Thirsty for More

Ethanol’s high octane rating may be the ticket for meeting escalating fuel efficiency standards in engines
By Kris Bevill | February 22, 2012

In November, the U.S. EPA and the National Highway Traffic Safety Administration jointly announced the next step in the Obama administration’s plan to improve vehicle fuel efficiency and significantly reduce emissions over the next 15 years. The proposed Corporate Average Fuel Economy standards and greenhouse gas (GHG) emissions standards unveiled by the agencies, which reportedly had the support of major automakers and environmental groups, would steadily increase fuel efficiency requirements for light-duty truck and passenger cars from an average of 34 miles per gallon (mpg) in 2016 to more than 50 mpg in 2025 and reduce allowable emissions to 163 grams of CO2 per mile in model year 2025 vehicles.

To meet the more stringent fuel standards, the NHTSA and the EPA said they believe engineers will continue to make advancements in vehicle technologies, including engines and transmissions, but also in areas such as vehicle weight reduction, aerodynamics and air conditioners. “NHTSA’s and EPA’s technology assessment indicates there is a wide range of technologies available for manufacturers to consider in improving fuel economy and reducing GHG emissions,” the NHTSA stated. “The proposals allow for long-term planning by manufacturers and suppliers for the continued development and deployment across their fleets of fuel-saving and emissions-reducing technologies.”

Automakers have already begun to roll out engine technologies that can be used to both improve efficiency and reduce emissions. General Motors Co.’s Ecotec engine and Ford Motor Co.’s Ecoboost engine, for example, feature turbocharging and direct fuel injection, which enable the smaller engines to consume less fuel than their predecessors while still offering similar performance.

This type of engine improvement is a definite step in the right direction, but will it be enough to meet the stringent requirements proposed for 2025? With this in mind, ethanol industry stakeholders recently funded two separate studies to examine ethanol’s true potential as a fuel and how it might be used to assist automakers in meeting national fuel efficiency and emissions reductions goals.

Technology Boosts
Recently, the Renewable Fuels Association contracted automotive engineering group Ricardo Inc. to evaluate engine technologies and to explore the potential role biofuels has in these changes, focusing specifically on how higher-octane fuels can contribute to increased efficiency in newly designed engines. “We saw the converging vehicle-specific regulations as an issue that is not simply solvable through new vehicle engineering,” says Kristy Moore, the RFA’s vice president of technical services. “We believe these regulations will force a change to the fuel as well as changes to the vehicles.” Ricardo’s independent testing reinforces that opinion, showing that higher octane fuels can play a valuable role in improving fuel efficiency and, as a direct side effect, also reducing emissions.

To complete the study, Ricardo researchers first plotted what they believe is a roadmap of engine technology improvements for the next 15 years. They determined that while electric vehicles will continue to be a popular concept, nearly all of the vehicles in the U.S. in 2025 will still be powered by some type of liquid fuel-fed engine. “They [electric vehicles] may be very high profile, but in terms of actual number of new vehicles sold, it’s going to be pretty small,” says John Kasab, chief engineer and

Ricardo and author of the RFA’s report. “The majority of vehicles are still going to have internal combustion engines and almost certainly have gasoline, spark-ignited engines in them. They may be in hybrids, they may be in advanced conventional vehicles, but people are still going to go to a fueling station, they’re still going to have to put liquid fuel in the tank.”

Ricardo further found that while some of the engine technologies being developed by automakers are neutrally impacted by higher-octane fuel usage, others—such as direct injection and turbocharging—readily lend themselves to the use of fuels with octane ratings greater than 87, which is the standard rating for unleaded gasoline today. This is due to several factors. Boosted engines such as the Ecoboost or Ecotec are designed to allow for increased air pressure to be pumped into the cylinder. This improves the efficiency of the engine but it also makes the engine thirsty, essentially, for higher octane, Kasab says, because while higher compression ratios improve fuel performance, they can also cause the engine to reach its knock limit (the point at which uncontrolled combustion occurs) more often. Higher octane fuels can push out the knock limit of engines, allowing them to run at higher speeds and higher loads before knock occurs. Ethanol specifically offers another benefit in that it has a higher latent heat of vaporization, meaning that the fuel can absorb more heat from the combustion, therefore the engine runs cooler than it would when using other fuels. Thus the compression ratio of an engine can be increased to compensate for the difference in combustion temperature and allow the engine to run at the original temperature.

