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A novel approach to study the effect of cetane improver on performance, combustion and emission characteristics of a CI engine fuelled with E20 (diesel – bioethanol) blend
Sustainable Chemistry and Pharmacy 14 (2019) 100185
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A novel approach to study the effect of cetane improver on performance, combustion and emission characteristics of a CI engine fuelled with E20 (diesel – bioethanol) blend Himansh Kumar a, b, Anil Kumar Sarma b, *, Pramod Kumar a a b
Mechanical Engineering Department, Dr B R Ambedkar NIT Jalandhar, Punjab, India Chemical Conversion Division, SSS-NIBE Kapurthala, Punjab, India
A R T I C L E I N F O
A B S T R A C T
Keywords: Cetane improver 2-EHN Mass fraction fuel burned Combustion analysis NOx emission
In this article an investigation was carried out to study the effects of cetane improver (2-Ethylhexyl nitrate) (2EHN) on performance, combustion and emission characteristics of a constant speed, single cylinder CI engine fuelled with E20 (bioethanol (20%) – petrodiesel (80%). A cetane improver, 2-EHN was used at concentration of 1000 ppm and 2000 ppm with the test fuel (E20) and the results were compared to petrodiesel. The results showed that E20EHN1000 had 3.8% higher brake power (BP) to that of petrodiesel and the brake specific fuel consumption (BSFC) was similar with E20 and petrodiesel. E20EHN1000 showed 4.9% higher brake thermal efficiency (BTE) to petrodiesel and the volumetric efficiency (ηvol) was almost identical for all the test fuels. The trend for cylinder pressure (CP), net heat release rate (NHR), rate of pressure rises (ROPR) and mass fraction fuel burned (MFFB) of E20EHN1000 were also identical to those of E20 and petrodiesel. Except hydrocarbon (HC) emission, E20EHN1000 showed acceptable emission results to that of petrodiesel and other test fuel blends. Carbon dioxide (CO2) and carbon monoxide (CO) emission for E20EHN1000 were comparable with petrodiesel but, the oxides of nitrogen (NOx) emission was slightly higher than petrodiesel. However, E20EHN2000 showed poor performance due to the excess amount of 2-EHN, which shortened the ignition delay and reduced the premixed combustion phase with increased combustion duration. From the results, it is clearly unveiled that E20 with 1000 ppm of 2-EHN showed better results than E20, E20EHN2000 and petrodiesel.
1. Introduction Inadequate reserves and exponentially rising demand of petroleum along with recent environmental consensus instantaneously drive the researchers and Industrialist for biofuel production and commerciali zation. The production cost of biofuel and availability of feedstocks stand as the major barriers of its implementation and progress in commercialization (Onuh and Inambao, 2018). To overcome these is sues, blending of biofuel with fossil fuel is considered as the best option to lower the trauma on it. Biofuel such as biogas, ethanol/bioethanol, methanol/bio-methanol, diethyl/methyl ether and biodiesel can be used as an intermediate fuel in CI engines (Ramalingam et al., 2018; Cam �ndez et al., 2012). pos-Ferna Ethanol can be used in CI engine by direct spraying in the combus tion chamber or blending with petrodiesel. However, for direct spraying, engine modification is required and also ethanol spraying in the
combustion chamber is a costlier process in terms of CI engine design and modification (Hansdah and Murugan, 2014). Ethanol blending on the other hand, is much easier and it requires no engine modification. However, ethanol is the best option for blending because of its friendly characteristics for CI engine functioning such as, no engine modifica tion, easy availability, low cost and no long-term operating issues. Tutak et al. (2017) studied the effects of hydrated ethanol, blended with pet rodiesel in a concentration up to 45% (v/v) with 5% increment, for the CI engine performance parameters. The same practice was repeated with biodiesel-ethanol (BE) blends in place of petrodiesel. The test was con ducted on a single cylinder direct injection-based CI engine operated at constant speed, 1500 RPM. It was reported that the highest value of indicated thermal efficiency (ITE) (35%) was obtained with 35% ethanol concentration in diesel-ethanol (DE) blend and the maximum of 31% ITE was obtained with biodiesel-ethanol blend. NOx emission for DE (30%) blend was higher with BE (45%) blends, but the CO emission was
* Corresponding author. E-mail address: [email protected] (A.K. Sarma). https://doi.org/10.1016/j.scp.2019.100185 Received 30 May 2019; Received in revised form 18 September 2019; Accepted 6 October 2019 Available online 16 October 2019 2352-5541/© 2019 Elsevier B.V. All rights reserved.
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Sustainable Chemistry and Pharmacy 14 (2019) 100185
lower with both the blends in all ranges of concentration. CO2 was little bit lower for BE (45%) in comparison with DE (45%). Odziemkowska et al. (2016) examined the effects of bioethanol with a co-solvent, 2-ethyl-1-hexanol (15% þ 5%) (v/v), blended with 80% petrodiesel and the same with petrodiesel and biodiesel (73% þ 7%) on a 4-cylinder CI engine. It was reported that up to 30% bioethanol with 5% co-solvent is a stable emulsion on or above 15� C. The first fuel blend reportedly showed similar trend for CO emission, slightly higher trend for HC, NOx emissions and low particulate emission (PM) with petro diesel. Maximum 10% decrement in power and torque was observed with these two test fuel blends. The second test fuel blend showed nonidentical results in all respects except PM emission. Hansdah et al. (2013) studied the effects of bioethanol-petrodiesel blend (in proportion of 5%, 10% and 15%, respectively) on performance parameters of a single cylinder CI engine at rated power 4.4 kW BP @ 1500 RPM, using Span80 (1%) as a surfactant on volume basis. The authors examined higher ignition delay (ID) for higher concentration of bioethanol in petrodiesel also, the high in-cylinder pressure and BP were observed for every bioethanol-diesel blend. NOx and smoke were lesser with petro diesel for all test blends. Kim and Choi (2010) examined the effects of bioethanol (99.5% purity)-petrodiesel blend (15% þ 85%) (v/v) with 7500 ppm ethyl hexyl nitrate (cetane improver) on suspended nano particles and other harmful emissions of CRDI diesel engine. For the test blend, 50% smoke reduction and increased NOx emission were observed. In case with biodiesel, except B20, the blend of 15% biodiesel þ5% bioethanol þ80% petrodiesel was more effective for reduction in par ticle number and particle mass. The fact that the first-hand distillation of bioethanol has about 5% (v/v) water content and their effects blending with petrodiesel, performance and emission parameters were not yet explored in those research articles. This is eminent that bioethanol can be obtained from the fermenta tion of sugar or starch bearing plants, lignocellulosic and cellulosic materials derived from non-edible food (MnTAP, 2008; Pal et al., 2018). Bioethanol contains only 95% ethanol with ~5% water, because during fermentation low boiling water-ethanol azeotrope is formed after first-hand distillation, and it is a very uneconomical distillation process to attain 99% pure bioethanol (Pal et al., 2018). This fact was estab lished (Pal et al., 2018) that an azeotropic mixture of bioethanol and water (95% þ 5%) (v/v) was formed due to traditional distillation and it was hard to dehydrate the ethanol, because almost 40% of the total energy was consumed to resolve this issue. However, Hammonda and Mansell (2018) reported that the bioethanol contains almost equal en ergy content (18.6 MJ/kg) to the conventional ethanol. It is therefore presumed that 95% pure ethanol without metal contaminants could be a suitable blending agent for petroleum diesel, if performance parameters are not changed appreciably in an existing CI engine. Cetane number (CN) of any diesel range fuel shows its ignition quality or in other words CN is inversely proportional to the ignition delay of CI engine (Ileri, 2016). Ethanol or bioethanol has an extremely low cetane number and mixing of bioethanol with petrodiesel results reduction in CN of the fuel blend (Lapuerta et al., 2007). The lower CN of fuel blend delays the start of combustion which results abnormal com bustion behaviour and higher exhaust emissions from CI engine (Guo et al., 2011; Turkcan, 2018). Atmanli (2016) studied the effects of 2-EHN on the physicochemical properties and CI engine performance parameters fuelled with the blends of petrodiesel, hazelnut oil and butanol/pentanol. The authors examined that 2-EHN helped to increase the CN but, no any significant effects were observed on other properties of test blends. The pentanol based blends showed less BSFC, NOx and HC as compared with butanol-based blend but, reciprocal in case CO emission. The polar nature of ethanol limits its utility in higher concentration with petrodiesel but, 2- EHN functions as a surfactant which helps to decrease the interfacial tension between polar and non-polar molecules (Kim and Choi, 2010; Ciniviz et al., 2017). Bora et al. (2014) studied that 2-EHN worked as a surface-active agent for decreasing the interfacial
