Delving into the Intermediate Blends Report

Two of the seven authors of U.S. DOE's recent initial report on the effect of midlevel blends on legacy vehicles and small engines discuss the results of the study and future work.
By Ron Kotrba | January 12, 2009
In October, the U.S. DOE released its initial report on midlevel ethanol blends and the effect on legacy, or conventional nonflexible-fuel vehicles, and small engines. It's the first part of a comprehensive investigation into how E15 and E20 will affect emissions, performance and mechanical durability. The report is titled "Effects of Intermediate Ethanol Blends on Legacy Vehicles and Small Non-road Engines, Report 1," and its authors say the study and report were pilot work for what's to come.

The DOE program under which this body of work is being conducted is co-led by the DOE's Office of Energy Efficiency and Renewable Energy (EERE) Biomass Program, and the EERE Vehicle Technologies Program. Technical support is provided by Oak Ridge National Laboratory and the National Renewable Energy Laboratory. The program was initiated by the DOE in the summer of 2007.

This whole effort on behalf of the federal government is to provide information that may be useful in forming the legal means to build-out the blend wall. The volume of renewable fuels required under the renewable fuels standard in the Energy Independence & Security Act, commonly referred to as RFS2, is 36 billion gallons by 2022, much of which is expected to be corn-based and second-generation ethanol. Saturating the national E10 market would require approximately 14 billion gallons, and while the effort to expand the number of E85 vehicles and pumping stations is commendable, few are convinced that E85 will become more than a niche market. Thus, to accommodate the volumes of ethanol required under RFS2, the U.S. EPA must be satisfied with the results from comprehensive testing to determine if any environmental, mechanical or operability issues arise from running legacy vehicles on E15 or E20.

E20 is a new fuel for legacy vehicles. "Under the Clean Air Act, a new fuel like E20 is illegal for use in conventional vehicles, basically guilty until proven innocent," says Brian West, deputy center director and research and development staff member with ORNL and co-author of this initial intermediate ethanol blends report. Like going to trial court where the U.S. EPA is judge and jury, a convincing case must be madeone that satisfies EPA enough to declare the fuel benign with respect to any negative effects on tailpipe emissions, catalyst durability and engine operability and performance.

By and large, the study and subsequent results yielded no great surprises in fuel economy, emissions and catalyst temperatures, according to Keith Knoll, senior NREL engineer and co-author of this report. "We were looking for data and nothing from this jumped out as a big surprise," he says. Knoll adds that this initial study helped identify certain areas of interest for further investigationsuch as how different automaker engine calibrations react to higher blends of ethanol, and in direct relation to that, what long-term impacts higher exhaust temperatures have on catalytic converters and emissions.

Vehicle Results: Points of Concern, Future Study
The vehicle fleet tested in this pilot study consisted of 16 vehicles but testing was completed on 13 of the 16 vehicles. Selection of the makes and models within that fleet was not random, but rather based on a representative sample of late-model vehicles (2000 to 2007) on U.S. roadways in 2007.

Fuel economy decreased relative to the amount of ethanol in the fuel mix. With E20, the average drop in fuel efficiency was 7.7 percent. "Limited evaluations of fuel with as much as 30 percent ethanol were conducted, and the reduction in miles per gallon continued as a linear trend with increasing ethanol content," the report states. A drop in fuel economy was fully expected because ethanol has two-thirds the energy density of gasoline on a volumetric basis thanks to its oxygen content.

Most vehicles run under what's called "closed-loop" operation, where oxygen sensors in the exhaust system send information to the vehicle's computer where it reads the data and adjusts fueling accordingly to get to a stoichiometric fuel/air ratio. However, when vehicles are cold or under high load such as wide-open throttle, they often operate in "open-loop" or power-enrichment mode, often a rich condition where there's more fuel in the fuel/air mixture. "As you add ethanol to the fuel, the engine computer has to add fuel to enrich the mixture to compensate for the oxygen that's in the fuel," West explains. "It goes hand-in-hand with the fuel economy penalty we saw, so with E20 we expected to add 7 [percent] to 8 percent extra fuel mass to compensate for the oxygen that's in the ethanol to maintain stoichiometric combustion under closed-loop conditionsall the cars did that well."

At wide-open throttle, seven of the 13 vehicles tested were found to maintain a consistent although not stoichiometric fuel/air equivalence ratio on E20. A true stoichiometric condition is when 100 percent of both the fuel and air are consumed in combustion, leaving no excess oxygen or unburned fuel in the exhaust stream. All vehicles used adaptive fuel trim during closed-loop operation to maintain stoichiometry. Seven of the vehicles tested in this study applied this adapted fuel trim to open-loop, power-enrichment operation.

The other six vehicles ran leaner during power enrichment on E20 than on E0 gasoline leading to higher exhaust temperatures, which may impact long-term catalyst durability and thus emissions over the vehicles' full life.

Some vehicles are designed to learn the fuel trim necessary for stoichiometry during closed-loop operation and apply that knowledge to open-loop operation. Other vehicles do not do this. West says one of the prevailing opinions as to why some vehicles do apply learned fuel to open-loop operation and some do not is that it takes a lot of engineering man hours to calibrate the controls to accomplish this. "So if automakers don't need to do this, it could potentially be a waste of effort," West says. "If the car is designed for E10 or E0, perhaps they don't need itif they can meet full useful life emissions standards without doing it, then why bother. Some have done it by choice. The ones that don't apply learned fuel at wide-open throttle run hotter, which makes perfect sense. It's combustion chemistry."

