a diesel engine at about 20 percent of the cost difference between a gasoline engine and a diesel.
To meet stringent emissions regulations around the world, today's diesels use expensive high-pressure common-rail fuel-injection systems and high-cost after-treatment devices in the exhaust system, such as diesel particulate traps. A gasoline HCCI engine could deliver almost the same fuel economy as a diesel for a lot less cost.
“The reason we think HCCI is such a great technology is that we get the fuel economy benefit, but we deal with emissions inside the combustion chamber,” Grebe says.
The HCCI combustion process can work in both gasoline and diesel engines. But it doesn't turn a gasoline engine into a diesel or vice versa. In other words, a gasoline engine would still burn gasoline, and a diesel engine would still use diesel fuel. But the operations of both engines would move closer together because each engine would mimic the other part of the time.
That means a gasoline engine would ignite its fuel not with a spark plug but by compression of air and gasoline in the cylinder, just as in a diesel. In a diesel with HCCI, a glow plug might be used to ignite the diesel fuel, as a spark plug does in a gasoline engine.
Engineers have several hurdles to overcome before the HCCI engine will be produced.
The engine only runs in HCCI mode part of the time, such as when a vehicle is cruising down the highway at a set speed. Engineers have to find a way to smooth the transition into and out of HCCI mode. An engine running in HCCI mode produces more noise and vibrations.
Also, engineers are working to perfect the shape of the pistons and combustion chambers as well as the amount of fuel and the direction in which it is sprayed into the combustion chambers. The temperature of the air entering the cylinder also is important, because engineers have to determine how to make the fuel in the cylinder ignite evenly.
5 years away
How long will it take to perfect the technology? It depends on whom you ask.
Each automaker is at a different stage in its research, but the HCCI engine is at least five years away.
“We are working on the HCCI engine, but clearly it is a future technology,” says Volkswagen AG spokesman Harthmuth Hoffman in Germany. “I believe we could see it on the road in five to 10 years.”
Last month in Tokyo, Masatami Takimoto, Toyota Motor Corp.'s executive vice president of powertrain research and development, said HCCI is a long way off and might not be ready before fuel cell vehicles. “In Toyota's research center, the HCCI and fuel cell departments are in competition to be first,” he said.
Ford Motor Co. engineers also are developing HCCI and say it could make production in as little as five years.
“We believe that the HCCI gasoline engine could deliver a substantial incremental efficiency benefit that could close the gap between gasoline and diesel engines,” says Tom Kenney, a Ford research engineer working on HCCI in Dearborn, Mich.
Nissan is another automaker spending heavily to bring HCCI to production. Nissan has been working with researchers at Stanford University in California to understand the combustion process.
GM's Grebe believes GM is on the road to HCCI production engines. He sees the engine's control system, not its internal workings, as the biggest challenge.
Says Grebe: “I think the technical problems can be resolved. What needs to be looked at is the complexity of the entire system and the cost-benefit of the technology. The cost-benefit is highly dependent on what the cost of energy is. It is a technical problem where the solutions are coming together.”
James Treece and Jens Meiners contributed to this report
HCCI facts
What it is: A combustion process in which a gasoline or diesel engine can run using either compression ignition or spark ignition
Benefits: Greater fuel economy and lower emissions of oxides of nitrogen
Who's doing it: General Motors, Ford, Toyota, Honda, Nissan, Volkswagen, BMW and others
Ready for production: 2011 at the earliest
