Effects of waste frying oil based methyl and ethyl ester biodiesel fuels on the performance, combustion and emission characteristics of a DI diesel engine
Introduction
Since biodiesel has increasing usage ratio among the alternative fuel sources, the most important issue for the sustainability of biodiesel is the feedstock type which is used in its production. In addition to its technical effects, the selection of feedstock type has also great influence on the economic growth of biodiesel industry of the country. From the point of view of reducing the dependence on foreign sources, biodiesel production from food-grade vegetable oils is not reasonable for the countries importing their vegetable oil needs. However, using waste vegetable oils as a biodiesel feedstock may be a solution for these types of countries. Turkey has considerable amounts of waste frying oil [1]. For commercialization of biodiesel, the cost price of biodiesel can be reduced by using waste frying oils and animal fats as feedstock. In addition to its economic benefit, this application helps to solution of serious environmental problems caused by the disposal of these types of waste oils [2], [3].
As known from the literature, biodiesel fuel has chemical bonds from the alcohol used in transesterification reaction affecting the fuel properties [4], [5], [6], [7], [8] and these properties make some impact on the performance, combustion and emissions of the diesel engines [9], [10], [11], [12]. When considering the related literature, it is seen that the alcohol used in biodiesel production is mainly methanol and the number of studies in which biodiesel fuels are produced via ethanol usage is insufficient and stricted only in laboratory scale as compared with methanol usage. At the same time, the methanol production is mostly based on fossil fuels, mainly natural gas. However, ethanol is generally produced from biomass. To use ethanol in biodiesel production instead of methanol makes the biodiesel fuel completely a bio-fuel. Turkey produces ethanol in important quantities from its own agricultural products such as sugar beet and so ethanol usage is also profitable for rural development. Compared to methyl ester biodiesel studies, there are limited numbers of investigation on the ethyl ester fuel’s effects on the engine performance, combustion and exhaust emission characteristics. Especially, the numbers of comparative studies between methyl and ethyl esters are too low.
Baiju et al. [13] compared the performance and emission characteristics of a diesel engine fueled with methyl and ethyl esters produced from Karanja oil and PBDF as baseline fuel. Engine tests were conducted in a single-cylinder, four-stroke, naturally aspirated diesel engine at constant engine speed of 1500 rpm. The engine load was increased from 0% to 100% with 20% increments. According to their results, the brake thermal efficiencies of PBDF were higher than those of ester fuels at all loads. PBDF emitted higher oxides of nitrogen emissions than ester fuels. The BSFC of methyl ester was higher compared with ethyl ester. Methyl ester produced slightly higher power and better emissions than ethyl ester.
Lapuerta et al. [14] produced methyl and ethyl ester fuels from waste frying oils and performed engine tests in a four-cylinder, four-stroke, turbocharged-intercooled, DI diesel engine. Although waste frying oils had similar properties, the feedstocks used in the methanolysis and ethanolysis reactions were different. As compared to PBDF, they found that pure methyl and ethyl ester fuels caused to slight increase in fuel consumption, slight differences in the NOx emissions and sharp reductions in the total hydrocarbon (THC), smoke opacity and particle emissions. However, volatile organic fraction of the particulate matter increased with ester fuels. Ethyl ester emitted lower NOx and THC emissions than methyl ester.
In this study, it was aimed to fill this gap partially in the literature by comparing the influences of waste frying oil based methyl ester and ethyl ester biodiesels on the engine performance, combustion and emission characteristics. According to the authors’ knowledge, there is no other study in which ethyl ester fuel’s performance, combustion and exhaust emissions are comprehensively investigated and compared with those of methyl ester fuel produced from the same feedstock and PBDF.
Section snippets
Materials and method
Waste frying oil used as feedstock in methanolysis and ethanolysis reactions was obtained from a pastry shop. To avoid the influences of different feedstocks on the reaction, the same waste frying oil sample was used for both transesterification. Some physico-chemical properties and fatty acid composition of the feedstock were given in Table 1. Methyl and ethyl ester biodiesels were produced in the pilot plant in the Alternative Fuel Research and Development Center (AFRDC)-Kocaeli University.
Brake specific fuel consumption
Brake specific fuel consumption (BSFC) is one of the fundamental parameters which are used for comparing the effects of fuels on the engine performance. The BSFCs belonging to five test fuels are shown in Fig. 2. For all test fuels, BSFCs decreased with increasing engine speed. Since in-cylinder air movement (turbulence) improves with the engine speed [15], [16], more homogeneous air–fuel mixture can be obtained. This enhancement in the air–fuel mixture formation might be effective on the
Conclusions
According to the results of this study, the following conclusions can be drawn:
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The fuel properties of ethyl ester met the EN 14214 biodiesel standard, showing that the fuel quality can be obtained through ethanolysis.
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Ester fuels had higher brake specific fuel consumptions and thermal efficiencies than those of petroleum-based diesel fuel. Ethyl ester biodiesel had better results in terms of these two parameters when compared to methyl ester biodiesel.
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Ester fuels emitted less CO, HC, but more NOx
Acknowledgement
This study was supported by the grants from the Scientific Research Foundation of Kocaeli University and Izmit Municipality (Project Nos: 2008/APP 002 and 2011/37).
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