tension between the two liquid films. Therefore, a commercial cetane improver 2-EHN is used as a cetane improver and it is expected to in crease the combustion efficiency and to improve the ignition timings. In this approach, the objective was set to determine the effects of 2EHN on CI engine performance fuelled with an E20 blend of petrodiesel and the ethanol with identical concentration as obtained from the lignocellulosic biomass by first-hand distillation. 2-EHN was added at a concentration of 1000 and 2000 ppm, respectively, to E20 blend. Moreover, the stability tests showed that the E20 blend was stable and could be used without any external surfactant. Performance, combustion and emission characteristics of CI engine was examined for E20, E20 with 1000 ppm 2-EHN and E20 with 2000 ppm 2-EHN and compared with those of petrodiesel and reported. 2. Materials and methods 2.1. Materials and characterisation In order to examine the effect of bioethanol (95%), ~5% deionized water was mixed with anhydrous ethanol (<99.9%), purchased from Merck India Ltd. Petrodiesel (LDO, Indian Oil Corporation) was pur chased from a local petrol pump located in Jalandhar District (Punjab), India. 2-EHN (97%) was purchased from Sigma-Aldrich (India). These blends were gently shaken for 15 min and their stability were tested using a centrifuge at 3000 RPM, 25� C for 30 min, and physical obser vation by 15 days. The concentration of 2-EHN and bioethanol in pet rodiesel is shown in Table 1. The cetane number of test blend is calculated using the empirical formula as suggested by Ruina et al. (2014). CN ¼ CNd � wd þ CNbe � wbe þ K � w2
(1)
EHN
Where CN is the cetane number of test blend, CNd is the CN of petro diesel, CNbe is the cetane number of bioethanol, K (K ¼ 4) is constant for 2-EHN, wd, wbe and w2-EHN is the blend ratio for petrodiesel, bioethanol and 2-EHN, respectively (Ruina et al., 2014). The blend ratio was calculated by the mass of respective vol. to the total mass of vol. The CN of test blend was increased 1.26 @ 01 ml addition of 2-EHN (Ruina et al., 2014). The effect of 2-EHN concentration upon CN of the test blends is shown in Table 2. The fuel properties such as density, viscosity, flash point, calorific value, cetane number and cold filter plugging point of E20, E20EHN1000, E20EHN2000 and petrodiesel were determined using standard test methods recommended by ASTM/EN also shown in Table 2 (Kumar et al., 2016; Singh et al., 2015). 2.2. Experimental procedure 2.2.1. Experimental set-up (CI engine test rig) A 4 stroke, single cylinder DI, stationery CI engine (Kirloskar India Ltd.) with rated power 5.2 kW @ 1500 RPM was used to conduct the experiments. Table S1 has shown the detailed specification of test rig. Water cooled eddy current dynamometer was used for loading on the crankshaft with the help of electromagnetic force which was regulated by the load cell (Kumar et al., 2016). Two piezometric sensors were used to determine inside cylinder pressure and fuel line pressure, respec tively. An optical crank-angle sensor was used to determine the degree Table 1 Concentration of test fuel blends.
2
Test fuel
Petrodiesel (%)
Bioethanol (%)
2-EHN (PPM)
Stability
E20
80
20
–
E20EHN1000 E20EHN2000 Petrodiesel
80 80 100
20 20 –
1000 ppm 2000 ppm –
Stable (05 days) Stable Stable
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Sustainable Chemistry and Pharmacy 14 (2019) 100185
equations as referred (Kumar et al., 2016; Heywood, 1988; Singh et al., 2015) and expressed in supplementary equations 2 to 9.
Table 2 Fuel properties of E20, E20EHN100 and E20EHN2000 in comparison with Petrodiesel. Test Fuels
density @15 � C gcm
E20 E20EHN1000 E20EHN2000 Bioethanol Petrodiesel
3
0.818 0.818 0.819 0.798 0.823
viscosity @40 � C
GCV
mm2s
MJkg
2.4 2.3 2.3 1.4 2.65
1
40.20 40.35 40.55 27.20 42.86
cetane index 1
36.6 37.86 39.12 7 44
flash point
CFPP
(� C)
(� C)
57.2 56.1 55.5 17 66.5
2.2.2. Experimental procedure The trials were performed in the order of petrodiesel, E20, E20EHN1000 and E20EHN2000. The engine was loaded with 0% (no load), 20%, 40%, 60%, 80%, and 100% load conditions using eddy current type dynamometer with the help of electrical resistance unit during the measurement. The engine was allowed to run on that con dition for 30 min until the engine reached at its steady state for each of the load measurement condition. The same was repeated for all test fuels to reduce the level of uncertainty. The engine was again run with pet rodiesel to maintain its initial stage of operation. The experiments were conducted in triplicate and average values are reported in the results and discussion section for its reliability. The standard deviation was also calculated and presented as the error bars in the graphs.
27.5 7 7 52 20
CFPP: cold filter plugging point temperature.
angle rotation of the crankshaft. The fuel consumption was measured with a fuel flow transmitter made by Yokogawa, Model No: EJA110A-DMS5A-92NN. It was attached with the fuel line and the signal of flow rate was transferred to the National Instrument make data acquisition device (DAD). This DAD was connected to the computer through USB port. All the signals recorded were conveyed to ‘Engine softLV’ version 9.0 software (Apex Innovations Pvt. Ltd.) for perfor mance and combustion analysis (Kumar et al., 2016; Heywood, 1988; Singh et al., 2015). AVL diGas 444 analyser was used to determine the exhaust emission from CI engine. The exhaust gases, namely CO, CO2, HC, and NOx were analysed under the test procedure approved by the Ministry of Road Transport and Highways, GOI, and specified in MoRTH/CMVR/TAP115/116, Issue No. 3, Part-VIII in 4-gas analyser. Table S2 has shown the technical specification of AVL diGas 444 analyser (Kumar et al., 2016; Heywood, 1988; Singh et al., 2015). The performance analysis is based upon the computation of basic
3. Result and discussion 3.1. Engine performance characteristics Fig. 1(a) illustrated the BP characteristics of CI engine fuelled with E20 E20EHN1000, E20EHN2000 and petrodiesel. The brake power showed an increase trend with respect to load. Mixing of 2-EHN with E20 enhanced the cetane number and reduced ignition delay, which resulted an average increment of 3.8% in brake power (BP) at full load for E20EHN1000 with respect to petrodiesel while E20EHN2000 showed lower value from other test fuels. E20 showed 1.1% higher BP to that of petrodiesel. This was because of high oxygen content and reduced viscosity and density due to addition of ethanol in test fuel
Fig. 1. (a–d) Variation in Brake Power, BSFC, Brake Thermal Efficiency and volumetric efficiency with respect to load. 3
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Fig. 2. (a–d) Variation in cylinder pressure, net heat release rate, rate in pressure rise and mass fraction fuel burned at different crank angle. (The values are at full load conditions of test engine).
