Design for the Environment/Automobile Engines II

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This page is part of the Design for the Environment course

The road transportation sector is a major player in greenhouse gas emissions (GHG) with 137.8 MT of CO2 E in 2005. Out of that, around 57% of GHG emissions originate from the passenger transportation sector alone [1] . The increase in environmental concerns as well as crisis of non-renewable resources coming to an end, entails the automotive industry to look into alternative fuel and engine designs that would run on renewable fuels, have low impact on environment and yet perform as efficiently as gasoline internal combustion engines, which are used in almost all mid-size passenger vehicle. Two different engine designs; Flex Fuel internal combustion engine and Fuel Cell, are studied from economical and environmental aspects over their entire life cycle, to be compared to gasoline internal combustion engine. Then the best alternative is to be chosen and suggested to Toyota.


Gasoline Internal Combustion Engine

"How car engine works: [1]
Hydrogen Fuel Cell Engine

" Ballard Fuel Cell power, : “Mark 902 user manual,” Accessed February 2008


Internal combustion engines utilize a four stroke design in which they intake a fuel, compress it, ignite it and the release the exhaust. In a gasoline internal combustion engine, gasoline is the fluid used to generate mechanical energy to power the vehicle, whereas in a flex fuel engine, a mixture of gasoline-ethanol is injected into engine and burned. Due to higher existence of oxygen atoms in ethanol, the combustion process of flex fuel engines is more complete, i.e. less CO is emitted and hence less pollution is generated with compared to gasoline. However the low fuel efficiency of these engines requires more frequent refueling, and hence higher energy consumption. As a result a newer concept of engine is introduced, which utilizes the electrical power generated from reaction of hydrogen and oxygen to power the vehicle; namely fuel cell. Even though there are no emissions involved in this new technique, there are high infrastructure costs as well as low to efficiency involved which implies higher degree of development is yet to be done before changing the automobile engine design. A comprehensive cost analysis, economic input-output life cycle analysis and streamlined life cycle assessment is performed to ascertain Toyota that gasoline internal combustion engine is thus by far the best engine design.


Project Information[edit | edit source]

Section 1 Group B4

Elmira Kalali (elmira_kalali)

Barzin Doroodgar (Barzin)

Bogdan Beca (Bbeca)

Sumin Baek (SBaek)

Highlights and Recommendation[edit | edit source]

The relative functional, environmental and economical merits of each fuel alternative are evaluated thoroughly with help of a comprehensive cost analysis, an economical input-output life cycle analysis and streamlined life cycle assessment. It is crucial to recognize that there are trade offs between environmental and economical aspects of a design.

According to the cost division chart shown below, it can be clearly observed that the capital cost of hydrogen fuel is roughly three times larger than that of counterparts; gasoline and flex fuel internal combustion engines. On the other hand, this new technology of using hydrogen and oxygen to generate electricity for powering a mid sized passenger vehicle has a much lower fuel production cost. Clearly, if these three engine design alternatives are compared against each other only based on costs over their entire life stage, gasoline internal combustion engine would have the lowest total cost $53632.02, flex fuel engine would have the second highest total cost, $66,874.58, and fuel cell would have the highest of all, $228,261.2, due to its high indirect and capital cost.

Cost[edit | edit source]
Cost division for the three alternatives


A closer look at associated costs for each life cycle stage reveals that fuel cell has twice as high manufacturing cost as other two engine designs. On the other hand in fuel production stage, hydrogen fuel cell has significantly lower cost in producing hydrogen than other alternatives, which have to produce gasoline from crude oil and ethanol form corn respectively. Further analysis shows that all three alternatives have similar associated costs during their use stage as well as their end of life stage. Moreover since there are relatively less moving parts in a fuel cell engine, the maintenance cost for such an engine is comparatively lower than gasoline internal combustion engine and flex fuel engine.


Now if all the aforementioned cost values are entered into the economic input-output life cycle analysis model as an input, one would be able to evaluate these alternatives based on their environmental impacts, such as level of air pollutant emission, global warming potential and level of greenhouse gas emissions from each sector of industry involved in the life stage of automobile engine.



