Combined influence of supercharging, EGR, biodiesel and ethanol on emissions of a diesel engine: Proposal of an optimization strategy
Introduction
Global energy demand is supplied by fossil fuel resources, substantially. However, growth of world population at an increasing rate and increase in energy demand of the developing industries worldwide causes rapid depletion of resources. On the other hand, utilization of fossil fuels causes damage to the environment. Therefore, legislative regulations on emissions are changing continuously. In this situation, turning to renewable and sustainable energy resources is inevitable [1,2]. In this context, utilization of ethanol fuel, produced from vegetables or animals, stands out [3].
Biodiesel is one of the potential fuels to be used on diesel engines [1]. Utilization of biodiesels on diesel engines has become widespread [6], because vegetable oils are renewable, biologically degradable, free of toxic materials, and have low emission profile, except NOx [4,5]. In some countries, biodiesel addition into commercial diesel fuel is a legal obligation.
Ethanol is another alternative fuel used in diesel engines. Ethanol is a renewable fuel, produced by fermentation of carbohydrates using enzymes as catalysts. Corn, sugar cane, wheat, potato, rice, rye and various fruits can be used as carbohydrate sources [7]. Ethanol utilization reduces some emissions, since ethanol is free from sulfur and heavy metals, unlike diesel fuel, has a smaller molecular structure, and has oxygen content [[8], [9], [10], [11], [12]].
One of the worse problems is the negative effect of diesel engines on the environment with NOx emissions. NOx production takes place at high combustion chamber temperatures at the presence of oxygen [13]. NOx emissions can be reduced by Exhaust Gas Recirculation (EGR). By redirecting some exhaust gasses back into the cylinder, charge in the combustion chamber is diluted, and as a result, peak combustion temperatures, so the amount of NOx, are reduced [[14], [15], [16]]. But, increasing EGR ratio above a threshold worsens engine performance parameters, and so, the specific fuel consumption increases [17], [18], [19]. Therefore, to control performance and emissions, both, combined implementations can be effective and successive. Hereby, besides alternative fuel utilization, EGR and supercharging applications parameter optimization of the mentioned should be done, as a whole.
Efe et al. [22] investigated effects of using blends of biodiesel, from corn, sunflower, soybean, canola and hazelnut oils, and diesel fuel on Diesel engine, experimentally. Experiment resulted in 20% biodiesel fraction blend fuel giving the best engine performance and for hazelnut oil. Also, testing various oil biodiesel-diesel fuel blends, increase in specific fuel consumption in comparison to standard engine data is stated. Ayhan et al. [20] tested diesel and sunflower oil methyl ester blend fuel on a Diesel engine and studied engine brake power, specific fuel consumption and emissions. And, indicated, B20 blend giving the optimum results compared to standard engine data among B10, B20 and B50 blends. Also pointed, significant decrease in HC, CO and smoke emissions, but increase in NO emission. And added, increasing biodiesel fraction in blend fuel caused increase in specific fuel consumption compared to standard engine data. Karabas [21] experimentally investigated the effect of using tobacco seed oil biodiesel blend fuels, B10, B20 and B50, on a Diesel engine for engine performance and emission characteristics. And reported, higher specific fuel consumption and NOx emissions, and lower HC, CO and smoke emissions, in comparison to diesel fuel. Manigandan et al. [20] conducted experimental studies using blend fuel, consist of corn oil methyl ester, pentanol and titanium at various fractions, at various speeds and loads. Significant reductions in CO, HC and smoke emissions are reported for using blend fuel consist of 25% corn oil methyl ester, 50% diesel fuel, 20% pentanol and 5% titanium, namely M25D50P20T5, compared to diesel fuel.
Jamrozik [12] conducted experimental studies on a direct injection Diesel engine to investigate effects of using ethanol and diesel fuel blend fuels on performance and emissions. Alternating alcohol fractions in the blend between 0 and 40%, reported improvements in engine performance by using diesel ethanol blend fuels throughout the mentioned range, CO emissions were reduced by 38%, whereas THC and CO2 emissions remained virtually unchanged, but NOx emissions increased. Ghadikolaei et al. [23] analyzed comparatively performance and emissions on a Diesel engine using diesel-biodiesel-ethanol blend using fumigation. To compare different fuel modes, a blend with constant fractions by volume of 80% diesel, 5% biodiesel and 15% ethanol is used. To the test results, in fumigation mode, CO2, CO and HC emission increased, but NOx and NO emissions decreased. And, in general, smoke emission is determined to be increased in comparison to standard engine. Pradelle et al. [24] studied experimentally performance and combustion characteristics of a Diesel engine using diesel-biodiesel-ethanol blend fuels. In engine tests, blend fuels used are obtained by adding ethanol in fractions of 0% up to 20% into B15 fuel. The test results of the various blend fuels are presented in comparison to B7E0, consisting of 7% biodiesel, 0% ethanol and 93% diesel, blend fuel. A 2% increase in specific fuel consumption is reported corresponding to each 5% increase in ethanol fraction. It is suggested to be caused by the decrease in blend fuel volume and the decrease in heating value. Shamun [25], testing on a Diesel engine using ethanol in high amounts, 30% ethanol fraction, reported significant decrease in NOx emissions. And, added HC and CO emissions to be higher than diesel fuel for using ethanol at low loads.