blends (Srivastava et al., 2017). Mixing of 2-EHN increased the CNs which resulted easy auto-ignition but, at the same time excess 2-EHN resulted advance ID and this lowered the BP for E20EHN2000 (Ruina et al., 2014). The BP for E20 and E20EHN1000 can also be rechecked from high in-cylinder pressure and heat release rate at pre-mixed burning stage. It was observed from Fig. 1(b) that, BSFC was highest for E20HN2000 blend. The BSFC for E20EHN1000 was almost similar with petrodiesel. In this case there was no significant effect of high concen tration of 2-EHN in E20 blend. From the analysis of results, it was found that E20 showed 9.5% higher BSFC while E20EHN1000 and petrodiesel showed almost similar BSFC. Improvement in BSFC for E20EHN1000 was due to the mixing of 2-EHN because that promoted the rate of diffusion in fuel and primarily formulate the air-fuel mixture into the combustion chamber (Park et al., 2012; Icıngur and Altiparmak, 2003). But, at the same time excess amount of 2-EHN in E20 shortened the ID which resulted incomplete combustion thus higher amount of fuel was accumulated in the engine cylinder to deliver the required power (Rakopoulos et al., 2007, Zheng et al., 2015). The BTE of test fuel blends at different load conditions is as shown in Fig. 1(c). It was found that E20EHN1000 showed 4.9% higher BTE than petrodiesel and E20EHN2000 showed lowest BTE as compared to other test fuel blends. For E20, the BTE was 2% lower with that of petrodiesel. This is attributed to the low GCV and lower CNs of E20. The addition of cetane improver in E20 enhanced the combustion phenomena due to the combined effect of oxygenated ethanol with cetane improver. However, the excess amount of 2-EHN advanced the ID in case of E20EHN2000 (Rakopoulos et al., 2007; Ileri, 2016). In addition, the low viscosity and
optimized proportion of 2-EHN in E20EHN1000 resulted proper com bustion. Furthermore, lower BSFC (as shown in Fig. 1(b)) of E20EHN1000 is attributed as another factor behind the increment in BTE (Atmanli, 2016). Fig. 1(d) showed the effect of test fuel on volumetric efficiency (ηvol) of CI engine. The results showed that ηvol of E20EHN1000 is highest among all the tested fuels. The ηvol of E20EHN1000 is 0.7% higher than petrodiesel at full load condition. E20 and E20EHN2000 also showed 0.6% and 0.4% higher ηvol than petrodiesel at full load condition of CI engine. The ηvol of E20, E20EHN1000 and E20EHN2000 are higher than petrodiesel due to their low viscosity and high cylinder temperature during combustion at full load condition (Ruina et al., 2014). 3.2. Engine combustion characteristics It is essential to study the chain reaction of burning fuel for better understanding the behaviour of 2-EHN. During burning, the fuel chain molecules initially undergoes through its dissociation phase. After wards, these dissociated molecules turn into free radicals and pass its energy to its neighbourhood molecules, which is the initial phase of flame propagation or start of combustion (SOC). 2-EHN has very low dissociation energy, which promotes combustion due to earlier disso ciation during flame initiation in combustion chamber. This can be easily validated with the degree of ignition advance during combustion of test fuels. The ID for test blends is determined by the difference (� CA) inbetween the start of injection (SOI) and the start of combustion (SOC) with an accuracy of �0.1� . The SOI for CI test rig was fixed at 23� BTDC. 4
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Sustainable Chemistry and Pharmacy 14 (2019) 100185
At this � CA, the fuel was injected with high pressure in the combustion chamber. The SOC for petrodiesel, E20, E20EHN1000 and E20EHN2000 was 13� , 13� , 14� and 16� CA BTDC, respectively. It was observed that for E20EHN1000 and E20EHN2000 has 1� and 3� advance SOC from E20 and petrodiesel. The SOC was considered from the � CA, at which the heat release-rate crosses the zero line and changes its value from the minus side to the plus side. The heat release rate is calculated by sup plementary equation (9). The cylinder pressure, net heat release rate, rate of pressure rises and mass fraction fuel burned of different test fuels with respect to crank angle are as shown in Fig. 2(a–d). The maximum cylinder pressure (CPmax) of E20, E20EHN1000 and petrodiesel (64.95–64.84~64.4) (bar) was almost identical but, E20EHN2000 showed lower CPmax (47.60 bar) with other tested fuels. It implies that at full load condition E20 and E20EHN1000 burnt out effectively in comparison with E20EHN2000. The crank angle corresponding with CPmax was almost equal (371� ) for E20, E20EHN1000 and petrodiesel. E20EHN2000 showed advance SOC than other test fuels which results opposite pressure on piston at compression stroke resulting lower CP. In addition, E20EHN2000 showed CPmax at crank angle 375� , which implies prolong combustion (at expansion stroke) due to insufficient charge. It is clear from Fig. 2(a) that the combined effect of 2-EHN and ethanol resulted proper com bustion due to high CNs and prior evaporation of ethanol but, at the same time, excess amount of 2-EHN advanced the ID and turned into incomplete combustion for E20EHN2000 (Ruina et al., 2014). Fig. 2(b) illustrated net heat release rate, which increases from compression stroke to expansion stroke and depends upon ID. The maximum net heat release rate (NHRmax) for E20 (39.24 J at CA 362� ), E20EHN1000 (38.63 J at CA 362� ) and petrodiesel (34.14 J at CA 361� ) was almost identical with each other, while E20EHN2000 (20.77 J at CA 366� ) showed lowest NHRmax from other test fuels. E20 and
E20EHN1000 showed little bit higher heat generation which resulted proper mixing of fuel-air due to low dissociation energy of ethanol and 2-EHN, respectively. In case of E20EHN2000, prolong and incomplete combustion was observed due to advance SOC, which resulted SOC at BTDC and hence low NHRmax was observed at the power stroke (Choi et al., 2017; Atmanli, 2016). The higher concentration of 2-EHN in E20 disturbed the combustion process due to increased cracking reactions of the hydrocarbon in the pre-combustion phases (Saravanan et al., 2011). The rate of pressure rise depends upon the mass rate of fuel injected into the combustion chamber. Also, with no load to full load condition, the mass of air-fuel mixture is also increased accordingly (Agarwal et al., 2013). Fig. 2(c) illustrated maximum rate of pressure rise (ROPRmax) of E20 (3.85 bar at CA361� ), E20EHN1000 (3.53 bar at CA 361� ), E20EHN2000 (1.16 bar at CA 347� ) and petrodiesel (3.42 bar at CA 360� ) at full load condition, respectively. The results showed that the ROPRmax was highest for E20 and slightly similar with E20EHN1000 and petrodiesel while ROPRmax was lowest with E20EHN2000. This was because of the excess 2-EHN, which advanced the ID and disturbed the stages of combustion (Agarwal et al., 2013; Ileri, 2016). E20 showed highest ROPRmax because at full load condition the fuel mixture evap orated speedily and promoted the combustion. ROPRmax for E20EHN1000 was comparable with petrodiesel but slightly lower with E20 because of slightly advanced ignition (Saravanan et al., 2011; Agarwal et al., 2013). Fig. 2(d) illustrated 90% of mass fraction of fuel burned (MFB) for E20 (392.8� CA), E20EHN1000 (405.42� CA), E20EHN2000 (428.18� CA) and petrodiesel (402.22� CA). From the results, it is clearly seen that E20EHN2000 required more time to burn 90% of fuel which was the result of after burning. This was because of insufficient fuel air mixture at power stroke, which resulted prolong combustion from compression stroke to power stroke. This Fig. 2(d) also indicated that MFB rate is
Fig. 3. (a–d) Variation in (a) CO (b) HC (c) CO2 and (d) NOx emission profiles with respect to load. 5
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Sustainable Chemistry and Pharmacy 14 (2019) 100185
highest for E20 but, E20EHN1000 and petrodiesel showed almost identical time (� CA) for 90% burning of the fuel. At full load condition and high in-cylinder temperature, mixing of air and fuel is faster due to low dissociation energy of ethanol, which resulted pre-combustion of E20. Moreover, due to high CNs of E20EHN1000 and petrodiesel, the combustion duration was slightly increased up to the burning of end part of fuel than E20 (Park et al., 2012; Ciniviz et al., 2017).
