Energy efficiency of engine-generator set using biofuels under varied loads
Introduction
Biodiesel, as an alternative fuel of diesel, is described as fatty acid methyl or ethyl esters from vegetable oils or animal fats. It is renewable, biodegradable and oxygenated [1].
The expansion of areas for energy crops, with emphasis on those destined for vegetable oil extraction and production of biodiesel is already in progress [2]. However, it is noted in the report of the International.
The constant preoccupations with the environment, has made in the last years the alternative sources of energy have taken center stage in the world scenario. Among these sources stands out biodiesel, which is a fuel that in addition to renewable, can reduce emissions of greenhouse gases [3].
Rising petroleum prices, increasing threat to the environment from exhaust emissions and global warming have generated intense international interest in developing alternative non-petroleum fuels for engines. The use of vegetable oil in internal combustion engines is not a recent innovation [4].
Renewable biofuels are increasingly important in the Brazilian energy matrix. In 2010, the country became the second world producer of biodiesel with a production of 2.4 million of m3 in that year, only behind Germany [5].
Although different raw materials result in biodiesel with different characteristics [6], overall, when compared with diesel, biodiesel is denser and more viscous, thus increasing the heterogeneity of combustion; it has a higher cetane number, what increases the quality of ignition; it also has a higher flash point, providing safety in transportation and storage; and higher values of cloud point and fluidity, tending to solidification under lower temperatures [7]. Another important feature is that burning biodiesel tends to be less polluting than diesel, resulting in lower emissions of CO2 and soot [8], besides providing greater energetic independence [9].
Despite its potential, biodiesel usage as a sustainable competitive product has not yet occurred, what is a great opportunity for academic and industrial research, mainly in what concerns to different raw materials, the chemical composition of the extracted oil, energy efficiency and its costs [10].
In Brazil, common sources for biodiesel production are soybean, beef tallow, sunflower, flaxseed, chickenfat, jatropha, palm, cotton, crambe, castor bean and domestic wasted oils, among others [11].
There are many questions about the sustainability of using vegetable oils regarding the exponential characteristic of the energy demand and the possibility of competition with food production [12]. The use of second harvest crops and residues to obtain biodiesel is an alternative to solve this problem. Crambe (Crambe abyssinica Hochst) is a winter crop that can be cultivated in the off-season and adapts to several Brazilian regions, besides having high oil content, which is an important feature for biodiesel production [13].
Soybean (Glycine max (L.) Merrill) is already established with soil and climatic characteristics that allow its installation in several regions of the country, what makes this crop one of the best options for obtaining oil for biodiesel production [14].
Waste frying oil consists of residues with pollutant potential that can be used as feedstock for biodiesel production, which is a viable solution for its destination [15].
Nietiedt et al. [16] evaluated the performance of the diesel cycle engine of a tractor with power outlet in a dynamometer bench, and assessed commercial diesel (B5) compared with mixtures containing 10%, 20% and 100% (B10, B20 and B100) of soybean biodiesel as fuel. The authors found that by increasing the proportions of biodiesel in the blend, the specific consumption (SC) of B100 was 10.9% higher than B5, and there was also a power reduction due to the lower calorific value of biodiesel.
Using binary biodiesel and diesel mixtures from residual fat of poultry in an engine-generator set under varying loads, Silva et al. [17] assessed specific consumption levels, observing that with biodiesel the best result was obtained using B20 with a load of 1.0 kW (SC of 812.3 g kW−1 h−1), which was 14% lower than the SC obtained with diesel (943.7 g kW−1 h−1). The worst performance occurred with B100, whose SC of 781.8 g kW−1 h−1 under the load of 1.5 kW was 23% higher than the SC achieved with diesel (634.0 g kW−1 h−1).
When evaluating different proportions (0%, 5%, 15%, 25%, 50%, 75% and 100%) of waste frying oil-based biodiesel in an agricultural tractor in order to evaluate their dynamic performance, Soranso et al. [18] found out that there was a 15.5% increase in the hourly volumetric consumption and an 18% increase in the specific fuel consumption of B100 (347 g kW−1 h−1) when compared to diesel (294 g kW−1 h−1). Despite the power in the drawbar not showing significant differences according to the different proportions of biodiesel, the effective yield on the drawbar with B100 decreased 14% in comparison to B0.
Given the above, this study aimed to evaluate the operational performance of an engine-generator set running on binary mixtures of petroleum diesel and different types of biodiesel obtained from waste frying oil, soybean oil (Glycine max (L.) Merrill) and crambe oil (Crambe abyssinica Hochst), and find out which biodiesel showed the best results.
Section snippets
Materials and methods
The experiment was conducted at the Laboratory of Gasification and Micro Electricity Generation, at the State University of West Paraná (UNIOESTE), between 02 and 15 October 2013. The experimental design was completely randomized, with 5 replications.
A diesel engine-generator set made by White, model BD 6500CF and single phase was used with 7.36 kW (10 hp) of power and 5.0 KVA of nominal power. Treatments were: petroleum diesel (DI) acquired in a commercial establishment in the area, and
Calorific power
The average value of inferior calorific power (ICP) obtained after 3 replications for crambe biodiesel was 36.68 MJ Kg−1 – the highest among all biodiesel types, however, with non-significant differences of 0.7% to soybean biodiesel (36.42 MJ Kg−1) and 1.3% to waste frying oil (36.20 MJ Kg−1). Diesel presented the highest ICP with 40.39 MJ Kg−1. Lower ICP leads to higher consumption of fuel mass to provide the same amount of energy.
Specific fuel consumption (SC)
The average SC values for the resistive loads of 2, 3, 4 and 5 kW are
Conclusion
Diesel calorific power was superior to those of the biofuels assessed.
Amongst all types of biofuels, crambe oil presented lower specific consumption. Some values did not differ statistically from diesel. Amongst the binary mixtures, the mixture with 20% biodiesel presented better SC for each type of biodiesel, being in average 4.8% better than pure crambe biodiesel; 3.84% better than soybean and 9.65% better than waste frying oil.
Pure biofuel tends to present better EE than the binary mixtures
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