E85 in standard engines

For more specific details of E85 fuel and other ethanol blends, and its compatibility with standard engines, see Common ethanol fuel mixtures and E85.

The use of E85 in standard gasoline engines requires engine and fuel system adaptation, as the use of ethanol blends in conventional gasoline vehicles is restricted to low mixtures or for specially designed flexible-fuel vehicles, because ethanol requires a different air/fuel ratio than conventional gasoline and can be corrosive, degrading some of the materials in the engine and fuel system in older vehicles. Tuning the AFR along with adjusting the timing and compression ratio as compared to a gasoline engine is also desirable in order to take advantage of ethanol’s higher octane rating, thus allowing an improvement in performance and fuel efficiency and a reduction of tailpipe emissions. Flexible fuel vehicles (FFV) in North America and Europe are designed to run on E85. Although standard engines can be adapted to run on E85 there are some shortcomings.

Experimental

E85 has an octane rating of 105 AKI, which is higher than typical commercial gasoline mixtures (octane ratings of 85 to 98 AKI); because of its higher octane it burns more efficiently and more cleanly (due to its oxygen content), significantly reducing particulates and NOx emissions. E85 contains less energy per volume as compared to gasoline. Although E85 contains only 72% of the energy on a gallon-for-gallon basis compared to gasoline, experimenters have seen slightly better than the 28% this difference in energy content implies. For example, recent tests by the National Renewable Energy Lab on fleet vehicles owned by the state of Ohio showed about a 25% reduction in mpg (see table on pg 5) comparing E85 operation to reformulated gasoline in the same flexible fuel vehicle (FFV). Results compared against a gasoline-only vehicle were essentially the same, about a 25% reduction in volumetric fuel economy with E85.

Benefits of E85

The main attractions of burning E85, of course, are the common benefits of renewable energy sources, such as increased economic benefits for rural populations, less reliance on foreign energy that keeps more fuel dollars in the domestic economy, with further research into increasing production efficiency, less carbon emissions per unit as compared to conventional fossil fuels.

Fuel-injection engines

Modern cars (i.e., most cars built after 1985) have fuel-injection engines with oxygen sensors that will attempt to adjust the air-fuel mixture, but the oxygen sensor only changes the air to fuel ratio at idle, and at light cruising speeds. Since the computer can not add more fuel without the input from the oxygen sensor at high loads, there will be significant power losses in modern cars.

Problems

Operating fuel-injected non-FFVs on more than 50% ethanol will generally cause the Malfunction Indicator Lamp (MIL) to illuminate, indicating that the electronic control unit (ECU) believes that it can no longer maintain closed-loop control of the internal combustion process not due to the presence of more oxygen in E85, but rather the fact that E85 has less carbon per volume, thus requiring more than the injectors can deliver, than gasoline. Once the MIL illuminates, adding more ethanol to the fuel tank becomes rather inefficient. For example, running 90% ethanol in a non-FFV (Flexible Fuel Vehicle) will reduce fuel economy by 33% or more relative to what would be achieved running 100% gasoline. Even more importantly, continuing to operate the non-FFV with the Malfunction Indicator Lamp (MIL) illuminated may also cause damage to the catalytic converter as well as to the engine pistons if allowed to persist. To run a non-FFV with amounts of ethanol high enough to cause the MIL to illuminate risks severe damage to the vehicle, that may outweigh any economic benefit of E85.

Under stoichiometric combustion conditions, ideal combustion occurs for burning pure gasoline as well as for various mixes of gasoline and ethanol (at least until the MIL illuminates in the non-FFV) such that there is no significant amount of uncombined oxygen or unburned fuel being emitted in the exhaust. This means that no change in the exhaust manifold oxygen sensor is required for either FFVs or non-FFVs when burning higher percentages of ethanol. This also means that the catalytic converter on the non-FFV burning ethanol mixed with gasoline is not being stressed by the presence of too much oxygen in the exhaust, which would otherwise reduce catalytic converter operating life.

