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Getting diesels to meet future emission standards won’t be easy or inexpensive, but engine developer AVL thinks the expected improvements in power and economy will be enough to keep fuel cells on the margins.

Conventional Engines: Not Dead Yet

Fuel cells and hydrogen may get all of the headlines, but gas and diesel internal combustion engines have a lot left to offer.

“European engines are, on average, much more expensive than North American engines,” says Chris Cowland, Technical Director, AVL Powertrain Engineering, Inc. (Plymouth, MI). The reason is that higher fuel prices traditionally have spurred demand for greater efficiency and power density per liter, while tightening emission regulations have increased demand for greater electronic control over things like valve timing and lift. That additional expense notwithstanding, Cowland believes some of these strategies can be used on the typical low-cost, two-valve per cylinder, overhead valve American V8.

 

By placing a cam phasing system on the camshaft, a pushrod engine can be tuned to take much higher levels of exhaust gas recirculation. “Effectively, you can de-throttle the engine this way, and increase fuel economy by a good 5%,” he says. The claim is based on a study AVL did for a European OEM whose engine designs were aging rapidly, while the profits necessary to develop new engines declined. “Technically, there is very little challenge involved,” Cowland says, “and the cost required is minimal.”

Unfortunately, the same can’t be said for diesel. “Beyond the challenges of meeting the proposed U.S. emission requirements,” says Cowland, “is whether or not the customer is willing to pay for the approximately 30% increase in fuel economy.” Based on the current $3,000 to $5,000 price differential between gas and diesel light truck engines, or the expected differential for passenger cars, Cowland doubts fuel economy improvements alone will drive customers toward diesel. “Diesels have tremendous torque, and torque equals drivability,” he says. “They’re 50% to 60% quicker in peak torque acceleration than gas engines, which makes them feel strong to the consumer.” Of course, that means getting the buyer into a diesel-powered vehicle in the first place, then hooking him for the extra cost.

And those costs aren’t insignificant. Cowland says a base diesel engine is about 15% more expensive than its lower compression gasoline counterpart. “The fuel system and their much tighter tolerances add most of the rest of the cost,” he says, “and aftertreatment adds about $100 more.” When asked to quantify the costs, Cowland estimated that just the fuel delivery system for a light truck diesel V8 costs, “almost as much as a U.S. V6 gasoline engine.” And that the total cost is equivalent to the price of a hybrid drive.

Of course, the costs associated with a switch to diesel pale in comparison to the challenge of meeting the emission standards of 2006 and beyond. Each of the domestic automakers has at least one diesel program under development. However, none will admit to meeting the 10 year/100,000 mile emission requirements, especially those for NOx and particulates. Whether it’s because he’s an optimist, or because his company sells its engine design and development services to OEMs, Cowland thinks the problems can be overcome. “It used to be that the peak firing pressure on a diesel was 150 bar, and it’s now 175 bar,” he says. “We are pushing existing designs harder than ever, and have seen a 100% improvement in the power of a light-duty diesel in the past 10 or so years. What comes next won’t be a linear improvement, but it will be enough, I think, to keep fuel cells at bay.”

As Cowland sees it, fuel cells are unsuited to powering trucks or heavy-duty vehicles due to their limited power density. “They are well below the efficiency or power density of a typical gasoline or diesel engine,” he remarks. Nor is it likely that the rate of progress in these areas will ever produce a fuel cell capable of replacing a 1,000-hp diesel in an over-the-road truck, or providing the performance and range a pickup or SUV driver expects. “There’s a lot of life left in the internal combustion engine.”