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Sandia study finds the alcohol isopentanol appears to have a good potential as a HCCI fuel, either neat or in a blend with gasoline

A study of isopentanol—a five-carbon, long-chain alcohol (C5H12O)—by researchers at Sandia National Laboratories as a fuel for homogeneous charge compression ignition (HCCI) engines found that isopentanol has superior physiochemical properties compared to ethanol and very similar HCCI combustion properties to gasoline. Results from the study suggest that isopentanol has a good potential as a HCCI fuel, either in neat form or in a blend with gasoline.

Yi Yang from Sandia presented the study at the SAE 2010 Powertrains Fuels & Lubricants Meeting in San Diego.

HCCI, which has been the focus of research for years as a potential way to provide diesel-like efficiency without the NOx and soot emissions, is hampered by inadequate combustion control and limited load range. Progress has been made recently in expanding the HCCI operating range using conventional gasoline fuels. However, the researchers note, future fuels could be significantly different from those used today due to the focus on biofuel technology.

One potential change is to replace the currently used ethanol with longer chain alcohols. Higher alcohols, containing four or more carbons, are more favorable gasoline constituents than ethanol. With longer alkyl chain, the polarity of alcohols rapidly decreases, and their physiochemical properties become more like those of the hydrocarbons in gasoline. For example, higher alcohols are less hygroscopic and less susceptible to separation in the presence of water when blending with hydrocarbon fuels. This is in sharp contrast with ethanol, and it makes higher alcohols more compatible with the existing fuel infrastructure. Material compatibility issues such as elastomer swelling are also much improved with higher alcohols. Additionally, in many cases, blending ethanol into gasoline enhances the vapor pressure of the gasoline, which causes high evaporative emissions and potential operational problems such as vapor lock.

...Another clear advantage of higher alcohols is their higher energy content, which would significantly improve fuel economy over ethanol. One potential drawback could be the increased fuel reactivity with the longer chain which diminishes the potential for improved antiknock performance for SI combustion. However the octane ratings of C4-C5 alcohols are still sufficient for gasoline SI engines, and they could work well for advanced HCCI or other low-temperature combustion engines, since these engines have different requirements for fuel autoignition quality.

—Yang et al.

New pathways for production of longer chain alcohols
Yang et al. note the advances in synthetic biology that engineer metabolic pathways in organisms to produce C4-C5 alcohols from sugar:
These advanced biochemical production routes for next-generation biofuels hold great promise in terms of generating a significant volume of fungible fuels that are more compatible with the existing fuel distribution and combustion infrastructure.”
Alternate thermochemical pathways are being developed as well, such as the catalytic synthesis technology being commercialized by IGP. IGP’s technology is a modified methanol conversion process using a patented catalyst, which has been altered to produce higher alcohols.
IGP is working on a Higher Alcohol Reference Plant planned to be commissioned in late 2011 in China. The company notes on its website that due to the Chinese overcapacity of methanol production and the similarity of the IGP process, it can integrate this technology into methanol plants at a fraction of the capital expense that building a catalytic chemical synthesis plant would typically cost.

Isopentanol is a C5 branched alcohol that has a greater similarity to gasoline in physiochemical properties than ethanol or butanol, including much lower miscibility in water and higher volumetric energy density.

The study examined the reactivity of isopentanol and compared it with gasoline and ethanol in terms of the intake temperature required to maintain a constant combustion phasing over a wide range of engine speeds. The team then studied the potential for high-load HCCI by examining the early stages of heat release as a function of intake temperature and pressure.

The HCCI research engine was derived from a Cummins B-series six-cylinder diesel engine, with five of the cylinders deactivated. The study covered a wide range of engine operating conditions, including engine speed, intake temperature, intake boost level, and equivalence ratio. Among the findings were:

  • Isopentanol shows higher HCCI reactivity than gasoline and ethanol, as evidenced by lower intake temperatures or higher EGR required to maintain a constant combustion phasing over a wide range of engine speeds.

  • Isopentanol shows relatively strong reactions at intermediate temperatures prior to hot ignition. The ITHR of isopentanol is similar to that of gasoline at naturally aspirated as well as boosted conditions, which enables similar capability to retard the combustion phasing to mitigate knock.

  • The intermediate temperature heat release (ITHR) of isopentanol is enhanced by increased intake pressure and simultaneously reduced intake temperature, which is similar to gasoline.

  • Due to the active ITHR and combustion retard capability, as well as the similar ITHR enhancement with Pin, isopentanol reaches high-load limits similar to those of gasoline at various intake pressures.

  • Isopentanol shows almost no sensitivity to equivalence ratio in ignition timing at atmospheric intake pressure, indicating that partial fuel stratification will not work to reduce heat release rates (HRR) or mitigate knock under these conditions.


  • Yi Yang, John Dec, Nicolas Dronniou and Blake Simmons (2010) Characteristics of Isopentanol as a Fuel for HCCI Engines (SAE 2010-01-2164)



These studies seem "interesting" but a terrible waste of time to me. Ok, so isopentanol or newie-alchie-something-ie will run great in HCCI.

