Gasoline cleaner choice for spark–plugless engine
COURTESY OF GM
GM and other automakers have demonstrated early concepts of the engine without spark plugs, although early ones can use both.
My recent column about a gasoline engine without spark plugs ignited a lot of questions.
The technology — homogeneous charge compression ignition, or HCCI — works by compressing the air-fuel mixture in the combustion chamber until heat generated by the increasing pressure sets it off.
It’s still in the experimental stage, but advocates say that by creating a faster, more uniform burn it could increase fuel efficiency by up to 30 per cent and reduce emissions of the pollutants that cause smog and damage human health.
Several readers wanted to know why carmakers would bother with something new and complex when a similar technology already works well.
“Why are we insistent on re-inventing old technology?” an anonymous correspondent asked. “If you want a 15 to 30 (per cent) reduction in fuel consumption, buy a vehicle with a diesel engine.”
Others wondered about using gasoline in a diesel-style engine, or whether HCCI could be improved with natural gas, propane or even hydrogen as its fuel.
“With hydrogen, we can be free of petroleum and Gulf (of Mexico) disasters,” wrote John Banka, at Ryerson University. “Note that hydrogen can be produced in a completely green way.”
Many of the answers came from Jason Easton, a spokesperson for GM Canada — the mainstream carmaker most involved in HCCI — and a professional engineer.
HCCI “is an advanced compression ignition engine that aims to function like a diesel, but using gasoline,” Easton says.
It’s an attempt to combine the best feature of diesel — better fuel efficiency — and the relative ease of cutting smog emissions with gasoline. It’s only necessary because gasoline is too volatile for current diesel technology.
With HCCI, the complexity lies in getting the ignition to work properly. In diesel, it’s eliminating the smog emissions as well as the huge numbers of microscopic, health-threatening particles created during combustion.
Mercedes Benz attacks the smog pollution issue with BlueTec, which, to be utterly basic about it, injects an ammonia-based substance — carried in a small tank — into the exhaust system to remove nitrous oxides. It requires that drivers remember to keep the tank replenished — U.S. Environmental Protection Agency rules require that the car automatically shut off when it runs out of the material.
Other manufacturers, including Volkswagen, use a system based on recirculating some of the exhaust into the engine.
Diesels adds $3,000 to $9,000 to a vehicle’s cost, and much of that is for the technology to make them as clean as gasoline engines. The expense might not be noticeable on a Benz price sticker but it’s obvious with cheaper cars.
HCCI, too, would make vehicles more expensive, and both systems face equally complex technical issues. So, which do you chose?
“It doesn’t make sense to exclude either,” Easton says. But, “with gasoline being the primary transportation fuel in most areas of the world, it makes sense to pursue it.”
Eventually, some advances required for HCCI — including the sophisticated compression and valve controls — might also apply to diesel, “but it’s too early to determine if these . . . could make cost-effective and meaningful improvements to existing diesel engines, as they already function with increased efficiency.”
Designing HCCI to handle natural gas and propane probably isn’t worth the investment. In sparked engines, they already emit far fewer greenhouse gases than gasoline. With lower energy content, they provide less driving range, and they’re not as widely available.
“Adapting (HCCI) technology to those fuels for an incremental increase in greenhouse-gas performance may not be cost effective,” Easton says.
Using hydrogen would only add to the cost and complexity. Besides, those developing HCCI agree, fuel cells would be a far more efficient and clean use of it.
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