Emissions and performance of a single cylinder diesel engine using walnut-diesel blends

This paper investigates performance and emission characteristics of a single cylinder diesel engine which is fuelled with different blends of walnut oil biodiesel and diesel. Crude walnut oil was converted into walnut oil methyl ester by alkaline-catalyzed transesterification process. Various proportions of walnut oil biodiesel and Diesel are prepared on volume basis, and physically-chemically characterized. Engine performance (brake specific fuel consumption, brake thermal efficiency, and exhaust gas temperature) and emissions (HC, CO, CO2 and NOx) were measured at five engine loads. The results obtained showed an increase in BSFC and EGT and a decrease in BTE for all biodiesel blends. The emissions showed that biodiesel leads to a reduction of CO by 61.53% and HC by 30.3% and an increase of CO2 by 5.11% and NOX by 14.68%. Therefore it is concluded from the present experimental study that biodiesel of walnut can be used as alternative fuel for diesel engines.


Introduction
Due to depletion of fossil fuels and resulting global warming and air pollution biofuels are getting worldwide consideration. The transportation system consumes increased quantity of non-renewable petroleum fuels. Scientists and researchers all over the world found that biodiesel can be used for partial replacement of mineral diesel in terms of engine performance, emissions and combustion characteristics [1][2][3][4]. There are different kinds of alternative fuels obtained from vegetable oils, animal fats and waste oil [5]. Several studies have investigated the use of biodiesel from castor oil [6], soybean oil [7], camelina seed [8], sunflower oil [9], palm oil [10] and rapeseed oil [11] in diesel engines. Biodiesel is referred as fatty acid alkyl esters and is derived from renewable lipid sources by a process of transesterification [12]. The transesterification process is a reaction in which the triglycerides of the vegetable oil react with an alcohol in the presence of a catalyst (sodium hydroxide and potassium hydroxide) [13,14]. Several experimental investigations have been performed to evaluate the performance and emission characteristics of biodiesel-fueled engines. Combustion of biodiesel fuel produces less particulate matter (PM), hydrocarbon (HC), smoke and carbon monoxide (CO) emissions [15,16]. In order to improve the psychical chemical properties of biodiesel many researchers had tried adding different blending components [17]. In comparison with other vegetable oils, walnut oil has the highest amounts of polyunsaturated fatty acids (up to 78% of the total content of fatty acids). The fatty acid composition of walnut oil contains linoleic acid (49 to 63%), α-linoleic acid (8 to 15.5%), oleic acid (13.8 to 26.1%), palmitic acid (6.7 to 8.7%), and stearic acid (1.4 to 2.5%) [18][19][20]. Romania is the 10th largest producer of nuts in the world with 28.700 tons produced in 2014 on a cultivated area of 1750 hectares. Almost 25% of total EU production comes from Romania 2 1234567890''"" investigated the effects of molar ratio of methanol to oil, catalyst dosage, and temperature on reaction yield and found a biodiesel transformation rate of (97.2%). A ratio methanol to oil 8:1, reaction time 90 min, 1% catalyst generate a walnut biodiesel with properties closed to diesel fuel. Moser R.B.
[23] studied the properties of blends (B2, B5, B10 and B20) from hazelnut, walnut and peanut biodiesel fuel. Blends containing biodiesel of hazelnut and walnut exhibited improved cold flow properties. With the increase in biodiesel content the oxidative stability and calorific value of blend was negatively affected, whereas lubricity was improved. Several experimental investigations have been carried out by Rasheda et al.
[25] conducted a comprehensive study on performance and emissions of 30% palm biodiesel blend with petrodiesel. According to their results all the biodiesel blends showed an increase of brake-specific fuel consumption (BSFC) by 8.55-9.03% and a decrease of the brake thermal efficiency by 3.84-5.03% compared to diesel fuel. Also CO and HC emissions decrease with 13.75-17.97% and 18.26-31.21%. In a previous study Khiari et al.
[26] on a single cylinder, direct injection diesel engine with pistacia lentiscus biodiesel combustion parameters, performance and pollutant emissions are compared with those of diesel fuel. The BSFC for biodiesel is is 17.6% and 9.7% higher than the diesel fuel and the emission of CO, HC particulate matter are reduced at full engine load with 25%, 45% and 17%. The aim of this study is to determine the fuel properties, parameters and emissions of a single cylinder engine fuelled with blends of walnut oil biodiesel. No research was conducted in the literature to investigate the performance and emissions characteristics of this type of fuel in diesel engine.