Nonetheless, even when the MIL does not illuminate on the non-FFV burning an ethanol-gasoline mixture, proper catalytic operation of the catalytic converter for a non-FFV burning higher percentages of ethanol may not be achieved as soon as necessary to prevent the emission of some pollution products resulting from burning the gasoline contained in the mixture, especially upon initial cold engine start. This is because the catalytic converter needs to rise to an internal temperature of approximately 300 °C before it can 'fire off' and commence its intended catalytic function operation. When burning large concentrations of ethanol in a non-FFV, the cooler burning characteristics of ethanol fuel than gasoline fuel may delay reaching the 'fire-off' temperature in a non-FFV as quickly as when burning gasoline. Any additional pollution, however, is only going to be emitted for a very short distance when burning E85 in a non-FFV, as the catalytic converter will nonetheless still 'fire off' quite quickly and commence catalytic operation shortly. It is not known whether the small amount of pollution emitted prior to catalytic converter 'fire off' may actually be reduced even during the cold startup phase, as well as once catalytic operation commences, when burning E85 in a non-FFV. Likewise, even once the catalytic converter 'fires off', operation with the MIL illuminated will still result in excess amounts of nitrogen oxides being released, greater than when operating the engine on gasoline. The solution is simply to add gasoline, and extinguish the Malfunction Indicator Lamp (MIL), at which time exhaust pollutants will return to within normal limits.

For non-FFVs burning E85 once the MIL illuminates, it is the lessened amount of fuel injection than what is needed that causes the air fuel mixture to become too lean; that is, there is not enough fuel being injected into the combustion process, with the result that the oxygen content in the exhaust rises out of limits, and perfect (i.e., stoichiometric) combustion is lost if the percentage of ethanol in the fuel tank becomes too high. It is the loss of near-stoichiometric combustion that causes the excessive loss of fuel economy in non-FFVs burning too high a percentage of ethanol versus gasoline in their fuel mix.

Turbocharged engines

E85 gives particularly good results in turbocharged cars due to its high octane. It allows the ECU to run more favorable ignition timing and leaner fuel mixtures than are possible on normal premium gasoline. Users who have experimented with converting OBDII (i.e., On-Board Diagnostic System 2, that is for 1996 model year and later) turbocharged cars to run on E85 have had very good results. Experiments indicate that most OBDII-specification turbocharged cars can run up to approximately 39% E85 (33% ethanol) with no MILs or other problems. (In contrast, most OBDII specification fuel-injected non-turbocharged cars and light trucks are more forgiving and can usually operate well with in excess of 50% E85 (42% ethanol) prior to having MILs occur.) Fuel system compatibility issues have not been reported for any OBDII cars or light trucks running on high ethanol mixes of E85 and gasoline for periods of time exceeding two years. (This is likely to be the outcome justifiably expected of the normal conservative automotive engineer's predisposition not to design a fuel system merely resistant to ethanol in E10, or 10% percentages, but instead to select materials for the fuel system that are nearly impervious to ethanol.)

Fuel economy does not drop as much as might be expected in turbocharged engines based on the specific energy content of E85 compared to gasoline, in contrast to the previously-reported reduction of 23.7% reduction in a 60:40 blend of gasoline to E85 for one non-turbocharged, fuel-injected, non-FFV. The reason for this non-intuitive difference is that the turbocharged engine seems especially well-suited for operation on E85, for it in effect has a variable compression ratio capability, which is exactly what is needed to accommodate varying ethanol and gasoline ratios that occur in practice in an FFV. At light load cruise, the turbocharged engine operates as a low compression engine. Under high load and high manifold boost pressures, such as accelerating to pass or merge onto a highway, it makes full use of the higher octane of E85. It appears that due to the better ignition timing and better engine performance on a fuel of 100 octane, the driver spends less time at high throttle openings, and can cruise in a higher gear and at lower throttle openings than is possible on 100% premium gasoline. In daily commute driving, mostly highway, 100% E85 in a turbocharged car can hit fuel mileages of over 90% of the normal gasoline fuel economy. Tests indicate approximately a 5%-20%increase in engine performance is possible by switching to E85 fuel in high performance cars.

