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Bobcat: an engine template for the future?

With gasoline and diesel prices in North America around US$2.12 to $2.35 a gallon – half the levels of a year ago – urgency to develop high-performance diesel engines has softened, especially as OEMs face an almost unprecedented financial plight. Ford’s product plans, for example, see its 4.4-litre V8 diesel for the F-150 delayed until 2013.

As many OEMs lack diesel engines for light-duty trucks and sports utility vehicles, pressure will grow for high performance gasoline engines with the power and torque, fuel economy and clean emissions of a diesel, especially with demands to raise CAFE standards. This raises the question of whether compacted graphite iron (CGI) will find use for cylinder blocks of North American V8 gasoline engines.

Under a shroud of secrecy, Ford, AVL and Ethanol Boosting Systems (EBS) of Cambridge, Massachusetts, working with the US Department of Energy, are testing an engine called Bobcat. Five new ‘ethanol boost’, twin-fuel turbocharged engines have been built and each variably blends gasoline and ethanol to produce diesel-like performance.

Bobcat engines run on E85, a mix of 15% gasoline and 85% ethanol and with such technology, a 5-litre engine could potentially produce diesel-like 500bhp and 750lbft torque. Bobcat uses a secretly-sourced CGI cylinder block which helps the engines cope with stress levels associated with high combustion pressures. It is believed Ford aims to use Bobcat in flex-fuel vehicles running on gasoline, ethanol or any combination of the two.

EBS claims its technology gives a 30-35% efficiency gain at one third of the cost of a gasoline electric hybrid, but this technology also requires a strengthened engine structure such as might be found with CGI. The CGI engine structure is essential to deal with 150bar peak cylinder pressures. Increased bolt diameters are likewise essential.

Fitted to a Ford F-series truck, a spark ignition engine optimised for E85 could give 15-20% fuel economy gains compared with a production gasoline engine and would meet at least ULEV ll/Tier ll Bin 5 requirements. E85 is used only as required at high loads to avoid knock, leaving the efficiency of gasoline improved by using a high compression ratio downsized engine.

The technology requires special cylinder heads, including variable cam timing, twin turbochargers with waste gates, special port injection of both fuels, and two high-pressure pumps driven by inlet camshafts. Also, EBS requires a second fuel tank or a separate tank-in-a-tank. In a car, this second tank for E85 could be replenished (5 gallons per 5,000 miles) at the dealer – like the urea refill for diesel SCR. A production vehicle is slated for 2012. EBS is also believed to be working with Mack Trucks/Volvo AB for heavy-duty vehicle applications.

Ricardo also is working on ‘optimised’ spark ignition engines with diesel-like efficiency. Ricardo’s system, Ethanol Boosted Direct Injection, uses a 3.2-litre GM gasoline engine to give the equivalent 660lbft peak torque of GM’s Duramax 6.6-litre diesel. However, the Ricardo engine uses a grey iron block with a special cradle to support the crankshaft. The engine has bespoke aluminium cylinder heads.

The opinions expressed here are those of the author and do not necessarily reflect the positions of Automotive World Ltd.