Study Compares Use of Hydrous and Anhydrous Ethanol Fuels in Direct-injection, Turbocharged Engine
31 January 2008
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
The Effect of E100 Water Content on High Load Performance of a Spray Guide Direct Injection Boosted Engine (presentation)
Some years ago, there was a brief trend toward stable micro-emulsions of diesel and water in order to reduce NOx emissions from legacy HDV diesel engines. The manufacturers even managed to persuade several governments to amend their fuel tax laws so that only the diesel portion of the blended fuel would be taxed. Of course, fuel flow rate had to be increased to compensate for the water content. The result was somewhat reduced NOx at the expense of operating range.
The whole thing became a moot point as the fleet churned, because the blend was poorly suited to direct injection at high pressures. Besides, other measures to deal with NOx had become available, e.g. EGR and SCR (urea injection).
The reason I mention all this is that similar emulsifiers might permit blending hydrous ethanol (e.g. the azeotropic E93h) with dinojuice. However, both the water and the ethanol would have to be in emulsion, otherwise the hygroscopic ethanol would simply attract moisture from any air present in the system.
IFF an emulsifier for ethanol in gasoline were available, the blend could be shipped in pipelines. Currently, California refineries have to bring in the ethanol from the Midwest by rail or truck and blend it in themselves, increasing prices at the pump.
Posted by: Rafael Seidl | 31 January 2008 at 09:32 AM
Miscibility is only half the problem with pipeline transport of ethanol; the other is corrosion.
The Ford/MIT turbocharged/downsized engine seems to be the best way to use ethanol. It maintains maximum power while cutting pumping and friction losses, and requires less ethanol than even an E10 mixture does. Last, it can use hydrous ethanol because blending is not required.
Posted by: Engineer-Poet | 31 January 2008 at 11:14 AM
@ Engineer-Poet -
the corrosion problem is a consequence of the fact that ethanol is hygroscopic. If too much water is absorbed, the ethanol-water mixture separates out from the lighter gasoline phase. If, for any reason, the pipeline is then operated at zero or low mass flow, the water will corrode the pipe.
If both ethanol and water were in a stable micro-emulsion prior to entering the pipeline system, this problem would not arise.
Posted by: Rafael Seidl | 31 January 2008 at 12:12 PM
Would such a hypothetical emulsion be compatible with current flex-fuel sensors?
One thing it would not do: it would not improve fuel economy. The Ford/MIT engine would appear to be able to improve economy by about 30% (23% reduction in fuel consumption) using only 1-2% ethanol on average. We would only need about 3 billion gallons/year of ethanol (hydrous would do), which we are already producing. This could yield a 23% reduction in our 140-odd billion gallon/year gasoline habit, or more than 33 billion gallons.
Trying to put ethanol through petroleum pipelines is a waste of effort.
Posted by: Engineer-Poet | 31 January 2008 at 12:46 PM
According to Orbital's SAE 2007-01-2648 paper, E93h is a blend of 93.5% ethanol and 6.5% water, not 83% and 7%.
Posted by: Spencer Knipping | 31 January 2008 at 01:22 PM
Water injection into air stream is widely used to increase output of performance turbocharged engines (especially gasoline), and diesel water emulsification is occasionally used to decrease NOx and slightly decrease diesel soot (additional water vapor erodes unburned carbon particles during combustion C+H2O=CO+H2 and resulted gases combust afterwards). Process works well on big diesel engines, like marine diesels, even yielding slight increase in thermal efficiency.
However, water technology has drawback which makes use of hydrous ethanol impractical. ALL water ingested by engine should be distilled from inorganic salts. Othervice, precipitated during evaporation salts contaminate engine oil, clog injector’s tips, and significantly increase wear due to it abrasive properties on cylinder walls, compression rings, and fuel pumps.
Posted by: Andrey | 31 January 2008 at 07:23 PM
A major Chinese automaker is coming out with a car that runs on hydrogen extracted from onboard 65% hydrous ethanol with a basic attachment to a standard engine. We need to look deeper into hydrous ethanol.
Posted by: Jeff Baker | 31 January 2008 at 10:53 PM
@ Engineer-Poet -
no-one has ever claimed ethanol - in whatever form - improves volumetric fuel economy relative to gasoline. It's energy density is simply a lot lower. However, MPG is relevant mostly for operating range in this context, for the economics you need to look instead at miles per dollar and, at subsidies/protectionst tariffs. E85 prices vary widely. California is one of the states for which ethanol definitely adds to the cost of transportation, though that could change if the ethanol were produced locally (cp. e.g. Vinod Khosla's ventures).
In environmental terms, it all depends on how the ethanol is produced. So far, US supplies of ethanol are produced almost exclusively from corn kernels. In terms of both field-to-tank energy balance and the impact on food markets, this is a questionable practice.
if hydrous ethanol is such a hazard to internal combustion engines, how come millions of cars are driving around on it in Brazil without breaking down?
Posted by: Rafael Seidl | 01 February 2008 at 03:58 AM
I think Andrey is wrong on some of his facts, and where he's right he's losing things in translation.
Rafael writes:Not necessarily. If you can reduce overall fuel demand 30% through the use of a 2% additive, you can have high losses in the production of that 2% and still be way ahead.
Posted by: Engineer-Poet | 01 February 2008 at 07:37 AM
@ Engineer-Poet -
don't tease us so! Please tell us more about this wondrous oleum serpentis of yours.
Posted by: Rafael Seidl | 01 February 2008 at 01:22 PM
If it's snake oil, it's your snake oil, Rafael; I'm just taking you at your word.
Posted by: Engineer-Poet | 01 February 2008 at 02:23 PM
Cars running on hydrous ethanol do not break right away. They just have increased engine wear. Check, for example, manual for any water injection kit: it requires distilled (deionized) water only.
Posted by: Andrey | 01 February 2008 at 10:57 PM
your last post was funny. and I was somewhat surprised that Rafael seemed unaware of the tech.
However in the link you attached, he mentioned reservations that I agree with. The need for the clueless motorist to fill with more than one fluid at the gas station. This is certainly an issue for the typical US driver, but not unsurmountable.
Posted by: John Schreiber | 02 February 2008 at 07:23 AM
If the average driver can cope with windshield washer fluid, they can manage that. Besides, having the engine limited to un-boosted power levels would be a strong incentive to watch the ethanol level too.
Posted by: Engineer-Poet | 02 February 2008 at 08:33 AM
Oh yeah, if I could get boosted performance and better mileage by filling a container of ethanol once a week, I would have a case of it in my garage.
Posted by: sjc | 02 February 2008 at 11:36 AM
Ooo, dueling slide rules, good time to jump in tangentially. EP usually is the one advocating more efficient machines (read electric drive). Guess it is up to a non-engineer. (Excuse me while I step into the nearby telecommunications booth.)
Consider if you would the REEV (Range Extended Electric Vehicle) instance, which then would be better, an ethanol boosting system or a small turbocharged, ICE with direct injection?
And, which technology is a better lead into spark-assisted, compression ignition and eventually HCCI / Dies Otto?
Posted by: jcwinnie | 02 February 2008 at 05:05 PM
Interesting story. I just found this today and linked this story to a discussion that's been going on for a few weeks about a technology proposal for a hypothetical Automotive X-Prize entry.
One of the members is a big fan of aqueous-fuel technology; there's been some effort to convince him that there's no free lunch.
The results of the above research don't present any major surprises.
Posted by: TDIMeister | 18 February 2008 at 10:53 AM