Knoll says the automakers use this power enrichment mode, where under high-load conditions the vehicle by design runs richer, in order to protect engine components and the catalyst from higher temperatures that result from high-power conditions. "They enrich the mixture and they are allowed by EPA to do that up to 6 percent beyond lean best torque," Knoll says. "If the [original engine manufacturers] go beyond that, they need to have special discussions with EPA as to why they went furtherin order to protect the engine components and emissions control devices. The question is: Do they apply learned fuel in that power enrichment mode?" Findings of this pilot study determined that about half the cars tested do apply it and the other half do not.

The vehicles that did not apply learned fuel with E20 at wide-open throttle ran leaner and hotter, and catalyst temperatures increased up to 35 degrees Celsius higher than when run on straight E0 gas. "That's probably one of the automakers biggest concerns," West says. Knoll tells EPM one of the big questions remaining is what are the long-term effects on the catalysts? "A small increase in catalyst temperature has a big impact on reactivity," he says.

The next step is an 80-vehicle study to investigate long-term catalyst durability and whether a higher cat temperature has any effect on long-term emissions. "The reason that's a concern is that the manufacturers could be fined if their cars are outside their emissions limits at full life, or they could have very expensive warranty repairsor both," West says.

The report indicates that regulated tailpipe emissions (nitrogen oxide, hydrocarbons and carbon monoxide) remained largely unaffected by the ethanol content in the fuel.

However, increases were observed in formaldehyde and acetaldehyde emissions. Formaldehyde emissions are regulated by EPA but acetaldehyde emissions are not.

Impact on Small Engines
Unlike some on-road vehicles with sophisticated closed-loop operation capability, small engines generally aren't equipped to adjust fuel/air ratio and apply long-term fuel trim.

Thus, when small engines like those found on chain saws or weed eaters are run on intermediate ethanol blends, they tend to run leaner and therefore hotter. "These open-loop engines are commonly air-cooled, and they customarily operate fuel-rich to achieve cooler combustion temperatures for longevity purposes," the report states. "With a fixed fueling calibration, as ethanol content in the fuel increases, combustion becomes leaner, leading to higher combustion temperatures and higher component temperatures, as well as changes in emissions and sometimes idle speed."

Twenty-eight small nonroad engines were tested for this report. "There was certainly concern that the higher ethanol blends might shorten the lives of those small engines," West says. "But it's fair to say these were accelerated aging tests. We put full life hours, for example 125-hours, 300-hours or 500-hours life, on the engines in a short period of time.

Running an engine to its full-life hours over a few months during aging' is not the same as letting it sit in your shed for five years, so there's more work to be done here before small engine makers would accept higher blends of ethanol."

The effect on small engine emissions was fairly expected. Nitrogen oxide (NOx) emissions increased as a direct result of the increased combustion temperatures from running leaner with higher concentrations of oxygen-rich ethanol. Hydrocarbons and carbon monoxide emissions in general went down. In most cases, regulated hydrocarbon plus NOx emissions decreased slightly, but West says, "Hydrocarbons plus NOx didn't change much because of the counteracting relationship between hydrocarbons and NOx."

Additional Information
The Coordinating Research Council, a consortium of automakers, auto engineers and petroleum interests, has also conducted several studies on legacy vehicles with E15 and E20. CRC Report No. 652 concluded that, from the testing of six legacy vehicles, it found no significant effect on fuel type or vapor pressure on drivability. Knoll says as DOE's effort to better characterize intermediate ethanol blends in legacy vehicles continues, he hopes to involve the CRC and its plethora of related studies to definitively pinpoint evaporative and permeation emissions with legacy vehicles. "Permeation emissions are long-term effects, it takes a while for ethanol concentrations in fuel to affect permeation emissions," Knoll says. "It's what's called the hangover effect wherein it takes time to dissipate those effects from greater ethanol concentration in the fuel mix."

It is also important to note this pilot study on intermediate blends used splash-blended fuels as opposed to match-blended fuels. West says "match-blended" means the fuels are carefully blended to try to match vapor pressure and octane levels with like fuels, where hydrocarbon content and fuel speciation are closely monitored. In essence, though, splash-blended fuels were used initially because it was quicker to obtain the fuels, and researchers wanted to get started testing. "Future projects will use match-blended fuels when warranted," West says, while the 80-vehicle long-term catalyst durability program now underway is using splash-blends for expediency and cost. "Comparing fuel A to fuel B at zero test miles or 50,000 test miles, having splash-blends should not affect the results."

The emissions testing protocol was the LA92 or "unified cycle," which is an inventory emissions cycle test used in California and in EPA's EPAct study. "Auto engineers say the LA92 is more representative of how people drive compared with the [Federal Test Procedure]," Knoll says. "And the wide-open throttle protocol was from an earlier program and we modified it slightly with input from CRC."

West and Knoll stress not to read too much into the preliminary results from this pilot study. "Although the results to date are encouraging, this was a small sample, and part of a much larger program," Knoll says. EPM will continue to follow the efforts of this important research. "We'll know a lot more in a year," West says. "Will we know enough? I don't know. That will be up to the EPA to decide."

Ron Kotrba is an Ethanol Producer Magazine senior writer. He can be reached at rkotrba@bbiinternational.com or (701) 738-4942.