INNOVA Research Journal, ISSN 2477-9024  
Enero-Abril, 2019). Vol. 4, No.1 pp. 21-35  
(
DOI: https://doi.org/10.33890/innova.v4.n1.2019.796  
URL: http://revistas.uide.edu.ec/index.php/innova/index  
Correo: innova@uide.edu.ec  
La eficiencia térmica de las mezclas de combustibles reciclados de aceites  
lubricantes y comestibles  
The thermal efficiency of recycled edible and lubricating oil fuel blends  
Marcos Gutiérrez  
Tablet School-Escuela de Ciencias y Centro de Investigación Científica, Ecuador  
Autor para correspondencia: marcosgutierrez@tablet-school.com  
Fecha de recepción: 15 de agosto de 2018 - Fecha de aceptación: 01 de diciembre de 2018  
Abstract: The energy demand increases with the social, industrial and technological requirements,  
independent of the sources to supply it. More than half of the total energy consumption is supplied by  
fossil fuels, which can be replaced by alternative and more environmentally friendly fuels. The present  
research evaluates thermal efficiency, net output work and energy availability from recycled vegetable-  
animal and synthetic-mineral substances, in a pure state and blended with neat diesel. The calculation  
uses mainly the heat value of each fuel and the air properties along each stroke of the diesel cycle. The  
purpose of the present research consists in the evaluation of the thermal efficiency of alternative fuels  
in functions of the whole engine cycle and not only Stoichiometric the heat value and quantity of each  
fuel. It was found that the neat fuel from recycled edible sources provides more net output work and is  
able to perform longer combustions, while the advantage of higher thermal efficiencies using recycled  
lubricating oil relies on its use as an additive in a blend with neat diesel. The use of alternative and  
ecological neat fuels of blends is conditioned by the efforts to produce them and by the resulting  
thermal efficiency, net output work and remaining energetic availability.  
Key words: biodiesel; recycled lubricating oil; thermal efficiency; heat value; energetic availability  
Resumen: La demanda energética aumenta con los requerimientos sociales, industriales y  
tecnológicos, independientemente de las fuentes para abastecerla. Más de la mitad del consumo total  
de energía es suministrado por combustibles fósiles, que pueden ser reemplazados por combustibles  
alternativos y más respetuosos con el medio ambiente. La presente investigación evalúa la eficiencia  
térmica, el trabajo de producción neta y la disponibilidad de energía a partir de sustancias vegetales-  
animales y minerales sintéticos reciclados, en estado puro y mezclado con diesel puro. El cálculo utiliza  
principalmente el valor de calor de cada combustible y las propiedades del aire a lo largo de cada  
carrera del ciclo diesel. El propósito de la presente investigación consiste en evaluar la eficiencia  
térmica de los combustibles alternativos en las funciones de todo el ciclo del motor y no solo en  
estequiométrico el valor calorífico y la cantidad de cada combustible. Se encontró que el combustible  
puro de fuentes comestibles recicladas proporciona más trabajo de salida neta y es capaz de realizar  
combinaciones más prolongadas, mientras que la ventaja de mayores eficiencias térmicas que utilizan  
aceite lubricante reciclado se basa en su uso como aditivo en una mezcla con diesel puro. El uso de  
combustibles puros alternativos y ecológicos de mezclas está condicionado por los esfuerzos para  
producirlos y por la eficiencia térmica resultante, el trabajo de salida neta y la disponibilidad energética  
restante.  
Palabras clave: biodiesel; aceite lubricante reciclado; eficiencia térmica; valor calorífico;  
disponibilidad energética  
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Introduction  
The population growth, industrial development, and technological breakthrough cause an  
increase of the energy demand, independent of its supply sources. Despite the existence of  
another abundant and clean energy sources, like the wind, solar, and the coming from biofuels,  
the fossil fuels are the most used. The main energy generation machines, like internal  
combustion engines, are still being developed in terms of the fossil fuels. For this reason, it is  
necessary to evaluate the thermal efficiency of waste substances that can be reused as alternative  
fuels for the existing and developed energy generation machines in order to reduce the  
environmental impact of the fossil fuels immediately.  
