Thermally decomposed ricebran oil as a diesel fuel

Aceite de germen de arroz, un aceite no comestible, fue descompuesto térmicamente usando diferentes cantidades de óxido calcico como catalizador. Las propiedades combustibles del producto craqueado fueron evaluadas comparándolas con las del gasóleo. Las propiedades consideradas incluyeron el poder calorífico, punto de inflamación, viscosidad, temperatura de fluidez crítica, características de destilación, número de cetano y otras propiedades de los combustibles. Los resultados han mostrado que las propiedades combustibles del aceite descompuesto fueron bastantes similares a la de los gasóleos estándar. El poder calorífico fue del 80-90% de la del gasóleo y la viscosidad ligeramente mayor. El combustible preparado fue ventajoso sobre el gasóleo ya que el primero estaba completamente libre de sulfuro, el cual produce en la combustión del carburante gases corrosivos de óxido de azufre.

is given reoently to ttose attemates derived from indigenous sources and preferably renewable energy sources.Vegetable oils have the advantage of being extracted from oilseeds which are renewable sources.They have also the advantage of being ready available and liquids.
Vegetable oils show technical promise as alternative fuel for diesel engines and have good potential as emergency fuels.However, they have certain inherent problems when used as fuels in diesel engines, generally attributable to inefficient combustion.The ^high viscosity and low volatily of vegetable oils are responsible for most of the combustion problems of neat oils.Viscous fuels are poorly atomized in the engine resulting in inefficient combustion with subsequent formation of carbon deposits on the injector nozzle and other engine parts.Thus, the engine performance using plant oils can be markedly improved if the oil viscosity is reduced.
Several approaches have been investigated to reduce the oil viscosity by physical and chemical modifications.Chemical modification of vegetable oils to less viscous products can be made either by esterification with short chain alcohols^^"^^ or bv cracking in presence of a suitable mineral catalyst^ I The present work was proposed to investigate the feasibility of utilizing thermally cracked, oil as a fuel for diesel engines.-Ricebranoil is produced in Egypt in considerable quantities annually as a byproduct from rice milling industry.Ricebran oil is completely unsuitable for edible purposes because it is usually hydrolysed during processing giving highly acidic products.The production rate of'ricebran in Egypt during 1993/1994 was about 434,570 ton which contains about 76,000 ton oil.

INTRODUCTION
With the gradual depletion of the world petroleum supplies, a possibility occurs that petroleum-based fuels will be available neither in sufficient quantities nor at reasonable price in the near future.This revived interest in exploring alternate fuels for automotive vehicles such as methanol, ethanol, biogas, hydrogen and vegetable oils.In order to avoid new dependencies, more interest

EXPERIMENTAL
Crude ricebran oil produced as a byproduct from rice milling industry was used in the present study Ricebran oil cracking was carried out in one litre reaction flask mounted in a thermostatically-temperature controlled heating.nriaptljearjd,attached to a condensing and receiving units.The oil, 500 g, was mixed with calcium oxide at a load ranging between 0.5-3% of the oil weight and the mixture was then heated to (c) Consejo Superior de Investigaciones Científicas Licencia Creative Commons 3.0 España (by-nc) http://grasasyaceites.revistas.csic.es450 °C.During the thermal cracking process, the temperature of the reaction batch and the rate of distillate formation from oil cracking were monitored.The cracking period was recorded as the time elapsed between the start and end of cracked oil distillation.The weight of the collected distillate (product) was then determined which gave an estimate for the process yield.
The cracked oil products were then tested for their fuel properties using the ASTM standard methods for petroleum products.The cetane index on the other hand, was determined using a special cetane index nomograph (D 976-91) in wich this index can be uetermined according to the API gravity and mid boiling point of the fuel.

RESULTS AND DISCUSSION
The results of the present work have been used to show the effect of CaO load on the cracking rate and yield as well as the properties of the product as a fuel.The maximun yield is almost 70% of the starting material and the average cracking rate is 6.4% per hour.(Table 1).The fuel properties of the cracked products compared to diesel ahd'their-^âistillation'Characteristics'âfé listed inTablés (2-6).

