Comparative testing by engineers at Orbital Corporation of hydrous (E93h, E87h, E80h) and anhydrous (E100) ethanol fuels on a direct injection multi-cylinder turbocharged engine found that the engine may be operated at high load with the same output and efficiency, with either hydrous or anhydrous ethanol. Orbital published its results in an SAE paper presented at Congresso SAE Brasil in late November, 2007.
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—about 95% ethanol and 5% 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.
Hydrous ethanol is currently used in Brazil and Sweden, and hydrous E10-15 is currently being used under the European BEST project in the Rotterdam area.
Although there have been a large number of published studies on the use of both hydrous and anhydrous ethanol fuels, the Orbital team noted, there is little available that directly compares the performance of the two types of ethanol fuel in spark ignition engines.
The researchers used a SI multi-cylinder turbocharged unit incorporating Orbital’s centrally mounted spray guide direct injection and compared the performance of four ethanol fuels: anhydrous E100, and hydrous E93h (83% ethanol, 7% water by mass), E87h (87% ethanol, 13% water by mass), and E80h (80% ethanol, 20% water by mass).
Orbital conducted their evaluation at high load, and initially at 2,000 rpm and manifold pressure of 100 kPa to assess variation in ignition timing. Subsequent testing at 2000 rpm evaluated increases in manifold pressure to 140 and 170 kPa. Finally, they assessed the effect of engine speed at a BMEP of 1,900 kPa.
The key findings of the study were:
Ignition delay and burn duration are increased with increasing water content at fixed ignition timing, as a consequence of charge dilution. Engine output, efficiency and combustion stability are decreased and MBT ignition timing is advanced.
Engine output, efficiency and combustion stability are typically recovered at MBT ignition timing. Some reduction remains at engine speeds of 4,000-5,000 rpm, and load of 1,900 kPa BMEP and above.
Emissions of CO are unaffected by fuel water content.
Emissions of NOx decrease linearly with increasing fuel water content at fixed ignition timing, as a function of diluent specific heat and consequent reduction of peak combustion temperatures. At MBT ignition timing the reduction is typically less than 10%.
Emissions of HC increase linearly with increasing fuel water content for E93h and E87h, the trend being largely independent of ignition timing. The mechanism is proposed to be an increase of flame quenching, and also the effect of water content on fuel preparation within the cylinder.
Exhaust gas temperature increases slightly with increasing fuel water content at fixed ignition timing, as a consequence of later combustion. The increase is in the order of 20°C. At MBT, increasing water content may reduce EGT in the order of 10°C. This is attributed to reduced combustion temperatures arising from increased heat capacity of the charge, and also the latent heat of vaporization.
MBT ignition timing was achieved at all conditions tested and with all levels of fuel hydration. Further increases in boost pressure and compression ratio are therefore feasible, and it is proposed that the suppression of knock and pre-ignition offered by hydration may present the greatest opportunity for extension of the engine operating regime.
When reviewing powertrain applications for anhydrous vs. hydrated ethanol fuels, key areas of difference may include fuel preparation, catalyst specification and control system calibration. Items not addressed within this study but also requiring consideration include compatibility and durability, lubrication, cold start capability, and fuel system capacity.
Further work in support of this area is on-going, and includes development of low temperature starting capability, and turbo-charger application development for transient performance and high specific output.
Brewster, S.C., “Initial Development of a Turbocharged Direct Injection E100 Combustion System”. SAE paper # 2007-01-3625.
Brewster, S.C., et. al., “The Effect of E100 Water Content on High Load Performance of a Spray Guide Direct Injection Boosted Engine”. SAE paper # 2007-01-2648