Biodiesel
Emissions
More than
just the smell of fried food!
A little story...
Rudolf Diesel, Inventor of the Diesel Engine
Background- Significance of Biodiesel and its Emissions
Summary of Biodiesel Emissions
Interesting Information on Biodiesel
For the consumer
Conclusion
References
A little story of how I became interested
in Biodiesel Emissions:
A couple of guys were celebrating Rudolf Diesel’s birthday at a local Irish pub on March 18, coincidentally the day after St. Patties day. It being the day AFTER St. Patties day, it was quiet enough at the pub that their celebration/ discussion of Rudolf Diesel was audible to the adjacent table, where I sat. These particular gents were big fans of biodiesel and were singing its praises… as a renewable energy source and as a benefit to emissions. Being an atmospheric science student, this made me wonder ‘are the emissions from biodiesel lower or in some way better than conventional diesel?’. So I did a bit of research and the following is what I found out. The primary source of info that I have is a preliminary report on biodiesel emissions published by the EPA. It is the longest, most dreadfully boring 120+ page report that I could imagine ( I worked as an engineer for 10 years, so I have seen my fair share of long, boring reports.). The report offers little or no interpretation of what the results mean to climate forcing so the significance of the results is probably meaningful only to climate folk. The bright side of the report, compared to many other pieces of information available on the web, is that the EPA is not trying to sell anything in making this information available.
Rudolf Diesel, Inventor of the Diesel Engine:
RUDOLF DIESEL 1858-1913
The following paragraph is from
http://inventors.about.com/library/inventors/bldiesel.htm
Rudolf Diesel was born in
A few noteworthy quotes from
Rudolf Diesel
·
~1911/1912- "The diesel
engine can be fed with vegetable oils and would help considerably in the
development of agriculture of the countries which use it.”
·
“The use of vegetable
oils for engine fuels may seem insignificant today. But such oils may become in
course of time as important as petroleum and the coal tar products of the
present time."
This is quite forward thinking considering he said these things in the early twentieth century. These comments probably weren’t made to promote an anti-fossil fuel agenda such as how the statements may be perceived if he spoke them today.
Mark you calendar to celebrate Rudolf’s birthday- March 18.
Background- Significance of Biodiesel and its Emissions
Petroleum is a finite resource. In today’s climate of energy awareness, renewable forms of energy are becoming increasingly important. As a renewable source, biodiesel fuels offer an attractive alternative to petro-diesel, since they can be used with little or no modification to the mechanical infrastructure. Biodiesel is also attractive because it is an alternative to foreign petroleum products and an opportunity for domestic agriculture. In this sense biodiesel definitely has an advantage over petroleum based diesel.
In parallel with energy resource awareness, the environmental harm caused by the burning of fossil fuels is becoming apparent. Everyone has heard by now: our consumption of petroleum results in emission of greenhouse gases (GHGs), especially CO2, into the atmosphere. The greenhouse gases trap the outgoing longwave radiation from the earth, warming the planet. Other fossil fuel emissions include NOx, particulate matter, carbon monoxide, and hydrocarbons. The following figures show the importance of these emissions and are discussed below.
figure from http://www.cgd.ucar.edu/cas/abstracts/files/kevin1997_1.html
figure from http://www.ipcc.ch/present/graphics/2001syr/large/06.01.jpg
Using the first figure, we can imagine increasing the GHGs, therefore increasing the ‘Back Radiation’, reducing the ‘Outgoing Longwave’, thereby altering the balance. The balance may also be altered by the aerosols emitted, since they will change the properties of the clouds. The second figure represents the climate forcing of GHGs and other atmospheric constituents, including aerosols (particulate matter). The figure shows the uncertainty of the effect of aerosols. Although the effect of the aerosols may be a net cooling, they will alter the microphysics of clouds in an unnatural and potentially harmful way.
The next figure is a cartoon representing the effect of NOx and hydrocarbons:
Figure from http://www.ncl.ac.uk/gane/page8.htm
The tropospheric ozone and NOx are irritants to those who breathe it. They can exacerbate health problems in those who have heart and lung problems. Ozone also affects the health of plants and can diminish crop yields. Also shown in the climate forcing figure above, tropospheric ozone also is considered to have a warming effect. This brief explanation of the environmental impacts of burning fossil fuels rationalizes the need for developing alternative sources of energy and why we should care about biodiesel emissions. The question is... should we expect biodiesel emissions to be better? Taking an educated guess at what we may expect for biodiesel emissions compared to petro-diesel, the use of biodiesel is not expected to entirely abate emissions, as it still involves combustion, but we can hope that it will emit good things other than the fragrance of a fried food.