Cold starting

Experimenters who have made conversions to 100% E85 report that cold start problems at very cold temperatures can easily be avoided through adding 1 - 2 gallons of gasoline to the E85 in the tank, prior to the arrival of the cold weather.

Another technique employed is the use of an external gasoline tank attached to an electronic device with a temperature sensor, such as the 1hourflex 1hourflex system.

Ignition timing

No significant ignition timing changes are required for a gasoline engine running on E85.

Risks

Corrosion

E85 can cause damage, since prolonged exposure to high concentrations of ethanol may corrode metal and rubber parts in older engines (pre-1985) designed primarily for gasoline. The hydroxyl group on the ethanol molecule is an extremely weak acid, but it can enhance corrosion for some natural materials. For post-1985 fuel-injected engines, all the components are already designed to accommodate E10 (10% ethanol) blends through the elimination of exposed magnesium and aluminum metals and natural rubber and cork gasketed parts. Hence, there is a greater degree of flexibility in just how much more ethanol may be added without causing ethanol-induced damage, varying by automobile manufacturer. Anhydrous ethanol in the absence of direct exposure to alkali metals and bases is non-corrosive; it is only when water is mixed with the ethanol that the mixture becomes corrosive to some metals. Hence, there is no appreciable difference in the corrosive properties between E10 and a 50:50 blend of E10 gasoline and E85 (47.5% ethanol), provided there is no water present, and the engine was designed to accommodate E10. Nonetheless, operation with more than 10% ethanol has never been recommended by car manufacturers in non-FFVs. Operation on up to 20% ethanol is generally considered safe for all post-1988 cars and trucks.

Water contamination

Although water phase separation can be a significant problem in ethanol-blended gasoline fuels such as E10, contamination by small amounts of water does not lead to phase separation in E85 fuel. The fraction of water required to induce phase separation is higher than 20% (by weight).

Air/Fuel mixture problems

Running a non-FFV with a high percentage of ethanol will cause the air fuel mixture to be leaner than normal in carbureted or open loop fuel injection engines, and cause closed loop fuel injection systems to adjust for the increase in oxygen content of the fuel mixture. A lean mixture, when leaner than stoichiometric, could cause heat related engine damage because combustion chamber temperatures can increase with a surplus of air during the combustion event. Some aftermarket E85 conversion kits for modern fuel injected vehicles operate by altering the duty cycles of electronic injectors to help offset air/fuel mixture issues. The effects of surplus oxygen on the catalytic converter may be undesirable, and if too lean the engine will display roughness in operation. If the percentage of ethanol used results in sustained operation in the range between stoichiometric and best power mixture, problems may develop. In this range, between peak exhaust gas temperature and approximately 50 degrees rich of peak, combustion temperatures are at the highest possible, and may exceed the design temperatures for the engine. Detonation margins are reduced, and if operation at elevated temperatures is allowed to persist over considerable periods of time, heat related damage to valves and pistons can occur.

Without in-depth knowledge of the engine's mixture control system and instrumentation to monitor exhaust gas temperature, cylinder head temperature, cylinder pressure, and/or exhaust oxygen content, it is difficult to know whether the engine is operating in the "red" zone, or an acceptable mixture zone. Closed loop fuel injection systems eliminate much of the risk. This is also why the check engine light will illuminate if you mix more than around 50% to 60% E85 by volume with your gasoline in a non-FFV. If this happens, just add more gasoline as soon as possible to correct the problem. (Keep in mind that retail stations dispensing E85 are likley dispening gasoline with 10% ethanol.) These fuel/air mixture related problems will not happen in a properly-converted vehicle.

