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Study: splash blended ethanol fuels with higher ethanol percentage enable higher thermal efficiency in SI engine

A team from the University of Birmingham (UK) and Shell Global Solutions has investigated the effect of RON, octane sensitivity and charge cooling in splash-blended ethanol fuels with different volume percentages of ethanol on a single-cylinder direct-injection spark ignition (DISI) research engine.

In a paper published in the journal Fuel, the researchers report that at the knock-limited engine loads, splash-blended ethanol fuels with a higher ethanol percentage enabled higher engine thermal efficiency through allowing more advanced combustion phasing and less fuel enrichment for limiting the exhaust gas temperature under the upper limit of 850 °C, which was due to the synergic effects of higher RON and octane sensitivity, as well as better charge cooling.

A downsized gasoline engine is one of the proven technologies that improves engine thermal efficiency and thus reduces automotive fleet CO2 emissions, by as much as 25%. Downsized engines equipped with turbo- or super-chargers operate at higher engine loads to deliver the same power outputs as larger engines, thus, downsized engines lead to lower pumping losses and higher efficiency at part load operating conditions.

… However, despite the proven advantages of downsized engines, engine knock, caused by the auto-ignition of the end gas, is one of the main challenges that stop downsized engines from achieving their full potential. High octane rating fuels are one of the key solutions for suppressing engine knock. Ethanol, a widely used renewable gasoline alternative, has a much higher octane rating than conventional gasoline fuel. Splash blending ethanol into gasoline improves the octane rating of the resulting fuel mixture.

… Currently, ethanol is largely used in low percentage blend forms such as E5 or E10. Higher octane splash blended ethanol fuels beyond E10 are expected to give better performance in downsized engines, however, their performance in modern downsized DISI engines, and the contributions of RON, octane sensitivity and charge cooling to combustion are not fully understood. In this study, eight fuels were designed and tested, including four splash blended ethanol (10 vol.%, 20 vol.%, 30 vol.% and 85 vol.% ethanol, noted as E10, E20, E30 and E85), one match blended fuel (E0-MB) with zero ethanol content but the same octane rating with those of E30, and three fuels (F1-F3) with different combinations of RON and octane sensitivity.

—Wang et al.

The team carried out load and spark timing sweep tests with an engine speed of 1800 rpm, and full load tests for E10-E85 to assess the combustion performance of ethanol blends. To investigate the effect of charge cooling, the load sweep was conducted for E0-MB, and the results were compared to those of E30. Load sweep tests were also carried out for F1-F3, to understand the impacts of RON and octane sensitivity on engine combustion.

Octane sensitivity is defined as the difference between the research octane number (RON) and motor octane number (MON). RON and MON are measured in CFR engines designed 90 years ago. However, modern spark ignition engines, especially turbo-charged downsized engines, tend to operate at relatively lower temperatures than CFR engines. To compensate for the disconnect between the CFR engine and modern engines, an octane index (OI) was proposed as: OI = RON + K ⁄ (RON-MON), where K is a scaling factor depending solely on the in-cylinder thermal and pressure history experienced by the end-gas prior to the onset of auto-ignition.

Based on the testing results, the team concluded:

  1. Splash blended ethanol has better anti-knock properties than base gasoline, enabling a larger knock-free engine load range and more advanced combustion phasing when the engine is knock-limited. Higher ethanol blends led to better engine indicated thermal efficiency, especially at high and full load operating conditions. Compared to E10, E20 led to 2.8–7% higher indicated thermal efficiency at the full load, depending on the engine speed; the improvements for E85 were in the range of 8.3–27%.

  2. Compared to E10, at knock-limited engine load, the combustion of higher percentage ethanol blends were less sensitive to spark timing retard, resulting in less negative impacts on IMEP and indicated thermal efficiency. At 1.6 bar intake pressure, advances in spark timing from knock-limited spark advance (KLSA) caused a more severe knock intensity rise for E10 than for other higher percentage ethanol blends.

  3. For E30, at knock limited operating conditions, the positive effect of charging cooling was reflected in the more advanced combustion phasing, higher engine thermal efficiency, and lower unburned gas temperature at TDC. The high heat of vaporization and low stoichiometric air/fuel ratio of ethanol blends both contributed to a better charge cooling effect. In addition, the faster burning rate of ethanol also contributed to this.

  4. High RON and high octane sensitivity both contributed to improve the fuel’s anti-knock quality, with the impact of RON being more significant than that of octane sensitivity. For ethanol blends, most of the anti-knock quality improvement was from the RON improvement.


  • Chongming Wang, Andreas Janssen, Arjun Prakash, Roger Cracknell, Hongming Xu (2017) “Splash blended ethanol in a spark ignition engine – Effect of RON, octane sensitivity and charge cooling,” Fuel, Volume 196, 15 May 2017, Pages 21-31 doi: 10.1016/j.fuel.2017.01.075


Trevor Carlson

So how much will a marginal increase in thermal efficiency translate to increase miles per gallon after all the additional hardware to make it emissions compliant is bolted on?
3-7% better at high loads (like towing on the highway) requires a transmission that won't kick down and users that don't over-ride that programming by switching to manual shift mode. In the mean time there's less energy per volume so a tankful of E20 may not get you as far as a tank of E10 even in a vehicle designed to optimize its operating conditions.