Summary of Biodiesel Emissions:
By sampling the emissions from a variety of heavy duty highway engines, the EPA developed the following curves representing the biodiesel emissions outputs using a statistical regression analysis, which is described in gruesome detail in the report. The fuels that are (or will be) available to the public will generally be blends of petro-diesel with biodiesel, hence the % biodiesel domain. The most common blend is a 20% bio, 80% petro. It is important to point out that their test method ran all of the tests at a given (relevant) power and RPM, so that the effect of fuel efficiency could be factored out. Figure (ES-A) shows the emissions results which the EPA reports (NOx=NO+NO2, PM=particulate matter, CO=carbon monoxide, HC=hydrocarbons). Looks pretty good, right? Everything is reduced except NOx increases a bit, probably about +2% for the 20-80 blend mentioned above. But what about the CO2 that everybody blames for global warming??!! It must be a conspiracy to overlook the best known greenhouse gas. That was what I thought when I read the executive summary of the EPA report, so I had to read further.
It turns out that it wasn’t a conspiracy to cover up the CO2 emissions, CO2 just doesn’t fall under the heading of ‘Regulated Pollutants’ for highway engines, such as the ones shown above. Figure IV.A.3-1 shows the results for CO2 emissions, note the small percentage range. The figure suggests that blending the biodiesel with a clean base fuel (petro) will adversely affect the CO2 emissions. On the contrary, it simply suggests that the clean base fuel most likely performs better in CO2 emissions than an average base fuel, and that adding biodiesel to it diminishes that performance. Also, the plot shows that animal based biodiesel (animal fats) will improve the performance in a CO2 sense. This is discussed in the 'interesting info' section below.
To conclude this summary, there is a very small change in CO2 emissions using biodiesel, and it varies depending on the type of biodiesel and cleanliness of the base fuel. So for CO2, the benefit/detriment of using biodiesel is approximately zero. Also, there is a small increase in NOx, while other emissions are reduced substantially. Since CO2 and NOx are of primary importance, we can conclude that biodiesel is not a significant benefit to emissions. The best reasons to use biodiesel are that it is a renewable source, employs agriculture, and is not dependent on foreign oil. These are definitely compelling reasons, but the average tree-hugger should know that while using biodiesel is a good way of ‘thumbing your nose’ at the oil industry, it's not going to save the planet.
Interesting Information on Biodiesel:
The differences in the types of biodiesel, plant or animal, is an interesting aspect of the data in the EPA report. Animal based biodiesel performs better than others, in an emissions sense, not just in CO2, as shown by the following figures:
Note that HC emissions are not plotted above, the report states that there was no discernable difference in HC emissions among the different types of biodiesel. Unfortunately, the report offers little explanation of why the animal based biodiesel has lower emissions than other types of biodiesel. The report does attempt to make sense of the carbon emitted in the form of CO2, CO, and HC, by evaluating the carbon content per BTU. The values are shown in the following table:
Obviously, these data seem only to further confuse. The carbon per BTU in biodiesel fuels is greater than conventional diesel, and virtually the same for the different types of biodiesel. While this may explain why the CO2 emitted is on average slightly greater for bio versus petro, it doesn’t explain why animal based would have lower CO2 and CO emission. In fact it seems that somewhere there is a conservation law being violated… conservation of mass of carbon. I, personally, conclude that something must have slipped thru the cracks in the emissions sampling, perhaps a form of hydrocarbon.
In the EPA report, there is a wealth of data on various aspects of biodiesel, most of which the biodiesel user doesn’t want or need to know. One aspect that he or she will probably want to know is the fuel efficiency. The report quantifies the fuel efficiency in a two ways, both of which say that the fuel efficiency is reduced using biodiesel. The more straightforward way that they quantify the fuel efficiency is by measuring the energy content in a given volume- units of BTU/gal- the results are shown in the tables below:
Bottom line for the consumer- you will need to buy up to ~10% more biodiesel to get you where you want to go.
The reader may be tempted to conclude that these fuel efficiencies explain the lower emissions from animal based biodiesel. As stated previously, the test procedure quantifying the emissions had the engines run at a specific power regardless of the amount of fuel required, and therefore the fuel efficiency is factored out of the equation. I welcome comments from anyone who can explain why the animal based biodiesel has lower emissions. email me: scott.gregory@colorado.edu .
There are good reasons to use biodiesel, but emissions improvement is not the most compelling argument. I prefer the ‘thumb your nose’ at the oil industry argument.
References:
EPA Draft Technical Report, A Comprehensive Analysis of Biodiesel Impacts on Exhaust Emissions, October 2002