Global warming potential in MTECO2


From the potential global warming graph shown, it is evident that in general hydrogen fuel cell’s contribution to global warming, measured in metric tones equivalent of CO2, is less than gasoline and flex fuel internal combustion engine. The nil contribution of these engines during their use stage, which reflects their zero tail pipe emission characteristics, makes them a desirable substitute for current gasoline internal combustion engines, which are one of the major contributors to global warming. However, once the fuel production stage of this design is evaluated, high levels of CFCs and CO2 are emitted. But comparing it to that of gasoline internal combustion engine and flex fuel engine, it can be seen that more CO2 is emitted during gasoline and ethanol production processes. An interesting trend is that flex fuel engine produces almost one sixth of CO2 produced when 100% gasoline is used a fuel in an engine to power a vehicle, i.e. gasoline internal combustion engine. That is because ethanol contains more oxygen atoms, which helps the combustion process and thus burns cleaner than counterpart gasoline. Thus the alternatives from least contributor to global warming to most are: hydrogen fuel cell, flex fuel engine and gasoline internal combustion engine.



Total Energy in TJ





In addition to global warming, the energy use can be utilized for evaluating the former designs. According to energy graph shown, all three designs, consume the most energy in their fuel production stage and use stage. A more detail examination reveals that flex fuel is the most energy intensive design of all three. This is primarily due to lower energy density of E85. Also the distillation process required in ethanol production involve large electricity input, thus making it the least environmental friendly engine design among the three at hand.








Last but not least, a scoring matrix is employed (shown below) to assess each life cycle of engine design based on material choice input, energy use, solid residues, liquid residues and gaseous residues. The important assumption that is made prior to streamlined life cycle assessment is that the fuel production stage is merged with use stage of the engine. However for a more realistic analysis the fuel production stage is ignored for solid, liquid and gaseous residues produced in use stage. According to total scores for each stage (sum column) one can see that the pre-manufacturing stage of fuel cell has the highest environmental impact. This is mainly due to platinum extraction required for manufacturing of fuel cell components. Even its manufacturing and end of life stages have relatively higher impact on environment when compared to gasoline internal combustion engine and flex fuel engine. The reason for high impact in manufacturing stage is because large infrastructures are required for manufacturing of fuel cell. Moreover the non-renewable characteristics of the polymers used in fuel cells entail incineration and landfill which would damage the environment. On the other hand the zero tail emission of these engines makes them an appealing alternative. This phenomenon is evident by a huge score for use stage. If one is to disregard the severe impact of gasoline internal combustion engine on environment, and look at its all other life stages, it is apparent that is a better choice than flex fuel. Even though ethanol burns cleaner that gasoline, it has lower energy efficiency with compared to gasoline. Based on efficiency of the fuel, gasoline is the best alternative for powering a mid-sized passenger vehicle.

SLCA[edit | edit source]
Streamlined life cycle assessment for three alternatives


Having examined the three alternatives at hand from economical and environmental aspects, it is acceptable to say gasoline internal combustion engine is still the best engine design for mid-sized passenger vehicles, in spite of its high level of air pollutant emission and greenhouse gas emission. One might argue that hydrogen fuel cell appears to be a good alternative with no emission during its operation. However it is clear that the technique is not implementable until an effective cost and energy way of producing it, is developed. Similar analogy exists for flex fuel engines; despite of a cleaner combustion process, the low efficiency of ethanol requires frequent refueling and hence greater energy consumption. In conclusion, based on the quantitative and qualitative data presented, it is suggested that Toyota should power its vehicles with an gasoline internal combustion engine.


Technical Analysis[edit | edit source]

Gasoline Internal Combustion Engine[edit | edit source]

A gasoline internal combustion engine (ICE) operates by converting the chemical energy from the exothermic reaction of a gasoline-air mixture to mechanical energy. In these engines, combustion of gasoline and an oxidizer occurs in a confined space called the combustion chamber. The first step in the combustion process is the intake stage, where the intake valve is opened and fuel mixture is allowed to flow in the combustion chamber. The piston is then moved upwards, compressing the fuel mixture in the compression stage. This is followed by the combustion stage, which is initiated by a high voltage electric spark. The fuel combustion expands the gas inside the chamber which drives the piston down with high power. Finally, in the exhaust stage, the exhaust valve is opened and the piston moves upward pushing the emissions created by the combustion out. The translational movement of a series of pistons are converted to rotational movement of the wheels by means of the crankshaft [2].

The performance of internal combustion engines varies depending on the size and manufacturer. A typical gasoline ICE of a midsized vehicle has a compression ratio of 10.0. These engines can be run with unleaded fuel with an octane rating of 87 and a fuel economy of 30 to 40 MPG [3]. .