Reports from 2011 to 2015 show that the fossil fuel keeps 78.36% of the global annual  
energy consumption. The nuclear energy registered an approximate decrease of 0.1%, sharing  
2
.3% of the global energetic consume. The alternative fuel sources like biomass keep an average  
consumption of 9.06% and 0.8% of it corresponds to the biofuels exclusively used for transport.  
The capacity to generate the energy from the biomass from 2012 to 2016 increases from 83GW  
to 112GW, registering an average growth of 7.5%. The total generated energy increases from  
3
35TW-h in 2011 up to 504TW-h in 2016. The liquid biofuels along these 6 years of monitoring  
demonstrate that they are the main renewable energy supply source for transport, even counting  
the expansion and acceptation of the electric vehicles. The capacity of energy generation grows  
each year for the biomass, in comparison with the fossil fuels [1].  
It is necessary to consider efficient energy generation with a balance between key aspects  
such as energetic, environmental and economic ones. Among the renewable energy sources, the  
biodiesel is considered as the most feasible cleaner fuel worldwide that can be considered as a  
real substitute for the diesel when its efficiency and output power are equivalent or improved  
compared to it. For this reason, the present research consists in evaluating of the thermal  
efficiency of two fuel types coming from recycled synthetic and mineral substances (such as  
lubrication oil) and from animal and vegetable substances (such as a used recycled edible palm  
oil). Four different concentrations of these fuels were studied and compared with the neat diesel  
under the same conditions that can occur in an engine without any changes or adjustments of  
engine components. This approach is performed in order to evaluate the thermal efficiency of the  
fuel in an isolated way, disregarding any external factor or condition that can alter the results.  
Thus, the conclusion and evaluation of each fuel determine its feasibility either to be an  
alternative or not.  
The process to obtain fuels from reusable substances, such as recycled lubricating and  
edible oil, consists of simple distillations and transesterification processes with heterogenic  
catalysts, because both processes are friendly with the environment. These fuels are analyzed in a  
pure state and blended with neat diesel as well.  
The fuels from recycled lubricating oil have a mineral and synthetic origin. This kind of  
substances was already used as a heavy fuel oil substitute showing advantages like better ignition  
quality and less smoke [2]. In the present research, the recycled lubricating oil was prepared due  
to three simple distillations, proving that the density value between the third and further  
distillations remains without any change and that the blending by agitation with neat diesel  
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INNOVA Research Journal 2019, Vol 4, No. 1, pp. 21-35  
remains stable, even under effect of external factors like conserving time, sunlight, ambient  
temperature and pressure.  
The fuels from recycled edible palm oil are obtained by the transesterification process  
with methanol and heterogenic catalysts like calcium oxide (CaO), because of its reusability, less  
water requirement during the obtaining process and easier separation of the glycerol and methyl  
esters [3]. Furthermore, the resulting methyl esters are more volatile compared with the resulting  
esters from the transesterification process with ethanol. The selection of methanol is based on its  
ability as reagent and its economy; however, it is more toxic and comes from non-renewable  
sources compared with ethanol, that can be obtained from starchy or sucrose sources [4].  
The use of biofuels from vegetal origin has the advantage of being renewables,  
biodegradable and having similar properties and characteristics like the neat diesel. The resulting  
pollutant emissions are significantly lower, excepting the nitrogen oxides (NOx). It is reported an  
increased fuel consumption, as well the reduced thermal efficiency because of its lower heat  
capacity [5], except the case when the lubricating oil used as a fuel blended with diesel, the heat  
value is higher than the diesel in a pure state [2]. According to similar researches, the reduced  
efficiency is more evident with an increase of a biodiesel concentration in a blend with neat  
diesel [6]. However, the investigation of Liu H., et al. [7], shows that the use of the neat biodiesel  
gives higher thermal indicated efficiency, at high engine loads; but lower at low engine loads,  
respectively.  
