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Combined effect of composite additive and combustion chamber modification to adapt waste plastic oil as fuel on a diesel engine
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Combined effect of composite additive and combustion chamber modification to adapt waste plastic oil as fuel on a diesel engine Pappula Bridjesh a,b,∗, Pitchaipillai Periyasamy a, Narayanan Kannaiyan Geetha c a
Department of Mechanical Engineering, St. Peter’s Institute of Higher Education and Research, Chennai 600054, India Department of Mechanical Engineering, MLR Institute of Technology, Hyderabad 500043, India c Department of Science and Humanities, Sri Krishna College of Engineering and Technology, Coimbatore 641008, India b
a r t i c l e
i n f o
Article history: Received 7 November 2018 Revised 20 January 2019 Accepted 15 February 2019 Available online xxx Keywords: Waste plastic oil Pyrolysis Composite additive Toroidal spherical grooves
a b s t r a c t In order to compensate energy demand using fossil fuels, the development of alternative energy sources is the order of the day. The production of fuel from plastic wastes will indeed tackle the environmental pollution problem of waste plastic management in the landfills along with overcoming fuel crisis. This experimental investigation is an endeavor to substitute diesel with waste plastic oil (WPO) as fuel on a diesel engine. Enhancing the physiochemical properties of WPO or hardware modifications on engine could not improve the performance. However, physiochemical properties of WPO are enhanced using composite additive, which is a mixture of soy lecithin and di-tert-butyl peroxide and to improve the in-cylinder air motion; subsequently to increase the swirl and turbulence, standard hemispherical open type combustion chamber is modified to toroidal combustion chamber with spherical grooves. The results of combined effect of addition of composite additive and modifying the combustion chamber suggest that improvements in brake thermal efficiency, brake specific fuel consumption and engine-out emission shall be obtained from current diesel engine by careful matching of combustion chamber geometry and physiochemical properties of fuel. © 2019 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
1. Introduction The exhaustion of petroleum holds and consistently expanding concern about nature has quickened the quest for utilization of alternative fuels. Waste management policies and global warming can be addressed simultaneously by producing fuel from plastic wastes [1,2]. The oil produced from plastic wastes is termed as Waste Plastic Oil (WPO). As the raw material cost for production of WPO is zero, it is acclaimed to be a promising alternative fuel. The demanding topic of research across the nations is the production of fuel from plastic wastes. Methods widely used to produce oil from plastic wastes are hydrocracking, thermochemical conversion and catalytic conversion [3]. In hydrocracking, the large hydrocarbons are cracked into smaller hydrocarbons of desired fuel-range at elevated temperatures in the presence of hydrogen [4]. Catalytic hydrocracking using catalyst such as zeolites, alumina and silica–alumina is much more effective to convert polymers into hydrocarbon. However, unfavorable circumstances with hydrocracking are the poisoning effect of poly vinyl chloride if at all present in the plastic wastes, high cost of hydrogen and
∗ Corresponding author at: Department of Mechanical Engineering, MLR Institute of Technology, Hyderabad 50 0 043, India. E-mail address: [email protected] (P. Bridjesh).
