Since the stoichiometric air-fuel ratio of ethanol is 9:1 whereas that of gasoline is 14.7:1, it clearly show that the richer fuel mixture is required to fire ethanol. Therefore ECU is able to handle such rich fuel mixture, the engine can switch over to run either high percentage ethanol blended into gasoline, assuming that using proper materials. In addition, heat of evaporation of ethanol is about 3 times higher than that of gasoline, cold start would be difficult. This could be solved with modifying the ignition system. Also ethanol has high octane number of about 107, the advance ignition timing shall be considered. Without engine modification combining with ethanol critical properties, the blended ethanol into gasoline shall not be over 20% (E20).

Some fuel system components may not survive high ethanol blending. Particularly rubber parts like o-rings and gaskets can be damaged by ethanol and cause leakage. Another problem can be cold starting which may require a special fueling procedure in cold climates. Finally the fuel metering and ignition control systems may encounter out-of-range problems due to the low energy content and high octane number respectively of ethanol.

hope it help

source: Sustainable biofuels: prospects and challenges. The Royal Society, 2008

There are many aspects. One among them is the tolernace against water and separation of EtOHa nd gasoline phases. It especially important if the weather is cool and the humidity condensates onto the EtOH-gasoline surface.

In addition to the above. To take advantage of the ethanol in the otto cycle is necessary to increase the compression ratio due to the low heating value and high octane number. In other words, the loss of heating value is compensated by increased efficiency due to the increase in compression ratio.

Other interesting effect in liquid ethanol is that has high enthalpy of vaporization compared with gasoline. During the intake procces, the ethanol vaporitzation consume more energy, decreasing temperature and increasing volumetric efficiency.

Thank you for the interesting responses.

Dear Prof. Tunestal, are there research works on the IC engine component material compatibility with ethanol?

Many car manufacturers have released cars suited for high ethanol blends so there has certainly been successful development work concerning component material compatibility with ethanol. Examples of manufacturers are Ford, GM and Mercedes.

Limitations in this case are compatibility of some materials used in fuel delivery system and need for higher air/fuel ratio.

Plastics, which are used in modern cars will do fine. Some rubber pipes and steel fuel tanks will not stand corrosive effect of ethanol. Regular gasoline fuel pump will have shorter lifespan.

For stoichiometric operation E85 require 25-30% more fuel per mass with the same mass of the air, comparing with pure gasoline. For cold start, even more fuel is required. Regular fuel injection system normally is not so tolerant and adaptive.

Since the stoichiometric air-fuel ratio of ethanol is 9:1 whereas that of gasoline is 14.7:1, it clearly show that the richer fuel mixture is required to fire ethanol. Therefore ECU is able to handle such rich fuel mixture, the engine can switch over to run either high percentage ethanol blended into gasoline, assuming that using proper materials. In addition, heat of evaporation of ethanol is about 3 times higher than that of gasoline, cold start would be difficult. This could be solved with modifying the ignition system. Also ethanol has high octane number of about 107, the advance ignition timing shall be considered. Without engine modification combining with ethanol critical properties, the blended ethanol into gasoline shall not be over 20% (E20).

ECU recalibration would not be sufficient. The fuel injectors would be unlikely to provide sufficient fuel quantity to maintain torque output at high engine loads if attempting to convert a vehicle from E0/E10 to E85. If the vehicle is equipped with on-board diagonstics (e.g., OBD II), the resulting fuel control hanging open-loop and lean will likely trigger the vehicle into an engine-protection limp-home-mode.

The specific fuel injector shall be required. The injector has long pulse width to give more fuel since it is rich mixer. On the other hand, the emission level such as hydrocarbon and carbon mono oxide level may increase due to rich mixer. But that can be reduced by optimizing the ignition timing and fuel delivery. The fuel supply system should be optimized to avoid the poor performance, fuel mileage, back exhaust and misfiring.

Standard ASTM methods showed that by increasing the ethanol content, the heating value of the blended fuels is decreased, while the octane number of the blended fuels increases. In addition, with increasing the ethanol content, the Reid vapor pressure of the blended fuels initially increases to a maximum at 10% ethanol addition, and then decreases. If the amount of ethanol is increased in blended fuel, the heating value decreases. But on the other hand, increase of ethanol amount in blended fuels enable to decrease of air–fuel ratio, so we can take much more fuel during the intake processes. Ignition timing, excess air ratios, latent heat of vaporization, compression ratio, and flame speed have also influence on engine performance.

Since the latent heat of vaporization of ethanol is more than gasoline, the engine will run at less temperature comparing to pure gasoline engine.The spark plug needs to be changed in this context.

The lower heating value of ethanol is less comparing to gasoline, so de-rating of power happens.

From a practical point of view, yes injectors need to be sized for higher E85 flowrate due to stoichiometric relationship. HIgher RON of E85 should give higher WOT (Wide Open Throttle) Power if ignition timing optimised as per E0, provided injectors sized correctly. With a simple fuel tank (not saddle tank) you do not need an Ethanol sensor, the ECU can figure out and adapt the current Ethanol content with the standard sensors and input (O2 and AFM sensor and injection timing) . The fuel system need to be corrosion protected for E85. Lower Volumetric Energy content of E85 only means that the volumetric Fuel Consumption will be similarly higher ("sweet spots of Ethanol blends has been reported where better FE then theoretical has been achieved, indicating improved combustion and efficiency from higher RON and other EXX properties). Properly calibrated most emissions are improved, in particular soot emissions in GDI engines.