The thermal efficiency is also known as the energetic efficiency that results from the ratio  
between the net output work produced in a thermodynamic system and the supplied heat into it  
coming from an external source [8]. In the present research the thermodynamic system for  
evaluation of the thermal efficiency is the engine; the produced net output work comes from the  
chemical energy conversion into calorific from the studied fuels; and the supplied heat to the  
system consists of the product between the fuel quantity and its lower heat value (Eq. 1).  
푊
ꢀ
휂푡ℎ푒푟푚  
=
(1)  
푚 ×퐻  
푓
푢푓  
The points to be observed to evaluate the thermal efficiency of alternative fuels are the  
exactitude to quantify the heat value of each fuel type and the calculation method for the thermal  
efficiency. The engine test with a biodiesel from a vegetable source (in a pure state as blended as  
well) showed the power and the thermal efficiencies similar and close to those that can be  
obtained with a neat diesel; but not higher than it. To this fact, it is necessary to mention that a  
simplification and generalization of different blends and sources of the biodiesel are studied as a  
single one, with a heat value of 37MJ/kg compared with the 42.7 MJ/kg of the neat diesel [9].  
Other researchers consider a range between 39 and 41 MJ/kg for biodiesel and a higher value  
that amounts up to 43MJ/kg for diesel [10].  
One of the limitations for a calculation with a high level of exactitude is the absence of  
experimental measurements of thermodynamic properties of the fuel blends, under pressure  
values around 60 bar and temperature around 970 K, which corresponds to the engine operating  
conditions at the end of the compression stroke. However, the reference specific heat value for  
diesel, recycled edible palm oil and recycled lubricating oil (all in pure states) corresponds to 2.1  
kJ/kg K [11, 12, 13], that is a value measured between 20 and 30°C, which is in the range to the  
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INNOVA Research Journal 2019, Vol 4, No. 1, pp. 21-35  
feed fuel temperature according to the studied engine [14].  
The importance of this research consists in a more exact method to calculate the net  
output work of an engine and the thermal efficiency, depending on the air and properties of each  
fuel type along all engine strokes, and on the engine operating conditions, as well. This method  
can be applied independently of the engine type and size.  
The thermal efficiency is evaluated by the first law of thermodynamics considering the  
net output work and the heat value of the fuel; as well as evaluation of the losses inherent to the  
combustion and the exhaust processes, by means of the second law of thermodynamics. The  
advantage of this approach is in identifying and locating of the factors, causes and effects of  
energetic losses that affect the thermal efficiency.  
Thereby, the thermal efficiency can be understood as a fact of obtaining of the maximum  
available net output work for each unit of fuel mass that was totally burned. However, it does not  
mean that the net output work can be increased in comparison with other fuels, understanding the  
net output work as the energy generated in the system by the fuel. Due to this approach, is  
possible to demonstrate that a fuel, which is able to give more net output work, is not necessarily  
a more thermal efficient one.  
The goal of the present research consists in determining of the neat output work, the  
thermal efficiency and energy availability, known as the ideal additional net output work that the  
engine could perform when it passes to an inactive state. The evaluation of these parameters  
takes place with the use of different concentrations of fuels from different sources, in function of  
their heat values, air intake conditions and its changes during the combustion process,  
compression, expansion and exhaust strokes of the engine.  
Materials and Methods  
Fuel properties  
With the characterization of the neat diesel and different concentration of fuel blends  
from synthetic and mineral sources as recycled fuel lubricating oil, and from animal and  
vegetable source as used recycled edible palm oil, was possible to get the exact experimentally  
measured values of the heat values of each type of the studied fuels. The meticulous analysis of  
each fuel sample allows to eliminate the uncertainty that implicates the assumption of a  
simplified and generic heat value for a certain fuel coming from a determined source,  
concentration and obtaining process. Thus, it is possible to evaluate the thermal efficiency  
exactly and to select properly the fuel type that is thermally more efficient and gives more net  
output work or define those fuels, which have or not any substantial difference between them.  
