Fuel Emissions: studying the differences between petroleum and biodiesel exhaust emission
A growing concern over the environmental effects of diesel and diminishing natural resources has lead to the development of biodiesel. Biodiesel has promising potential as eventually replacing most of the diesel used in automobiles. Currently, a significant amount of air pollution is contributed by pollutants from car exhaust and fuel emissions. This then leads to the question of how does exhaust and emissions from biodiesel differ from diesel. Would using biodiesel improve fuel emissions or will this new fuel have no substantial affect on the environment?
Petroleum diesel has many combustion products such as: carbon dioxide, carbon monoxide, nitrogen oxides, sulphur dioxide, polycyclic aromatic hydrocarbons, and particles of soot, dust, smoke, and aerosols (particulate matter). Carbon dioxide contributes to global warming by acting as a “greenhouse gas” and keeps heat from escaping into the atmosphere. Nitrogen oxides lead to formation of ozone along with hydrocarbons and accounts for the ground level smog present in major cities. Hydrocarbons are also suspected of being carcinogenic and particulate matter can lead to complications in health and the respiratory system [1]. Long term diesel emission is harming the environment, so if biodiesel does produce a significantly lower amount of air pollution then the incentive for everyday use is even stronger.
The definition of biodiesel is the mono alkyl esters of the fatty acids derived from vegetable oils (1). Alcohol and a catalyst are mixed with vegetable oil producing glycerin and methyl esters, the biodiesel component, through transesterification [2]. This process is necessary in order to lower the viscosity of the oil and increase fuel efficiency (1). It is also important to remember that there are multiple types of biodiesel based on the type of oil used. Palm seed, soybean, and peanut oil are all commonly used for biodiesel [3]. Different types of oil may lead to slightly different emission results.
Based on current research the most popular and most successful way of collecting and analyzing car exhaust and emissions is by using a dilution tunnel for the initial collection [3]. A dilution tunnel is a large tube or tunnel that provides space where the gases from car exhaust can mix and become diluted enough for later analysis. In order to determine the differences between petroleum and biodiesel emission, car exhaust will be collected and analyzed with a dilution tunnel. Car exhaust is a logical source for fuel emissions because the exhaust is a mixture of gases, vapors, and solids providing a source for multiple emission products [1].
For the experiment two cars of the same make, model and engine will be used. Prior to the experiment each of the exhaust systems should be cleaned to ensure that there are no outside contaminants from old car exhaust. One car will run on petroleum diesel and the other will run on biodiesel, because there are several different types of biodiesel there will be several trials for each type of biodiesel in order to compare for any differences between the different biofuels. Each car will have an individual collection set up. The exhaust from the vehicle is carried to the dilution tunnel by piping the exhaust into the tunnel using clean tubing that will not attract particles onto the sides of the piping or allow gases to diffuse out. The exhaust should be piped into the tunnel rather than directly connecting the dilution tunnel to the exhaust pipe. Directly attaching the dilution tunnel will increase the likelihood of unwanted particles such as large pieces of dirt and soot entering the tunnel, affecting the precision and accuracy of the experiment. The exhaust is then diluted with clean, cooled air flowing in from an outside source. The amount of both the clean air and exhaust entering the tunnel are monitored and measured. The gas volumes are recorded so the initial concentration of particles and gases can be determined later. The exhaust and air mix in the tunnel, diluting the exhaust. This dilution is important for the instruments used in analysis later on. Diluting the exhaust prevents instruments from becoming overwhelmed or oversaturated [4]. The dilution tunnel is created in a way that allows most of the exhaust to flow through several filters. These filters are designed to catch particulates such as the soot, polycyclic aromatic hydrocarbons, and other small particles that might be pertinent to biodiesel emissions. Further along the dilution tunnel the gases from the exhaust are rerouted towards a smaller compartment that is capable of holding the gases until they can be analyzed. The dilution tunnel then ends with an exhaust exit for the remaining exhaust that was not contained or filtered.
Before measuring for differences in the emission amounts between fuels the exhaust should be first analyzed to determine what type of compounds biodiesel emits. The filter catches particles indiscriminately so for analysis of a specific compound, it needs to first be isolated from the filter mixture. In order to determine what is in fuel emissions in general, less specific procedures can be used. The filters should first be weighed in order to determine the net mass of all the particles. For the particulate matter a flame ionization detector can be used to determine the identities of the solid compounds [3]. An IR and mass spectrometer can also be used to confirm what the exact particles were that were caught in the filter. Chromatography can also be used later on for separating specific molecules from the entire filter mix. The compounds could also be dissolved into solution and run in a liquid chromatography. The liquid chromatography should be run several times due to the different natures of multiple compounds. The hydrocarbons need a very polar solution for a successful elution, and other compounds may need non polar solutions for clear elution. After this general analysis further examination should be done to look more closely at the hydrocarbons that are entering the air directly through fuel emissions. Hydrocarbons lead to the formation of ground level ozone and are suspected of also inducing cancer [1]. If the amount of hydrocarbons entering the air can be accounted for than comparing the differences between diesel and biodiesel becomes much clearer.