Flex-Fuel Internal Combustion Engine[edit | edit source]

The flex fuel internal combustion engine (FFICE) used in flexible fuel vehicles (FFVs) works on the same principle as the regular gasoline internal combustion engine. The major difference is that the FFICE uses a mixture of 85% ethanol and 15% gasoline (E85) as the main fuel source. The FFICE usually has lower fuel efficiency compared to the gasoline ICE due the energy density of the fuel being lower than that for gasoline [4]. E85 contains more oxygen atoms than regular gasoline and this produces a cleaner burn with fewer hydrocarbons left in the actual combustion chamber [5]. E85 has a theoretical octane rating of 113 in its purest form [6] which produces a compression ratio of 15 [7] . As noticed, a higher octane rating produces a higher compression ratio which is very important for increasing the thermodynamic efficiency of the engine. However, because the engine has to be compatible with 100% gasoline, lower compression ratios that prevent auto-combustion of gasoline have to be used, thus lowering the thermodynamic efficiency. Additionally, the flex fuel engine contains an Engine Control Unit (ECU) that regulates the flow rate and adjusts the timing of the spark plugs to ensure proper combustion.

Hydrogen Fuel Cell[edit | edit source]

The direct hydrogen fuel cell automobile propulsion system is composed of a Proton Exchange Membrane Fuel cell (PEMFC) system and a compressed hydrogen tank. Hydrogen fuel is provided to the anode of the fuel cell while oxygen is provided to the cathode through the channel formed on the bipolar plates. At the anode, the platinum catalyst facilitates the breakdown of hydrogen molecules into positively charged hydrogen protons and negatively charged electrons, and these electrons are forced to flow through an external circuit. Meanwhile, at the cathode, the negatively charged electrons, positively charged protons and oxygen combine to produce by-product such as water [8]. For example, the Ballard® Mark902™ fuel cell, used for the automobile propulsion system, produces a continuous stack power of 85kW, 300 Amps of current, and 284volts of DC voltage [8]. In general fuel cells used in automobiles produce 50-85kW, which is a sufficient requirement to power a conventional mid sized vehicle. In general, hydrogen fuel used for the system has the octane rating of 130+ [9] and exhibits energy characteristics of 113,600-134,500 Btu/kg [10] .


Cost Analysis[edit | edit source]

Gasoline Internal Combustion Engine[edit | edit source]

The life cycle cost analysis of the ICE is performed based on the 2009 Toyota Corolla CE. The capital cost of the engine is estimated as $2,718, which is based on the assumption that the manufacturing cost of the engine is about 30% of the automobile production cost. Furthermore, for comparison with the other engine alternatives, the fuel production is included as part of the ICE life time cost analysis, $2.85 per gallon. This takes into account the crude oil production and refinements costs which are reported in 2004 as 50% and 18.5% of the gasoline retail price, respectively [11]. Furthermore, the operating cost of this engine is found to be $31,174 over its life time [12]. which contributes the most to the overall cost of the entire life cycle. Another cost taken into consideration is the maintenance and repair cost of the engine. The maintenance cost is estimated based on the typical costs that are needed to maintain the engine over the entire life time; such as engine tune up, timing belt replacement, engine oil change, radiator flush, etc [13]. The repair costs in this study are based on the revenue data reported by repair services of Canada in 2005 [14]. Taking these factors into account over the life cycle of the engine the total maintenance and repair costs are estimated to be $15,117. In addition, in order to integrate the end of life of the engine into the cost analysis, earnings obtained by recycling the engine is included in the cost analysis [15][16]. This is found to be about $59 and does not have an overall effect on the total cost. Last but not least, the insurance cost of the engine is taken as an indirect cost in this study, which is estimated as 30% of the total insurance cost; i.e. $4,563 [17].

