Evaluation of the Specific Fuel Costs for Combination of Diesel Fuel- Biodiesel -Bioethanol in a Diesel Engine

The researchers have been currently focused on replacing fossil fuels by biofuels to reduce dependence on fossil fuels.  Biofuels provide low greenhouse emissions with the reduction of oil import. The biofuels can play an important role economically becomes more clear when their relatively developed agricultural sector is taken into account. Bioethanol, biodiesel and to a lesser extent pure vegetable oils are recently considered as most promising biofuels. Since 19 century, ethanol has been used as a fuel for the diesel engines. The cost of bio-diesel for IC engine is slightly greater than that of diesel oil. The specific fuel consumption, a function of the engine speed, is higher in bio-diesel than in diesel oil. The results previously of Bench-test indicated that the average value of SFC for bio-diesel was 17% greater than that of diesel oil. As for the properties of biodiesel, the lower heating value, higher density and higher viscosity play a primary role in engine fuel consumption for biodiesel. Most of the authors, who agreed that fuel consumption increased for biodiesel compared to diesel, contributed to the loss in the heating value of biodiesel. Of course, some authors only explained the increased fuel consumption as the result of the higher density of biodiesel, which causes a higher mass injection for the same volume at the same injection pressure. The equipment and instruments used in the present research were a diesel engine (OM 314), a dynamometer, a dynamometer control panel and a fuel tank. A four-cylinder direct injection diesel engine, model OM 314, made by Idem Company, Tabriz, Iran, was used to conduct the experiments. The fuel used in the present research was from waste oil. Ethanol was also used to feed the engine. The blends of diesel–ethanol–biodiesel were prepared on a volumetric basis. The experiments were conducted based on the response surface methodology and using Central Composite Rotatable Designs (CCRD). The response surface methodology, as one of the best methods to optimize processes and determine the effect of different variables on the responses, has special popularity among researchers. Applied research design in this study was CCRD that has the most application among other designs of the method. Independent variables were different ratios of ethanol, biodiesel, and diesel, engine load, and engine rotational speed and responses were included engine brake specific fuel consumption. The P-values for both total and prediction models of specific fuel costs were less than 0.01. This result showed that the models statistically have high abilities to predict the impacts of independent variables on specific fuel costs at 1% probability level. The linear, quadratic and interaction of the overall model had a P-value less than 0.05 that indicated their statistical validity. The specific fuel costs decreased for all blends by increasing the engine load. The reduction of specific fuel costs was more aggressively observed in low loads. With increasing engine rotational speed, the specific fuel costs were increased at low loads and at middle and high loads it was decreased and then increased. The increasing of volume ratio of biodiesel in the blended fuels, specific fuel costs were increased. By increasing the volumetric ratio of ethanol and biodiesel, specific fuel costs were increased due to lower calorific value and the direct relationship of this variable with brake power compared to that of diesel fuel in all test conditions and all fuel blends. By increasing of biodiesel ratio in the blended fuels, the specific fuel costs were increased at the low percentage of ethanol ratio. But by the increase of ethanol ratio the specific fuel consumption firstly was increased and then slightly decreased at high levels of biodiesel. The minimum of the specific fuel costs (580 R kW-1h-1) occurred at full load and engine rotational speed of 2139 rpm for pure diesel (B0E0D100). Also, the maximum of specific fuel consumption was obtained by 9951 R kW-1h-1 at 20% engine load and rotational speed of 2800 rpm and for a fuel blend containing 0.8 l biodiesel, 0.4 l ethanol and 1l diesel (B45.2E36.6D18.2).