The approximated values to produce 100 kg of biodiesel from recycled vegetable oil  
amounts 870000 KJ, while the energy content in the produced biodiesel amounts 3700000kJ; so  
the energy gain is 4 times higher [15] that means at least 25% of biodiesel in a fuel blends must  
be used in order to avoid any unprofitable economic and energy balance. Based on it, the studied  
fuels consist of 25% and 100% of the recycled edible oils blended with neat diesel, as well as the  
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INNOVA Research Journal 2019, Vol 4, No. 1, pp. 21-35  
same proportion for the recycled lubricating oil in order to have the same comparison pattern.  
Table 1. Heat Values.  
Heat value  
Fuel Type  
[
kJ/kg]  
D100  
00% Diesel  
4
2781.7  
1
B100  
00% Methyl ester of recycled edible palm oil  
L100  
00% Distilled of recycled lubricating oil (L100)  
3
9925.4  
1780.4  
1
4
4
1
B25  
2845.3  
2518.9  
2
5% Methyl ester of recycled edible palm oil and 75% diesel  
L25  
4
2
5% Distilled of recycled lubricating oil and 75% diesel  
Experimental measured heat value of each fuel blend. Source: Authors  
The general formula of the type CnH(2n+2) for dodecane and hexadecane and  
CnH(n+2)O for fatty acid methyl esters represent the formulas for diesel, lubricating oil, and  
biodiesel from vegetable edible oil, respectively. In the case of the fuel blends, the atom numbers  
of carbon, hydrogen, and oxygen, is determined by the concentration of each component of the  
blend. With the general formula of each fuel type, the mole number and molecular mass of the  
reagents and products can be calculated. These inputs are required to complete the calculation of  
the enthalpies (Eq. 6) and an exact air-fuel ratio of each fuel type.  
The proposed methodology to calculate the thermal efficiency, the net output network and  
the energetic availability allows to perform this task independent of the engine size and  
application. The present calculation is based on the diesel cycle and on the standard air, where  
the working fluid along the whole cycle is diesel. The combustion process is replaced by the heat  
transfer from an external source, like the energy corresponding to the heat value of the fuel. The  
processes are reversible and the specific heat capacities are constant. The present method can be  
applied to any engine and any fuel that performs the diesel cycle.  
The required data of the engine for the calculation is air intake pressure, temperature, fuel  
feed temperature and compression ratio. The values from a diesel generator engine [14] are used  
as a reference for the calculations.  
Table 2. Engine parameters.  
Air intake pressure into the cylinder [bar]  
Air intake temperature [°C]  
1.7  
25  
Fuel feed temperature [°C]  
30  
Compression ratio of the engine [-]  
16.5  
Initial data for the air properties calculation in each stroke of the cycle with each fuel type.  
Reference data for diesel engine generators [14].  
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Table 3. Stoichiometric equations and properties of each fuel blends.  