Flex-Fuel Internal Combustion Engine[edit | edit source]

The most important direct costs shown in the cost division table, are composed of capital costs, fuel production cost, operating cost, repair & maintenance cost and recycling cost. The capital cost is mainly the cost of purchasing the engine minus the inflation and the profit margin. Following the assumption that, typically the cost of an engine is 30% of the cost of a car, using the cost of a 2009 Toyota Corolla CE basic model and including the cost of a Fuel Flex Gold Conversion Kit [18], which ensures that all the settings of any combustion engine are properly adjusted in order to work with the E85 fuel mixture, the capital cost is $3098.3. The fuel production cost including the cost of feedstock and variable costs such as maintenance, labour and electricity of facilities used for processing is $0.73/gallon. The operating cost of the FFICE includes the cost of the fuel throughout the lifecycle of the FFV and therefore it is found to be $39,927.05. The repair and maintenance cost, $19,226.8, is mainly concerned with recurring costs such as for tuneups (e.g. engine oil and drive belts replacement) [19] [13][20]and with the average cost for repairing or refurbishing an engine. Finally, at the end of the life cycle, the engine is recycled and it is assumed that 95% of it is made of mixed steel and cast iron scrap and 5% of it is made of aluminum. After the engine has been recycled the amount received back from selling the metallic parts back to the recycling companies is $59.43. The indirect cost is mainly composed of the cost of the insurance for the sedan, i.e. 30%, under analysis as given by the Transportation Energy Data Book [17]. Thus at the end of the life cycle the total insurance cost sums to $4563.

Hydrogen Fuel Cell[edit | edit source]

Despite its environmental merits, fuel cells are slow to commercialize due to their high production cost. Furthermore, the implementation of fuel cell as an automobile propulsion system means establishing a new infrastructure system for the production and delivery of hydrogen fuel. The capital cost associated with a fuel cell automobile propulsion system is $8824 and this cost is considerably higher than the operating, maintenance, or disposal cost which are $3843, $7500, and $441.2, respectively.(see the cost division table above) In addition to the direct cost, the indirect cost related to warranty, health, environment, and society is $207,653. The most significant source of indirect cost is from road infrastructure establishment,health and environmental impacts. The fuel cell automobile propulsion system is not yet widely commericalized and the capital cost of a fuel cell is being actively investigated by many research groups [21] [22] [23]. Moreover, the production cost of the fuel cell is expected to decrease once they are widely implemented by the automobile industry. The capital cost of a fuel cell encompasses a fuel cell stack cost, auxiliary system cost, and a fuel tank cost. The operating cost of the fuel cell is based on the cost of the hydrogen fuel, $0.7/gallons of gasoline equivalent, that the system consumes over its entire life cycle. The cost incurred from maintaining the fuel cell automobile propulsion system is comparatively small since there are very few moving parts. A minimum level of maintenance is required for fuel cell systems. The only maintenance that is required is the occasional changing of air filters and pump check ups. At the end of the life cycle of a fuel cell system, a large portion of the membrane assembly and other fuel components are either incinerated or landfilled at the end of its use. From this it is assumed that the end of life disposal cost of a fuel cell is estimated as 5% of the capital cost.



Economic Input-Output Life Cycle Analysis[edit | edit source]

To evaluate the environmental impact of automobile engine design, the economic input-output life cycle analysis is employed, based on 1997 Us dollar amount of production.

Gasoline Internal Combustion Engine[edit | edit source]

Gasoline Internal Combustion Engine GWP Graph

Looking at the GWP of each life stage, shown on the figure above, it can be observed that the use phase is the largest contributor to GHG emissions. This is expected since the gasoline engine has a relatively long use phase in which high amounts of CO2 are emitted. Also, it can be concluded from the graph that the gasoline production is a significant factor to the lifetime GWP of the gasoline engine. The major contributing sub- sectors in fuel production are petroleum refineries and oil and gas extraction emitting large amounts of CO2 and CH4, respectively.

Gasoline Internal Combustion Engine Energy Graph

The figure above shows the energy use of various life stages of the gasoline engine. The most energy intensive stages are use and fuel production, which is the same trend as seen for the GWP. This is once again due to the relatively long use phase of the engine and the energy intensive processes that take place in petroleum refinement in order to convert heavy hydrocarbons into valuable by-products [24].

Flex-Fuel Internal Combustion Engine[edit | edit source]

Energy use for the lifecycle of the FFICE

In the figure above, it is very noticeable that throughout all the life stages of the life cycle of the flex fuel engine, the fuel production phase has the highest global warming potential. The highest contributing sub-sector is the “Basic Organic Chemical Manufacturing” sector which emits large amounts of CO2 and N2O to process and refine ethanol. The farming industry also uses large amounts of diesel powered machinery, which contribute to the overall GWP during the fuel production phase [25]. Furthermore, the advantage of using a flex fuel engine is visible through the low global warming potential during the use phase. There are significantly less emissions during this phase since E85 burns more cleanly due to its high number of oxygen atoms.

