Biofuels are oxygenated compounds. Oxygenated compounds such as ethanol, methanol, and biodiesel provide more efficient combustion and cleaner emissions. At a stoichiometric air:fuel ratio of 9:1 in comparison with gasoline’s 14.7:1, it is obvious that more ethanol is required to produce the chemically correct products of CO2 and water.

Ethanol has a higher octane number (108), broader flammability limits, higher flame speeds, and higher heats of vaporization than gasoline. These properties al­low for a higher compression ratio, shorter burn time, and leaner burn engine, which lead to theoretical efficiency advantages over gasoline in an internal combustion en­gine. The octane number of ethanol allows it to sustain significantly higher internal pressures than gasoline, before being subjected to predetonation.

Disadvantages of ethanol include its lower energy density than gasoline, its cor­rosiveness, low flame luminosity, lower vapor pressure, miscibility with water, and toxicity to ecosystems.

Methanol also allows one to take advantage of the higher octane number of methyl (114) alcohol and increase the engine compression ratio. This would increase the efficiency of converting the potential combustion energy to power. Finally, alco­hols burn more completely, thus increasing combustion efficiency. Some technical properties of fuels are presented in Table 5.7.

Biofuels such as bioethanol, biomethanol, biohydrogen, and biodiesel generally have lower emissions than fossil-based engine fuels. Many studies on the perfor­mances and emissions of compression ignition engines, fueled with pure biodiesel and blends with diesel oil, have been performed and are reported in the literature (Laforgia and Ardito 1994; Cardone et al. 1998).

Vegetable oils have become more attractive recently because of their environ­mental benefits and the fact that they is made from renewable resources. Dorado et al. (2003) describe experiments on the exhaust emissions of biodiesel from olive oil methyl ester as alternative diesel fuel in a diesel direct injection Perkins engine.

The methyl ester of vegetable oil was evaluated as a fuel in CIE by researchers (Dunn 2001), who concluded that the performance of the esters of vegetable oil did not differ greatly from that of diesel fuel. The brake power was nearly the same as with diesel fuel, while the specific fuel consumption was higher than that of diesel fuel. Based on crankcase oil analysis, engine wear rates were low but some oil di­lution did occur. Carbon deposits inside the engine were normal, with the exception of intake valve deposits.

The results showed that transesterification treatment decreased the injector cok­ing to a level significantly lower than that observed with diesel fuel (Shay 1993). Although most researchers agree that vegetable oil ester fuels are suitable for use in CIE, a few contrary results have also been obtained. The results of these stud­ies point out that most vegetable oil esters are suitable as diesel substitutes but that more long-term studies are necessary for commercial utilization to become practi­cal.

The use of biodiesel to reduce N2O is attractive for several reasons. First, biodiesel contains little nitrogen, as compared with diesel fuel, which is also used as a reburning fuel. The N2O reduction is strongly dependent on initial N2O concen­tration and only slightly dependent upon temperature, where increased temperature increased N2O reduction. This results in lower N2O production from fuel nitrogen species for biodiesel. In addition, biodiesel contains a virtually trace amount of sul­fur, so SO2 emissions are reduced in direct proportion to the diesel fuel replacement. Bioesel is a regenerable fuel; when a diesel fuel is replaced by a biodiesel, there is a net reduction in CO2 emissions. As an energy source used in a diesel engine it reduces the consumption of diesel fuels and thereby reduces the greenhouse effect. Additional effects are a reduction in the ash volume and the SOx and NOx emis­sions of a biodiesel-fueled CIEs. Neat BD and BD blends reduce particulate matter, hydrocarbons (HC), and carbon monoxide (CO) emissions and increase nitrogen ox­ide (NOx) emissions compared with diesel fuel used in an unmodified diesel engine (Grassi 1999).

The total net emission of carbon dioxide (CO2) from biodiesel is considerably less than that of diesel oil, and the amount of energy required for the production of biodiesel is less than that obtained with the final product of diesel oil. In addition, the emission of pollutants is somewhat less. CO2, one of the primary greenhouse gases, is a transboundary gas, which means that, after being emitted by a source, it is quickly dispersed in the atmosphere by natural processes. Table 5.8 shows the aver­age biodiesel emissions compared to conventional diesel, according to EPA (2002).

Table 5.9 shows the average changes in mass emissions from diesel engines using biodiesel mixtures relative to standard diesel fuel.

Results indicate that the transformities of biofuels are greater than those of fossil fuels, thus showing that more resources are required to obtain the environmental friendly product. This can be explained by the fact that natural processes are more efficient than industrial ones. On the other hand, the time involved in the forma­tion of fossil fuels is considerably different from that required for the production of biomass (Carraretto et al. 2004).

