Another important difference from previous designs is that the fuel injector is positioned centrally in the head of the cylinder, rather than in the side. This enables fuel and air to mix better, though it means that the injector is located at the hottest part of the engine and so requires improved water flow to keep it cool. An added benefit of better combustion is lower amounts of unburnt fuel in the exhaust, resulting in fewer hydrocarbon emissions.
Lotus Engineering and Continental Powertrain have already adopted the technology in a low-carbon concept car. A three-cylinder, 1.5-liter engine based on the combustion concept has been fitted to the Opel Astra and shown to cut carbon dioxide emissions by 15 percent compared to the Astra’s standard, 1.8-liter, four-cylinder engine. At the same time, the concept car produces a 36-percent increase in torque and a 14-percent increase in power output.
According to Geraint Castleton-White, power-train leader at Lotus Engineering, the outcome is a car that emits 140 grams or less of carbon dioxide per kilometer. In 2007, cars sold in Europe averaged 158 grams of carbon dioxide per kilometer; proposed legislation in the European Parliament would require cars to meet standards of 130 grams per kilometer by 2012.
“We have had tremendous interest from manufacturers around the world and the concept will be in production in the future,” says Castleton.
The prototype engine is more cost effective than other direct-injection, “lean burn” engines, because it avoids the need for expensive equipment to trap nitrogen oxides, he says.
John Heywood, professor of mechanical engineering at MIT, isn’t surprised by the improvements. “There has been a nearly linear improvement in performance of internal combustion engines over the last couple of decades or so,” he points out. “We need to pursue all possibilities that look promising.” But he suggests there are other potential ways of increasing engine efficiency, such as reducing friction, which might end up being more cost effective. “There are questions over the long-term market attractiveness of variable-valve technology,” he says.