To determine what is in the gas exhaust from the cars, samples are taken from the containment chambers that collected the gas emissions from the exhaust pipe. A solid-phase microextraction is used to easily remove a sample of the gas for gas chromatography. This microextraction is done using a syringe with a fused-silica fiber with a stationary liquid phase coating. The needle is inserted into the gas compartment and the filament then is then extended into the gaseous space. The gases such as carbon monoxide, carbon dioxide, and nitrogen oxides adhere to the stationary phase. The filament is then retracted into the needle. The syringe can transport these gases to a port for the gas chromatography [5]. Using this method allows easy collection and transport of gas samples for chromatography. Connecting the gas chromatography outlet to a mass spectrometer forms a transmission quadrupole mass spectrometer [5]. This spectrometer is able to determine the mass and structure of each compound as it is eluted from the chromatography column. Using this one in all type method is useful because one does not have to perform 2 separate tests thereby reducing the chance of contaminating samples or loss of precision. In past experiments carbon monoxide and carbon dioxide have also be analyzed by using a nondispersive infrared detector has also been used to past experiments and could be another resource for investigating the presence of these specific gases [3].
After the car exhaust has been examined to determine what compounds are produced from the fuels we are now able to then look at the difference between the amounts of each product produced by the different fuels. Similar methods of analysis are used to measure these differences. Additional gas and solid chromatography trials are run. Since previous runs have identified the compounds present in the exhaust they can easily be obtained separately during the elution. The basic conceptual idea is if the exhaust from diesel emits more byproducts than biodiesel the amount of substance available for analysis will be greater. There will be more sample collected from the diesel exhaust initially than from the biodiesel exhaust. Diesel exhaust is expected to have exhaust with a higher concentration. Gravimetric analysis can be used to determine the exact emission amount. Determining the original concentration of the exhaust requires the same steps and logic that is needed to figure out the initial concentration of a liquid sample. Finding the total amount of compounds is similar to any other dilution problem. Once the initial concentrations have been determined we are then able to compare the end results. The fuel of emissions of diesel and biodiesel are now appropriately quantified in a way that the results can be compared against each other and examined.
According to the current literature discussing biodiesel, the purposed experimental methods should show an overall decrease in pollutant emission when biodiesel is used compared with petroleum diesel. Most of the fuel exhaust is expected to decrease in carbon dioxide, carbon monoxide, smoke, and hydrocarbon emission [2]. The concentration of nitrogen oxides though may stay constant or even increase. The increase in nitrogen oxides could cause further problems by further contributing to the greenhouse gases dealing with global warming [1].
The development of biodiesel is a positive sign of the growing concern for the environment and the impact we are leaving on it. Researching the affects of biodiesel emission is a forward step because it begins to look at what other consequences the daily use of this new fuel might bring. The majority of the research done on biodiesel has suggested that the use of biodiesel in main stream traffic has few negative impacts on the environment. The by-products with the exception of nitrogen oxide are less than those from petroleum diesel. Producing this fuel is also more environmentally responsible than diesel. The main reason biodiesel has yet to become widely available is due to the fact that producing the fuel is still much more expensive than the cheaper petroleum. Hopefully research will continue to be done on the effectiveness of biodiesel, as well as other alternative fuels and in the near future finding biodiesel at any local gas station will soon become a more realistic expectation.
References
1. Demirbas, A. Biodiesel Impacts on Compression Ignition Engine (CIE): Analysis of Air Pollution Issues Relating to Exhaust Emissions; Energy Sources 2005, 27, 549-558.
2. Lue,Y.; Yeh, Y; Wu, C. The Emission Characteristics of a Small D.I. Diesel Engine Using Biodiesel Blended Fuels; J. Environ. Sci. Health 2001, A36(5),845-859.
3. Chen, K.; Lee, W.; Lin, Y.; Wu, T. A New Alternative Fuel for Reduction of Polycyclic Aromatic Hydrocarbon and Particulate Matter Emissions from Diesel Engines; Air & Waste Manage. Assoc. 2007, 57, 465-471.
4. Aulich, T.; DeWitt, M.; Corporan, E.; Larson, V.; Monroig, O.; Reich, R.; Seames, W. Impacts of Biodiesel on Pollutant Emissions of a JP-8-Fueled Turbine Engine; Air & Waste Manage. Assoc. 2005, 55, 940-949.
5. Harris, D. Exploring Chemical Analysis Freeman and Company, New York, 2005.
