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Study Finds Strong Synergy Between Spark Ignition Engine Downsizing and Low-to-Moderate Alcohol Blend Fuels

A study by engineers from Mahle Powertrain Ltd and BP found strong synergy between spark ignition (SI) engine downsizing and fuel containing low-to-moderate amounts of alcohol, including ethanol and butanol. The team presented a paper on their work at the recent SAE 2009 World Congress in Detroit.

The researchers found that the combination of technologies allowed improvements in fuel economy over the engine drive cycle. Furthermore, a reasonable improvement in dilution tolerance could be achieved at higher engine loads, which could eliminate over-fueling requirements under such conditions.

Among their findings was that for gasoline fuels, aggressively downsizing the engine and adopting homogeneous direct fuel injection enabled an improvement in fuel consumption of ~17% over the New European Drive Cycle compared to a naturally aspirated PFI unit.

When alcohol was added to the blend, fuel consumption over the drive cycle increased in direct proportion to the reduction in calorific value of the fuel. For example, with E85, the calorific value was 32% lower than the 98 RON fuel while the fuel consumption was 33% higher.

Small improvements in thermal efficiency when using E85 under part-load drive cycle conditions are vastly outweighed by the deficit in the calorific value of this fuel.

—Cairns et al. (SAE 2009-01-0138)

The team studied three variants of gasoline (95, 98 and 102 RON) , three gasoline-ethanol blends (E10, E22 and E85), and a gasoline-butanol blend (Bu16) covering a range of oxygen concentrations and octane numbers.

Key Properties of the Test Fuels
Property 95 RON 98 RON 102 RON Bu16 E10 E22 E85
Lower Heating Value (MJ/kg) 43.16 43.06 42.34 41.88 41.64 39.96 29.28
RON 95 98 102 98 98 102 108
MON 86 88 91 87 88 88 90
(R+M)/2 91 93 96 92 93 95 99
Density @ 15 °C (kg/m3) 0.74 0.75 0.74 0.75 0.75 0.75 0.78
H/C ratio 1.891 1.796 1.869 1.943 1.945 2.021 2.769
O2 (% wt) 0 0 2 3.35 3.35 6.8 29.5

Combustion of the fuels was evaluated in a turbocharged four-cylinder 2.0-liter four-valve per cylinder direct fuel injection research engine equipped with a standard three-way catalyst (TWC) and an external EGR circuit that allowed use of either cooled or non-cooled EGR.

The team studied fuel injection timing and pressure; excess air tolerance; EGR tolerance; and spark retard limits at both part and boosted high load conditions. They determined relative in-vehicle fuel economies via drive cycle simulation for comparison to a naturally aspirated (NA) gasoline port fuel injection (PFI) engine.

Among the other conclusions for operation under part load conditions were:

  • Alochol blends generally performed better when injected at slightly later timings and marginally lower fuel pressures.

  • E22 produced the highest smoke readings with early injection timing; E85 produced negligible smoke in this engine, even at late injection timings and low fuel rail pressures.

  • Blends with lower alcohol content allowed small improvements in EGR tolerance; only E85 showed a notable increase in tolerance.

  • The addition of alcohol did not improve excess air tolerance.

  • E10 and Bu16 produced similar fuel consumption values under the conditions tested.

Future work shall be concerned with the combustion, performance and emissions of alcohol fuels across the speed-load map of an aggressively downsized, state-of-the-art, twin-turbocharged three cylinder SI engine.

—Cairns et al. (SAE 2009-01-0138)


  • Alasdair Cairns, Neil Fraser, Hugh Blaxill, Martin Gold, John Rogerson, Craig Goodfellow. A Study of Gasoline-Alcohol Blended Fuels in an Advanced Turbocharged DISI Engine. (SAE 2009-01-0138)



I must be missing something.

The title says "synergy between engine downsizing and alcohol blends".

• (synergy means cooperate advantageously)

The text says that the small efficiency improvements of alcohol blends are vastly outweighed by the lower caloric value of the alcohol.


I don't see why the calorific value would be a problem. I can see cost being an issue, but not many people really care about how energy-dense their fuels are.

Here's an example: coal has higher calorific value than wood. Would you rather heat your home with coal than firewood because of this? How about a solar water heater vs. electric. Solar takes-up a lot more space, but does that make it a lot worse?


I agree with Tom. The title said "synergy" which means you get some type of improvement from the two working together. This shows that they get much worse fuel economy from adding the alcohol blends.

It's obvious that with less energy content, you're going to get less mpg, all else being equal. I was hoping to see some hard data on the things people are always talking about where you run at higher pressures, or whatever, and it is that's supposed to let you take advantage of the higher octane numbers and get mpg that rivals straight gasoline.

All I got out of this article is that you can make an engine 17% more efficient by adopting more efficient fuel injection techniques....oh and by the way alcohol blends hurt your mileage.

What am I missing here?

fred schumacher

Minnesota State University Mankato has been doing ethanol and ethanol blend research for many years. In their most recent studies, they have discovered a synergistic effect with ethanol concentrations of 20 to 30 percent in a gasoline mix. In that range, fuel economy stays the same or is slightly higher than pure gasoline. See http://www.mnsu.edu/news/read/?id=1201016489&paper=topstories
Dr. Bruce Jones is leading the research team.

Ethanol has a much higher octane rating than gasoline allowing for more advanced ignition timing. Turbocharging is more amenable than natural aspiration for taking advantage of this phenomenon, although best would be variable compression ratio. I would really like to see how Fiat's agressively downsized 900 cc 2-cylinder Multiair engine would do on a 20 to 30 percent ethanol mix.

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