These days, more and more research dollars are flowing toward advanced flex-fuel alternatives to diesel engines in attempts to find drivetrains with similar power and fuel economy ratings but smaller displacements, lower costs and cleaner emissions.
Flex-fuel engines are designed to run on gasoline, ethanol or any combination of the two, such as E85, which is 15 percent gasoline and 85 percent ethanol. Several companies are working on variations.
Last year, when diesel fuel carried a 20 percent price premium over regular gasoline – all but eliminating its 20 percent to 25 percent advantage in operating efficiency over gas — we looked at Ford’s alt engine research efforts with a group of MIT scientists. The two paired to develop a radical new “ethanol boost” twin-fuel turbocharged engine, code-named "Bobcat," that would variably blend gasoline and ethanol on demand to realize diesel-like performance. With such technology, a 5.0-liter engine could potentially produce 500 horsepower and 750 pounds-feet of torque.
Contract engineering firm Ricardo Inc. is the latest company to announce a research breakthrough that’s said to optimize spark ignition engine performance to diesel-like levels of efficiency. Ricardo calls its new engine technology Ethanol Boosted Direct Injection. Its goal is similar or better fuel economy, with the same peak of 660 pounds-feet of torque, found in today’s GM 6.6-liter Duramax V-8 diesel, but from a 3.2-liter flex-fuel V-6.
“We want to create an engine that’s competitive with diesel but without diesel’s substantial costs,” said Rod Beazley, product group director for gasoline at Ricardo. “The engine [we’ve developed] has a much cheaper fuel system and much simpler [exhaust] after-treatment. We also want to take advantage of the positive properties that current flex-fuel engines don’t do.”
It’s taken spark ignition technology decades to catch up to diesel. Diesel is so efficient and powerful because it contains more energy per gallon of fuel than gasoline, and it combusts using compression ignition, which is the tremendous frictional heat generated from the extreme compression of air in the cylinder. Such high temperatures and pressures produce the large amounts of torque that trailer-towers love, but they inhibit thorough mixing of the fuel-air charge in the cylinder, which leads to incomplete fuel burns that produce soot and other pollutants. Conventional gas and flex-fuel engines use spark ignition to detonate the fuel-air mix when the charge is optimally distributed throughout the cylinder chamber. That has two results: The mix burns cleaner, and it burns with less relative power than diesel
Ethanol, however, has a higher octane and heat-of-vaporization point than gasoline, meaning it combusts at a higher temperature and with greater force (higher compression) than gasoline, while also having a greater capacity to cool the fuel/air mix in the cylinder before combustion. This allows a larger charge to be drawn into the cylinder before ignition. This inherent efficiency is what enables a smaller-displacement engine to perform with the same power as a bigger motor if the engine is built to take advantage of it.
Ricardo’s EBDI engine adaptively changes its combustion cycle to match fuel blend and it's built to withstand high compression ratios. This, together with the use of direct injection and turbochargers, makes it almost as efficient as a diesel engine, Ricardo says.
Ricardo has been working on the EBDI engine concept since November 2007 with a number of partner companies.
General Motors supplied Ricardo with its all-new 3.0-liter gasoline direct-injection V-6 as the test engine. The 3.0-liter engine is expected to debut in the 2010 Cadillac SRX and 2010 Chevrolet Equinox crossovers, with power ratings estimated to be 260 hp and 221 pounds-feet of torque.
“The 3.0-liter engine has been highly modified,” said Luke Cruff, chief engineer for the EBDI program at Ricardo. “You might still recognize it from the outside, but we converted it to 3.2 liters so we could get 900 newton-meters [663 pounds-feet] of torque from it. We did this by increasing the [cylinder] stroke plus many other changes. We’re dealing with diesel levels of cylinder pressure in a gasoline-engine packaging environment.”
Other partners collaborating with Ricardo include: Behr (coolers), Bosch (fuel injection system), Delphi (continuously variable valve lift system), GW Castings (engine casting) and Honeywell (turbocharging system).
“Each of our collaborative partners have hit some point during the development of the engine that technically stretches them,” Cruff said. “We’re putting every innovation on the engine to try to find the ultimate fuel economy potential.”
The goal is to place the experimental engine in a GMC Sierra 3500 heavy-duty dual-rear-wheel pickup by the third quarter of 2009.
“We want to have the same vehicle performance, trailer-towing capacity and improved fuel economy in certain drive cycles as the current Duramax 6.6-liter provides today,” Beazley said.
A properly equipped Sierra HD with that configuration can tow up to 16,500 pounds with a fifth-wheel hitch.
The biggest challenge facing Ricardo is not just to achieve the same torque peak as the Duramax, but also to generate lots of torque throughout the engine’s rpm power band while returning similar or better fuel economy because of its small displacement.
“Low-speed torque is important,” Cruff said. “At 1,600 rpm, we’re at 700 nm [516 pounds-feet], at 2,000 rpm we’re at 800 nm [590 pounds-feet], and peak torque is at 3,000 rpm. We have [at least] 70 percent of our max torque from 1,600 rpm all the way up to 5,000 rpm. We’re not going to get market acceptance with a powertrain that doesn’t have the torque capacity that it needs. The challenge then becomes to try to get the [torque] performance out of an engine that’s small enough to still return great fuel-economy numbers. We call this concept extreme downsizing because we’re planning to put a 3.2-liter V-6 spark-ignited engine in a dually one-ton pickup. People kind of look at you funny at first when you tell them about it.”
If Ricardo’s EBDI power expectations prove correct in real-world testing, those funny looks could give way to serious consideration by future truck buyers.