After-market conversions

After-market conversion kits, for converting standard engines to operate on E85, are generally not legal in U.S. states subject to emissions controls, unless the converted vehicle is independently EPA certified. This is despite the fact that the exhaust emissions from any such converted cars are improved by utilizing higher percentages of ethanol in the gasoline blend. Unfortunately, EPA certification costs in excess of $23,000 and requires proof that the vehicle will maintain low emissions for at least 50,000 miles after the conversion. Most individuals won't give up their vehicles for the requisite 50,000 mile test period. Likewise, conversion kit manufacturers generally don't certify their kits due to the onerous and expensive burden of these laws. The kits would have to be tested with every model vehicle for which they are to be sold. If a kit is already certified as described, the EPA Federal Test Procedure for an individual's conversion costs $750. One can request a reduction of payment of down to 1% of the car's added retail value due to the conversion.

Similarly, U.S. Federal law prohibits the manufacture of many such conversion kits for sale in the U.S. unless they are EPA certified. The origin of this ban dates to when conversion kits for using compressed natural gas were originally sold. The ban was enacted to prevent the sale of such conversion kits due to safety concerns. This ban on the manufacture of kits is at odds with the fact that these kits, once existing, are legal in all states but CA, and most states offer some sort of tax break for converting your vehicle.

One Brazilian after-market kit is available legally in US States that do not have restrictive emission controls. The kit will permit the conversion of 4, 6, or 8 cylinder engines to operate from fuels ranging from pure gasoline to a mix of gasoline and ethanol to pure ethanol, including E85. It operates by modifying the fuel-injection pulses sent to the fuel injectors when in 'A', or ethanol mode instead of 'G', or gasoline mode. (In 'G' mode, no modification to the fuel-injection pulses is performed.) This conversion kit modification serves to extend the control range over which the ECU can adjust the air-fuel ratio to achieve an oxygen sensor reading measured before the catalytic converter that falls within nominal stoichiometric ideal combustion limits. The general belief is that this conversion kit operates in its 'A' mode simply through lengthening the individual pulse-widths of fuel-injection pulses, thereby increasing fuel flow per injection pulse by roughly 30%, whereas in 'G' mode, it acts simply as a straight pass through for fuel-injection pulses. Due to the nature of this kit, it is fully reversible (see below for other approaches).

As of 2009 there are a number of after-market kits available from many different manufacturers, that all more or less work in the same way as the Brazilian kit, some with added features, such as cold start assist for the colder climates of northern US states. Nonetheless, it is still possible to modify existing non-FFV engines to operate on pure E85 without the use of this particular after-market kit.

Carburetor engines

The primary method used to convert non-fuel-injected cars is two-fold. First, any non-compatible rubber parts and gaskets and terne gas tanks and terne fuel lines are replaced. Then, it remains necessary to increase the fuel rate of flow by roughly 25% - 30%. This can be accomplished in one of several different ways, depending on the specific details of the fueling system. In the early 80's auto makers were required to make vehicles ethanol compatible, so most new vehicles will handle E85 with no problem. If a car is converted though, the ethanol will clean out the gunk left over from the gasoline and plug the fuel filter. The fuel filter needs to be replaced after about 600 miles.

For non-fuel-injected engines, this may be accomplished through increasing the diameter of the carburetor running jets to a size that is slightly larger in diameter. The theoretical change is not to increase the hole diameter by 25% to 30%, but rather to increase the area and hence the fuel flow rate by 25%-30%. Hence, the diameter of the jets must be increased by 11.8% to 14%, while keeping the general shapes at the opening of the jets as close to nearly the same as possible. (The idling jet must also be increased in diameter in addition to the running jet, primarily to accomplish successful starting in colder weather.) An excellent starting point, if one doesn't want to experiment with multiple test trials over the 25% to 30% range, is simply to increase the fuel flow by 27%, which just requires increasing the diameter of the jets by 13%.

For older vehicles, an even simpler non-conversion 'conversion' is possible once any non-compatible rubber gas hoses and cork gaskets and such are all replaced with ethanol-resistant materials. For older vehicles with a manual choke, it is possible simply to leave the choke slightly engaged even when the motor is warmed up, and the conversion is complete.

