Study Shows Higher Compression Ratios Boost the Performance of Both Hydrous Ethanol and E22 Blend

A study by a team at the Pontifical Catholic University of Minas Gerais (Brazil) found that higher compression ratios in a spark-ignition engine improved performance of both an E22 blend (78% gasoline, 22% ethanol) as well as neat hydrous ethanol. The paper was published online 15 September in the journal Applied Thermal Engineering.

In ethanol production, the beer resulting from the fermentation is processed in distillation columns where an azeotropic mixture of ethanol and water is separated out from the rest of the stillage. This product is referred to as hydrous ethanol—approximately 93% ethanol and 7% water. To be used as a supplementary blend in low levels with gasoline, this hydrous ethanol needs to be dehydrated, resulting in anhydrous ethanol.

The process of dehydration is costly and energy-consuming. A study on the use of E10-E26 hydrous ethanol blends by HE Blends BV in the Netherlands noted that hydrous ethanol is 10%-20% less expensive than anhydrous ethanol, is easier to produce and to handle, and offers a better life cycle emissions profile than anhydrous ethanol. (Earlier post.)

Rodrigo Costa and José Sodré from PUC Minas tested a 1.0-liter eight-valve, four-cylinder, production engine in a dynamometer bench varying the speed in the range from 1500 to 6500 rev/min. Three compression ratios were investigated: 10:1, 11:1 and 12:1.

Performance parameters evaluated were torque, brake mean effective pressure (BMEP), power, specific fuel consumption (SFC), thermal efficiency, exhaust gas temperature and volumetric efficiency. The results showed that higher compression ratios improved engine performance for both fuels throughout all the speed range investigated, with major effects being observed when hydrous ethanol was used.

An earlier study by the team, published in 2009 in the journal Fuel, compares the performance and emissions from a 1.0L engine fueled by hydrous ethanol (6.8% water content in ethanol) or the E22 blend. In addition to investigating torque, brake mean effective pressure (BMEP), brake power, specific fuel consumption (SFC), and thermal efficiency, the study compared carbon monoxide (CO), carbon dioxide (CO2), hydrocarbons (HC) and oxides of nitrogen (NOx) exhaust emissions levels are also presented.

The results of this earlier study showed that torque and BMEP were higher when the gasoline-ethanol blend was used as fuel on low engine speeds. On the other hand, for high engine speeds, higher torque and BMEP were achieved when hydrous ethanol fuel was used. The use of hydrous ethanol caused higher power at high engine speeds, whereas, for low engine speeds, both fuels produced about the same power.

Hydrous ethanol produced higher thermal efficiency and higher SFC than the gasoline-ethanol blend throughout all the engine speed range studied. With regard to exhaust emissions hydrous ethanol reduced CO and HC, but increased CO2 and NOx levels.


  • Rodrigo C. Costa, José R. Sodré (2010) Compression ratio effects on an ethanol/gasoline fuelled engine performance. Applied Thermal Engineering, in press, doi: 10.1016/j.applthermaleng.2010.09.007

  • Rodrigo C. Costa, José R. Sodré (2009) Hydrous ethanol vs. gasoline-ethanol blend: Engine performance and emissions. Fuel Volume 89, Issue 2, Pages 287-293 doi: 10.1016/j.fuel.2009.06.017

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