2.2.1. Viscosity Measurements

The kinematic viscosity has been measured in an Ostwald–Cannon–Fenske capillary viscometer (Proton Routine Viscometer 33200, size 150), determining the time required for a certain volume of liquid to pass between two marked points on the instrument, placed in an upright position. From the flow time (t), expressed in seconds, we obtain the kinematic viscosity expressed in centistokes, υ = C·t, where C is the calibration constant of the measurement system, specified by the manufacturer (0.040350 mm<sup>2</sup>/s<sup>2</sup> at 40 ◦C). All measures have been performed in duplicate and are presented as the average of both, with an experimental error less than 0.35%, as required by the standard ASTM (American Society for Testing and Materials) D2270-79 method for calculating the viscosity index from kinematic viscosity at 40 and 100 ◦C [16].

#### 2.2.2. Determination of the Pour Point and Cloud Point of Biofuels

The Pour Point and Cloud Point are determined by introducing the different double or triple blends, of different composition, in a glass tube having a flat bottom [16]. The tube was tightly closed with the help of a cork carrying a thermometer with a temperature measuring range of −36 to 120 ◦C. The tube was introduced in a digitally controlled temperature refrigerator for twenty-four hours. The tubes were brought out from time to time and checked until the oil did not show any movement when the jar was horizontally tilted for 5 s. After this time, the loss of transparency of the solution is evaluated. The appearance of turbidity in the samples is indicative that the Cloud Point temperature has been reached (Cloud Point). After a progressive decrease in temperature, the samples are kept under observation until they stop flowing (Pour Point).

2.2.3. Energy Performance and Pollutant Emissions Generated in a Diesel Engine Electric Generator, Fueled with Different Biofuel Blends

Following a previously described experimental methodology [16], the mechanical and environmental characterization of a compression ignition diesel engine has been carried out, working at a rate of 3000 rpm coupled to an AYERBE electric generator, 5KVA, 230v type AY4000MN, for the generation of electricity, operating at a crankshaft constant rotation rate and under different degrees of demand for electrical power. This is achieved by connecting heating plates of 1000 watts each one (Figure 1a). This diesel engine will operate at a constant rate of rotation of the crankshaft and torque, so that the different values of electrical power obtained will be an exact consequence of the mechanical power obtained after the combustion of the corresponding biofuel. Different tests were obtained by providing to the engine double and triple mixtures of different biofuels. The electrical power generated can be easily determined from the product of the potential difference (or voltage) and the electric current intensity (or amperage), see Equation (1), both obtained by means of a voltmeter-ammeter.

$$\text{Electrical power generated (Watts)} = \text{voltage (Volts)} \times \text{amperage (Amps)}.\tag{1}$$

The consumption of the diesel engine was calculated estimating the speed of consumption of the biofuel studied with the engine working at a pre-determined demand of electric power. Thus, by operating under the same volume of fuel (0.5 L), different operation times are achieved. It must be indicated that the values represented are the average of at least three measurements. The error bars are not indicated in Figures for better display, although in none of the cases the error in the measurements exceeded the 5%.

The contamination degree is evaluated from the opacity of the smoke generated in the combustion process. This is obtained by using an opacimeter (TESTO 308, Arquitecsolar, Granada, Spain) under the operating conditions studied, Figure 1b [16]. The data here compiled are the media of three

repeated measures, attaining an experimental error lower than 6%. The results obtained with the biofuels evaluated were compared with the measurements obtained when conventional diesel was fueled. The opacity value can be expressed as a percentage (being 100% totally cloudy and 0% totally clear) or as an equivalent number called the k value (Opacity Bacharach) in a scale which goes from white (0 Bacharach unit) to black (9 Bacharach units), as established by the ASTM D 2156-94, Standard Test Method for Smoke Density in Flue Gases from Burning Distillate Fuels [21].

**Figure 1.** Electrogenerator AYERBE, 5KVA, 230v tipo AY4000MN, heating plates of 1000 watts of power each and voltmeter-ammeter devise (yellow color, on the floor) (**a**); TESTO 308 opacity meter, which operates as established by the ASTM D 2156-94, Standard Test Method for Smoke Density in Flue Gases from Burning Distillate Fuels (**b**).