Non-carburetor engines

For converting later-model fuel-injected cars and trucks, fuel injection-pressure boosters can be installed, to increase fuel-injector fuel rate flow. It may be difficult to get your mixture right, plus there is a safety risk of more leaks in your fuel system. Likewise, if you do choose this method, you may lose some of your compatibility with running on pure gasoline, from moving the air fuel mix farther from optimum for what is needed for running on pure gasoline.

The disadvantage of most of the above conversions is the conversion is permanent, without changing out or removing added parts.

Fuel filter

If any of these conversion techniques are used, especially in older vehicles in which there may be rust or other residue present in the fuel tank, it may be necessary additionally to replace the fuel filter within 400 to 600 miles, as ethanol has a tendency to release any trapped rust or gasoline fuel gum or residue, which can cause the fuel filter to become blocked. Once replaced, life expectancy of the new fuel filter should be normal, barring an exceptionally dirty gas tank or fuel system.

Running E85 in a vehicle can actually improve fuel efficiency if the fuel delivery system was especially clogged up. This improvement remains if the vehicle is returned to operation on gasoline only.

Air fuel ratio comparison

E85 fuel requires a richer air fuel mixture than gasoline for best results. Successful conversions generally require up to 60% more fuel flow than when the engine burns 100% gasoline. (In contrast, methanol conversions require even more fuel flow increase than ethanol conversions.) Flexible fuel vehicles additionally impose a wider range of air fuel ratios that must be achieved than what is required for vehicles that operate only on gasoline or ethanol. This is because a wider range of air fuel ratios is required to use all the varying percentages of ethanol and gasoline efficiently that may be present in the fuel tank at any given time.

The nominal (chemically correct) air fuel ratio is 14.64:1 by mass (not volume) for burning 100% gasoline, but in practice the nominal air fuel ratio for most 100% gasoline fuel injection systems ranges from about 14.6 to 14.7 for a typical nominal value, depending on manufacturer, with the ratio of 14.7 being slightly preferred for increasing fuel economy under light load conditions.

Table

The following table shows the range of air fuel ratios typically used for burning gasoline, E85, and pure ethanol (E100) under an assortment of assumed operating conditions:

Fuel	AFRst	FARst	Equivalence Ratio	Lambda
Gasoline stoichiometric	14.7	0.068	1	1
Gasoline max power rich	12.5	0.08	1.176	0.8503
Gasoline max power lean	13.23	0.0755	1.111	0.900
E10 stoichiometric	14.0 - 14.1	?	?
E85 stoichiometric	9.765	0.10235	1	1
E85 max power rich	6.975	0.1434	1.40	0.7143
E85 max power lean	8.4687	0.118	1.153	0.8673
E100 stoichiometric	9.0078	0.111	1	1
E100 max power rich	6.429	0.155	1.4	0.714
E100 max power lean	7.8	0.128	1.15	0.870

The term AFRst refers to the air fuel ratio under stoichiometric or ideal air fuel ratio mixture conditions. (See stoichiometry.) FARst refers to the fuel air ratio under stoichiometric conditions, and is simply the reciprocal of AFRst.

Equivalence ratio is the ratio of actual fuel air ratio to stoichiometric fuel air ratio; it provides an intuitive way to express richer mixtures. Lambda (λ) is the ratio of actual air fuel ratio to stoichiometric air fuel ratio; it provides an intuitive way to express leanness conditions (i.e., less fuel, less rich) mixtures of fuel and air.

Calculations

Air fuel ratio is always computed on the basis of ratios of mass (not volume). The following is a computation of the theoretical E100 (100% ethanol, C₂H₆O) air fuel ratio, based on stoichiometric (perfect combustion) principles:

C₂H₆O + 3 O₂ = 2 CO₂ + 3 H₂O

Adding up the molar mass for ethanol:

(6 x 1.00794) + (2 x 12.0107) + (1 x 15.9994) = 46.0684 grams per mole of ethanol

1 mol x 46.0684 g/mol ethanol : 3 mol x 2 x 15.9994 g/mol oxygen

46.0684 : 95.9964 = 1:2.0838 for the fuel:oxygen ratio for perfect (i.e., stoichiometric) combustion.

