A team at the International Council on Clean Transportation (ICCT) has released a paper assessing technical barriers to the use of higher blends of ethanol. Broadly, the study by Stephanie Searle, Francisco Posada Sanchez, Chris Malins, and John German concludes that (a) technical barriers do not prevent the use of higher blends of ethanol, and (b) slow uptake of blends such as E15 and E85 is due to other factors, including high cost, legal and warranty issues, and consumer awareness and acceptance.
The paper was commissioned by the Bipartisan Policy Center (BPC) as part of a yearlong effort aimed at fostering “constructive dialogue and action” on reforming the Renewable Fuel Standard (RFS2). BPC is convening a diverse RFS advisory group to discuss opportunities for reform, hosting public workshops to solicit broad input, and ultimately publishing viable policy options based, in part, on the advisory group’s deliberations. The ICCT paper is one of five background papers to be released on different aspects of the problem. The others are:
Petroleum and Renewable Fuels Supply Chain, Stillwater Associates LLC
Inventory of Federal Regulations Affecting Biofuels other than the Renewable Fuel Standard, Van Ness Feldman
The Environmental Protection Agency’s Authority to Amend the Renewable Fuel Standard, Sutherland Asbill & Brennan LLP
The Environmental Protection Agency’s Authority to Amend the Renewable Fuel Standard, Bracewell & Giuliani LLP
The non-profit BPC was founded in 2007 by former Senate Majority Leaders Howard Baker, Tom Daschle, Bob Dole and George Mitchell to be an organization focused on driving principled solutions through analysis, negotiation and dialogue.
The ICCT ethanol paper. Pressure on the RFS2 has increased as statutory mandated volumes of biofuel exceed the “blendwall” of 10% ethanol in gasoline. With stagnating demand for gasoline due to rising fuel economy in the nation’s fleet and other factors, further increases to US ethanol consumption would require the use of higher blends of ethanol, either in conventional vehicles or in flex-fuel vehicles (FFVs) designed to tolerate blends of up to 85% ethanol (E85).
The ICCT team only examined technical barriers to the consumption of blends of ethanol above 10%: the effect of higher ethanol blends on passenger vehicles and smaller engines and the impact on infrastructure. The study does not address non-technical barriers to the use of higher blends (e.g., car warranties, cost, food-vs-fuels arguments).
Primary technical concerns with using intermediate-level blends of ethanol in the vehicle fleet include:
Fuel economy. Ethanol has about one-third lower energy density than gasoline; accordingly, cars drive fewer miles per gallon when operating on ethanol blends compared with unblended gasoline. Fuel tanks could be made larger in new vehicles partially to address this problem, but there is no way directly to offset the lower energy density of ethanol compared with gasoline.
Tailpipe emissions of CO2 from the combustion of ethanol and gasoline are similar on an energy basis—i.e., using ethanol does not affect a vehicle’s tailpipe CO2 emissions per mile driven.
EPA has investigated the potential that cars running on E30 could be more efficient on an energy basis if their engines are designed for that fuel mix. Higher ethanol blending raises the octane rating, and provides much higher evaporative cooling of the intake charge. These effects can allow the engine to operate more efficiently by enabling an increased compression ratio and higher levels of turbocharger boost with smaller engines. Operators of such cars would have to exercise caution as misfueling on lower ethanol blends could lead to engine knocking or greatly reduced performance. (Earlier post.)
Effects on emissions. Theoretically, cars operating on higher ethanol blends than the design point could emit greater concentrations of pollutants in exhaust gas. Under normal operation, the air/fuel ratio is carefully controlled so that the fuel burns optimally. In the cylinder where combustion takes place, the fuel evaporates before it is burned, and this evaporation helps cool off the air/fuel mixture and exhaust gas.
Ethanol contains oxygen in its molecular structure (while gasoline does not), and so requires less air for combustion per unit fuel—i.e., the optimal air/fuel ratio for ethanol blends is lower than for pure gasoline. If the same air/fuel ratio for gasoline is used for ethanol blends, there will be too much air for the amount of fuel in the cylinder—a condition called “enleanment.” In this situation, there is not enough fuel evaporation to cool the mixture, and the temperature of the exhaust gas rises. This in turn raises temperatures inside the catalytic converter, and over time, this can accelerate catalyst deterioration. In addition, excess oxygen in the exhaust can inhibit proper functioning of the catalytic converter and lead to increased emissions of NOx.
Modern cars have the ability to prevent enleanment by adjusting the air/fuel ratio depending on the ethanol content of the fuel; an oxygen sensor on the exhaust line in between the engine and the catalytic converter. If the sensor detects elevated oxygen in the exhaust, it signals the fuel injector to decrease the air/fuel ratio. This keeps the catalytic converter operating at the right air/fuel conditions. Vehicle systems with an oxygen sensor are referred to as “closed-loop,” whereas those without control over the air/fuel ratio are referred to as “open-loop” systems.
