The Biodiesel Handbook Editors Gerhard Knothe National Center for .. Martinez de Vedia, R., Vegetable Oils as Diesel Euels, Diesel Power Diesel Transp. No studies comparing results from manual and automated methods have been. Olaf Schröder.5 9 10 Other Uses of Biodiesel Gerhard Knothe Other Alternative Sur un Mode d’Utilization Possible de l’Huile de Palme à la Fabrication d’un No studies comparing results from manual and automated methods have. The Biodiesel Handbook. By Gerhard Knothe, Jon Van Gerpen and Jürgen Krahl (Eds.) Paolo Bondioli Dr. Head of Technology Department.
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Dunn and Marvin O. They have advanced from being purely experimental fuels to initial stages of commercialization. They are technically competitive with or offer technical advantages compared manuap conventional diesel fuel. Besides being a renewable and domestic resource, biodiesel reduces most emissions while engine performance and fuel economy are nearly identical compared to conventional fuels.
Several problems, however, remain, which include economics, combustion, some emissions, lube oil contamination, and lowtemperature properties. An overview on a Less. An overview on all aspects of biodiesel is presented. The use of vegetable oils in diesel engines is nearly as old as the diesel engine itself. The inventor of the diesel engine, Rudolf Diesel, reportedly used groundnut peanut oil as a fuel for demonstration purposes in 1. Some other work was carried out on the use of vegetable oils in diesel engines in the s and s.
The fuel and energy crises of the late s and early s as well as accompanying concerns about the depletion of the world s non-renewable resources provided the incentives to seek alternatives to conventional, petroleum-based fuels.
In this context, vegetable oils as fuel for diesel engines were remembered. They now occupy a prominent position in the development of alternative fuels. Hundreds of scientific articles and various other reports from around the world geryard with vegetable oil-based alternative diesel fuels “biodiesel” have appeared in print.
Nevertheless, various technical and economic aspects require further improvement of these fuels. Numerous different vegetable oils have been tested as biodiesel. Often the vegetable oils investigated for their suitability as biodiesel are those which occur.
Therefore, soybean oil is of primary interest as biodiesel source in the United States while many European countries are ferhard with rapeseed oil, and countries with tropical climate prefer to utilize coconut oil or palm oil. Other vegetable oils, including sunflower, safflower, etc. Furthermore, other sources of biodiesel studied include animal fats and used or waste cooking oils.
Sources of biodiesel with some emphasis on developing countries have been discussed 2. Several problems, however, have impaired the widespread use of biodiesel.
They are related to the economics and properties of biodiesel. For example, neat vegetable oils reported to cause engine deposits. Attempting to solve these problems by using methyl esters causes operational problems at low temperatures.
Production and Evaluation of Biodiesel from Field Pennycress Oil
Furthermore, problems related to combustion and emissions remain to be solved. The problems associated with the use of biodiesel are thus very complex and no satisfactory solution has yet been achieved despite the efforts of many researchers around the world.
This article will briefly discuss economics and regulatory issues as well as conventional diesel fuel petrodiesel and then focus on research on the use of biodiesel in a diesel engine. Economics and Regulatory Issues Economic reasons have been one of the major obstacles in the use of biodiesel. Diesel fuel DF derived from vegetable oils is more expensive than petroleum-based DF. The feedstock for biodiesel is already more expensive than conventional DF.
For example, in the United States, a gallon of soybean oil costs approximately two to three times as much as a gallon of conventional DF. However, in the case of conversion of vegetable oils or fats to their esters, the resulting glycerol co-product, which has a potential market of its own, may offset some of the costs.
In most European countries, however, transportation fuels are so heavily taxed that tax incentives can be applied to encourage the use of biodiesel in the form of lower or no taxes on the biofuel and higher taxes on the petroleum-based fuel 3,4.
This subsidy artificially cheapens the biodiesel to make it competitive. In many developing countries, the overriding concern is to become independent of the imported commodity petroleum. In the United States, the tax mechanism is inapplicable because of the comparatively low taxes on transportation fuels. Artificially regulating the demand for fuels from specific sources by means of taxation is currently politically not feasible.
Nevertheless, biodiesel is attractive for other reasons. Besides being a renewable resource and therefore creating independence from the imported commodity petroleum and not depleting natural resources, health and environmental concerns are the driving forces overriding the economic aspects in some cases.
A life-cyle analysis of biodiesel 5 has shown that it is competitive with other alternative fuels such as compressed natural gas CNG and methanol in the urban transit bus market.
It is generally recognized that biodiesel has lower emissions, with the exception of nitrogen oxides NOxthan conventional petroleum-based DF. For example, due to its lack of sulfur, biodiesel does not cause SO2 emissions. The lower emissions have caused biodiesel to be used in urban bus fleets and manula make it especially suitable for. Besides environmental kjothe health reasons with accompanying Government regulations, focusing on the use of biodiesel in niche markets is rendered additionally attractive because not enough vegetable oil is produced to supply the whole diesel market with biodiesel.