high instrument and operating costs [5,6]. Thermo chemical treatment deals with breaking of large polymers into smaller fuel-range hydrocarbons in an inert environment [7,8]. The yield of thermo chemical treatment is influenced by type of plastic degradation temperature, time and type of catalyst used. However, this method is highly effective with organic non-biodegradable matter having less moisture content. Lest, more energy should be consumed in pre-treatment of raw plastic wastes. Pyrolysis is thermal degradation of long chain and complex organic material into smaller and less complex material in inert atmosphere in the presence of catalyst by regulating heat and pressure [9–11]. Pyrolysis yields liquid after condensation and solid residue. Addition of catalyst not only reduces pyrolysis temperature but also influences the production of hydrocarbons on lower range i.e., between C3 and C5. The parameters that influence pyrolysis are operating temperature, residence time, type of catalyst, polymer to catalyst ratio, type of reactor, type and size of raw material, rate of waste heating, initial moisture, mineral matter content and method of contact of catalyst with raw material (liquid phase contact or vapor phase contact) [12]. A high pyrolysis temperature is favorable for production of gaseous products as in case of fast pyrolysis where as medium temperatures are favorable for liquid oil yield at short residence time [13,14]. Plastics have high viscosity and low thermal conductivity which refrains the mass and energy transfer during pyrolysis
https://doi.org/10.1016/j.jtice.2019.02.022 1876-1070/© 2019 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Please cite this article as: P. Bridjesh, P. Periyasamy and N.K. Geetha, Combined effect of composite additive and combustion chamber modification to adapt waste plastic oil as fuel on a diesel engine, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/ 10.1016/j.jtice.2019.02.022
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and these are affected by the type of reactor and prevailing operating conditions in reactor. Addition of solvents tends to reduce viscosity of plastic wastes [15]. Reactors that have been used for pyrolysis are batch and semi-batch reactor, fixed and fluidized bed reactor and conical spouted bed reactor. Batch reactors are widely used as lab scale in which high conversion of plastic waste into oil could be achieved [16]. However, batch reactors are not desirable for large scale production and the yield variability in batch to batch is also observed apart from high labor costs. To increase the yield selectivity also, catalysts are used. The rate of reaction speeds up with reduced optimum temperature in catalytic pyrolysis process. Needless to say, significant improvement in hydrocarbon distribution could also be achieved using catalyst. Widely used catalysts in pyrolysis are AlCl3 [17], Zeolites like silica-alumina, HZSM-5, HUSY, HMOR [18–20]. Temperature has significant effect in pyrolysis. The energy needed to break C–C bond in the polymer chain is called thermal degradation temperature, which depends on the type of plastic waste used. For HDPE, degradation initiated at 378–404 °C and completed at 517–539 °C [21]. Whereas, high liquid yield from LDPE was obtained at 410 °C [22]. The desired yield of plastic wastes i.e., liquid, gas or char is regulated by the pyrolysis temperature. For liquid yield (automobile range) temperature range from 300 to 500 °C is required whereas, temperature above 500 °C is favorable for gas or char [23]. Many researchers have proclaimed that chemical and physical properties of WPO are close to mineral diesel [24,25]. Further they have investigated WPO as fuel on diesel engine either by blending or by adding additives. In this regard, utilization of neat WPO in diesel engine drives into an imperative area of research. The utilization of neat WPO and WPO blends with diesel in engine demonstrated very much clashing outcomes in performance combustion and emission along with engine lifespan. Research established by Ananthakumar et al. [26] and Devaraj et al. [27] with diethyl ether (DEE) as additive to WPO-diesel blends resulted in decrease in oxides of nitrogen (NOx ), carbon monoxide (CO) and smoke emissions along with decrease in brake thermal efficiency (BTE) and increase in brake specific fuel consumption (BSFC). Addition of alcohols can decrease sulphur content and aromatics of fuel. There can be beneficial reduction in harmful emissions with n-butanol as additive to WPO-diesel blends [28]. With addition of n-butanol, not only the spray characteristics, but also the performance of engine has improved. However, NOx emission increased rapidly with increase in volume of n-butanol. With addition of methoxyethyl acetate to diesel favored in lessening of smoke, hydrocarbon (HC) and CO penalty in NOx [29]. Use of dimethoxymethane with diesel