Rod Beazley, Ricardo’s project director, engines, says his group’s research proves that to meet future fuel efficiency and emissions requirements, vehicles will likely require a combination of engine technology improvements and higher-octane fuels, whether it be ethanol-blended fuel or another high-octane fuel. “There is some low-hanging fruit in terms of fuel economy because for every unit increase in compression ratio, there’s a 3 percent fuel economy benefit,” he says. “And to increase your fuel compression, you need a higher-octane fuel.” This presents an interesting quandary for automakers, however, because while they are required to meet national fuel standards, they must also continue to design engines to operate on the fuels available to consumers. And high-octane fuels are not currently widely demanded on the market. “They can’t develop an engine for a higher-octane fuel if it’s not available in the field,” Beazley adds.

The Optimum Number
Ricardo did not attempt to determine which ethanol blend would be ideal for use in technologically advanced engines, but another year-long test recently completed by powertrain systems developer AVL Powertrain Engineering and funded by ICM Inc. and the National Corn Growers Association came a little closer to identifying that optimum number. For this research, AVL engineers added various ethanol percentages to base fuels and tested them in three fuel delivery systems—the port injection system commonly used in vehicles today, a direct injection system and a system that simulated testing procedures for current octane test measurements—to accurately evaluate how ethanol performs at specific blends. ICM’s research data also showed that higher-octane fuels, such as ethanol, can be beneficial in meeting fuel efficiency requirements, but further concluded that midlevel ethanol blends offer more value than has previously been estimated, particularly when used in direct injection fuel delivery systems.

“The findings of this study further support our existing understanding of ethanol in that they [the ethanol industry] demonstrate its inherent ability to meet our nation’s need for an affordable, sustainable domestically produced fuel source,” NCGA Ethanol Committee Chairman Chad Willis said in a statement. “NCGA, together with the states that also contributed, funds studies such as this to add to the data on biofuel. We do this not only as proponents of corn farmers, but also as citizens concerned with finding the innovative solutions that will help our nation improve the economy, environment and national security.”

ICM’s full report will be released in April at the annual Society of Automotive Engineering conference, but early details indicate that E30 may be the so-called sweet spot for octane performance. A summary released by ICM noted that it will be “critically important” for vehicles to operate at higher loads to obtain higher efficiencies and meet future fuel standards. The data supports that intermediate blends such as E30 can play an important role in meeting those standards, according to the summary.

“This new testing data has proven to be a great tool to illustrate how much performance can be achieved by simply adding ethanol to gasoline,” says Steve Vander Griend, head of ICM’s research and development of ethanol engines. “We are seeing a significantly higher value for ethanol and use of intermediate blends to support the changing needs of the automakers and the new fuel efficiency standards that have been issued.”

Vander Griend says ICM is already working on the second phase of testing, which will further demonstrate the value of high-octane ethanol in new engines as well as focus more attention on emissions aspects and validate actual mileage per gallon. He expects that phase of research to be complete by the end of March. Moore says the RFA will also continue to fund research dedicated to identifying optimal ethanol blends.

So far, no study has attempted to determine exactly which octane rating would be the preferred step up for fuel-efficient engines. It is generally believed this is a question best left for the original equipment manufacturers (OEMs) to answer. In a statement provided to EPM, GM says it supports the need for higher-octane fuels in concert with other manufacturers through the Alliance of Automobile Manufacturers, a group that represents 80 percent of new car sales in the U.S. and includes members such as Ford, GM, BMW, Mercedes-Benz and Toyota. GM further stated that it supports higher-octane fuels, including ethanol, because of their favorable impact on fuel economy.

“Gasoline-ethanol blend fuels can be formulated to have octane characteristics that are very desirable for displacement-reduced or turbo-downsized engines,” says Mark Maher, GM’s executive director of powertrain vehicle integration. “Additionally, these blends have combustion chamber cooling characteristics that, when combined with direct injection technology, are helpful to enable marginally higher compression ratios, which improves engine thermal efficiency. The ability to capitalize on this opportunity in production vehicles depends upon alignment of certification fuels with in-use field fuels as well as with stringent emission and fuel economy regulations.”

In testimony delivered to the EPA earlier this year at a hearing on the proposed CAFE and emissions standards, Mitch Bainwol, president and CEO of the Alliance of Automobile Manufacturers, said it will ultimately be the consumers who decide if more fuel efficient vehicles are worth the additional costs. Future fuel prices are difficult to predict, he said, and fuel economy often ranks low on the consumer’s list of priorities when selecting a new vehicle. He recommended that the agency seek out peer reviews to determine whether the costs of advanced engine technologies are declining as expected, evaluate consumer response to fuel prices and determine whether liquid fuels can support the fuel-efficient technologies being introduced by engine designers. “Ultimately, consumers should decide what best meets their needs,” Bainwol said in his testimony. “Vehicles that run on gasoline, diesel, biofuels, electricity, hydrogen and natural gas will all play a role in improving fuel efficiency and reducing greenhouse gas emissions.” 

Author: Kris Bevill
Associate Editor, Ethanol Producer Magazine
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