Materials
The walnuts nuts were purchased from a local vendor in Romania. Diesel fuel was purchased from a Lukoil gas station in Craiova (type Euro L Diesel). The chemicals used for the transesterification reaction were purchased from Laborex Romania.

Production of WME
The walnut kernels were subjected to an extraction process using a press PU-200 to produce raw oil. After pressing, the raw oil was filtered to remove impurities. A titration was performed to determine the steps for biodiesel production. Alkaline-catalyzed transesterification was used to produce WME. A ratio of 6:1 methanol and catalyst (NaOH 1 w/w% of oil) in a reactor at constant temperature (65°C) was stirred for 2 hours. The mixture was cooled to room temperature and to settle down for 24 hours.
The mixture separated by gravity into biodiesel and glycerol. Biodiesel is separated and purified to remove catalyst and methanol (magnetic separation).
The homogenizer was set at 1800 rpm to mix the samples for 30 min.

Properties analysis
The chemical and physical properties of all samples were assessed in the Laboratory of Thermodynamics and Thermal Machines and Laboratory of Fuels, University of Craiova. The major properties including viscosity, density, flash point, calorific value, cetane number, cloud and pour point were determined using several methods. Table 1 shows the important properties of fuel along with biodiesel standards. 3

Engine test facility and experimental conditions
In this study a Ruggerini RY 50 model, single cylinder, four-stroke diesel engine, typically used in the agricultural sector was used for tests. The schematic diagram of experimental setup is shown in figure  1. The technical details of the engine are listed in table 2. The engine was coupled with a generator (type Ce 160s, 110V, 44A) and the speed of the engine was kept constant at 1500 rpm. A resistive load bank was used to load the engine at 20, 40, 60, 80 and 100% for different blends of biodiesel and diesel fuel. Fuel consumption (model DFM 250D) and exhaust temperatures (KIMO MP 200 thermocouple type K, temperature range -200...1300 °C) were also measured. Exhaust gas emissions were measured with a gas analyzer type Stargas 898 (table 3). This analyzer measures CO, CO 2 , HC, O 2 and NO in the exhaust gas. The ambient conditions were monitored by a barometer and a thermometer. The engine is first started with diesel fuel until a steady operating condition was obtained (cooling water and lubricating oil and have reached 85°C). The experiments were repeated three time and the average values of emission and performance were taken for measurements.    Figure 2 shows the variation of brake thermal efficiency for the blends of walnut biodiesel. From the chart it is seen that BTE increases with the load of the engine up to 80% and decreases at maximum load due to the incomplete combustion. [32] found a decrease in BTE of jatropha biodiesel in a single cylinder direct injection diesel engine. The decrease in BTE of jatropha blends was due to the early start of combustion of biofuel with an increase in compression work and heat loss. Figure 3 shows the variation of brake specific fuel consumption for diesel and blends of walnut biodiesel. It was observed that BSFC values are higher for biodiesel blends at all engine loads.  At full load BSFC values for diesel, B10, B20, B30, B75 and B100 are 380 g/kWh, 391 g/kWh, 406 g/kWh, 410 g/kWh, 436 g/kWh, and 455 g/kWh, respectively. This phenomenon occurs due to lower calorific value and higher density of biodiesel [33]. These findings are supported in the literature by various rapports [34,35]. McCarthy et al. [36] found that a mixture of animal tallow (80%)-canola oil methyl ester (20%) and chicken tallow (70%)-waste cooking oil methyl ester (30%) increase BSFC with 7% and 10% compared to diesel. Also Utlua and Kocak [37] reported an increase with 14.34% of BSFC of biodiesel from waste frying oil.