Numerous reports exist showing that fuel economies of certain biodiesel blends and conventional DF are virtually identical.
No significant engine problems were reported as discussed later. In contrast to gasoline which is spark-ignited, DF after injection is knohhe by the heat of compression in a diesel engine. The diesel engine is therefore also termed a compression-ignition CI engine. The differences in the ignition processes entail significant differences in chemical composition and physical properties of the fuels.
Conventional DF is, like gasoline, obtained from cracking of petroleum. Ignition quality is defined by the ignition delay time of the fuel in the engine. The shorter the ignition delay time, the higher the CN. To rank different compounds on the cetane scale, hexadecane C16H34; also called cetanewhich has a very short ignition delay, has been assigned a CN of At the other end of the scale, 2,2,4,4,6,8,8-heptamethylnonane HMN; also C16H34which has poor ignition qualities, has been assigned a CN of The CN scale clarifies an important aspect of the composition of, or, on a more fundamental level, the molecular structure of the compounds comprising DF.
Longchain, unbranched, saturated hydrocarbons alkanes have high CNs and good ignition quality while branched hydrocarbons and other materials such as aromatics have low CNs and poor ignition quality. Since both too high and too low CN can cause operational problems in case of too high CN, combustion can occur before the fuel and air are properly mixed, resulting in incomplete combustion and smoke; in case of too low CN, engine roughness, misfiring, higher air temperatures, slower engine warm-up and also incomplete combustion occurmost engine manufacturers designate a range of required CN for their engines.
In most cases, this range is around CN This classification is the following: They are applicable for high-speed engines whose operation involves frequent and relatively wide variations in engine load and.
Such fuel is required for use at abnormally low temperatures. This grade is suitable for use in high-speed engines under relatively high loads and uniform speeds. DF2 can be used in engines not requiring fuels having the greater volatility and other properties specified for No. DF2 is the transportation diesel fuel to which biodiesel is usually compared. It is usually satisfactory only for low-speed and medium-speed engines operated under sustained load at nearly constant speed.
Besides the just discussed characteristics of conventional DF, other properties such as heat of combustion, pour point, cloud point, and viscosity are of great significance. These properties also play very important roles in the use of biodiesel. The two general types of diesel engines are the direct injection DI engine and the indirect injection IDI engine 8. In DI engines, the fuel is directly injected into the combustion chamber in the cylinder.
Biodiesel: The Use of Vegetable Oils and Their Derivatives as Alternative Diesel Fuels
In IDI engines, the fuel is injected into a prechamber which is connected with the cylinder through a narrow passage. Rapid air transfer from the main cylinder into the prechamber promotes a very high degree of air motion in the prechamber which is particularly conducive to rapid fuel air mixing 8. Combustion beginning in the prechamber produces high pressure and the fuels are subjected to high shear forces.
The IDI engine is no longer used for heavy bus and truck engines due to somewhat lower efficiency and higher fuel consumption than the DI system 8. However, for special purposes, such as underground work, IDI engines are still made in the heavier class due to low exhaust emissions. For smaller vehicles such as cars and light trucks, the IDI system is used because of its ability to cover a wider speed range.
The low exhaust emissions in combination with the wider speed range may lead to a continued use of IDI engines in urban areas, where the demand for low emissions can be more important than a somewhat higher fuel consumption combined with low annual mileage.
The IDI engine is also less sensitive to fuel quality 8. Definition of Biodiesel The term biodiesel has no unambiguous definition.
Full text of “The Biodiesel Handbook Knothe, van Gerpen and Krahl”
It stands for neat vegetable oils used as DF as well gernard neat methyl esters prepared from vegetable oils or animal fats and blends of conventional diesel fuel with vegetable oils or methyl esters. For use in the United States, the U.
Chemically, TGs are the triacylglyceryl esters of various fatty acids with glycerol Figure 1. Some physical properties of the most common fatty acids occurring in vegetable oils and animal fats as well as their methyl esters are listed in Gerharrd I. Besides these fatty acids, numerous other fatty gerhardd occur in vegetable oils and animal fats, but their abundance usually is considerably lower.
Table II lists the fatty acid biodkesel of some vegetable oils and animal fats that have been studied as sources of biodiesel. The most common derivatives of TGs or fatty acids for fuels are methyl esters. These are formed by transesterification of the TG with methanol in presence of usually a basic catalyst to give the methyl ester and glycerol see Figure 1.
Other alcohols have been used to generate esters, for example, the ethyl, propyl, and butyl esters. For esters these properties are given in Table IV. Also listed in Table III are the ranges of iodine values centigrams iodine absorbed per gram of sample of these oils and fats. The higher the iodine value, the more unsaturation is present giodiesel the fat or oil. The heat Table I. Selected properties of some common fatty acids and esters.
Trivial Systematic namea ; Acronymb Mol. For example, in oleic acid, Melting points and boiling points of Other CNs given in Ref. CNs amnual combustion quality numbers deviating from Ref. Methyl laurate 54, methyl myristate 72, methyl palmitate 91, methyl stearate