�ndez nitro groups of 2-EHN enhanced the NOx emission (Campos-Ferna et al., 2012, Ileri, 2016). No any significant effect was observed with higher amount of 2-EHN in test blends. 4. Conclusion The experimental investigation of CI engine fuelled with E20, E20EHN1000, E20EHN2000 and petrodiesel revealed that the BP and BTE of E20EHN1000 were 3.8% and 4.9% higher than petrodiesel. Also, The BSFC and ηvol of E20EHN1000 were almost identical to that of petrodiesel under all load conditions. E20EHN1000 showed appropriate combustion than that of petrodiesel and the net heat release rate was 12.88% higher than petrodiesel. The CO emission for E20EHN1000 was lower, but the CO2 emission was almost identical to that of petrodiesel at 0–100% engine load. HC emission for all the test fuel blends was higher than petrodiesel, but, E20EHN1000 showed lowest HC among other test fuel blends. The NOx emission for E20EHN1000 was almost comparable with petrodiesel at 0–80% load condition. In summation, the results confirmed the uniqueness of E20EHN1000 as an alternative fuel for CI engine application which can be recommended for application in CI engines without any modification.
3.3. Emission characteristics CO is the chief transitional product during incomplete combustion. Less amount of oxygen, low cylinder temperature and ignition advance or delay are the main causes of CO generation. Fig. 3(a) illustrate the CO emission of E20, E20EHN100 and E20EHN2000 in comparison with petrodiesel. E20 showed higher CO emission from E20EHN1000 and petrodiesel and almost identical with E20EHN2000 at full load condi tion. This may be due to higher latent heat of vaporisation of ethanol, which creates cooling effect during combustion. E20EHN1000 showed the combined effect of fast evaporation of bioethanol and high CNs, which promoted the oxidation reaction resulting negligible ID and hence complete combustion (Kim and Choi, 2010; Guo et al., 2011). The CO emission for E20EHN2000 was higher due to combined effect of ignition advance and higher latent heat of vaporisation, which resulted incom plete combustion. HC emission is the by-product of incomplete combustion and due to trapped fuel inside the crevice volume of combustion chamber. The HC emission for test fuel blends in comparison with petrodiesel is as shown in Fig. 3(b). Ethanol has higher latent heat of vaporisation and that resulted longer ID due to low combustion temperature at no load and part load condition (Hansdah et al., 2013). HC emission was highest for E20EHN2000 among other test fuel blends. This was due to the high amount of 2-EHN, which enhanced the combustion quality of the test fuel blends but, at the same time advanced ID resulting incomplete combustion. HC emission for E20EHN1000 was next to petrodiesel and lesser than E20 and E20EHN2000. This was because of 2-EHN presence which decreased the mixing rate of fuel/air and increased the diffusion rate of combustion. At the same time ~5% water had obstructed the burning of end part of test blend, which resulted incomplete combustion and generated more unburned hydrocarbon (Hansdah and Murugan, 2016; Ileri, 2016). Higher CO2 emission is the result of complete combustion and it is reciprocal of CO and HC emission. Fig. 3(c) illustrated variation in CO2 emission for E20, E20EHN1000 and E20EHN2000 in respect of petro diesel at all engine load conditions. The trend of CO2 showed increment with respect to load and at low to part load condition, CO2 for E20, E20EHN1000 and E20EHN2000 were almost identical with that of petrodiesel. But, at full load condition, E20EHN1000 showed highest CO2 emission which was similar to petrodiesel, but E20 and E20EHN2000 showed lower CO2 emission. This demonstrates that at full load condition E20 and E20EHN2000 showed incomplete combustion due to prolong and advance SOC (Hansdah and Murugan, 2016; Tutak et al., 2017). Whereas, E20EHN1000 showed the combined effect of fast evaporation and increased dissociation, which resulted complete com bustion (Choi et al., 2017, Zheng et al., 2015). NOx emission is high if the combustion temperature, injected fuel amount and oxygen concentration in the fuel are high (Campos- �ndez et al., 2012). Fig. 3(d) illustrated that the NOx emission for Ferna E20, E20EHN1000 and E20EHN2000 was little bit higher than that of petrodiesel. This was because of the high oxygen percentage in E20 and nitro compound in E20EHN1000 and E20EHN2000, respectively. The tested fuel blends contain ethanol, which prolonged the ID and increased the amount of accumulated fuel in the combustion chamber (Choi et al., 2017; Agarwal et al., 2013). Also, the nitro compound of 2-EHN enhanced the combustion temperature resulting high NOx emission (Ruina et al., 2014). The prolong ID resulted very small effect of NOx emission due to high latent heat of vaporisation of ethanol, while
Declaration of competing InterestCOI None. Acknowledgments The author Himansh Kumar would like to thank Ministry of Human Resource and Development, Government of India for teaching assis tantship during PhD research work and Sardar Swaran Singh National Institute of Bio-Energy Kapurthala, Punjab for platform of experimental works. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.scp.2019.100185. References Agarwal, A.K., Srivastava, D.K., Dhar, A., Maurya, R.K., Shukla, P.C., Singh, A.P., 2013. Effect of fuel injection timing and pressure on combustion, emissions and performance characteristics of a single cylinder diesel engine. Fuel 111, 374–383. Atmanli, A., 2016. Effects of a cetane improver on fuel properties and engine characteristics of a diesel engine fueled with the blends of diesel, hazelnut oil and higher carbon alcohol. Fuel 172, 209–217. Bora, P., Konwar, L.J., Boro, J., Phukan, M.M., Deka, D., Konwar, B.K., 2014. Hybrid biofuels from non-edible oils: a comparative standpoint with corresponding biodiesel. Appl. Energy 135, 450–460. Campos-Fern� andez, J., Arnal, J.M., G� omez, J., Dorado, M.P., 2012. A comparison of performance of higher alcohols/diesel fuel blends in a diesel engine. Appl. Energy 95, 267–275. Choi, K., Roh, H.G., Lee, C.S., 2017. Comparative investigation of emissions and combustion characteristics between ethanol-biodiesel-diesel blends and diesel fuel in a passenger car diesel engine. Int. J. Oil Gas Coal Technol. 16 (2), 203–216. € _ Kul, B.S., 2017. The effect of adding EN (2-ethylhexyl nitrate) to Ciniviz, M., Ors, I., diesel-ethanol blends on performance and exhaust emissions. Int.l J. Automot. Sci. Technol. 1 (1), 16–21. Guo, L., Yan, Y.Y., Tan, M., Li, H., Peng, Y., 2011. An experimental study on improving the ignition of ethanol-diesel blended fuel (EDBF). Chem. Eng. Commun. 198 (10), 1263–1274. Hammond, G.P., Mansell, R.V.M., 2018. A comparative thermodynamic evaluation of bioethanol processing from wheat straw. Appl. Energy 224, 136–146. Hansdah, D., Murugan, S., 2014. Bioethanol fumigation in a DI diesel engine. Fuel 130, 324–333. Hansdah, D., Murugan, S., 2016. Comparative studies of a bioethanol fuelled DI diesel engine with a cetane improver. Int. J. Oil Gas Coal Technol. 11 (4), 429–450. Hansdah, D., Murugan, S., Das, L.M., 2013. Experimental studies on a DI diesel engine fuelled with bioethanol-diesel emulsions. Alexandria Eng. J. 52, 267–276. Heywood, J.B., 1988. (1988). Internal Combustion Engine Fundamentals. McGraw- Hill, New York.
