Turbocharging, direct injection, and a variable compression ratio make four greater than six.
“The company that decides it wants to establish a new trend will take a chance with a technology like this,” says Robert Last, v.p. of Operations and Communications, FEV Engine Technology (Auburn Hills, MI; www.fev.com). The technology he’s talking about is actually two tech-nologies that started life in separate test programs, and were joined together late in 2006 as part of a project to take advantage of the increased interest in alternative fuels and overall fuel economy brought about by rising gasoline prices. The risk isn’t that the technology won’t work. It’s that the market might not accept it.
“The turbocharging and direct injection portion of this program continue to be developed separately, and are much closer to commercial viability in North America given the rising cost of fuel,” says Last. (Though the VW Group already offers a version of this technology in North America, FEV announced it is partnering with Ford to develop a production-ready version of the Lincoln MKR concept’s turbocharged direct injection Cyclone V6 engine.) However, it is the other part of this study that is the most intriguing: VCR. That is, variable compression ratio.
According to Last, there were three goals for this program: (1) to prove that a downsized, turbocharged, and directly injected inline four-cylinder engine can equal a port-injected V6 in terms of performance; (2) to show a 25% improvement in fuel consumption compared to that V6; and (3) to replicate the cruising range of a gasoline V6 while running on E85. The last item is particularly difficult given the fact that E85’s power density is 30% less than that of gasoline. However, the alcohol content gives it much higher knock tolerance, which means the engine can run closer to the limit under load. “In a conventional gas or diesel engine,” says Last, “you choose a compression ratio for the worst-case condition near the knock limit. With VCR, we have the ability to increase or decrease the compression ratio depending where we are on the engine map so we can take advantage of the increased knock tolerance of E85 and get much greater combustion efficiency.”
The engineers at FEV added a simple gear mechanism to the bottom end of a standard Audi 1.8-liter engine block to engage a carrier on the crankshaft that rolls in an eccentric path to alter the stroke of the piston. “A computer-controlled electric motor drives the main shaft,” says Last, “and alters the compression ratio based on where the engine is on the curve, and what type of fuel it is running.” A fuel sensor is an integral part of the design.
The engine can vary its compression ratio continuously between 8.0:1 and 16.0:1, which brings it to near-diesel combustion efficiency on the upper end. “Though it doesn’t appear like it would take more work than an OEM would invest in a mid-life engine upgrade to add the VCR system,” says Last, “the effort increases with a V engine for the simple reason that you have two banks of pistons to control in a confined sump area.” That doesn’t mean it can’t be done—or that FEV’s gear set is the only way to do it—just that it will take a little more time to develop for production.