HIGH OCTANE REDUX
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.
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.