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Sustainable Chemistry and Pharmacy 14 (2019) 100185 Park, S.H., Cha, J., Lee, C.S., 2012. Impact of biodiesel in bioethanol blended diesel on the engine performance and emissions characteristics in compression ignition engine. Appl. Energy 99, 334–343. Rakopoulos, C.D., Antonopoulos, K.A., Rakopoulos, D.C., Hountalas, D.T., Andritsakis, E. C., 2007. ‘Study of the performance and emissions of a high-speed direct injection diesel engine operating on ethanol–diesel fuel blends’. Int. J. Altern. Propuls. 1 (2/ 3), 309–324. Ramalingam, S., Ganesan, R., Rajendran, S., Ganesan, P., 2018. A novel alternative fuel for diesel engine: a comparative experimental investigation. Int. J. Glob. Warming 14 (1), 40–60. Ruina, Li, Zhong, W., Peiyong, Ni, Yang, Z., Mingdi, Li, Lilin, Li, 2014. Effects of cetane number improvers on the performance of diesel engine fuelled with methanol/ biodiesel blend. Fuel 128, 180–187. Saravanan, S., Nagarajan, G., Sampath, S., 2011. Investigation on combustion characteristics of crude rice bran oil methyl ester blend as a heavy duty automotive engine fuel. Int. J. Oil Gas Coal Technol. 4 (3), 282–295. Singh, N., Kumar, H., Jha, M.K., Sarma, A.K., 2015. Complete heat balance, performance and emission evaluation of a CI engine fuelled with Mesua ferrea methyl and ethyl ester’s blends with petrodiesel. J. Therm. Anal. Calorim. 122 (2), 907–916. Srivastava, A.K., Soni, S.L., Sharma, D., Sonar, D., Jain, N.L., 2017. Effect of compression ratio on performance, emission and combustion characteristics of diesel–acetylenefuelled single-cylinder stationary CI engine. Clean Technol. Environ. Policy 19, 1361–1372. Turkcan, A., 2018. Effects of high bioethanol proportion in the biodiesel-diesel blends in a CRDI engine. Fuel 223, 53–62. Tutak, W., Jamrozik, A., Pyrc, M., Sobiepanski, M., 2017. A comparative study of cocombustion process of diesel-ethanol and biodiesel-ethanol blends in the direct injection diesel engine. Appl. Therm. Eng. 117, 155–163.
Icıngur, Y., Altiparmak, D., 2003. Effect of fuel cetane number and injection pressure on a DI Diesel engine performance and emissions. Energy Convers. Manag. 44, 389–397. Ileri, E., 2016. Experimental study of 2-ethylhexyl nitrate effects on engine performance and exhaust emissions of a diesel engine fueled with n-butanol or 1-pentanol diesel–sunflower oil blends. Energy Convers. Manag. 118, 320–330. Kim, H., Choi, B., 2010. The effect of biodiesel and bioethanol blended diesel fuel on nanoparticles and exhaust emissions from CRDI diesel engine. Renew. Energy 35, 157–163. Kumar, H., Konwar, L.J., Aslam, M., Sarma, A.K., 2016. Performance, combustion and emission characteristics of a direct injection VCR CI engine using a Jatropha curcas oil microemulsion: a comparative assessment with JCO B100, JCO B20 and petrodiesel. RSC Adv. 6 (44), 37646–37655. Lapuerta, M., Armas, O., García-Contreras, R., 2007. Stability of diesel–bioethanol blends for use in diesel engines. Fuel 86, 1351–1357. Minnesota Technical Assistance Programme, 2008. Ethanol Benchmarking and Best Practices. MnTAP, Minneapolis. http://www.mntap.umn.edu/resources/DOC/in dex.html. Odziemkowska, M., Matuszewska, A., Czarnocka, J., 2016. Diesel oil with bioethanol as a fuel for compression-ignition engines. Appl. Energy 184, 1264–1272. Onuh, E.I., Inambao, F.L., 2018. An evaluation of neat biodiesel/diesel performance, emission pattern of NOx and CO in compression ignition engine. Int. J. Glob. Warming 14 (1), 21–39. Pal, P., Kumar, R., Ghosh, A.K., 2018. Analysis of process intensification and performance assessment for fermentative continuous production of bioethanol in a multi-staged membrane-integrated bioreactor system. Energy Convers. Manag. 171, 371–383.
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Sustainable Chemistry and Pharmacy journal homepage: http://www.elsevier.com/locate/scp
A novel approach to study the effect of cetane improver on performance, combustion and emission characteristics of a CI engine fuelled with E20 (diesel – bioethanol) blend Himansh Kumar a, b, Anil Kumar Sarma b, *, Pramod Kumar a a b
Mechanical Engineering Department, Dr B R Ambedkar NIT Jalandhar, Punjab, India Chemical Conversion Division, SSS-NIBE Kapurthala, Punjab, India
A R T I C L E I N F O
A B S T R A C T
Keywords: Cetane improver 2-EHN Mass fraction fuel burned Combustion analysis NOx emission
In this article an investigation was carried out to study the effects of cetane improver (2-Ethylhexyl nitrate) (2EHN) on performance, combustion and emission characteristics of a constant speed, single cylinder CI engine fuelled with E20 (bioethanol (20%) – petrodiesel (80%). A cetane improver, 2-EHN was used at concentration of 1000 ppm and 2000 ppm with the test fuel (E20) and the results were compared to petrodiesel. The results showed that E20EHN1000 had 3.8% higher brake power (BP) to that of petrodiesel and the brake specific fuel consumption (BSFC) was similar with E20 and petrodiesel. E20EHN1000 showed 4.9% higher brake thermal efficiency (BTE) to petrodiesel and the volumetric efficiency (ηvol) was almost identical for all the test fuels. The trend for cylinder pressure (CP), net heat release rate (NHR), rate of pressure rises (ROPR) and mass fraction fuel burned (MFFB) of E20EHN1000 were also identical to those of E20 and petrodiesel. Except hydrocarbon (HC) emission, E20EHN1000 showed acceptable emission results to that of petrodiesel and other test fuel blends. Carbon dioxide (CO2) and carbon monoxide (CO) emission for E20EHN1000 were comparable with petrodiesel but, the oxides of nitrogen (NOx) emission was slightly higher than petrodiesel. However, E20EHN2000 showed poor performance due to the excess amount of 2-EHN, which shortened the ignition delay and reduced the premixed combustion phase with increased combustion duration. From the results, it is clearly unveiled that E20 with 1000 ppm of 2-EHN showed better results than E20, E20EHN2000 and petrodiesel.
1. Introduction Inadequate reserves and exponentially rising demand of petroleum along with recent environmental consensus instantaneously drive the researchers and Industrialist for biofuel production and commerciali zation. The production cost of biofuel and availability of feedstocks stand as the major barriers of its implementation and progress in commercialization (Onuh and Inambao, 2018). To overcome these is sues, blending of biofuel with fossil fuel is considered as the best option to lower the trauma on it. Biofuel such as biogas, ethanol/bioethanol, methanol/bio-methanol, diethyl/methyl ether and biodiesel can be used as an intermediate fuel in CI engines (Ramalingam et al., 2018; Cam �ndez et al., 2012). pos-Ferna Ethanol can be used in CI engine by direct spraying in the combus tion chamber or blending with petrodiesel. However, for direct spraying, engine modification is required and also ethanol spraying in the
combustion chamber is a costlier process in terms of CI engine design and modification (Hansdah and Murugan, 2014). Ethanol blending on the other hand, is much easier and it requires no engine modification. However, ethanol is the best option for blending because of its friendly characteristics for CI engine functioning such as, no engine modifica tion, easy availability, low cost and no long-term operating issues. Tutak et al. (2017) studied the effects of hydrated ethanol, blended with pet rodiesel in a concentration up to 45% (v/v) with 5% increment, for the CI engine performance parameters. The same practice was repeated with biodiesel-ethanol (BE) blends in place of petrodiesel. The test was con ducted on a single cylinder direct injection-based CI engine operated at constant speed, 1500 RPM. It was reported that the highest value of indicated thermal efficiency (ITE) (35%) was obtained with 35% ethanol concentration in diesel-ethanol (DE) blend and the maximum of 31% ITE was obtained with biodiesel-ethanol blend. NOx emission for DE (30%) blend was higher with BE (45%) blends, but the CO emission was
* Corresponding author. E-mail address: [email protected] (A.K. Sarma). https://doi.org/10.1016/j.scp.2019.100185 Received 30 May 2019; Received in revised form 18 September 2019; Accepted 6 October 2019 Available online 16 October 2019 2352-5541/© 2019 Elsevier B.V. All rights reserved.