Fuel Type  
Stoichiometric equation  
2
26 + 18.5 O + 69.56 N = 13 H O + 12  
12  
C H  
2
2
CO +
 69.56
 N  
Air mole number  
Products mole  
88.06  
94.56  
170  
D100  
Fuel molar mass  
Air molar mass  
Products molar mass  
Air fuel ratio  
28.970  
28.656  
15.02  
17 34 2 2 2 2  
C H O + 24.5 O + 92.12 N = 17 H O + 17  
Air mole number  
Products mole  
116.62  
126.12  
270  
B100  
L100  
Fuel molar mass  
Air molar mass  
28.970  
28.809  
12.52  
Products molar mass  
Air fuel ratio  
16  
C H  
34 + 24.5 O  
2
+ 92.12 N  
2
= 17 H  
2
O + 16  
Air mole number  
Products mole  
116.62  
125.12  
226  
Fuel molar mass  
Air molar mass  
Products molar mass  
Air fuel ratio  
28.970  
28.687  
14.96  
13  
C H  
28O + 19.5 O  
2
+ 73.32.56 N = 14 H O +  
2 2  
Air mole number  
Products mole  
95.2  
100.32  
190  
B25  
Fuel molar mass  
Air molar mass  
28.970  
28.678  
14.53  
Products molar mass  
Air fuel ratio  
C
13  
H
28 + 20 O  
2
+ 75.2 N  
2
= 14 H  
92.82  
102.2  
184  
2 2  
O + 13 CO +  
Air mole number  
Products mole  
L25  
Fuel molar mass  
Air molar mass  
Products molar mass  
Air fuel ratio  
28.970  
28.665  
14.62  
Stoichiometric equations, mole number, and molecular mass of reagents and products for each fuel type. Source:  
Authors.  
Mathematical Formulation  
The calculation of the thermal fuel efficiency begins defining the standard air properties  
during the intake process. These properties embrace the internal energy, enthalpy, absolute  
entropy, relative pressure and relative volume. All these properties are determined at a given air  
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INNOVA Research Journal 2019, Vol 4, No. 1, pp. 21-35  
intake temperature [8].  
The relative pressure and volumes allow to calculate pressures and volumes of the engine  
between the intake and compression stroke, and between the combustion and exhaust stroke as  
well. The values of the relative pressure are proportional to the ratio between the absolute  
entropy and universal gas constant, while the relative volume is proportional to the ratio between  
the universal gas constant, temperature, and relative pressure according to the equations below.  
푃
푃ꢂ2  
푃ꢂ1  
2
(푃  
)
푆ꢁ퐶  
=
(2)  
1
푉
푉ꢂ2  
2
(푉  
)
= 푉  
푆
(3)  
1
ꢂ1  
푆ꢁ퐶  
푅×푇  
푃ꢂ  
ꢃ푟 ∝  
ꢄ푟 ∝  
(4)  
푅
The air properties corresponding to the compression stroke are calculated as a function of  
the relative volume of the admission stroke and the compression ratio of the engine (Eq. 5).  
ꢆ
ꢄ푟ꢅ = ꢄ × ( )  
(5)  
푟ꢆ  
푟
푘
The pressure corresponding to the compression and exhaust stroke is calculated with the  
equation (2). The resulting value of the compression is the same value for the combustion pressure,  
considering the ideal diesel cycle.  
The values of the air properties corresponding to the combustion process are determined  
by the calculated value of the enthalpy at this point.  
[푛  
×ꢈ ×ꢉ푝 ×(ꢊ −ꢊ  
)]+ꢌ푛푎×ꢈ푎×ꢍꢎ −ꢎ ꢏꢐ+[ꢈ ×푞 ]  
푓_ꢂꢋ푓 푓  
2 1  
푙
ꢑℎ푝_ꢂꢋ푓  
푓
푓
푓
푓
푛푝  
ꢇ3 =  
(6)  
푚푝  
The relative volume 4, calculated with the Eq. 7, allows to calculate all the air properties  
corresponding to the exhaust stroke.  
푇2  
ꢄ푟4 = ꢄ × ꢒ ×  
(7)  
푟3  
ꢓ
푇ꢔ  
The net output work is calculated with the Eq. 8.  
ꢆ
ꢆ
ꢕꢖ푒푡_표ꢗ푡ꢘꢗ푡 = ꢙ푟 × ꢚ ꢜ ꢝ ꢞ ꢟ ꢠꢙꢡ ꢝ  
ꢜ × ꢞ4ꢢ  
(8)  
ꢛ
ꢆ
푎/푓  
푟푎/푓  
The calculated thermal efficiency of the present research (Eq. 9), implies the calculated  
net output work (Eq. 8), the air-fuel ratio, and the lower heat value of the fuel. In comparison  
with Eq. 1, the difference relies on that the mass of fuel is replaced by the air-fuel ratio, but the  
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INNOVA Research Journal 2019, Vol 4, No. 1, pp. 21-35  
net output network must be expressed in energy units per mass units of air into the engine. This  
approach allows to calculate the thermal efficiency in a more versatile way, based mainly on the  
air intake engine conditions and fuel feed temperature; instead of the necessity to determine the  
air flow and fuel quantity during the injection.  