demonstrated a decrease in soot but, BTE of engine has deteriorated [30]. Challenges in using WPO as fuel are low cetane number, low calorific value, poor atomization, high aromatic content and high viscosity along with injector hole deposits. Apart from that, the delay period is increased during combustion with neat WPO. And these challenges unfavorably influence the performance and emissions. Despite the higher efficiency, diesel engines emit higher NOx and soot emissions. In an attempt to mitigate these emissions, tradeoff between NOx and HC props up that always influenced the design of engines. The injected fuel has to atomize vaporize and mix properly with air so as to attain better combustion which can be achieved either by modification of geometry of combustion chamber or by increasing fuel injection pressure. In employing high pressure injector, major modifications are needed on the engine. Superior choice to create turbulence is to use high swirl induced pistons [31]. It is inevitable that the combustion quality is significantly influenced by the charge motion inside the engine cylinder. Accordingly, the combustion chamber geometry has been considered as an incredible plan in incrementing efficiency and emission lessening. Numerical investigation carried out by
Subramanian et al. [32] revealed that better squish and high heat release rate (HRR) can be acquired with smaller bowl size. However, engine performance was adversely affected by increasing the bowl radius. Out of the various combustion chamber profiles like toroidal combustion chamber, Mexican hat combustion chamber, double lip combustion chamber and bow combustion chamber it was investigated numerically that turbulence was greatly enhanced with toroidal combustion chamber profile [33]. It is clear from the above literature that either enhancing physiochemical properties of WPO or hardware modifications on engine could not improve performance of engine with neat WPO. These issues motivated authors to look for composite additive to enhance those properties of WPO which are inferior to diesel and also to modify the geometry of combustion chamber to enhance the charge turbulence. The goal of this study is to explore combined effect of addition of composite additive i.e., mixture of soy-lecithin and di– tert–butyl peroxide (DTBP) to WPO, Waste Plastic Oil – Composite Additive (WPOCA) and modifying combustion chamber i.e., the standard hemispherical open type combustion chamber (HCC) is modified to toroidal combustion chamber with spherical grooves (TSG) to analyze performance emission and combustion characteristics of a single cylinder diesel engine. 2. Materials and methods 2.1. WPO extraction WPO is produced from plastic wastes constituting polyethylene (75% in weight) with high and low density, terephthalate polyethylene (15% in weight) and polypropylene (10% in weight) using pyrolysis process. Plastic wastes are cut into little bits of size 1–2 cm2 and washed incessantly with water and then dried. Those bits are taken into a laboratory scale batch reactor, with an inner diameter of reactor shell as 494 mm outer diameter as 500 mm, height of reactor is 476 mm and the capacity of reactor is 91 l approximately to undergo pyrolysis in the presence of nitrogen gas which acts as a fluidizing agent. Fluid catalytic cracking catalyst, ZSM5 (Zeolite Socony Mobil-5) was used not only to reduce the optimum temperature of pyrolysis but also to enhance hydrocarbon dissemination in pyrolysis. Catalyst to polymer ratio of 20 wt% was used in the process for higher yield. ZSM-5 was subjected to mild steaming at 750 °C for 5 h to increase the production of diesel fraction in WPO. Proportional integral derivative controller maintains temperature in reactor between 300 and 450 °C at a heat rate of 5 °C min−1 . Degradation of plastic bits initiated around 325–352 °C and maximum of it has occurred at 419 °C. The vapors are passed through condenser and collected as WPO. Utmost care was taken to aloof polyvinyl chloride waste in this pyrolysis process as it produces harmful and toxic gases like hydrogen chloride [34]. The vital chemical compounds of WPO as analyzed by GC/MS are presented in Table 1 and the physiochemical properties of WPO are presented in Table 2. 2.2. Composite additive Many types of fuel additives like oxygenates, antioxidants, organic compounds, antiknock agents, combustion improvers etc., have been used along with diesel and alternative fuels either to lessen emissions or to improve engine performance. Based on comparison of physiochemical properties of WPO with diesel, those properties of WPO which are inferior to diesel cannot be improved with single additive [35]. In this regard, a composite additive which is a mixture of soy lecithin and DTBP is used. Soy lecithin, CAS No.:8002-43-5 is extracted from soybeans and is a bio-additive known for its surfactant and emulsifying properties.