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lower with both the blends in all ranges of concentration. CO2 was little bit lower for BE (45%) in comparison with DE (45%). Odziemkowska et al. (2016) examined the effects of bioethanol with a co-solvent, 2-ethyl-1-hexanol (15% þ 5%) (v/v), blended with 80% petrodiesel and the same with petrodiesel and biodiesel (73% þ 7%) on a 4-cylinder CI engine. It was reported that up to 30% bioethanol with 5% co-solvent is a stable emulsion on or above 15� C. The first fuel blend reportedly showed similar trend for CO emission, slightly higher trend for HC, NOx emissions and low particulate emission (PM) with petro diesel. Maximum 10% decrement in power and torque was observed with these two test fuel blends. The second test fuel blend showed nonidentical results in all respects except PM emission. Hansdah et al. (2013) studied the effects of bioethanol-petrodiesel blend (in proportion of 5%, 10% and 15%, respectively) on performance parameters of a single cylinder CI engine at rated power 4.4 kW BP @ 1500 RPM, using Span80 (1%) as a surfactant on volume basis. The authors examined higher ignition delay (ID) for higher concentration of bioethanol in petrodiesel also, the high in-cylinder pressure and BP were observed for every bioethanol-diesel blend. NOx and smoke were lesser with petro diesel for all test blends. Kim and Choi (2010) examined the effects of bioethanol (99.5% purity)-petrodiesel blend (15% þ 85%) (v/v) with 7500 ppm ethyl hexyl nitrate (cetane improver) on suspended nano particles and other harmful emissions of CRDI diesel engine. For the test blend, 50% smoke reduction and increased NOx emission were observed. In case with biodiesel, except B20, the blend of 15% biodiesel þ5% bioethanol þ80% petrodiesel was more effective for reduction in par ticle number and particle mass. The fact that the first-hand distillation of bioethanol has about 5% (v/v) water content and their effects blending with petrodiesel, performance and emission parameters were not yet explored in those research articles. This is eminent that bioethanol can be obtained from the fermenta tion of sugar or starch bearing plants, lignocellulosic and cellulosic materials derived from non-edible food (MnTAP, 2008; Pal et al., 2018). Bioethanol contains only 95% ethanol with ~5% water, because during fermentation low boiling water-ethanol azeotrope is formed after first-hand distillation, and it is a very uneconomical distillation process to attain 99% pure bioethanol (Pal et al., 2018). This fact was estab lished (Pal et al., 2018) that an azeotropic mixture of bioethanol and water (95% þ 5%) (v/v) was formed due to traditional distillation and it was hard to dehydrate the ethanol, because almost 40% of the total energy was consumed to resolve this issue. However, Hammonda and Mansell (2018) reported that the bioethanol contains almost equal en ergy content (18.6 MJ/kg) to the conventional ethanol. It is therefore presumed that 95% pure ethanol without metal contaminants could be a suitable blending agent for petroleum diesel, if performance parameters are not changed appreciably in an existing CI engine. Cetane number (CN) of any diesel range fuel shows its ignition quality or in other words CN is inversely proportional to the ignition delay of CI engine (Ileri, 2016). Ethanol or bioethanol has an extremely low cetane number and mixing of bioethanol with petrodiesel results reduction in CN of the fuel blend (Lapuerta et al., 2007). The lower CN of fuel blend delays the start of combustion which results abnormal com bustion behaviour and higher exhaust emissions from CI engine (Guo et al., 2011; Turkcan, 2018). Atmanli (2016) studied the effects of 2-EHN on the physicochemical properties and CI engine performance parameters fuelled with the blends of petrodiesel, hazelnut oil and butanol/pentanol. The authors examined that 2-EHN helped to increase the CN but, no any significant effects were observed on other properties of test blends. The pentanol based blends showed less BSFC, NOx and HC as compared with butanol-based blend but, reciprocal in case CO emission. The polar nature of ethanol limits its utility in higher concentration with petrodiesel but, 2- EHN functions as a surfactant which helps to decrease the interfacial tension between polar and non-polar molecules (Kim and Choi, 2010; Ciniviz et al., 2017). Bora et al. (2014) studied that 2-EHN worked as a surface-active agent for decreasing the interfacial
tension between the two liquid films. Therefore, a commercial cetane improver 2-EHN is used as a cetane improver and it is expected to in crease the combustion efficiency and to improve the ignition timings. In this approach, the objective was set to determine the effects of 2EHN on CI engine performance fuelled with an E20 blend of petrodiesel and the ethanol with identical concentration as obtained from the lignocellulosic biomass by first-hand distillation. 2-EHN was added at a concentration of 1000 and 2000 ppm, respectively, to E20 blend. Moreover, the stability tests showed that the E20 blend was stable and could be used without any external surfactant. Performance, combustion and emission characteristics of CI engine was examined for E20, E20 with 1000 ppm 2-EHN and E20 with 2000 ppm 2-EHN and compared with those of petrodiesel and reported. 2. Materials and methods 2.1. Materials and characterisation In order to examine the effect of bioethanol (95%), ~5% deionized water was mixed with anhydrous ethanol (<99.9%), purchased from Merck India Ltd. Petrodiesel (LDO, Indian Oil Corporation) was pur chased from a local petrol pump located in Jalandhar District (Punjab), India. 2-EHN (97%) was purchased from Sigma-Aldrich (India). These blends were gently shaken for 15 min and their stability were tested using a centrifuge at 3000 RPM, 25� C for 30 min, and physical obser vation by 15 days. The concentration of 2-EHN and bioethanol in pet rodiesel is shown in Table 1. The cetane number of test blend is calculated using the empirical formula as suggested by Ruina et al. (2014). CN ¼ CNd � wd þ CNbe � wbe þ K � w2
(1)
EHN
Where CN is the cetane number of test blend, CNd is the CN of petro diesel, CNbe is the cetane number of bioethanol, K (K ¼ 4) is constant for 2-EHN, wd, wbe and w2-EHN is the blend ratio for petrodiesel, bioethanol and 2-EHN, respectively (Ruina et al., 2014). The blend ratio was calculated by the mass of respective vol. to the total mass of vol. The CN of test blend was increased 1.26 @ 01 ml addition of 2-EHN (Ruina et al., 2014). The effect of 2-EHN concentration upon CN of the test blends is shown in Table 2. The fuel properties such as density, viscosity, flash point, calorific value, cetane number and cold filter plugging point of E20, E20EHN1000, E20EHN2000 and petrodiesel were determined using standard test methods recommended by ASTM/EN also shown in Table 2 (Kumar et al., 2016; Singh et al., 2015). 2.2. Experimental procedure 2.2.1. Experimental set-up (CI engine test rig) A 4 stroke, single cylinder DI, stationery CI engine (Kirloskar India Ltd.) with rated power 5.2 kW @ 1500 RPM was used to conduct the experiments. Table S1 has shown the detailed specification of test rig. Water cooled eddy current dynamometer was used for loading on the crankshaft with the help of electromagnetic force which was regulated by the load cell (Kumar et al., 2016). Two piezometric sensors were used to determine inside cylinder pressure and fuel line pressure, respec tively. An optical crank-angle sensor was used to determine the degree Table 1 Concentration of test fuel blends.
2
Test fuel
Petrodiesel (%)
Bioethanol (%)
2-EHN (PPM)
Stability
E20
80
20
–
E20EHN1000 E20EHN2000 Petrodiesel
80 80 100
20 20 –
1000 ppm 2000 ppm –
Stable (05 days) Stable Stable
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equations as referred (Kumar et al., 2016; Heywood, 1988; Singh et al., 2015) and expressed in supplementary equations 2 to 9.