푊푛ꢋꢣ_ꢤ푢ꢣ푝푢ꢣ×푟푎/푓  
휂푡ℎ푒푟푚  
=
(9)  
ꢥ푙  
Finally, the energy availability of the engine with each type of fuel (Eq. 6) allows to  
quantify an additional ideal output work that could be obtained.  
푃
1
ꢟ∆풜ꢖ/0 = ꢞ ꢟ ꢞ ꢟ {ꢦ × ꢧ푠 ꢟ 푠 ꢟ [ꢨ × ꢩꢪ ( )]ꢬ}  
(10)  
4
ꢆ
ꢆ
ꢆ
4
푃
ꢫ
Results  
The calculations with the above described equations, beside determination of the net  
output work and thermal efficiency of each fuel type and energy availability, allow to determine  
the temperature and pressure in each stroke of the engine. With the relationship between  
temperatures of the final of compression and the beginning of the expansion stroke, it is possible  
to evaluate how long the combustion process goes, and consequently to evaluate the combustion  
capacity of each fuel under the same conditions.  
Table 4. Pewrformance and efficiency.  
Fuel type  
D100  
B100  
L100  
1241  
B25  
L25  
Net output work [kJ/kg]  
Thermal efficiency [%]  
1538  
1705  
1536  
1622  
5
4.001  
796  
53.471  
905  
44.401  
1028  
52.479  
851  
55.351  
786  
Energetic availability [kJ/kg]  
Percentage of the possible obtainable additional  
output work [%]  
5
1
53  
83  
55  
48  
Ratio T  
3
/T  
2
3.22  
3.47  
3.17  
3.33  
3.21  
Performance and efficiency properties of each fuel type.  
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INNOVA Research Journal 2019, Vol 4, No. 1, pp. 21-35  
Figure 1. Comparative chart of the Thermal efficiency of each fuel type.  
Figure 2. Comparative chart of the net output work and the energetic availability of each fuel type.  
Figure 3. Comparative chart of the air-fuel ratio and the ratio T3/T2 as a measure of the combustion duration.  
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INNOVA Research Journal 2019, Vol 4, No. 1, pp. 21-35  
Figure 4. Comparative chart of the calculated combustion and exhaust temperatures with each fuel type.  
Discussion  
Despite the lower heat value of the fuel consisting of 100% biodiesel (Fig. 1), this fuel  
type gives more net output work, thermal efficiency is very close to the neat diesel (Fig. 2). This  
is explained by the higher molar concentration for the fuel and air components of the  
stoichiometric equations of this type of biodiesel that increases the enthalpies and internal energy  
at the combustion process. By means of the cutoff ratio (T3/T2), it is also observed that the  
combustion goes longer and consequently most of the fuel will be burned compared with other  
fuel types (Fig. 3), this fact also supports the experiments, in which the harmful exhaust  
emissions are lower with the neat biodiesel.  
The fuel consisting of 100% lubricating oil has the lowest performance regarding the net  
output network and a big potential of the energy, which could be transformed as an additional  
work, is not used, as the values of the energetic availability reveal (Fig 1). However, the fuel  
consisting of 100% biodiesel, and the blend consisting of 25% recycled lubricating oil and 75%  
diesel, show the higher net output work (Fig. 1). The ratio between the combustion and the  
compression temperature and the exhaust temperatures as well reveal that this kind of fuel is able  
to perform shorter combustion processes with higher net output work and thermal efficiencies  
(Fig. 4).  