(a) Distillation characteristics of the cracked products
Distillation characteristics of a fuel exert a great influence on its performance, particularly in medium and high speed engines.The average volatility requirements of diesel fuel vary with engine speed, size and design.However, fuels having too high volatility may reduce power output and fuel economy throught vapour lock in the fuel system or inadequate droplet penetration from the nozzle._ The results-^of^herASTMidistiHatiQn are listed in table (2).It can be seen that the 50% point, known as the mid boiling point for the oil cracked using CaO was mostly in the recommended range for the majority of automotive type diesel engines (232-280°C).It can be also observed that all samples have their 90% point at close temperatures which indicates that the carbon residue from the ignition of these products will be similar^^°^ However, there is some variations in the 10% point of the prepared samples which ranges between 130-175°C.This will be reflected on the ignition starting quality being worse for the samples having their 10% point at higher temperatures.
The ASTM distillation curves have been also used to determine the product content of the fractions which have sjmijar^boilinq range as diesel, kerosene and gásóírhe in ^aditíori%lts"coñteht of the compounds iDoUiñg over 350°C.The boiling range of gasoline, kerosene and diesel were taken as 35-180, 180-250 and 230 -350°C, respectively.The volumetric percentages of those four fractions in the cracked products are listed in Table (3).It should be emphasized that the total of the four fractions may exceed 100% because of the overlapping of the boiling range of kerosene and diesel fractions.
It is obvious that the fraction which has boiling range similar to diesel fuel constitutes the major fraction in all products.The percentage of this fraction is more or less similar in most samples and its greatest level (-65%) was found in the sample cracked using ?%CaO.On the other hand, the volumetric percentage of the-fraction which is heavier than diesel fuel ranges between 15-20% in most samples.

(b) The fuel properties of the cracked products of ricebran oil compared to the Egyptian standard specifications of a diesel fuel
The properties of the cracked products of ricebran oil relevant to their performance as a diesel engine fuel are compared to the Egyptian standard specifications of diesel fuel in Tables (4)(5)(6).
Physical properties of the products such as API gravity, specific gravity, pour point and kinematic viscosity are recorded in Table (4).It is clear that these properties are more or less similar to those of standard diesel fuel.Regarding the^iscosity of the products; it can be seen that the viscosity of ricebran oil (33x10'^ m^.S'^) has been markedly reduced by cracking to less than one third its original value.This reduced viscosity is, in most cases, very close to the maximum recommended viscosity limit according to the standard specifications.Fuel viscosity is a very important property affecting its atomization in the engine and hence its ignition properties.The atomization of the products which are slightly mole viscous than diesel fuel can be greatly improved by slight changes in the design characteristics of the engine such as the use of nozzle orifice with increased sizes.
The fuel content of water and sulfur as well as the carbon residuedue to fuel combustion and the percentage ash are alsoJniF)qçtan|-^uel,£ropertie$, Theçe affect thp engine perfomnance and thé composition of the exhaust gases which may have an adverse impact on the environment.These properties are listed in Table (5).All samples are free from sulfur which if present in the fuel may give nse to low temperature sulfur corrosion owing to the fact that SO2, SO3 and water may condense in the colder engine parts.They are also free from non-burnable materials as detected by the ash % which is zero in all samples.These nonbumable materials, if present, may cause some abrasion of the fuel injection components which are usually made with great precision to extremely close fits and tolerances.In addition, the ash can cause wear within the engine itself by increasing the overall deposit level and by adversely affecting the nature of the deposits.
Although the sulfuncontent and ash % in the prepared samples agree well with the standard specifications of diesel fuel, their water content is beyond the allowable limits.Water can contribute to filter blocking and cause corrosion of the injection system components.According to the standard specifications, the water content should not exceed 0.15% in diesel fuel.
It can be also observed from the listed results that the carbon residue from combustion of all cracked products is within the standard limits (0.1%).Increased deposits of carbon due to fuel combustion in a diesel engine may cause injector coking which, in turn, results in a lot of ignition troubles due to poor fuel atomization.