In addition, in the figure above, shows that the energy use during the operation of the vehicle throughout its life cycle is very large. This fact can be explained through the lower energy density of E85 than gasoline and also its lower MPG. This causes frequent refuelling which, in turn, causes more energy consumption. Moreover, the energy use during the fuel production phase is also high as a result of intensive processes, such as distilling, which heavily relies on electricity that is generated from coal, which is the source of most emissions that cause a high global warming potential [26].

Hydrogen Fuel Cell[edit | edit source]

From the analysis, see figure above, it is apparent that fuel production stage of the fuel cell life cycle constitutes most of the total global warming potential. Furthermore, it is quoted that in central steam methane reforming stations the mass of CO2 produced during the production of the hydrogen is twice the mass of hydrogen produced [27]. On the other hand, the global warming potential during the use phase is shown nil, reflecting the zero tail pipe emission characteristic of a fuel cell propulsion system.

Energy use for the lifecycle of the PEMFC

As shown in the figure above, it is noticeable that the fuel production and use phase consume a large amount of energy. The steam methane reforming (SMR) process includes a reformation of natural gas, two stages of water gas shift reactions at a very high temperature, and repetitive purifications [27]. The SMR is an energy intensive process and this explains the highenergy consumption estimation from EIOLCA. Furthermore, relatively low 22% power plant-to-wheel efficiency of the hydrogen fuel requires a lot of energy input to operate.



Streamlined Life Cycle Analysis[edit | edit source]

Gasoline Internal Combustion Engine[edit | edit source]

The SLCA matrix indicates that delivery and end of life are the two most environmentally friendly stages of the engine’s life cycle. This is mainly due to the very low solid and liquid residues that result from this stage in delivery and the ability to recycle almost all the components in the engine. On the other hand, pre-manufacturing and manufacturing of the engine seem to have the most environmental impact. This results from the relatively high-energy use and residues in these processes. Looking at the different inputs and outputs of the life cycle, it is observed that energy use and gaseous residues have the most impact on the environment which is caused by the energy intensive processes and the large amounts of air pollutants in fuel production, engine manufacturing and use phase of the engine.

Flex-Fuel Internal Combustion Engine[edit | edit source]

It is visible in the SLCA Matrix shown in the middle of the page that for the flex fuel engine, the material choice column has overall the highest score, meaning that the use of virgin material is minimized and the amount of recycled materials is maximized. The column with the lowest score is the energy use and this can be reflected through the energy intensive processes of extracting and manufacturing the engine. Frequent refueling during the use phase is also an issue during the use phase. The rows with the lowest scores are the pre-manufacturing and the manufacturing life stages due to the high amount of energy input and also large number of residues being created.

Hydrogen Fuel Cell[edit | edit source]

The hydrogen fuel cell may be conceived as a zero emission automobile propulsion system, however when entire life cycle of the vehicle is considered, it shows that it in fact does contributes to green house gases and air pollution. From the SLCA matrix , it is shown that premanufacturing and manufacturing stage has the most negative impact on the environment. On the other hand, the use phase of the vehicle has a relatively small impact on the environment due to the non-combustible nature of a fuel cell.


See also[edit | edit source]

References[edit | edit source]