In Exhaust Gas Recirculation (EGR) applied studies, worsening in engine performance and increase in HC, CO and smoke emission, but decrease in NOx emissions are observed [14,[26], [27], [28]]. He et al. [27] added alcohol at different fractions, 15% ethanol, 15% butanol and 40% butanol, into diesel fuel, and also applied EGR on a Diesel engine, and to investigate combustion properties and changes in emissions at high load conditions, experimentally. And concluded that, at moderate alcohol fraction and EGR ratios improvements in engine performance and emissions can be achieved, in common. Verma et al. [28], using dual fuel (diesel and biogas) on a Diesel engine at different EGR ratios and compression ratios studied engine performance and emissions experimentally. During testing, 5%, 10% and 15% EGR ratios are used. Inducing EGR into engine at low loads resulted in a slight increase in engine efficiency and decrease in NOx emissions. Also, at high loads and increasing EGR ratios decrease in engine efficiency is reported.
In this study, engine tests are designed as suggested in Taguchi method. In this method, instead of conducting all the test in the factorial combination, just a factorial combination of orthogonal series is determined for the optimal emission characteristics and tested [41]. Reviewing the literature within this context, Taguchi design of experiments method is chosen by many researchers [29,[33], [34], [35], [36], [37], [38], [39]] to reduce time and costs. In the literature [[29], [30], [31]] optimization of various engine input parameters to sustain the best engine emissions are performed by Taguchi method. Ansari et al. [32] investigated engine performance and emissions of a Diesel engine using various biodiesel blend fuels by Taguchi method. As a result, input parameters are optimized for the best engine performance and emissions. Wu et al. [33] studied combustion characteristics by Taguchi method on an EGR applied Diesel engine run on Liquefied Petroleum Gas (LPG) and diesel-biodiesel blend fuel and stated the optimum operating factors. Wu and Wu [34] investigated engine emissions and combustion properties on a single cylinder engine using diesel and biodiesel blends and induction of H2 at various fractions and EGR into inlet manifold at various fractions, and determined the best combinations of input parameters by Taguchi method. Also, time savings of 67% is pointed out during tests by using L9 orthogonal series of Taguchi method.
Reviewing the literature, the following information is concluded. Biodiesel utilization in engines improves engine performance parameters and emissions, but NOx, at different amounts, instead increases NOx emissions. And, ethanol decreases CO emissions, but increases NOx emissions, while do not effect HC and CO2 emissions. EGR decreases NOx emissions, significantly, but deteriorates rest of the engine parameters, particularly under high EGR rates. However, differences in test results are observed regarding differences in testing conditions in the studies. In the literature, in any study using different fuels and emission reductions techniques, comprehensively, like in this study is reported. In this study, factors are chosen considering improvements provided by different alternative fuels, supercharging and EGR. With EGR utilization, NO emission reduction is predicted. And with biodiesel, ethanol and supercharging utilization, improvements on deteriorated emissions remaining and specific fuel consumption are aimed. In comparison to standard engine data, reductions in all the emissions and specific fuel consumption are intended. For this reason, the effects of using alternative fuel blends and ethanol fumigation as alternative fuels and EGR at various rates and supercharging on specific fuel consumption and emissions for a diesel engine operating at various loads and engine speeds are investigated experimentally. Taguchi method is used for the design of experiments. The optimum factor levels of parameters are evaluated using the Signal/Noise (S/N) ratios suggested by Taguchi method. Variation analysis is used to evaluate the effect of different factor levels on specific fuel consumption and emissions characteristics.
Section snippets
Biodiesel production
The biodiesel fuel used in experiments was produced from corn oil by transesterification method in laboratory. Alcohol, and catalyst used in transesterification process were methyl alcohol and KOH (potassium hydroxide), respectively. At first, KOH catalyst was dissolved in alcohol. In the meanwhile, corn oil was placed in a mixing container and its temperature was brought to 60 °C, constant. Afterwards, alcohol and catalyst mixture was transferred into a closed reaction container. And, corn oil
Brake specific heat consumption
In Fig. 2, Changes in S/N values of factors and levels for brake specific heat consumption is presented. Optimum BSHC is obtained at 80% load, for B10 biodiesel blend fuel and E20 ethanol ratio, EGR0 (without EGR), at 1600 rpm and SC2.1 (supercharging at 2.1 bar). And, the best combination corresponds to A3-B2-C4-D1-E1-F2 (Load:80%-Biodiesel:10%-Ethanol:20%-EGR:0%-Speed:1600rpm-SC:2.1 bar).
Engine load increases with the fuel quantity delivered. Brake specific heat consumption is defined as
Conclusion
In this study, using Taguchi design of experiments method, changes in engine parameters, specific fuel consumption and emission characteristics at various biodiesel fractions, ethanol fractions, EGR ratios and charging pressure, are investigated for a Diesel engine running at various loads and speeds. In conclusion, as determined, engine load and engine speed at various biodiesel, ethanol, EGR and supercharging levels have influence on SFC and emission characteristics. Overall results are
Credit author statement
We would like to inform you that all authors have contributed to the preparation of the manuscript. The study was prepared with the contribution of all authors, both in the conduct of experimental studies and in the writing of the manuscript, literature research, drawing and interpretation of the figures, writing and editing.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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