*3.4. Fuel Consumption*

Additionally, a key parameter in the development of new fuel as an alternative to diesel, is its consumption. Figure 5 shows the consumed volume (in liters per hour) by the engine fueled with the different diesel/DEE/sunflower oil and diesel/DEE/castor oil blends, at different power demands (1, 3, and 5 kW).

As can be seen, at lower power demands (1 kW), the consumption of the blends is always higher than that obtained with the fossil diesel, independently of the oil employed. This is probably due to the initial engine start requires a greater amount of fuel. However, at the higher powers demanded (3 and 5 kW), there have been no noticeable differences in fuel consumption compared to conventional diesel fuel. It can also be seen that mixtures with castor oil (Figure 5b) have slightly higher consumption than sunflower equivalents (Figure 5a). For all fuels tested, the fuel consumption increased as the biofuel ratio (DEE/SVO) is increased in the blends (from B0 to B40). The explanation for this increment could be the reduction in engine power when the concentration of diethyl ether is higher because the energy content in blends is reduced as a consequence of its lower calorific value. In the case of the B40 blend with sunflower oil, fuel consumption was between 3–29% higher than that of diesel, while the biofuel containing castor oil in the same proportion consumed 8−29% more than the diesel case. A reduction of fuel volume up to 9% can be achieved by employing biofuels with 9% of DEE and 11% of vegetable

oil, especially when sunflower oil is employed (B20 blend). It was definitive that the tested triple blends B20 and B40 show an excellent ability to eliminate smoke emissions, generate very similar and even higher power values than those with diesel, and a biofuel consumption analogous to diesel.

**Figure 5.** Consumption values (L/h) as a function of the power demanded by the engine for the blends diesel/DEE/sunflower oil (**a**) and diesel/DEE/castor oil (**b**).

#### *3.5. Comparison with Reported Studies in Literature*

The diesel replacement and smoke emissions of the blend, with which the best results are obtained in the present work, have been compared with the results of some of the reported blends as biofuels in the literature, Table 4. It is important to take into account the different parameters in the engine as well as the different fuel loads that have been employed in each study. As can be seen in Table 4 and, to the best of our knowledge, literature about diesel engine fueled with diesel/DEE/oils blends is very recent and limited to a few studies belonging to M. Krishnamoorthi and A. Kumar [36–38,50]. Among these diesel/SVO/DEE triple blends, the greater percentage of substitution has been reached in [38,50] and, also, in the present study (40%). However, with regard to soot emission, a higher reduction of 77%, is achieved in this work, comparing to a reduction from 9.2% to 64.6% obtained with the other triple blends [37,38,50]. The blend containing biodiesel from vegetable oil instead of SVO shows lower diesel replacement and minor reduction of opacity, 22.5% and 8.1%, respectively [40]. In another study, the incorporation of a non−renewable fuel like kerosene only allows a fossil diesel replacement of 13% and the smoke opacities decreased by 6% [51]. There are two trends when double blends containing DEE are employed. On one hand, the blends containing diesel lead to a substitution of diesel up to 24% and to a considerable decrease in emissions [28]. On the other hand, if a renewable fuel like oil derived from waste plastic pyrolysis is used [52], the entire replacement of diesel is attained, at the same time, the pollutant emission is reduced by almost 20% in comparison with the diesel/DEE blend. It has been seen that the triple blends which do not use DEE as an oxygenated additive, for example, the diesel/gasoline/sunflower oil blend [31], allow higher incorporation of SVO than the rest of blends, and generate a similar performance in the diesel engine.

**Table 4.** Comparison of smoke emissions and the percentage of replaced diesel obtained on the blend investigated here and, on several blends reported in the literature.



**Table 4.** *Cont*.

 Smoke opacity reduction with respect to conventional diesel.