Table 2 Fuel properties of E20, E20EHN100 and E20EHN2000 in comparison with Petrodiesel. Test Fuels
density @15 � C gcm
E20 E20EHN1000 E20EHN2000 Bioethanol Petrodiesel
3
0.818 0.818 0.819 0.798 0.823
viscosity @40 � C
GCV
mm2s
MJkg
2.4 2.3 2.3 1.4 2.65
1
40.20 40.35 40.55 27.20 42.86
cetane index 1
36.6 37.86 39.12 7 44
flash point
CFPP
(� C)
(� C)
57.2 56.1 55.5 17 66.5
2.2.2. Experimental procedure The trials were performed in the order of petrodiesel, E20, E20EHN1000 and E20EHN2000. The engine was loaded with 0% (no load), 20%, 40%, 60%, 80%, and 100% load conditions using eddy current type dynamometer with the help of electrical resistance unit during the measurement. The engine was allowed to run on that con dition for 30 min until the engine reached at its steady state for each of the load measurement condition. The same was repeated for all test fuels to reduce the level of uncertainty. The engine was again run with pet rodiesel to maintain its initial stage of operation. The experiments were conducted in triplicate and average values are reported in the results and discussion section for its reliability. The standard deviation was also calculated and presented as the error bars in the graphs.
27.5 7 7 52 20
CFPP: cold filter plugging point temperature.
angle rotation of the crankshaft. The fuel consumption was measured with a fuel flow transmitter made by Yokogawa, Model No: EJA110A-DMS5A-92NN. It was attached with the fuel line and the signal of flow rate was transferred to the National Instrument make data acquisition device (DAD). This DAD was connected to the computer through USB port. All the signals recorded were conveyed to ‘Engine softLV’ version 9.0 software (Apex Innovations Pvt. Ltd.) for perfor mance and combustion analysis (Kumar et al., 2016; Heywood, 1988; Singh et al., 2015). AVL diGas 444 analyser was used to determine the exhaust emission from CI engine. The exhaust gases, namely CO, CO2, HC, and NOx were analysed under the test procedure approved by the Ministry of Road Transport and Highways, GOI, and specified in MoRTH/CMVR/TAP115/116, Issue No. 3, Part-VIII in 4-gas analyser. Table S2 has shown the technical specification of AVL diGas 444 analyser (Kumar et al., 2016; Heywood, 1988; Singh et al., 2015). The performance analysis is based upon the computation of basic
3. Result and discussion 3.1. Engine performance characteristics Fig. 1(a) illustrated the BP characteristics of CI engine fuelled with E20 E20EHN1000, E20EHN2000 and petrodiesel. The brake power showed an increase trend with respect to load. Mixing of 2-EHN with E20 enhanced the cetane number and reduced ignition delay, which resulted an average increment of 3.8% in brake power (BP) at full load for E20EHN1000 with respect to petrodiesel while E20EHN2000 showed lower value from other test fuels. E20 showed 1.1% higher BP to that of petrodiesel. This was because of high oxygen content and reduced viscosity and density due to addition of ethanol in test fuel
Fig. 1. (a–d) Variation in Brake Power, BSFC, Brake Thermal Efficiency and volumetric efficiency with respect to load. 3
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Fig. 2. (a–d) Variation in cylinder pressure, net heat release rate, rate in pressure rise and mass fraction fuel burned at different crank angle. (The values are at full load conditions of test engine).
blends (Srivastava et al., 2017). Mixing of 2-EHN increased the CNs which resulted easy auto-ignition but, at the same time excess 2-EHN resulted advance ID and this lowered the BP for E20EHN2000 (Ruina et al., 2014). The BP for E20 and E20EHN1000 can also be rechecked from high in-cylinder pressure and heat release rate at pre-mixed burning stage. It was observed from Fig. 1(b) that, BSFC was highest for E20HN2000 blend. The BSFC for E20EHN1000 was almost similar with petrodiesel. In this case there was no significant effect of high concen tration of 2-EHN in E20 blend. From the analysis of results, it was found that E20 showed 9.5% higher BSFC while E20EHN1000 and petrodiesel showed almost similar BSFC. Improvement in BSFC for E20EHN1000 was due to the mixing of 2-EHN because that promoted the rate of diffusion in fuel and primarily formulate the air-fuel mixture into the combustion chamber (Park et al., 2012; Icıngur and Altiparmak, 2003). But, at the same time excess amount of 2-EHN in E20 shortened the ID which resulted incomplete combustion thus higher amount of fuel was accumulated in the engine cylinder to deliver the required power (Rakopoulos et al., 2007, Zheng et al., 2015). The BTE of test fuel blends at different load conditions is as shown in Fig. 1(c). It was found that E20EHN1000 showed 4.9% higher BTE than petrodiesel and E20EHN2000 showed lowest BTE as compared to other test fuel blends. For E20, the BTE was 2% lower with that of petrodiesel. This is attributed to the low GCV and lower CNs of E20. The addition of cetane improver in E20 enhanced the combustion phenomena due to the combined effect of oxygenated ethanol with cetane improver. However, the excess amount of 2-EHN advanced the ID in case of E20EHN2000 (Rakopoulos et al., 2007; Ileri, 2016). In addition, the low viscosity and
optimized proportion of 2-EHN in E20EHN1000 resulted proper com bustion. Furthermore, lower BSFC (as shown in Fig. 1(b)) of E20EHN1000 is attributed as another factor behind the increment in BTE (Atmanli, 2016). Fig. 1(d) showed the effect of test fuel on volumetric efficiency (ηvol) of CI engine. The results showed that ηvol of E20EHN1000 is highest among all the tested fuels. The ηvol of E20EHN1000 is 0.7% higher than petrodiesel at full load condition. E20 and E20EHN2000 also showed 0.6% and 0.4% higher ηvol than petrodiesel at full load condition of CI engine. The ηvol of E20, E20EHN1000 and E20EHN2000 are higher than petrodiesel due to their low viscosity and high cylinder temperature during combustion at full load condition (Ruina et al., 2014). 3.2. Engine combustion characteristics It is essential to study the chain reaction of burning fuel for better understanding the behaviour of 2-EHN. During burning, the fuel chain molecules initially undergoes through its dissociation phase. After wards, these dissociated molecules turn into free radicals and pass its energy to its neighbourhood molecules, which is the initial phase of flame propagation or start of combustion (SOC). 2-EHN has very low dissociation energy, which promotes combustion due to earlier disso ciation during flame initiation in combustion chamber. This can be easily validated with the degree of ignition advance during combustion of test fuels. The ID for test blends is determined by the difference (� CA) inbetween the start of injection (SOI) and the start of combustion (SOC) with an accuracy of �0.1� . The SOI for CI test rig was fixed at 23� BTDC. 4
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At this � CA, the fuel was injected with high pressure in the combustion chamber. The SOC for petrodiesel, E20, E20EHN1000 and E20EHN2000 was 13� , 13� , 14� and 16� CA BTDC, respectively. It was observed that for E20EHN1000 and E20EHN2000 has 1� and 3� advance SOC from E20 and petrodiesel. The SOC was considered from the � CA, at which the heat release-rate crosses the zero line and changes its value from the minus side to the plus side. The heat release rate is calculated by sup plementary equation (9). The cylinder pressure, net heat release rate, rate of pressure rises and mass fraction fuel burned of different test fuels with respect to crank angle are as shown in Fig. 2(a–d). The maximum cylinder pressure (CPmax) of E20, E20EHN1000 and petrodiesel (64.95–64.84~64.4) (bar) was almost identical but, E20EHN2000 showed lower CPmax (47.60 bar) with other tested fuels. It implies that at full load condition E20 and E20EHN1000 burnt out effectively in comparison with E20EHN2000. The crank angle corresponding with CPmax was almost equal (371� ) for E20, E20EHN1000 and petrodiesel. E20EHN2000 showed advance SOC than other test fuels which results opposite pressure on piston at compression stroke resulting lower CP. In addition, E20EHN2000 showed CPmax at crank angle 375� , which implies prolong combustion (at expansion stroke) due to insufficient charge. It is clear from Fig. 2(a) that the combined effect of 2-EHN and ethanol resulted proper com bustion due to high CNs and prior evaporation of ethanol but, at the same time, excess amount of 2-EHN advanced the ID and turned into incomplete combustion for E20EHN2000 (Ruina et al., 2014). Fig. 2(b) illustrated net heat release rate, which increases from compression stroke to expansion stroke and depends upon ID. The maximum net heat release rate (NHRmax) for E20 (39.24 J at CA 362� ), E20EHN1000 (38.63 J at CA 362� ) and petrodiesel (34.14 J at CA 361� ) was almost identical with each other, while E20EHN2000 (20.77 J at CA 366� ) showed lowest NHRmax from other test fuels. E20 and