From the stoichiometric equations (Tab. 3) and the (Fig. 3) it is observed that all the  
studied alternative fuels of the present research will produce an increased fuel consumption  
compared to the neat diesel, this effect is especially significant for the 100% biodiesel, and lower  
for the L25 fuel blend of recycled lubricating oil.  
The fuel blend consisting of 25% recycled edible oil and 75% diesel shows results close  
to the neat diesel, justifying its use, as a reduction of the neat diesel consumption by 75% and  
increasing the use of alternative recycled substances as a fuel by 25%.  
The thermal efficiency of B100, B25 and particularly L25 fuel blends, are equivalent to  
the neat diesel, but even when this parameter remains stable, there are considerable variations  
regarding air-fuel ratio and the combustion duration expressed by the ratio between the  
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combustion and the compression temperatures.  
The use of 100% recycled lubricating oil as an alternative fuel showed poor results in all  
the parameters, disregarding its use as an alternative fuel in a pure state. However, its use in a  
fuel blend of 25% of this recycled oil type and diesel showed that it is the most efficient fuel  
blend. It has the lower remaining available energy, as an indicator that the most of the fuel is  
transformed in net output work, and has the lower calculated exhaust temperature, which means  
better conditions to reduce the formation of nitrogen oxides (NOx).  
Conclusion  
The methodology presented in this research showed a way to determine the net output  
work and efficiency of the fuel depending on the fuel heat value, air intake and engine operation  
conditions. This methodology allows to evaluate the sustainability and applicability of any fuel  
by a thermodynamic approach, before it can be tested in a real engine, optimizing time and  
resources.  
Due to a thermodynamic calculation based on the engine parameters and the air  
properties, considered as an ideal gas, the present research demonstrates that the neat biodiesel  
(B100) gives more net output work, than neat diesel and other fuel blends, even under the effect  
of a lower heat value, but considered that all the studied fuels are injected, atomized and mixed  
to form a stoichiometric air-fuel mixture, compensating any variation regarding densities and  
viscosities, of each fuel type.  
The recycling of mineral-synthetic substances, such as lubricating oil, has the potential to  
improve the thermal efficiency of an engine when these substances are used as an additive  
blended with the neat diesel, but not in a pure state. The use of this fuel type as an alternative  
neat fuel to substitute diesel or fuels from the vegetable-animal origin is not recommended. In  
the same way, the efforts to produce the biodiesel by means of transesterification and to use it as  
a blend in a concentration lower than 25% without any significant improvement compared to  
neat diesel is questionable.  
By means of the present methodology to evaluate the thermal efficiency of different fuels,  
it is demonstrated that an increased net output network does not mean an increase in the thermal  
efficiency.  
The available net output work and thermal efficiency of a fuel blend not only depends on  
its heat value, as observed in the results. The fuels with lower heat values but higher molar  
concentrations have a bigger energy release during the combustion process that results in higher  
net output work.  
The fuels able to give higher efficiency values are not those with the higher net output  
work values because the efficiency of a fuel consists of a required energy to produce a  
determined net output work.  
Lower cutoff ratios mean higher thermal efficiencies; while higher cutoff values represent  
more net output work of the engine, and consequently higher combustion temperatures that will  
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INNOVA Research Journal 2019, Vol 4, No. 1, pp. 21-35  
produce more nitrogen oxides (NOx).  
The results of the present research of the alternative fuels from recycle edible oils and  
form lubricating show that they are an alternative and have a chance to occupy more of 78% of  
the total demand of the fossil fuels.  
The use of the biofuel represents a necessity in order to reduce the impact on the  
environment of the fossil fuels and a way to reuse mineral-synthetic, and vegetable-animal waste  
oil to generate net output work in a system with the less energy required for it.  
