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บทคัดย่อ/Abstract |
Currently, the world confronts global wanning and future shortages or even crises in the supply of fossil fuels. Biodiesel or methyl ester has been considered as one of the most practical alternative fuels for diesel engines because of its many attractive characteristics such as its renewability and its freedom from sulfur and aromatics. From the Food and Agriculture Organization (FAO) of the United Nations report in 2008, rubber harvested area in Thailand is 1.82 million hectares and from the Rubber Research Institute of Thailand reported, each hectare gives an approximate amount of 62.5 kg of seeds annually. The rubber seed kernels (52% of seed) contain 43% of brown oil. Thus, the aim of this study is to produce biodiesel from rubber seed oil, and then to investigate its effect to the engine as performance, emissions, spray characteristics, combustion efficiency, combustion characteristic, and heat balance. A 2-step reaction is used for the rubber seed oil (RSO) biodiese1 production. The first step is the acid esterification which purposes to reduce the free fatty acid (FF A) from crude rubber seed oil (CRSO). At the same time, it also extracts the gum from the CRSO and converts some of FF A molecules to be methyl ester and water at this stage. The optimum condition is by using 2.5% by mass of sulfuric acid, and molar ratio of methanol to oil is 6:1. This condition can reduce FFA from 20% in CRSO to 3%. The second step is the alkaline transesterification which is the core reaction process. The optimum conditions are 1.5% by mass of KOH for catalysis and v molar ratio of methanol to oil is 6: 1. The yielded RSO biodiesel is tested for its fuel properties and meet required standard except methyl ester content meets nearby lower. The engine performance is tested on a single cylinder, 411 cc, and direct injection diesel engine. The brake torque and brake power of RSO biodiesel are always lower than those ofdiesel by an average of about 5%. This reduces to only around 2% at 1300 rpm. An average of around 10% more fuel is consumed by the RSO biodiesel due to its lower heating value but this is less at 1300 rpm, reducing to about 4.5%. The brake thermal efficiency is better for the RSO biodiesel at 1300-1900 rpm. Spray characteristic testing, both fuels are injected into a 15 bar test chamber. The spray tip penetration of RSO biodiesel is close to diesel. Also, the spray cone angle is close to diesel. These results present that the fuel spray ofRSO biodiesel does not significantly difference from diesel. At 1300-1900 rpm, the combustion efficiency ofRSO biodiesel is higher than that of diesel. In addition, the specific emission of carbon dioxide from RSO biodiese1 is lower than that of diesel due to the structure of RSO biodiesel containing a higher proportion of hydrogen to carbon than diesel. At the same time, the toxic from carbon monoxide of RSO biodiesel is lower.The RSO biodiesel shows earlier starting of combustion (SOC) than diesel for O.6% lier SOC than diesel is less compressibility than diesel that causes earlier injection. Accordingly, the maximum heat release rate of RSO biodiesel in the premixed combustion is lower than diesel, due to smaller accumulation of fuel during the shorter ignition delay time. After that premixed combustion phase, initial heat release rate during the diffusion combustion is higher and later falling only slightly. This is due to the higher oxygen content of biodiesel which improves oxidation and ensures the completion of combustion in the initial stage of diffusion combustion.The heat balance, at low engine speed, the brake thermal efficiency of RSO biodiesel is quiet better than that of diesel. At the same time, heat loss in cooling water obtained from RSO biodiesel is more than that of petroleum diesel and both fuels trend to decrease with engine speed increasing. Heat loss through the exhaust gases ofRSO biodiesel is nearby diesel. From these results, the biodiese1 produced from RSO should be appropriate for use in low speed diesel engines such as those for farm machineries.<br />
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