E20EHN1000 showed little bit higher heat generation which resulted proper mixing of fuel-air due to low dissociation energy of ethanol and 2-EHN, respectively. In case of E20EHN2000, prolong and incomplete combustion was observed due to advance SOC, which resulted SOC at BTDC and hence low NHRmax was observed at the power stroke (Choi et al., 2017; Atmanli, 2016). The higher concentration of 2-EHN in E20 disturbed the combustion process due to increased cracking reactions of the hydrocarbon in the pre-combustion phases (Saravanan et al., 2011). The rate of pressure rise depends upon the mass rate of fuel injected into the combustion chamber. Also, with no load to full load condition, the mass of air-fuel mixture is also increased accordingly (Agarwal et al., 2013). Fig. 2(c) illustrated maximum rate of pressure rise (ROPRmax) of E20 (3.85 bar at CA361� ), E20EHN1000 (3.53 bar at CA 361� ), E20EHN2000 (1.16 bar at CA 347� ) and petrodiesel (3.42 bar at CA 360� ) at full load condition, respectively. The results showed that the ROPRmax was highest for E20 and slightly similar with E20EHN1000 and petrodiesel while ROPRmax was lowest with E20EHN2000. This was because of the excess 2-EHN, which advanced the ID and disturbed the stages of combustion (Agarwal et al., 2013; Ileri, 2016). E20 showed highest ROPRmax because at full load condition the fuel mixture evap orated speedily and promoted the combustion. ROPRmax for E20EHN1000 was comparable with petrodiesel but slightly lower with E20 because of slightly advanced ignition (Saravanan et al., 2011; Agarwal et al., 2013). Fig. 2(d) illustrated 90% of mass fraction of fuel burned (MFB) for E20 (392.8� CA), E20EHN1000 (405.42� CA), E20EHN2000 (428.18� CA) and petrodiesel (402.22� CA). From the results, it is clearly seen that E20EHN2000 required more time to burn 90% of fuel which was the result of after burning. This was because of insufficient fuel air mixture at power stroke, which resulted prolong combustion from compression stroke to power stroke. This Fig. 2(d) also indicated that MFB rate is
Fig. 3. (a–d) Variation in (a) CO (b) HC (c) CO2 and (d) NOx emission profiles with respect to load. 5
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Sustainable Chemistry and Pharmacy 14 (2019) 100185
highest for E20 but, E20EHN1000 and petrodiesel showed almost identical time (� CA) for 90% burning of the fuel. At full load condition and high in-cylinder temperature, mixing of air and fuel is faster due to low dissociation energy of ethanol, which resulted pre-combustion of E20. Moreover, due to high CNs of E20EHN1000 and petrodiesel, the combustion duration was slightly increased up to the burning of end part of fuel than E20 (Park et al., 2012; Ciniviz et al., 2017).
�ndez nitro groups of 2-EHN enhanced the NOx emission (Campos-Ferna et al., 2012, Ileri, 2016). No any significant effect was observed with higher amount of 2-EHN in test blends. 4. Conclusion The experimental investigation of CI engine fuelled with E20, E20EHN1000, E20EHN2000 and petrodiesel revealed that the BP and BTE of E20EHN1000 were 3.8% and 4.9% higher than petrodiesel. Also, The BSFC and ηvol of E20EHN1000 were almost identical to that of petrodiesel under all load conditions. E20EHN1000 showed appropriate combustion than that of petrodiesel and the net heat release rate was 12.88% higher than petrodiesel. The CO emission for E20EHN1000 was lower, but the CO2 emission was almost identical to that of petrodiesel at 0–100% engine load. HC emission for all the test fuel blends was higher than petrodiesel, but, E20EHN1000 showed lowest HC among other test fuel blends. The NOx emission for E20EHN1000 was almost comparable with petrodiesel at 0–80% load condition. In summation, the results confirmed the uniqueness of E20EHN1000 as an alternative fuel for CI engine application which can be recommended for application in CI engines without any modification.
3.3. Emission characteristics CO is the chief transitional product during incomplete combustion. Less amount of oxygen, low cylinder temperature and ignition advance or delay are the main causes of CO generation. Fig. 3(a) illustrate the CO emission of E20, E20EHN100 and E20EHN2000 in comparison with petrodiesel. E20 showed higher CO emission from E20EHN1000 and petrodiesel and almost identical with E20EHN2000 at full load condi tion. This may be due to higher latent heat of vaporisation of ethanol, which creates cooling effect during combustion. E20EHN1000 showed the combined effect of fast evaporation of bioethanol and high CNs, which promoted the oxidation reaction resulting negligible ID and hence complete combustion (Kim and Choi, 2010; Guo et al., 2011). The CO emission for E20EHN2000 was higher due to combined effect of ignition advance and higher latent heat of vaporisation, which resulted incom plete combustion. HC emission is the by-product of incomplete combustion and due to trapped fuel inside the crevice volume of combustion chamber. The HC emission for test fuel blends in comparison with petrodiesel is as shown in Fig. 3(b). Ethanol has higher latent heat of vaporisation and that resulted longer ID due to low combustion temperature at no load and part load condition (Hansdah et al., 2013). HC emission was highest for E20EHN2000 among other test fuel blends. This was due to the high amount of 2-EHN, which enhanced the combustion quality of the test fuel blends but, at the same time advanced ID resulting incomplete combustion. HC emission for E20EHN1000 was next to petrodiesel and lesser than E20 and E20EHN2000. This was because of 2-EHN presence which decreased the mixing rate of fuel/air and increased the diffusion rate of combustion. At the same time ~5% water had obstructed the burning of end part of test blend, which resulted incomplete combustion and generated more unburned hydrocarbon (Hansdah and Murugan, 2016; Ileri, 2016). Higher CO2 emission is the result of complete combustion and it is reciprocal of CO and HC emission. Fig. 3(c) illustrated variation in CO2 emission for E20, E20EHN1000 and E20EHN2000 in respect of petro diesel at all engine load conditions. The trend of CO2 showed increment with respect to load and at low to part load condition, CO2 for E20, E20EHN1000 and E20EHN2000 were almost identical with that of petrodiesel. But, at full load condition, E20EHN1000 showed highest CO2 emission which was similar to petrodiesel, but E20 and E20EHN2000 showed lower CO2 emission. This demonstrates that at full load condition E20 and E20EHN2000 showed incomplete combustion due to prolong and advance SOC (Hansdah and Murugan, 2016; Tutak et al., 2017). Whereas, E20EHN1000 showed the combined effect of fast evaporation and increased dissociation, which resulted complete com bustion (Choi et al., 2017, Zheng et al., 2015). NOx emission is high if the combustion temperature, injected fuel amount and oxygen concentration in the fuel are high (Campos- �ndez et al., 2012). Fig. 3(d) illustrated that the NOx emission for Ferna E20, E20EHN1000 and E20EHN2000 was little bit higher than that of petrodiesel. This was because of the high oxygen percentage in E20 and nitro compound in E20EHN1000 and E20EHN2000, respectively. The tested fuel blends contain ethanol, which prolonged the ID and increased the amount of accumulated fuel in the combustion chamber (Choi et al., 2017; Agarwal et al., 2013). Also, the nitro compound of 2-EHN enhanced the combustion temperature resulting high NOx emission (Ruina et al., 2014). The prolong ID resulted very small effect of NOx emission due to high latent heat of vaporisation of ethanol, while
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