Studies have found slightly higher emissions of NOx and lower emissions of carbon monoxide (CO) and unburned hydrocarbons in vehicles operating on E15 or E20 compared with those using E0.
Ethanol blends are associated with higher emissions of the toxic substances formaldehyde and acetaldehyde, but they produce lower levels of benzene and the carcinogen 1,3- butadiene. Using California’s relative toxicity factors, one study calculated that the overall toxicity of emissions from ethanol blends was lower than for gasoline. All ethanol blends can also be expected to result in lower concentrations of PM in the exhaust gas than gasoline.
Another emissions-related concern is that that higher blends of ethanol could increase evaporative emissions because ethanol blends have a higher vapor pressure than gasoline at low to mid concentrations. For example, the CRC reported higher evaporative emissions in fuel systems with 5.7 percent ethanol compared with pure gasoline.
Corrosion of metals and other materials in engines and fuel systems. Ethanol is more corrosive than gasoline because it contains more dissolved oxygen, and this has led to concerns that ethanol blends above E10 could damage materials in car engines and fuel systems. Ethanol damage to materials could potentially lead to leaks or fuel filter blockage, especially in older vehicles. Partly for these reasons, most car warranties in the United States only cover usage of E0–E10.
However, metals used in engines and other vehicle parts have generally not been found to be susceptible to corrosion by low- to mid-blends of ethanol. Ethanol may affect elastomeric components (elastic polymers, or rubber- and plastic- like materials) in vehicles by changing their dimensions and by reacting with the material. However, an NREL review found that elastomer properties changed when exposed to E10 versus E0, but that there was no difference in properties when comparing E15 with E10. As with metals, studies on legacy vehicles (model years 1994–2001) did not observe any degradation of elastomers, polymers, or any other materials with E15 or E20.
Phase separation of water and ethanol from gasoline. Gasoline typically contains small amounts of water contamination, but since gasoline and water don’t mix with each other, the water stays at the bottom of the fuel tank. Ethanol, on the other hand, readily mixes with both gasoline and water, and allows water to become incorporated in the fuel blend.
If water contamination is high enough, the ethanol/water mix will separate from the gasoline, forming a layer at the bottom of the tank—“phase separation.” The fuel line is at the bottom of the tank, and so a high concentration of water/ethanol may be drawn out and cause problems starting the car. However, phase separation only occurs at relatively high concentrations of water and generally is not a major concern. The risk of phase separation can be reduced by the addition of solubility improvers.
The ICCT study also examined the impact on small engines and off-road applications, as well as impact on the fueling infrastructure.
Next, the report explores the amount of time needed to make necessary technological changes to vehicles and infrastructure in order to consume higher blends of ethanol.
The major concerns with using higher blends of ethanol in vehicles are increased emissions, material incompatibility, and phase separation of water and ethanol from gasoline. The last it limited in general and could be addressed by adding solubility improvers to fuel.
Cars manufactured in 2001 and later—approximately 50% of the US car parc—have the proper controls and materials to handle E15 and likely E20 and do not need any modification. By 2022, virtually all gasoline-fueled cars driven in the United States will be capable of operating on E15.
Additionally, many cars manufactured today are FFVs, and other cars could relatively easily be retrofitted to be flex-fuel. Technically, the US fleet could be technologically ready to consume significant amounts of E15 and E85 within a few years.
Implementation. The ICCT report then compares the rate at which ethanol blends could technically be scaled up against three projections of RFS2 implementation and two scenarios for the consumption of ethanol to 2022, considering only technical barriers:
implementation of the RFS2 targets for 2014–2022 as originally set in the statute;
revised implementation of the RFS2 with greatly reduced cellulosic volumes, following EPA’s annual volume rulemakings for 2010–2013;
immediate repeal of the RFS2;
E15 in 2022; and
25% E85 in 2022.
…scaling up E15 to 100 percent market penetration would be approximately sufficient to satisfy the “revised RFS2” scenario after 2015. Scaling up both E15 and E85 (the latter to 25 percent penetration) would be sufficient even to allow fulfillment of the “original RFS2” projection from 2017 onward, and would be much more than enough to allow the “revised RFS2” scenario to be fulfilled starting in 2015. Although both of these scenarios for the consumption of ethanol through E15 and E85 are technically possible given today’s availability of vehicle and materials technology, the “E15 in 2022” scenario would require fewer modifications to infrastructure. The E85 scenario would require retrofits and potentially replacement of pipelines, storage tanks, and dispensers.
Current trends in car sales suggest the US vehicle fleet will be technologically ready to consume the amounts of ethanol in these two scenarios. This clearly indicates that technical capacity does not stand in the way of being able to consume adequate ethanol volumes to allow compliance with the RFS2 in the medium timeframe. On the other hand, our scenarios show that, even without considering non-technical barriers, it may be difficult to comply with the RFS2 in 2014–2016, because the necessary infrastructure is not yet in place.—Searle et al.
Stephanie Searle, Francisco Posada Sanchez, Chris Malins, and John German (2014) Technical barriers to the consumption of higher blends of ethanol