Results and discussion
Exhaust Gas Temperature (EGT) increases with the increase in load for all the blends and diesel (figure 4). The EGT is an indicator of the heat of the blends tested during combustion period [38]. From the results it can be seen that the EGT in full load for B100 (335°C) is very closer to that of diesel (318°C). Higher blends of biodiesel exhibits high temperature due to the higher oxygen content which leds to better combustion [39]. Godiganur et al. [40] tested mahua oil methyl ester and its blends with diesel and observed an increase with 12% of EGT of biodiesel. Buyukkaya [41] investigated the EGT of rapeseed biodiesel and reported a temperature of 490°C in the case of B100 whereas the corresponding value with diesel was 475°C.
CO is formed during the combustion process and depends upon carbon content, oxygen content and combustion efficiency of the fuel [42]. CO is an indicator of incomplete combustion and is produced when the carbon from the fuel is partially oxidized. Figure 5 shows the variation in CO emission with  respect to variation in load. Compared with diesel, a decrease in CO emission is observed when walnut biodiesel and its blends are used. The average CO emission for B10, B20, B30, B75 and B100 were less than that of diesel by 2.98%, 12.5%, 19.34%, 30.5% 61.53% at 60% load of the engine. It is observed that CO emissions decrease up to 60 % load and increase after for all the tested fuels.
The decrease of CO emissions with the increase of biodiesel percent in the blend is due to the increase of oxygen content and temperature of combustion. Raheman and Phadatare [43] investigated in diesel engine different blends of karanja oil methyl ester and found a reduction in CO emissions by 74% compared with diesel fuel. A 25.8% reduction in CO emission was found by Subbaiah and Gopal [44] with rice bran oil biodiesel.
The variation of CO 2 emission with engine load is shown in figure 6. CO 2 is a parameter which indicates complete combustion of a fuel and its efficiency inside the combustion chamber [45]. The CO 2 emissions increased with load for all biodiesel blend and diesel fuel. The overall CO 2 emissions of B10, B20, B30, B75 and B100 were higher than that of diesel by 0.29%, 0.99%, 2.22%, 3.92% and 5.11% at 100% load of the engine. As blend increases there is an increase in CO 2 emissions due to the higher oxygen content of biodiesel which results in better combustion [46]. An increase in CO 2 emissions of soybean biodiesel was observed by Randazzo and Sodré [47] with the increase of biodiesel percentage in blend. Similar results were observed by other researchers [48,49].
The emission of unburned hydrocarbon (HC) results depends on the combustion efficiency. If combustion is improved HC decrease and vice versa. Variation of HC emission in p.p.m. for all the tested fuels versus load is presented in Figure 7. The average HC emission for B10, B20, B30, B75  and B100 were less than that of diesel by 2.12%, 5.40%, 7.65%, 22.2%, and 30.30% at 100% load of the engine. Since biodiesel contains more oxygen in his structure and has a higher cetane number, the emissions of HC will decrease with the use of biodiesel blends. Amarnath and Prabhakaran [50] found that biodiesel of karanja and blends from 20% to 100%, reduce emissions of HC with 50% due to the better combustion. Sahoo et al. [51] found a reduction in HC emissions of neat karanja, jatropha and polanga biodiesels of 20.64%, 20.73% and 6.75%.  NOx emission with load for B100, B75, B30, B20, B10 and diesel. The NOx formation depends of combustion temperature and oxygen content. The NOx emission level increases with load due to higher cylinder pressure and temperature for all bends of biodiesel and diesel. The overall increase in NOx emissions for biodiesels blends (B10, B20, B30, B75 and B100) were 0.72%, 1.21%, 2.40%, 10.4% and 14.68%, respectively, when compared with diesel fuel at full load. The results obtained in the tests are in concordance with the reports of other researchers that found a higher NOx emission due to higher oxygen content, higher specific fuel consumption and higher viscosity of biodiesel [52,53]. Aydin and İlkiliç [54] tested biodiesel of rapeseed and found an increase of NO X with 16.7% for B20 and 11.8% for B100.

Conclusion
In the present work several tests were carried out on a single cylinder air cooled direct injection diesel engine using diesel, walnut biodiesel and different blends under various engine loads. The characterization of biodiesel blends prepared by alkaline-catalyzed transesterification process has shown that properties are comparable with diesel fuel. From the test the following conclusions have been drawn: -Brake thermal efficiency decrease with increase in biodiesel percentage and is lower in the case of walnut biodiesel; -Brake specific fuel consumption and exhaust gas temperature was found highest for pure biodiesel. This may be due to the high density, high volatility and high oxygen content of biodiesel; -CO and HC emissions are highest for diesel fuel and lowest for biodiesel blends with high content of biodiesel because of higher oxygen content; -CO 2 and NO X were found highest for diesel because of high combustion temperature of biodiesel.