Please cite this article as: P. Bridjesh, P. Periyasamy and N.K. Geetha, Combined effect of composite additive and combustion chamber modification to adapt waste plastic oil as fuel on a diesel engine, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/ 10.1016/j.jtice.2019.02.022
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Table 1 Vital components in waste plastic oil. Compound name
Molecular Formula
Composition (%)
2,2,9-Trimethyldec-5-ene-3,8-dione Ethyl dodecyl ether 1-Dodecanol, 3,7,11-trimethyl-1-ol 1-Hexadecanol, 2-methyl-1-ol 3-Chloropropionic acid, octadecyl ester 4-Octadecanal 2.5-Dimethyl-4-benzyl-pyridine 2-Hexadecanol 4-[1,5-Dimethylhexyl]-1-Cyclohexane carboxylic acid Z-5-Methyl-6-heneicosen-11-one Oleyl chloride 1-(Triethylsiloxy)−3,7-dimethyl-2,6-octadiene Spiro(3H-cyclopenta(a)pentalene-3,2 -oxiran)−2(1H)-one, 1,7a-epoxyoctahydro-4,7-dihydroxy-3a,5,5-trimethyl-, stereoisomer Xylofuranose, cyclic 1,2:3,5-bis[butylboronate] Toluene-4-sulfonic acid, 2,7-dioxatricyclodec–10-yl ester
C13 H22 O2 C14 H30 O C15 H32 O C17 H36 O C21 H41 ClO2 C18 H36 O C14 H17 N C16 H34 O C15 H26 O2 C22 H42 O C18 H35 Cl C16 H32 OSi C15 H20 O5
5.9 4.5 10.8 2.5 3.3 11.0 10.7 5.1 7.4 8.0 3.5 4.3 9.7
C13 H24 B2 O5 C15 H18 O5 S
9.2 3.8
Table 2 Properties of test fuels. Property
Diesel
WPO
WPOCA
ASTM method
Density @15 °C (kg m−3 ) Calorific value (MJ kg−1 ) Kinematic viscosity (cSt) Flash point (°C) Boiling point (°C) Self ignition temperature (°C) Cetane index (calculated)
0.835 45.4 2.15 49 180–330 210 45
0.782 38.2 3.12 58 120–375 261 31
0.786 38.1 2.78 56 – 252 42
D4052 D240 D445 D93 D7169-16 D1929-16 D4737
Phospholipids present in soy lecithin are the principal surface active agent and also an excellent emulsifier apart from dispersing agent [36]. The amount of soy lecithin was optimized as 0.2% using critical micelle concentration method. Another property that is inferior in WPO to diesel is cetane number. The delay period in the combustion process is greatly influenced by the cetane number. The shorter ignition delay period during combustion leads to better combustion which in turn reduces engine noise and exhaust gas emissions. As such, the delay period is longer with WPO. In this study DTBP with CAS No.:110-05-4 is chosen from among various cetane number improvers. DTBP is an organic compound with peroxide group and bonded to two tert–butyl group. Chemical analysis shows that DTBP undergoes homolysis at temperature greater than 100 °C and thus it acts as a radical initiator. The produced free radicals accelerate the combustion rate when mixed with free radicals of fuel [37].
Fig. 1. Piston bowl (a) standard HCC, (b) modified TSG.
2.3. Piston bowl 2.4. Experimental setup and procedure The shape of combustion chamber is one of the decisive factors for creating air turbulence that determines the quantity and quality of combustion. To enhance the turbulence effect in combustion chamber, the HCC is modified to TSG. Piston bowl volume was kept consistent for both configurations with the goal that compression ratio should be same. It is understood that TSG geometry of piston bowl helps to allow more fuel and air with high velocity over the grooves. While the piston compresses the charge, the squish velocity takes over the flow for the duration of fag end of compression stroke. Some part of charge remains on piston land is forced into the bowl directly that helps to create whirl flow to get more atomization. The increase fuel air motion may effect to develop high turbulence. HCC and TSG profiles are presented in Fig. 1(a) and(b), respectively.
Test rig for this study has a 5.2 kW diesel engine of model TV1, Kirloskar make. This engine is coupled with an eddy current dynamometer. Instruments needed to measure combustion performance and emission characteristics such as AVL H12D pressure transducer, AVL 364 angle encoder, AVL Digas 444 gas analyzer, AVL make smoke meter are installed onto the test rig. AVL INDI MICRA-602-T10602A version V2.5 interfaces for online analysis. The detailed description of setup is presented in [38]. The photographic view of setup is presented in Fig. 2 and alongside specifications of test engine is presented in Table 3. Fuels used for test are diesel, neat WPO and WPOCA (97.8 vol% WPO+0.2 vol% soy lecithin+2 vol% DTBP). The chemical and physical properties of fuels for test are given in Table 2.
Please cite this article as: P. Bridjesh, P. Periyasamy and N.K. Geetha, Combined effect of composite additive and combustion chamber modification to adapt waste plastic oil as fuel on a diesel engine, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/ 10.1016/j.jtice.2019.02.022
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Fig. 2. Single cylinder diesel engine test rig. Fig. 3. In-cylinder pressure variations as a function of crank angle at 100% load.
