KAJI EKSPERIMENTAL PENGARUH TEMPERATUR BIODIESEL MINYAK SAWIT TERHADAP PERFORMANSI MESIN DIESEL DIRECT INJECTION PUTARAN KONSTAN

Abstract

The imperfect combustion process is a problem in the development effort of diesel engine’s performance. Nonhomogen air–fuel mixing process is one of the factors which cause the imperfect combustion. By heating up the diesel fuel and biodiesel up to a certain temperature before it goes through the high pressure injection pump become lower to its density and viscosity. Therefore, when fuel injected in the combustion chamber, it forms smaller droplets of fuel spray which result in a more homogenious air–fuel mixture. Also by using fuel which has higher temperature will make the diesel fuel easily to ignite in order to compensate the limited time which is available in high speed operating conditions. Biodiesel is an alternative fuel for substitution to diesel fuel. Biodiesel has several advantages compared to diesel fuel. These advantages are lower hydrocarbon and monoxide carbon emission. But biodiesel has several disadvantages those are lower its caloric value and viscosity compared to diesel fuel. In this thesis, the effect of temperature on the viscosity and density of palm oil biodiesel and diesel fuel was studied experimentally. Subsequently, the study of the effect of fuel temperature on the brake specific fuel consumption (bsfc) and thermal efficiency of diesel engines was also conducted. Diesel engine Dong Feng 1 cylinder direct injection at constant speed was used in this research. The fuel used are diesel fuel and biodiesel with temperature variations in the range from 33oC to 70oC for diesel fuel and 33oC to 90oC for biodiesel fuel. The best thermal efficiency for biodiesel fuel is 21.3 % at 70oC with 11 % BSFC. In this condition, the fuel consumption was decreased 8 % by comparing with that at 33oC. Mean while, the best thermal efficiency of diesel fuel is 23.7 % at 60oC with 4 % BSFC, and the fuel consumption was decreased 4 %. The best temperature lies at 70 °C for biodiesel and 60 °C for diesel. Furthermore, the fuel consumption required by engine was increased as the fuel temperature continuous vi raising. This increase occurs becouse the raise of fuel temperature couses the fuel easier to ignite, so it will shorten the period of pre-combustion (ignition delay). Pre-combustion period can be defined as the time of preparation of fuel measured from the beginning of injection to the self-ignition condition. High temperature of fuel causes the fuel achieving quickly self-ignition. If this period is too short, then the combustion period occurs within the compression stroke or far before top dead center (TDC). Consequently, the peak pressure also occurs on the piston prior to reach the top dead center (TDC). This condition is deprivation because the pressure is used for works. As a result, the power generated are reduces and brake specific fuel consumption(BSFC) raises. The increase of fuel consumption and engine power reduction couses the reduction of thermal efficiency, because the thermal efficiency of a combustion engine is defined as the amount of heat generated from burning fuel into mechanical work. Heat or power supplied by the fuel can be predicted by the amount of fuel consumption, while the major mechanical work can be determined from the measured engine power. Therefore, the value of thermal efficiency is affected by the change of engine power and rate of fuel consumed by the engine. In addition, the pressure generated during combustion produces an againts compression force on the piston and piston drive mechanism, so that it can damage some components. Therefore, adjustment between fuel temperature and injection period that are able to avoid the energy lossis, so the available power for works was even greater.