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Ethanol and E85 FlexFuel have been common in the racing and high performance circles for a long time as they can be used as an inexpensive race fuel, and it’s becoming more popular to use various blends of ethanol fuels in the common non-FlexFuel equipped vehicles solely for performance purposes. There are two key performance-adding attributes to the standard E85 you can find at local gas stations: it has a very high octane rating of 105 (R+M/2) and, more importantly in my opinion, is the molecular composition and its’ effect on cylinder charge and combustion. Without going into too much chemistry and combustion theory, here are the effects of the two key ethanol fuel attribute and why it is used:
1) E85 has a high octane rating of 105 – This is rather straight forward; the higher octane rating yields greater resistance and less volatility to detonation. In many of the popular turbocharged engines on the road today, significant gains can be had from tuning alone with the stock engine hardware. However, many of them inevitably become detonation limited from a variety of constraints, such as:
- Inferior or excessively small turbine or turbine housing, exhaust manifolds, etc. This can result in extremely high exhaust gas temperatures and/or cylinder head temps, therefore increasing the chances for hot spots inside the combustion chamber, piston, etc
- Inefficient cylinder head/combustion chamber/piston design. This is similar to the turbine limitation above, except with the emphasis on the fluid dynamics of the air charge entering and exhaust gas exiting the combustion chamber. The efficiency and stability of the combustion characteristics – including raw power – are dramatically impacted by the cylinder head ports, cam profiles, valve shape and combustion chamber design. When compromised design or limited technology characterize the contributors to combustion efficiency and stability, the characteristics of the fuel become more crucial.
Note - It’s not my intention to describe these modern engines as primitive or lacking technology; quite the opposite is true. The key to this particular discussion is that the intended operation range of these Stg 1 and Stg 2 engines has been elevated, therefore the performance we are attempting to optimize will be constrained by a design and limitations of a different intent. As is the case with many of the modern turbo engines either stock + tune or with bolt-on upgrades, a primary limiting factor to additional power output is detonation volatility and stability. This means if we can use more stable, less volatile fuels and therefore take advantage of more consistent combustion, we can comfortably move the peak cylinder pressures closer to the optimum mechanical angle - generally 15* ATDC – we’ll see a significant increase in torque and power output.
2) The molecular attributes of ethanol have a very dramatic effect on performance. There are common misapprehensions regarding energy release and temperature at which E85 burns, but hopefully separating two functions of the fuel can help illustrate the nuanced discussions regarding E85 and temperatures.
a. In Direct Injection engines especially, fuel does much more than provide a chemical for oxygen to react with upon ignition. The high-pressure injection of the liquid fuel into the combustion chamber provides a function of absorbing a significant amount of heat from previous combustions, which consequently raises the knock/detonation threshold considerably. As such, the more heat we can remove, the higher the knock/detonation threshold and subsequently more power. This measure of the liquid’s ability to absorb heat is known as the Latent Heat of Vaporization. Pump gasoline has a low rating of ~150btu/g, whereas E85 has nearly 2.5x the thermal absorption at ~360btu/g. However, most impressing of all is an E30 blend which still has over 2x the rating with ~330btu/g! It’s in this context that it’s possible to describe an engine as “running cooler” with E85, as overall peak combustion temperatures and EGTs can be cooler.
b. The molecular differences between ethanol and gasoline also has an effect on power and performance, which can be illustrated by comparing the heat and byproducts released upon combustion. This is where additional confusion comes into play with regards to which fuel burns cooler, which fuel makes more power, etc. One common claim is that combusting one unit of ethanol produces 4x less heat than combusting one unit of gasoline - which is true – however in the case of an engine where we’re looking to make the biggest bang, we are usually oxidizer limited, meaning the raw combustion energy is limited by the amount of oxygen that can be crammed into the combustion chamber. As such, we must look at the total combustion byproducts and their respective pressures to get an understanding of the impacts to the temperatures and pressures in the chamber using the P=nRT/V equation. In general, the given airmass will combust 4x as much E85 as it would gasoline, therefore we can consider the overall combustion thermal energy release to be equal. Then the byproducts of combustion come into play, where E85 produces ~20% more than gasoline, raising cylinder pressure accordingly.
What this all means for us concerned with engine performance is that we have numerous strategies that can be used to extract significantly more power with E85 or an E30 blend of fuel, all while keeping the knock/detonation, peak pressures and CHT & EGTs in their healthy ranges- at or below levels prior.
The concerns of ethanol being used in non-FlexFuel vehicles is
Stage 1 E30 (Stage 1 - 321whp/334wtq) thats +83whp/+58wtq OVER STOCK Stage 2 E30 (Stage 2 - 345whp/355wtq) thats +19whp/+15wtq over our Stage 2 93 MAP and +107whp/+79wtq OVER STOCK!
Stage 2 E30 (Stage 2 - 345whp/355wtq) thats +19whp/+15wtq over our Stage 2 93 MAP and +107whp/+79wtq OVER STOCK!