Most E20 will be wasted in engines that aren't programmed to utilize the fuel as the above research indicates. Therefore I'm led to believe the push for E20 is to get votes via continuation of subsidies to farmers who grow the feedstock to make the ethanol.


This makes sense, smaller displacement, turbo charging and more ethanol allows higher efficiency.


I was fully expecting a nerdy neanderthal to comment along the lines of -We've known that from alcohol 'fuel dragsters, performance tuning etc back to 1950's.

Its always nice to put the numbers on what may have a bit ' common knowledge as understanding of the desirable / undesirable pro's and con's develops.

But Trevors comment is insightful in relation to splash blended fuels as described.
Dual ethanol direct injection plus gasoline port injection (EDI+GPI)system would be a way to realise the potential including emissions reduction.
The lower energy content of ethanol as (especially) with LPG does not always translate to higher fuel usage
as long as the advantages are properly exploited as possible with effective ECU program and downsizing lightweighting etc.


Again an article that is a plain nonsense. First ethanol is 30% lower btu content and in real price cost 10 times gasoline if you factor in increase in food price. They can also increase octan with other products than limp ethanol and the current car fleet is fine tune to gasoline 87 octans with 10% ethanol blend so don't change fuel and engines. Hear this song to see what i mean.

Dr. Strange Love

'The high heat of vaporization and low stoichiometric air/fuel ratio of ethanol blends both contributed to a better charge cooling effect. In addition, the faster burning rate of ethanol also contributed to this.'

You run these downsized engines like you would run a Diesel on a track loader or a farm tractor or farm mower. For Off-road diesel equipment, it is 1700 to 2300 rpm. The rpm stays fixed. There are No pumping losses. You will operate this downsized DISI high ethanol blend high compression/turbo in the same way as the the off road equipment. It will operate in its Sweat RPM spot, maybe 2000 to 2500 RPM, and there will be NO pumping losses because you are at near full load.

It could be a range extender for BE. It could be a hydrostatic drive with hydrostatic Regenerative braking. Some kind of CVT may work as well.

Emissions should be easy since it is mostly in the RPM sweatspot.


That is the idea of series hybrid, get an efficient prime mover that runs in the most efficient part of the band.


I find it interesting that they use the term "splash blended." Splash blending is inherently less accurate than other methods so you can never be sure of ratio in your tank. And some fuel pairs, like biodiesel/petro-diesel don't mix very well so stirring is needed.


Ethanol owns the octane boost market and has no challenger to the low cost of doing so. Same for oxygenate market. Food vs fuel argument has been proven bunk. Historical data of agriculture energy is proving a correlation of improved agronomics with increase farm wealth. Agriculture is very adept at continually improving yield. Farmers prefer that route to purchasing land. This is more of a force within poor nation status countries for their agricultural communities. As farmers gain wealth and resources they gain ability to grow more. The entire industry is greening with ever more efficiency and renewable power. Farm fields already produce most all of the wind energy.

Quality of fuel is very important as well as btu rating. Both are needed. Some very high btu liquids are worthless for fuel use. Also, the engine must be tuned to exploit the particular character of the fuel to maximize efficiency. Engineers have decades of experience and have learned how to exploit gasoline and diesel fuel to maximize efficiency and lower pollution. They barely started on biofuels, but already have impressive results. For example the Cummins E85 engine surpassed the competitive diesel engine for efficiency and beat gas engine mileage. The engine offered better hp and torque than the competition with a much smaller engine. The E85 engine was a cheaper engine as compared to diesel and had typical low cost catalytic pollution control. The diesel engine lacked hp and the gasoline lacked torque. E85 engine had both and used cheaper fuel.



Good to know, just wish E85 was more available in Canada. I know of one station that sells it in West Vancouver and I think there's a station somewhere in Ontario. ---- Going to need a very big aux tank when I drive cross-country pulling my trailer.


This IS the problem, the lack of E85 pumps is designed by oil companies. They will not allow it in their stations...period.


This might be a way to get around the lack of E85 pumps;


Another idea: Bi-fuel - E85 and propane or CNG. All have 100+ octane numbers and could be run in the same high compression engine. In Canada propane/autogas and CNG is more available than E85, there's only one E85 station that I'm sure of vs ~40 CNG stations listed on a website I found vs almost 450 autogas stations. Using E85 would be best for the environment but falling back on propane would be cheaper and still better than gasoline or diesel.


Just allow E85 in stations, one anti trust case could change that.


That wouldn't work because there is NO effort to keep ethanol out of gasoline here. Quite the opposite: "Since December 2010 federal regulations have required that gasoline in Canada contain 5% renewable fuel content overall" and every pump I've filled up at these last 6 years has had the label "May contain up to 10% ethanol" on it.

The problem then is two fold: What fuel grade ethanol we can produce gets spread out to all the gasoline supply leaving little left for higher ratios. And because Canadian driver see themselves as doing something "ECO" collectively there less call for individuals to go that extra step and those that want to have already found their extra step in propane/CNG or BEV/hybrid cars, so there's little market demand for E85.

That one station I mentioned? It doesn't cater to environmentalists. It's located in the rich end of town where young punks with too much allowance drive souped-up streetracers.


The government mandates 10% but allows oil companies to exclude 85%. There are millions of vehicles made for E85 that don't use it because they can't get it.

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