  1. ↑ Us Department of Energy, Energy efficiency and renewable energy, “Flexible fuel vehicles,” [online article], (November 2007), available at: < http://www.eere.energy.gov/afdc/vehicles/flexible_fuel.html>
  2. ↑ ] Charles Fayette Taylor, “Internal Combustion Engine in Theory and Practice,” Massachusetts institute of technology, [Book, pp 10-33], (1985),
  3. ↑ ] Automobile magazine, new cars, “2009 Toyot Corolla”, [Online], (March 2008), available at: <http://www.automobilemag.com/am/2009/toyota/corolla/index.html>
  4. ↑ NAFA fleet management association, “Energy Equivalents of Various Fuels,” [online article], (1998-2008), available at: <http://www.nafa.org/Content/NavigationMenu/Resource_Center/Alternative_Fuels/Energy_Equi valents/Energy_Equivalents.htm>
  5. ↑ Glen Beanard, Technical contributor of Babcox,“ Alcohol-Based Fuel,” [online article], (February 2008), available at: < http://www.babcox.com/editorial/us/us020628.html>
  6. ↑ Ethanol, Fuelling America’s future, “Ethanol facts,” [online article], (February 2008), available at: <http://www.drivingethanol.org/ethanol_facts/ethanol_facts.aspx>
  7. ↑ American Energy Independence, “Ethanol and energy independence,” [online article], (February 2008), available at: <http://www.americanenergyindependence.com/ethanol.html>
  8. ↑ 8.0 8.1 Ballard, “fuel cell power specification sheet,” [online article], (March 2008), available at: < http://www.ballard.com/files/pdf/Spec_Sheets/SPC5000035_-_0D_Mark902.pdf>
  9. ↑ National hydrogen association, “Hydrogen as an energy carrier,” [online article], (March 2008), available at: <http://www.hydrogenassociation.org/general/faqs.asp#1kWh>
  10. ↑ Air Products, “Hydrogen energy, energy values,” [online article], (March 2008), available at: <http://www.airproducts.com/Products/MerchantGases/HydrogenEnergyFuelCells/EnergyValues.htm>
  11. ↑ Energy information administration, “A Primer on Gasoline Prices,” [online article], (2005), available at: < https://archive.is/20121213035709/www.eia.doe.gov/bookshelf/brochures/gasolinepricesprimer/eia1_2005primerM.html>
  12. ↑ Ontario Ministry of Energy, “Gasoline Report,” [online article], (March 17, 2008), available at: < http://www.energy.gov.on.ca/index.cfm?fuseaction=oilandgas.gasreport>
  13. ↑ 13.0 13.1 Cost helper, “How much does a Tune-up cost? ,” [online article], (November 2006), available at: < http://www.costhelper.com/cost/cars/tune-up.html>
  14. ↑ Statistics Canada, “Automotive repair and maintenance services,” [online article], (2005), available at: <http://www.statcan.ca/Daily/English/070328/d070328a.htm>
  15. ↑ Recycle exchange, “Steel & Iron Scrap Recycling (Fe) Exchange,” [online article], (March 2008), available at: <http://www.recyclexchange.com/a/0460.html?affilid=100000>
  16. ↑ Recycle exchange, “Aluminum Scrap Recycling (Al) Exchange,” [online article], (March 2008), available at: <http://www.recyclexchange.com/a/0403.html?affilid=100000>
  17. ↑ 17.0 17.1 Davis, S.C., and S.W. Diegel. “Transportation Energy Data Book”: [Book], (Edition 22 ,2002), Oak Ridge, TN: Oak Ridge National Laboratory.
  18. ↑ Felx fuel International, “Injector connectors” [online article], (2007), available at: <http://www.fullflexint.com/pages/products1.htm>
  19. ↑ Hybrid cars &alternative fuels, “Routine Maintenance Schedule for Alternative Fuel Vehicles” [online article], (2008), available at:< http://alternativefuels.about.com/od/vehiclemaintenanceguide/a/genmaintsched.htm>
  20. ↑ Cost helper, “How much does replacing a timing belt cost? ,” [online article], ( November 2006), available at:< http://www.costhelper.com/cost/cars/timing-belt.html>
  21. ↑ C.E Thomas et al. “Fuel options for the fuel cell vehicle: hydrogen methanol or gasoline?,” International Journal of hydrogen Energy 25 (Book, pp551-567) (2000)
  22. ↑ Bent SORENSEN, “Total life-cycle assessment of PEM fuel cell car,” Roskilde University, Energy & Environment Group (Book) (February 2008)
  23. ↑ E.J. Carlson, “Cost Analysis of PEM Fuel cell Systems for Transportation,” NREL/SR-560- 39104, (Book) (December 2005)
  24. ↑ UNational Center for Manufacturing Sciences, “Petroleum Refining; Impacts, Risks and Regulations,” (November 2004),
  25. ↑ Transport Canada, “Global warming potential,” [online article], (March 2008), available at:<http://www.tc.gc.ca/programs/environment/UTEC/GhgEmissionFactors.aspx>
  26. ↑ Green Centre, Technology articles, “Ethanol Myth”, [online article], (February 2008), available at:< http://autos.yahoo.com/green_center-article_115/>
  27. ↑ 27.0 27.1 New York State Energy research and Development Authority , “Hydrogen fact sheet, hydrogen production- Steam Methane Reforming (SMR),” [online article], (March 2008), available at: < http://www.nyserda.org>
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