Different scenarios for the use of agricultural residues as fuel for heat or power generation have been analyzed. Reductions in net CO2 emissions are estimated at 77 to 104 g/MJ of diesel displaced by biodiesel. The predicted reductions in CO2 emissions are much greater than values reported in recent studies on biodiesel de­rived from other vegetable oils, due both to the large amount of potential fuel in the residual biomass and to the low-energy inputs in traditional coconut farming tech­niques. Unburned hydrocarbon emissions from biodiesel fuel combustion decrease compared to regular petroleum diesel.

Biodiesel, produced from different vegetable oils, seems very interesting for sev­eral reasons: it can replace diesel oil in boilers and internal combustion engines without major adjustments; only a small decrease in performance has been reported; it produces almost zero emissions of sulfates; it generates a small net contribution of CO2 when the whole life cycle is considered; the emission of pollutants is compara­ble with that of diesel oil. For these reasons, several campaigns have been planned in many countries to introduce and promote the use of biodiesel (Carraretto et al. 2004).

The brake power of biodiesel was nearly the same as with diesel fuel, while the specific fuel consumption was higher than that of diesel fuel. Based on crankcase oil analysis, engine wear rates were low but some oil dilution did occur. Carbon deposits inside the engine were normal, with the exception of intake valve deposits.

Several results related to the influence of micronutrition on oil yields have been reported (Nithedpattrapong et al. 1995; Tilman et al. 2006; Thamsiriroj 2007; Thamsiriroj and Murphy 2009). Suitable climatic and soil conditions have increased plant oil yields (Thamsiriroj 2007). Biomethane generated from grass requires four times less land than biodiesel from rape seed to produce the same gross energy (Thamsiriroj and Murphy 2009). Grass is a low-energy, carbon-negative input crop (Tilman et al. 2006; Thamsiriroj and Murphy 2009).

Biofuel consumption in the EU is growing rapidly, but major efforts will need to be undertaken if the EU’s objectives for 2010 and beyond are to be achieved. Cur­rent and future policy support therefore focuses on creating favorable economic or legal frameworks to accelerate the market penetration of biofuels. The EU member states will promote specific types of biofuels, depending on their main objectives and natural potentials. The main EU directives that have an impact on sustainable energy development are those promoting energy efficiency and use of renewable energy sources, those implementing greenhouse gas mitigation and atmospheric pollution reduction policies, and other policy documents and strategies targeting the energy sector. Promotion of use of renewable energy sources and energy effi­ciency improvements are among the priorities of the EU’s energy policy because the use of renewable energy sources and energy efficiency improvements has a pos­itive impact on energy security and climate change mitigation. In the EU, climate change has been the principal policy driver for promoting the use of energy from renewable resources. The spring European Council of 2007 set ambitious targets by 2020 of a 20% reduction in greenhouse gas emissions compared to 1990 lev­els and a 20% renewables share in the EU’s final energy consumption, including a 10% share of biofuels in each member state. The greenhouse gas emission savings from the use of biofuels will be at least 35% compared to fossil fuels (Demirbas 2009b).

On 23 January 2008, the Proposal for a Directive of the European Parliament and of the Council on the Promotion of the Use of Energy from Renewable Re­sources was issued. Article 15 of this proposal defined environmental sustainability criteria that both domestic and imported biofuels must satisfy. These criteria in­clude a minimum greenhouse-gas-reduction requirement, limits on the types of land where conversion into biofuel crop production is acceptable, and reinforcement of best agricultural practices. The first sustainability criterion defined in the European proposal is a 35% reduction in greenhouse gas emissions for biofuels relative to their fossil fuel counterpart. The second sustainability criterion relates to the preser­vation of diverse ecosystems. The greenhouse gas emission savings from the use of biofuels and other bioliquids shall be at least 35%. Biofuels and other bioliquids shall not be made from raw material obtained from highly biodiverse land and from land with high carbon stock. Agricultural raw materials cultivated in the European Community and used for the production of biofuels and other bioliquids shall be ob­tained in accordance with the requirements and standards under the provisions of the proposal, and in accordance with the minimum requirements for good agricultural and environmental conditions (Demirbas 2009b).

Specifically for biofuels and bioliquids the draft directive establishes environ­mental sustainability criteria to ensure that biofuels that are to count towards the target are sustainable. They must achieve a minimum level of greenhouse gas emis­sion reduction (35%) and respect a number of binding requirements related to envi­ronmental impact and biodiversity. The sustainability criteria aim to reduce green­house gas emissions and to prevent loss of valuable biodiversity and undesired land use changes. For the foreseeable future the EU will have to rely on first-generation biofuels to achieve the 10% target by 2020: vegetable oils for biodiesel and sugar and starch crops for bioethanol. These import requirements may be between 30 and 50%. The sustainability criteria under discussion in the EU constitute an important step forward, their shortcomings notwithstanding. They should be implemented in a nondiscriminatory way without conferring undue competitive advantage to domes­tic producers and allowing developing countries export opportunities for bioethanol and biomass. A speedy transition to second-generation biofuels is of particular im­portance. Sustainability criteria should progressively ensure that only advanced bio­fuels are available for end users (Demirbas 2009b).