February 24, 2015 § 4 Comments

My 2012 post High Octane has consistently had very high readership to this day.  This merited a revisit.  It is also a fitting topic on the heels of my last post regarding alternatives to petroleum based fuels being hurt by low oil prices.  This price crash did more damage to that cause than just the already extended sojourn to the depths.  It raised a specter that has always been in the psyche of oil old timers: the price can crash any time and it has in the past.  In the recent past the dogma has shifted to volatility only north of about $90 per barrel.  This was based in large measure on OPEC providing a floor and the juggernaut represented by the growing economies of China and India keeping demand pumped up.  This last was bolstered by the well-known relationship between per capita GDP and car ownership.

car ownership revised

Then the economic growth rates of China and India faltered.  Furthermore, China started making a concerted push to use coal derived methanol as a gasoline substitute.  India is experimenting with ultra-small cars such as the Tata Nano (70 mpg).  Indian Prime Minister Modi recently lifted the restraints on genetically modified (GM) oil seeds.  Rape seed oil (a variant is more conservatively named Canola) is expected to be an early beneficiary.  Canola oil, ordinarily used for cooking, can be processed very simply into diesel with a process known as transesterification.  In fact it is so simple that a garage operation would be quite economical.  Also to be noted is that India consumes nearly three times as much diesel as it does gasoline, so oil seed conversion is advantaged.

But my favorite is Jatropha, which is indigenous to India, much of East Asia and Florida, for that matter.  As I mentioned in a post two years ago, the time is right, and even more so now than when I wrote that piece.  Jatropha created a lot of excitement in India and other places a decade ago because it was not a food crop and was drought resistant.  The problem was that wild type jatropha was too variable in yield and other economically important parameters.  Now with the plummeting in the costs of DNA sequencing, high throughput screening and associated data analytics a GM jatropha with great qualities need not be far away.

In some ways the foregoing discussion is something of a distraction from the premise of the original High Octane.  There I suggested that ethanol, the legislative favorite displacer of gasoline, was not being properly utilized.  Today Congress is seriously considering revising the flawed Renewable Fuel Standard.  The principal flaw is the insistence on cellulosic ethanol, which has proved economically intractable.  In today’s gasoline pricing scenario it is even more so.  Technology simply has not kept up with congressional wishes and is unlikely to do so.

The biggest problem, however, is not that at all.  It is the fundamental problem of trying to fit a round peg into a square hole.  The two most viable gasoline substitutes, ethanol and methanol, will deliver 33% and 50% fewer miles to the gallon, respectively, in today’s conventional engines.  These engines have been optimized for gasoline for a hundred years, which is why they have compression ratios of around 9.  Higher compression ratios deliver more energy per gallon but cannot be tolerated by 87 octane gasoline.  However, ethanol and methanol respectively have octane ratings of 113 and 117.  A high compression engine will operate effectively with these fuel blends and give back much of the intrinsic energy penalty.

This is essentially a repeat of what I said in the last post.  Now I have more ammunition to enable the substitutes.  Both ethanol and methanol have one more very useful attribute that allows even higher compression ratios.  They have high latent heats of evaporation.  When injected into the cylinder the evaporative cooling effect reduces the temperature.  This is a key because at high compressions the problem is temperature rise causing premature ignition of the fuel, also known as knocking.  This cooling effect will enable very high compressions.

Now to the final point: is it asking too much of the automotive industry to modify the engines for higher compression?  First of all race cars have high compression.  But a more mass produced example just appeared a couple of years ago.  Mazda introduced the Skyactiv engine which operated at a compression ratio of 13 with regular gasoline.  The key step appears to be dual injection of the gasoline, the second one coming in response to temperature sensing and presumably producing evaporative cooling.  This car is rated at about 35% higher highway mileage than the regular counterpart. One of the technology advances along the way has been to measure cylinder temperature and react to it. So they can do it if they want to.

Now consider the following facts.  The cooling from injecting ethanol vapor would be about 2.6 times that from gasoline.  A blend would be somewhere between and Mazda likely are getting a bit of that benefit with the 10% ethanol in most gasoline.  And here is the kicker.  With methanol that number is 3.7 times.  So, even a 20% blend ought to give heck of a boost.  Higher blends are completely feasible and China is piloting these, albeit in conventional engines.  And methanol from inexpensive natural gas is more affordable than ethanol.  Aside from the higher efficiencies, a cooler running engine produces less NOx.  Also, a high compression engine delivers more torque.  Such vehicles will be fuel efficient in the extreme, use less petroleum products, have vastly reduced tail pipe emissions compared to all but electric vehicles, and drive like muscle cars.  They should move off the lot.

Vikram Rao


§ 4 Responses to HIGH OCTANE REDUX

  • Joel Thigpen says:

    The blog/article provides a lot of food for thought.

    Can the author or others clarify what might be a misperception or misunderstanding on my part…that the cost to create and deliver ethanol and methanol as a component of gasoline exceeded the benefit derived from its inclusion in the formula. And, that the requirement to include ethanol in gasoline is a significant factor in escalating food prices as corn and other crops used to make the ethanol are being diverted into the energy market and not available in the food market.

    With oil prices around $50 per barrel and automotive engine compression rates not likely to change in the short-term, would it not make economic sense to eliminate the ethanol requirement in gasoline and let the corn, sugar and grain crops used to make the ethanol be used in the food market to lower prices there?

  • rtecrtp says:

    Others can weigh in but here are my comments

    First, we need to separate ethanol and methanol. Ethanol is currently sanctioned in engine use, methanol is not, in this country (it is in Europe and China).

    Ethanol from cellulose or lignin will be expensive unless some breakthrough technology appears. Ethanol from sugar is the simplest and most cost effective. Depending on where it comes from it may or may not compete with food. Ethanol from corn does compete and has other issues such as fertilizer sourced water contamination, high use of water and so forth. BUT some ethanol is required in gasoline since we outlawed MTBE (probably hastily). It is needed as an oxygenate to assure a more complete burn but only about 6% is needed for that, not 10.

    Methanol can be produced for less then $0.70 per gallon from natural gas at todays prices. Especially in high compression engines this will be cost effective. Methanol could be used as an oxygenate today. It is more effective than ethanol. Only about 3% is needed as an oxygenate.

    Vikram Rao

  • Ward says:

    On the ethanol question, there is less competition for food than is often suggested. In ethanol production, you take the starch out of the grain and convert that to sugar, which is then turned into alcohol. The vast majority of the nutrient content of the corn remains in distillers dried grains or corn gluten (not really gluten) meal, depending on if you are wet milling or dry milling. These two co-products are used primarily in animal feed. So the question would be, if you stopped processing the corn for ethanol, would there be any change in the flow of nutrients in the food chain? Since there is not really a shortage of starch in our diets, I’m not sure what the change would be.

    Because most of the nutrient remains and is used as animal feed, it is difficult to come to a consensus on the energy balance of ethanol. If you attribute, unfairly, all of the energy inputs of corn farming and processing to ethanol alone, you’ll have a negative energy balance. But if you factor in the retained value of the animal feed and other co-products, you can get a relatively good energy balance. Fiddling with that balance is a great way for researchers to solicit funding and for advocates on one side or the other to make their case to politicians.

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