Boosting an engine with ethanol has a longer history than you might think. Here's how turbocharging, direct injection, and ethanol could work together.
Thanks to the adoption of direct fuel injection, teaming gas and ethanol has the potential to beat diesel efficiency.
We can hear your groans already: Our federal government's effort to curb oil imports by lacing gasoline with ethanol has been a boon to American farmers but a bust to the driving public. The problem is simple economics—pumping E85 (85-percent ethanol and 15-percent gasoline) into today's flex-fuel cars costs more per mile than fueling the same car with regular gas. We're suffering from ethanol's detriments without exploiting its advantages.
Ethanol's balance sheet has been well understood for decades. Because ethanol's energy density is roughly 66 percent that of gasoline, mpg suffers when ethanol is used as a straight substitute. On the opposite side of the ledger, ethanol has an octane rating of 100, versus 85 to 100 for gasoline, enabling much higher compression ratios. (Unleaded, 100-octane racing gas is expensive and not widely distributed. Readily available premium gas tops out at 94 octane.) And when ethanol changes from liquid to gas on the way to combustion, it absorbs 2.6 times more heat than gasoline, a highly beneficial cooling effect. So how do we take advantage of those attributes to optimize ethanol's role in modern transportation? The history books are a good place to start.
During World War II, BMW and Daimler-Benz sprayed methanol and water mixtures into their supercharged aircraft engines to forestall detonation (premature ignition of the fuel-air charge). In the U.S., a postwar GM applied similar research in its 1951 LeSabre dream car, which was powered by a supercharged V-8 capable of running on gas or methanol. That paved the way for the 1962 Oldsmobile F-85 Jetfire, the world's first turbocharged production car, which used "Turbo-Rocket Fluid"—a mix of water, methanol, and rust inhibitor—to skirt detonation with a then-ambitious 10.25:1 compression ratio and 5.0 psi of boost.
Today's racers use all manner of fluids—water, alcohol, nitromethane, lead substitutes, and nitrous oxide—in pursuit of power. There's also a government-backed experiment at Chrysler aimed at running both gasoline and diesel fuels through the same engine. But the most sensible approach for the public at large is to use technology now in hand to achieve significant mpg gains. The tech? Gasoline, E85, and direct fuel injection.
British-based Ricardo and Ethanol Boosting Systems (EBS) of Cambridge, Massachusetts, both have E85-fueled engines under test that deliver diesel efficiency—at least 30-percent better than a typical gas engine—without the need for cumbersome, ultra-high-pressure fuel-injection and exhaust-treatment equipment.
Both firms propose aggressive turbocharging, a 12.0:1 or higher compression ratio, and about half the normal piston displacement. Ricardo uses an octane sensor, variable valve lift, and variations in valve and ignition timing to take maximum advantage of any ethanol pumped into the fuel tank. EBS adds a second complete fuel system that enables an engine to run on port-injected gas during cruising and direct-injected E85 only during full-load conditions to spare its consumption.
Heavy-duty pickups are the first candidates for this technology. Both EBS and Ricardo pitch their ethanol-based systems as diesel fighters capable of delivering 600 or more pound-feet of torque at low rpm from a 3.0-liter engine. Assuming that manufacturers agree with these ethanol boosters, the dual-fuel strategy could be handy for meeting the 35.5-mpg CAFE standard for 2016. By then, four-cylinder performance cars will be commonplace, and they'll definitely be thirsty for all the Turbo-Rocket Fluid they can get.
Drinking in the '60s
As noted, the 1962 Oldsmobile F-85 Jetfire's V-8 tried this whole multifuel thing a while back. The turbocharged 3.5-liter engine, eating five pounds of boost, made 215 horsepower and 300 pound-feet of torque. If the reservoir of "Turbo-Rocket Fluid" ran out, a mechanical system would automatically reduce the amount of boost to avoid detonation. In our test of a 1963 F-85 Jetfire, we recorded a 0-to-60 time of 8.5 seconds, with the quarter-mile falling in 16.8 seconds. The system proved problematic, and over two years GM put fewer than 10,000 of these engines on the road.
Source: Car and Driver
