Experimental heat release analysis and emissions of a HSDI diesel engine fueled with ethanol–diesel fuel blends
Introduction
Engine manufacturers all over the world have achieved to develop diesel engines with high thermal efficiency and specific power output, always trying to keep inside the limits of the imposed emissions regulations, which every day become more stringent. Significant achievements for the development of cleaner diesel engines have been made, over the last years, by following various engine-related techniques, such as for example the use of common-rail systems, fuel injection control strategies, exhaust gas recirculation, exhaust gas after-treatment, etc. [1], [2].
Furthermore, especially for the reduction of pollutant emissions, researchers have focused their interest on the domain of fuel-related techniques, such as for example the use of alternative fuels often in fumigated form [3], [4], or gaseous fuels of renewable nature that are friendly to the environment [5], [6], [7], or oxygenated fuels that show the ability to reduce particulate emissions [8], [9] usually with an escorting increase of the emitted nitrogen oxides. Sometimes, in order to obtain the desirable results, resort is being made to the simultaneous use of engine- and fuel-related techniques.
Dwindling crude oil reserves and their constantly increasing prices have placed increasingly sensitive loads on the trade balances of the non-oil producing countries and, meanwhile, have come to represent a threat to the existence of the developing and industrialized countries. Then, considerable attention has been paid on the development of alternative fuel sources in various countries, with particular emphasis on the bio-fuels that posses the added advantage of being renewable fuels that can be replenished through the growth of plants or production of livestock, showing an ad hoc advantage in reducing the emitted carbon dioxide [10], [11]. There is a commitment by the USA government to increase bio-energy three-fold in 10 years, which has added impetus to the search for viable bio-fuels [12].
Concerning the environmental aspect, rational and efficient end-use technologies are identified as key options for the achievement of the Kyoto targets of greenhouse gas emissions reduction. For the transport sector of European Union (EU), energy savings of 5–10% in the medium term and an aggregated of 25% in the long term (2020) are aimed at, with an expected cut of carbon dioxide (CO2) emissions by 8% by the year 2010. The EU has issued a directive on the use of bio-fuels accounting to at least 2% of the market for gasoline and diesel fuel sold as transport fuels by the end of 2005, increasing in stages to a minimum of 5.75% by the end of 2010 [11], [13].
Bio-fuels made from agricultural products (oxygenated by nature), may not only offer benefits in terms of exhaust emissions, but also reduce the world's dependence on oil imports. Moreover, local agricultural industries can be supported and farming incomes enhanced, besides providing a better energy security for many developing countries. Among these, bio-alcohols and vegetable oils or their derived bio-diesels (methyl or ethyl esters) are considered as very promising fuels [14], [15], [16], [17], [18], [19]. A work has been presented by this research group [11], which evaluates and compares the performance and environmental behavior of a multitude of vegetable oils and their bio-diesels, in blend ratios with diesel fuel of up to .
Because of its high octane number, ethanol is a good spark-ignition engine fuel, while vegetable oils and bio-diesels are good diesel engine fuels owing to their reasonably high cetane number. It is true that alcohols, mainly ethanol and to a much lesser extent methanol, have been considered as alternative fuels for diesel engines too [12], [20], [21]. Methanol can be produced from coal or petrol based fuels with low cost production, but it has a restrictive solubility in the diesel fuel. On the other hand, ethanol is a biomass based renewable fuel, which can be produced by alcoholic fermentation of sugar from vegetable materials, such as corn, sugar cane, sugar beets, barley, sweet sorghum, cassava, molasses and the like, and agricultural residues, such as straw, feedstock and waste woods by using already improved and demonstrated technologies [19]. Therefore, it has the advantage over methanol of higher miscibility with the diesel fuel and of being of renewable nature (bio-ethanol).
Section snippets
Use of ethanol in diesel engines: short literature review
The initial investigations into the use of ethanol in diesel engines were carried out in South Africa in the 1970s and continued in Germany and the USA during the 1980s. Most of these works related to the use in farm equipment (tractors and combines) or to the reduction in smoke and particulate emissions [22], [23], [24], [25], [26].
Nonetheless, there are several critical issues to consider with the use of ethanol in the diesel fuel. While anhydrous ethanol is soluble in gasoline, additives
Engine description
Facilities to monitor and control engine variables such as engine speed, load, water and lube-oil temperatures, fuel and air flows, etc., are installed on a fully automated test bed, single cylinder, four-stroke, water cooled, Ricardo–Cussons, “Hydra”, high speed, experimental standard engine located at the first author's laboratory. This engine has the ability to operate on the Otto (spark-ignition) or DI diesel or IDI diesel, four-stroke principle, by changing various parts of the crank gear
Properties of fuels
The conventional diesel fuel was supplied by the Aspropyrgos Refineries of the ‘Hellenic Petroleum SA’ and represents the typical, Greek automotive, low sulphur (0.035%) diesel fuel (gas oil); it forms the baseline fuel of the present study. The properties of the diesel fuel and the ethanol are summarized in Table 2.
The ethanol (CH3CH2OH) is blended with the normal diesel fuel at blend ratios of , and (by volume). For the present experiments, no cetane improving additives (ignition
Parameters tested and experimental procedure
The experiments were performed without any modification on the engine. The series of tests are conducted using each of the above fuel blends, with the engine working at a speed of 2000 rpm, at a static (pump spill) injection timing of 29 °CA before TDC, and four loads corresponding to brake mean effective pressures of 0.00 (no-load), 1.40, 2.57 and 5.37 bar, respectively. Owing to the differences among the lower calorific values ‘Θ’ and oxygen contents of the fuels tested, the comparison must be
General description
The measured pressure data to be processed for the DI diesel engine under study concern the closed part of the thermodynamic cycle. The equations and sub-models for developing the thermodynamic analysis using the measured pressure data for the cylinder (combustion chamber) are described in the following subsections. A spatial uniformity of pressure, temperature and composition in the combustion chamber (single-zone model), at each instant of time, is assumed. The gas medium is assumed to obey
Presentation and discussion of the experimental heat release (combustion) analysis results
It is pointed out that as far as the heat release analysis is concerned, only the results for the neat diesel fuel and the blend of 15% (by volume) ethanol in diesel fuel, denoted hereafter as E15-D, will be shown. This is dictated, on the one hand, by the conservation of space of this paper and, on the other hand, by the differences in the respective diagrams (of neat diesel fuel against the E15-D blend) that are relatively well discernible in this case.
The results of this section refer to all
Discussion of the performance and exhaust emissions results and their interpretation
Based on the very interesting combustion characteristics of the ethanol–diesel fuel blends revealed by the results of the previous section, derived after the application of the experimental heat release analysis, the performance and exhaust emission measurements results, for the present engine, can be interpreted as exposed in the following. They refer to measurements only for the three load cases and not the no-load one.
Fig. 11 shows in a bar chart diagram, at the three loads considered, the
Conclusions
An extended experimental study is conducted to evaluate and compare the use of ethanol as supplement to the conventional diesel fuel at blend ratios (by volume) of , and in a high-speed, DI diesel engine located at the authors’ laboratory.
The series of tests are conducted using each of the above fuel blends, with the engine working at a speed of 2000 rpm and at four loads. In each test, exhaust smokiness and exhaust regulated gas emissions such as nitrogen oxides, carbon monoxide
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