A team of researchers from Ford Motor Company are asserting in a paper published in the journal Fuel that “substantial societal benefits” would arrive for consumers by using higher volume blends of ethanol to leverage the alcohol’s inherent high octane rating to produce ethanol-gasoline blends with higher octane numbers.
Octane numbers measure in scale the ability of a fuel to resist “knock” an ignition event resulting from premature fuel burning in spark-ignited engines. The early ignition drives the piston back down the cylinder the wrong direction, which can cause engine damage when the “knock” is severe or prolonged.
Higher octane ratings in fuel blends would enable greater thermal efficiency in future engines through higher compression ratios and/or more aggressive turbocharging and downsizing of current engines on the road today through more aggressive spark timing under some driving conditions.
Ethanol's Impact on RON Octane Ratings in Gasoline.
Ethanol and methanol offer higher research octane numbers (RON) and motor octane numbers (MON) when compared to gasoline. The alcohols also have a greater latent heat of vaporisation than gasoline, which contributes to their higher RON values and provides additional charge cooling in direct-injection (DI) engines. That means when the alcohols are sprayed into the engine’s induction air the charge of air is cooled more by the evaporation of the alcohol.
The two alcohols are not equal to gasoline. Detractors focus on the lower energy density than gasoline, potentially higher or lower vapour pressures, altered distillation properties, and potential for water-induced phase separation. These are all valid points – easily compensated for by proper engineering.
Today the situation is that ethanol is blended into a gasoline blendstocks formulated with a lower octane rating such that the net octane rating of the resulting final blend for sale is unchanged from historical levels.
Ford is making the case, with a hard scientific, peer reviewed, repeatable study what racing folks, hot rodders, engineers, and smart consumers with high compression engines have known for years.
The high octane rating of ethanol could be used in a mid-level ethanol blend to increase the minimum octane number (Research Octane Number, RON) of regular-grade gasoline.
Ford suggests that the societal benefit comes from automakers having an opportunity to improve their engines to a higher compression ratio. The compression ratio is a comparison of the volume of the open cylinder to the cylinder volume when the piston has squeezed the cylinder to the smallest volume. The same amount of fuel and air squeezed into a smaller space sets up a more energetic fuel burn that equals more mechanical energy out and less heat lost.
The Ford team used their already developed linear molar octane blending model to quantify RON potential from ethanol and blendstock. From the results the team estimated that an increase of 4-7 points in RON are possible by blending in an additional 10–20% by volume of ethanol above the 10% already present.
Here’s the opportunity Ford sees, keeping the blendstock RON at 88 (which provides E10 with a 92.5 RON), the estimated RON would be increased to 94.3 for E15 to as much as 98.6 for E30. The team further suggests RON increases may be achievable assuming changes to the blendstock RON and/or hydrocarbon composition. An increase in blendstock RON from 88 to 92 would increase the RON of E10 from 92.5 to 95.6, and would provide higher RON with additional ethanol content (e.g., RON of 97.1 for E15 to 100.6 for E30). This is high performance territory.
From the scenarios considered in the paper, the team estimated compression ratio increases to be on the order of 1–3 compression ration units for port fuel injection engines as well as for direct injection engines in which the greater evaporative cooling of ethanol can be fully utilized.
Ford is making a case that has been obvious to many for decades. That has not stopped the detractors and the ill-informed followers from thinking up an assortment of ways to mislead consumers, the media and policy makers. The facts the detractors have can prove up with low compression engine builds, poor maintenance, and skewing results. There is also a strong motive. The oil industry isn’t thrilled to lose 10% of the gasoline market to a competitor.
For everyone else, a higher compression ratio would be a good thing. More efficiency, less fuel used and for the environmental types, less air would be cycled through engines.
What is, and as Ford points outs could be, the important issue is keeping the gasoline supply for sale with octane ratings high enough and priced so that higher levels of compression can be engineered into production vehicles at mass scale.
The point not being made was a significant point a couple decades ago when unleaded gasoline became the rule – lowering compression ratios. It’s a waste of engineering, materials and air to mandate low octane ratings when the science and experience have proven otherwise for about one hundred years.
Perhaps Ford will be marking a turning point, getting the fuel market quality high enough to put efficiency with simple economy back into the automobile market. It’s certainly been a long enough wait so far.
By. Brian Westenhaus