Optimization Performance Indices of Diesterol Fuel in Diesel Engine by Response Surface Methodology

Diesterol is a new specific term which denotes a mixture of fossil diesel fuel (D), vegetable oil methyl ester called biodiesel (B) and plant derived ethanol (E). Recently, much attention has been paid to the development of alternative fuels in order to meet the emission standards and to reduce the dependency on fossil fuel. Biodiesel and ethanol have been considered as major alternative fuels, as they are derived from renewable sources. These fuels are well oxygenated and therefore have a great potential to reduce emissions. Biodiesel is an oxygenated diesel fuel made from vegetable and animal fats by conversion of the triglyceride fats into esters via transesterification.
The engine test bed consisted of a diesel engine, a dynamometer, a gas analyzer and a fuel tank. The control bench also consisted of control units, data logger and a PC. Engine was loaded by a ferromagnetism dynamometer of 400 kW capacity and load was measured with spring balance. The experiments were designed using a statistical tool known as Design of Experiments (DoE) based on central composite rotatable design (CCRD) of response surface methodology (RSM) and the optimum points were found using RSM. Four experimental variables in the present study including the operating parameters, load and speed and the added volume of biodiesel and ethanol in one liter of diesel fuel were considered to be effective factors on the brake power and torque. Designs that can fit as a model must have at least three different levels in each variable. This is satisfied by central composite rotatable designs (CCRD), which have five levels per variable. The most successful and best among the designs is the central composite design which is accomplished by adding two experimental points along each coordinate axis at opposite sides of the origin and at a distance equal to the semi diagonal of the hyper cube of the factorial design and new extreme values (low and high) for each factor added in this design. In the present work, the response surface methodology based on desirability approach is used for the optimization of experiment parameters (load, speed, biodiesel and ethanol volume) for the measured properties of response (brake power and torque). The optimization analysis was carried out using SAS 9.2 software, where each response is transformed into a dimensionless desirability value (d) and it ranges between d = 0, which suggests that the response is completely unacceptable, and d = 1, which suggests that the response is more desirable.
The resultant quadratic models of the response surface methodology were helpful to predict the response parameters including the performance characteristics of engine and further to identify the significant interactions between the input factors on the responses. By increasing the amount of biodiesel, the brake power is reduced compared to diesel fuel. This is due to two factors: the first is concerned with the percentage of biodiesel in the fuel mix because of the low calorific value of biodiesel compared to diesel fuel, calorific value fuel mixture is reduced. On the other hand, due to the high viscosity of biodiesel than diesel fuel combined with an increase in these enhanced features and fuel atomization when spraying will be difficult. It is generally desirable outcome of these two factors have prevented the ignition and brake power somewhat reduced. Increasing the volume percent biodiesel fuel mixture to the engine braking torque is reduced diesel fuel engines in all working conditions. The reason for this decline is the low calorific value of biodiesel compared to diesel fuel. Also, by increasing the concentration of ethanol in the fuel mix engine braking torque is reduced. The reason for this decline in addition to the low calorific value of ethanol compared to diesel fuel may be related to cetane number and low latent heat of vaporization of ethanol.
The results depicted that low percentages of biodiesel and bioethanol into synthetic fuel also somewhat have same power and torque but increasing biodiesel and ethanol contents into synthetic fuel reduced power and torque. The maximum brake power (79 kW) occurred for the pure diesel fuel (equivalent to D100B0E0) at 2800 rpm and full load (100%) and the most brake power (325 N.m) occurred for the pure diesel fuel (equivalent to D100B0E0) at 1630 rpm and full load (100%).