Fuel Economy

After taking a detour into auto-mechanics in the last post, I think it's time to get back on track. This post will involve both evolving ethanol knowledge and its application in car engines. Before going any further, I want to add that this research is new and needs more verification before any of the results should be implemented. However, it is always good to keep track of the newest information.

The research, released in November of 2007, was conducted by the University of North Dakota and Minnesota State University and can be found at

http://www.ethanol.org/pdf/contentmgmt/ACE_Optimal_Ethanol_Blend_Level_Study_final_12507.pdf. This study mirrors the call for more information on blending standards for cars in the United States. Currently, car makers will only honor their warranties on cars that fill up to E10 or a 10% ethanol blend in non-flex fuel capable cars. However, partly because of an anticipated excess of ethanol and because of a desire to blend ethanol in higher amounts to displace US imports of foreign oil there has been a call to look into the possibility of higher blends in non-flex fuel cars. The study looked at the the use of regular unleaded gasoline, E20, and E30 blends in four different cars. These cars were the 2007 models of the Toyota Camry, the Chevrolet Impala (flex fuel), the Chevrolet Impala (non-flex fuel), and the Ford Fusion. Results are displayed below.

As I mentioned before, the researchers would be the first ones to point out that the results are preliminary, but they are interesting. The above bar graph reveals the results of their tests showing that two models showed an increase of 1% in fuel economy for the E30 blend over conventional gasoline (the Camry and the Fusion), and the flex-fuel vehicle saw an amazing 15% increase in its E20 blend over conventional gasoline. Although unexpected, the researchers believe that some engines might have 'sweet spots' at which a certain blend might have the optimum combination of ethanol and gasoline to allow for a high mileage.

But what might be even more interesting is that all of the models of cars in all of the blends outperformed their calculated MPG based on their penalties for decreased energy densities. In other words, ethanol's energy density should result in a decrease in mileage by 2.7% for every 10 percent of ethanol blended into the gasoline. Below is an example from the sited study to reveal how the data bumped above the calculated energy density for the Toyota Camry.

As you can see above, the apparent 'sweet spot' in the Camry is around E30. Even though these tests need to be corroborated, they agree with similar results seen in 2005 in the study found at http://www.ethanol.org/pdf/contentmgmt/ACEFuelEconomyStudy_001.pdf.

While these studies show that E20 and E30 could be incorporated into non-flex fuel vehicles, a better potential benefit of this study is the realization that it may be possible to engineer a car engine to favor ethanol over gasoline, thereby relieving any potential MPG dip due to lower energy density. This would seem to parallel the finding in the previous post that a turbocharged engine built with ethanol in mind might be able to alleviate several of the potential negative aspects of ethanol.

Turbocharged Ethanol

While some are busy at work creating the next generation of ethanol produced from cellulosics, MIT's best and brightest are continuing to work hard for the development of the next generation engine. In the process of developing industry and technology that will benefit the environment and our energy security it may be easy to lose track of how the system needs to come together. What I mean by this is that whether or not ethanol's lower energy density results in decreased MPG than gasoline, doesn't necessarily mean that we need to live with this problem. In fact, the engine may be optimized for gasoline usage without taking into consideration the advantages that ethanol might bring.

This case is illustrated in J. B. Heywood's work titled "Calculations of Knock Suppression in Highly Turbocharged Gasoline/Ethanol Engines Using Direct Ethanol Injection," and can be found at http://www.ethanolboost.com/LFEE-2006-01.pdf. The basis of the study attempts to answer the problem of knock suppression in turbocharged engines using ethanol. But first, let's back up for a second. Turbocharging in an internal combustion engine is the use of the exhaust gas from the engine to drive a wheel that compresses the air to deliver to the engine. This allows for more air to enter the engine than a naturally aspirated engine and improves on the energy-to-size ratio of the engine. In other words, using the turbocharged engine allows for the use of much smaller engines with the same or more energy and torque output of the engine. The one problem with this is that a turbocharged engine is more susceptible to engine knock. Knocking occurs when the fuel/air mixture is ignited correctly in the piston but then a second pocket of fuel ignites as well. These two countering fronts of energy create destructive interference for each other, which can range from mistiming the stroke of the engine causing a loss of power all the way to possibly destroying the engine.

Ethanol has two key components that make it a prime candidate to combat engine knock in turbocharged engines -- 1) its high octane rating, and 2) ethanol's capability for evaporative cooling of the system after ignition.

Ethanol's octane rating (115 versus 87 for normal gasoline), prevents engine knock because, by definition, ethanol's fuel has the right kind of molecules that will ignite correctly and uniformly under pressure. A second requirement in turbocharged engines is to quickly decrease the in-cylinder (charge) temperatures so as to prevent the detonation of unexploded fuel/gas mixtures. This is accomplished by ethanol's ability to quickly cool the mixture to 355K versus 383K (Heywood et. al 2006).

According the Heywood, he concludes that a turbocharged engine would allow for the size of a modern fuel-injected engine to be decreased by half. At the same time, the manifold pressure and compression ratios could be increased allowing for comparative engine performance compared to the larger gasoline fueled engines. This is all possible because of the knock suppression of an ethanol blend. Heywood calculates that with the engine downsizing and performance enhancement of the turbocharged engine, efficiency of the automobile could actually increased by 30%! This would, in effect, completely offset the calculated energy density penalty of ethanol on the MPGs of a car, (which is approximately 27%).

As a final note, I found an update on this technology today that these researchers are working closely with Ford in the production of this engine and are progressing quickly. Hopefully we will see these engines in the near future.