Now, oxygen is 20.9% of air by volume, or equivalently, 23.1% of air by mass, assuming that atmospheric gases behave as ideal gases. (See Earth's atmosphere.)

Hence, the theoretical air fuel ratio for E100 (100% ethanol) is:

(2.0838/0.23133) : 1 = 9.0078 : 1

So, for E85 (summer blend), the required air fuel ratio can be estimated as:

0.85 x 9.0078 + 0.15 x 14.64 = 9.8526

Likewise, for E85 (winter blend), the required air fuel ratio can be estimated as:

0.70 x 9.0078 + 0.30 x 14.64 = 10.6975, which is closer to the gasoline air fuel ratio.

Discussion

The estimated required E85 summer blend air fuel ratio compares very closely to the value of 9.765 given in the table. In practice, though, the exact stoichiometric air fuel ratio for gasoline varies as a function of the exact blend of gasoline, which, in turn, is varied by time of year by refineries to increase or decrease volatility, prevent vapor locking, etc., for better matching seasonal climatic changes.

Deviations from stoichiometric combustion computed values are required during non-standard operating conditions such as heavy load, or cold weather operation, in which case the mixture ratio can range from 10:1 to 18:1 for burning 100% gasoline. Slightly wider ranges than even this on the low end of the air fuel ratio, dropping to below 8:1, are required for burning all possible blends of E85 and gasoline efficiently under all conditions of engine loads and inlet air temperatures.

At inlet air temperatures below 15 °C (59 °F), it is likewise not possible to start the typical internal combustion engine on pure ethanol (E100); for cold engine starts, starting the engine on gasoline and then shifting to E100 can be done. Similarly, for starting a vehicle on E85 summer blend in extremely cold weather, it is likewise required to add additional gasoline during at least the starting of the engine, before switching to burning the E85 summer blend. In practice, it is easier simply to add more pure gasoline to the fuel tank when extremely cold weather is expected, prior to the arrival of the cold weather, to avoid cold engine start difficulties.

Fortunately for those converting non-FFVs to operate on E85, the wide range of inherent air fuel control required for burning pure gasoline is very nearly the same range required for burning many blends of E85 with gasoline up to approximately 60% E85, at least for non-extreme engine loads and non-extreme weather conditions. Hence, the common success seen in practice for burning many blends of E85 with gasoline even in non-FFVs at blends in excess of 50% E85, especially under light engine loads cruising under benign weather conditions.

All of these theoretical stoichiometric combustion estimated values should be taken only as approximations to what may really be required for achieving perfect combustion. The lambda sensor is what ultimately confirms whether stoichiometric combustion is taking place in practice.

Additionally, the ideal stoichiometric mixture typically burns too hot for any situation other than light load cruise. This is the target mixture that the ECU attempts to achieve in closed-loop fueling to get the best possible emissions and fuel mileage at light load cruise conditions. This mixture typically can give approximately 95% of the engine's best power, provided the fuel has sufficient octane to prevent damaging detonation (i.e., knock).

The "max power rich" condition is the richest air fuel mixture (more fuel than best power) that gives both good drivability and power levels, within approximately 1% of the absolute best power on that fuel.

The "max power lean" condition is the leanest air fuel mixture (less fuel than best power) that gives good drivability, acceptable exhaust gas temperatures to prevent engine damage, and power levels within approximately 1% of the absolute best power on that fuel.

Lambda, typically used for referring to lean versus rich air fuel mixtures, is normally measured by the lambda sensor] (also known as an oxygen sensor.)

Depending on seasonal blend variations E85 will weigh approximately 6.5 pounds per U.S. Gallon, having a liquid density of approximately 0.77 - 0.79 g/ml compared to gasoline which has typical values of 6.0 - 6.5 pounds per U.S. gallon and a density of 0.72 - 0.78 g/ml.