They totally ignore the realities of whether this is useful. How many HCCI engines are there going to be on the road in the next 5 years? How would you get it distributed and build a new infrastructre for it? Would we have pumps now for unleaded, mid grade, premium, E10, E15, E85, Butanol, diesel, bio-diesel, methanol and throw in a few charge points for EVs!

Seems like a solution in search of a problem....causing lots more problems.


Knowledge is power. I just googled "isopentanol" and found... next-to-nothing in relation to fuels so this study tells us something we didn't know.


yeah, and as someone who did grad work myself, I'm really not against gaining general knowledge because you never know where you might get some kind of breakthrough.

But it seems like we have some fairly urgent needs coming up to get us off of gasoline and there are some obvious areas where more direct research could be helpful to speed that up. Areas like this where it really would take multiple changes including infrastructure seem to be a waste. Better battery chemistries or work to flex fuel all existing vehicles or even cellulosic ethanol, etc...things that are already well on their way that have known issues to be solved would give us more bang for the buck right now.

I keep watching $400Billion+ going out of the US economy every year to buy petroleum and I want something to slow that down NOW! And our national labs should be cranking out those solutions that can be implemented NOW. This would require lots of new HCCI engines plus new production and distribution of isopentanol to make a dent.

Just my opinion.

I keep watching $400Billion+ going out of the US economy every year to buy petroleum and I want something to slow that down NOW!
Demand that any pol you vote for help to enact another $2/gallon in gas taxes over the next few years.

Seriously, it's the one thing we know works but that we've never done because of whining about "the poor". No more excuses.


The 'problem' with HCCI not being able to run over a wide range of speeds and loads becomes moot if it is being used as a range extender, although the power density is not as good as an SI engine.

There is an option to run a range extender on HCCI when the battery depletes between 80 and 50% and then switch to SI when you need the extra power.

If you needed 30kW to cruise and could get 20kW from an engine on HCCI it would triple your EV range and still allow you to drive firther if you had to


3PS has the right idea.


Seems to me the Window of Opportunity for HCCI came and went.
The only advantage of HCCI is higher efficiency at partial load. Hybrids and particularly series-hybrids have less need to run the ICE at partial load.

The 'problem' with HCCI not being able to run over a wide range of speeds and loads becomes moot if it is being used as a range extender, although the power density is not as good as an SI engine.
That is exactly the problem. HCCI is only needed when an engine is much too big for the average load and can't be cycled off. It does nothing to reduce the excess friction losses and weight of the too-large engine. It's much better to size the engine appropriately and use e.g. the Atkinson cycle to raise efficiency to the maximum the hardware can provide.
If you needed 30kW to cruise
Most cars need closer to 15 kW at 60 MPH.

That must be why GM is working on HCCI for the Volt.


Please look at the efficiency achievable with better combustion control using Partially Premixed Combustion (PPC) and/or Low Temperature Combustion (LTC):

Lund Team Shows 57% Thermodynamic Efficiency in a Gasoline-Fueled Heavy-Duty Diesel Engine Using PPC

specifically the results at
Vittorio Manente (2010) Gasoline Partially Premixed Combustion: An Advanced Internal Combustion Engine Concept Aimed to High Efficiency, Low Emissions and Low Acoustic Noise in the Whole Load Range (PhD Thesis)

LTC is being studied at Argonne:
Don't put gasoline in your diesel engine, unless you work at Argonne

It's interesting to see all those works in making longer chain alcohols as butanol and this isopentanol, but the problem is COST.

What premium such a process would demand ? Will it be cheaper/better than the paths being developed by GEVO or by Amyris ?


I just noticed that the GM-L850, one of the engines used to test PPC with gasoline, is the Ecotec GM-Family-II block used in so many vehicles around the world.

I wonder if there is an easy way to test it with readily available parts. One immediate candidate came to my mind: the Ecotec LNF version with DCVVT, DI and Turbo available in the US since 2006 in the Pontiac Solstice GXP and Saturn Sky Red Line seems to have most of the hardware needed to test this proposition. VW/Audi TFSI would probably be good alternatives.

(Don't know if standard parts like Cylinder heads/Combustion chamber, Injector type and position, EGR, fuel pressure control,etc. would fit.)

It's quite a bit out of the DIY Megasquirt realm, but wouldn't it be interesting if someone really tried it ?

Coke Machine

I hate it when they do not use the correct method of naming the chemicals. Isopentanol could be either of the following chemicals, 2-pentanol, 3-pentanol, 2 methyl 1-butanol, or 3 methyl 1-butanol. Is it just one of these or a combination. Googleing (sp?) Isopentanol shows it to be 3-methyl 1-butanol. All organic chemists would prefer using the proper name rather than an ambiguous one to insure you are dealing with the same compound. The iso prefix just means that something is not bonded at the end carbon. Is it the OH group, a -CH3 group. I prefer to avoid confusion.

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