Definitions/Abbreviations  
ηtherm: Thermal efficiency  
Wi: Net output work [kJ/kg]  
mf: Mass of fuel [kg]  
Huf: Lower heat value of the fuel [kJ/kg]  
D100: Diesel fuel  
B100: Biodiesel from 100% recycled vegetable oil  
L100: Fuel from 100% recycled lubricating oil  
B25: Fuel blend from 25% recycled vegetable - animal oil and 75% neat diesel  
L25: Fuel blend from 25% recycled lubricating oil and 75% neat diesel  
C: Carbon  
H: Hydrogen  
O2: Oxygen  
N2: Nitrogen  
H2O: Water  
CO2: Carbon dioxide  
P: Pressure [ bar ]  
T : Temperature [°C]  
Pr : Relative pressure  
Vr : Relative volume  
h: Enthalpy [kJ/kg]  
u: Internal energy [kJ/kg]  
S: Entropy [kJ/kg K]  
C: Constant  
R: Universal air gas constant: 287.08 [J/kg K]  
rk: Compression ratio [-]  
nf: Fuel molar number [mole]  
mf: Fuel molar mass [kg/mole]  
Cpf: Specific heat value of the fuel [kJ/kg K]  
Tf: Fuel feed temperature [°C]  
Tf_ref: Fuel temperature at a reference value of 25°C [°C]  
na: Air mole number [mole]  
ma: Air molar mass [kg/mole]  
np: Products mole number [mole]  
mp: Products molar mass [kg/mole]  
hp_ref: Reference enthalpy of the products at a reference temperature of 25°C [kJ/kg]  
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INNOVA Research Journal 2019, Vol 4, No. 1, pp. 21-35  
Wnet_output: Net output work [kJ/kg]  
ra/f: Air fuel ratio [-]  
ql: Lower heat value of the fuel [kJ/kg]  
-ΔAn/0: Energetic availability [kJ/kg]  
Suffix: 1 = intake, 2 = compression, 3 = combustion, 4 = exhaust  
Biboliography  
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Appendix  
Appendix 1. Air properties, temperatures, and pressures in each engine stroke / process and with  
each full type.  
Fuel Type  
D100, B100, L100,  
B25, L25  
D100  
B100  
L100  
Enthalpy [kJ/kg]  
297.961  
1.359  
212.899  
146.34  
2.51  
896.502  
65.215  
647.53  
8.869  
3.621  
594  
3259.185  
1926.465  
1167.107  
1427.877  
1.06  
3535.171  
2113.082  
1649.351  
1571.188  
0.804  
3205.732  
8519.438  
2416.132  
0.126  
2221.602  
Relative pressure  
9140.664  
2457.658  
0.207  
13467.328  
2672.51  
0.169  
1991.128  
1654.654  
0.656  
Internal energy [kJ/kg]  
Relative volume  
Entropy function [kJ/kg*K]  
5.036  
4.435  
5.126  
4.539  
5.017  
4.596  
Temperature in each point of  
the stroke / process [°C]  
25  
2520  
1464  
2733  
1615  
2478  
1702  
Pressure in each point of the  
stroke / process [bar]  
1.7  
81.561  
81.561  
10.414  
81.561  
9.989  
81.561  
19.092  
Fuel Type  
D100, B100, L100, B25, L25  
B25  
L25  
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Enthalpy [kJ/kg]  
297.961  
1.359  
212.899  
146.34  
2.51  
896.502  
65.215  
647.53  
8.869  
3.621  
594  
3415.057  
11584.28  
2579.002  
0.185  
2035.217  
1448.138  
1511.393  
0.911  
3231.572  
8760.192  
2436.09  
0.211  
1906.146  
1114.601  
1412.274  
1.088  
Relative pressure  
Internal energy [kJ/kg]  
Relative volume  
Entropy function [kJ/kg*K]  
5.087  
4.496  
5.027  
4.449  
Temperature in each point of the stroke  
process [°C]  
25  
2640  
1552  
2498  
1448  
/
Pressure in each point of the stroke /  
1.7  
81.561  
81.561  
10.196  
81.561  
10.377  
process [bar]  
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