Table 3 Engine specifications. Make and model
Kirloskar, TV1
Number of cylinders Bore, mm Stroke, mm Piston bowl Compression ratio Rated power, kW Rated speed, rpm Fuel injection type No. of nozzle holes Injection pressure, Mpa Injection timing, °CA bTDC
1 87.5 110 Standard: Hemispherical Modified: Toroidal spherical groove 17.5:1 5.2 1500 Direct injection 3 22 23
Standard operating procedure has been followed in conducting experiments. Tests were conducted with diesel at various loads using HCC piston. These values are utilized as baseline all through for correlation. Then, tests were conducted with diesel, WPO and WPOCA using HCC and TSG pistons at 20%, 40%, 60%, 80% and 100% load. Engine was kept running for 20 min at all loads ensure that engine has stabilized and then readings have been taken. At each step of fuelling along with other fuels, engine continues to run for 30 min to utilize the fuel taken in fuel lines. Repeatability was ensured by repeating the experiments twice. The uncertainties [39] percentage of various parameters is presented in Table 4.
3. Results and discussion 3.1. Cylinder pressure In-cylinder pressure variations with crank angle at 100% load conditions for all test fuels with HCC and TSG are shown in Fig. 3. Maximum in-cylinder pressures of TSG with diesel, TSG with WPO and TSG with WPOCA are 5.67, 5.86 and 5.47 MPa respectively. The peak pressure for WPOCA with TSG is slightly lower than diesel with TSG by 1.93 MPa which could be due to shorter period of ignition delay; subsequently because of emulsifying and surfactant property of composite additive. Soy lecithin present in the composite additive being a surfactant tends to diminish surface tension of fuel which specifically relates to internal pressure and compressibility which leads to shorter period of ignition delay resulting in lower cylinder pressure [40]. Also, with addition of DTBP in composite additive to WPO, the peroxide molecules breakdown amid combustion and shape as free radicals prompting higher disintegration of fuel. The cetane index of WPOCA was enhanced with
Fig. 4. Heat release rate variations as a function of crank angle at 100% load.
DTBP, which accelerates the start of combustion [41] and similar enhancement in cetane number was observed with [37]. 3.2. HRR Variations of HRR using HCC and TSG for diesel, WPO and WPOCA at 100% load are shown in Fig. 4. HRR is affected by period of ignition delay and premixed combustion phase. It can be seen from figure that HRR with all test fuels for TSG is higher than that of HCC. TSG is likely to generate a stronger squish; subsequently a better and intense combustion to take place [42]. Under 100% load conditions, maximum HRR with TSG profiles for diesel, WPO and WPOCA are recorded as 53.13, 58.94 and 51.33 J °C A−1 , respectively, and with HCC profiles for diesel, WPO and WPOCA the maximum HR were recorded as 47.73, 49.51 and 46.36 J °C A−1 , respectively. The maximum HRR for WPO with HCC and TSG is higher than other test fuels. Higher viscosity of WPO deteriorates the spray atomization during premixed combustion phase and lengthens combustion delay [24]. Albeit, ignition delay is shortened by use of composite additive in WPOCA. The surface area and volume of droplets along with bulk modulus of fuel are of essential significance for evaporation of fuel and combustion which strongly influences ignition delay [43]. Soy lecithin in composite additive acts as surfactant bringing about speedier vaporization and atomization of fuel. Also, the higher volatility of DTBP increases dissemination rates of fuel vapor which accelerates the mixture preparation before the ignition and as well increases the rate of fuel burnt in the
Please cite this article as: P. Bridjesh, P. Periyasamy and N.K. Geetha, Combined effect of composite additive and combustion chamber modification to adapt waste plastic oil as fuel on a diesel engine, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/ 10.1016/j.jtice.2019.02.022
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Table 4 List of instruments and their range, accuracy, and uncertainties. Instrument
Range
Accuracy
Percentage Uncertainty
Gas analyzer
CO: 0–10% HC: 0–20,0 0 0 ppm NOx : 0–50 0 0 ppm 0–31,999 mg m−3 0–10 0 0 °C 0–9999 rpm 0–100 kg 0–100 cc 0–50 cc 0–25 MPa 0–360 °CA
± ± ± ± ± ± ± ± ± ± ±
±0.5 ±5.0 ±10.0 ±5 ±0.15 ±0.1 ±0.2 ±1 ±1 ±0.1 ±0.2
Smoke meter Thermocouple (K type) Speed measuring unit Load indicator Volumetric fuel flow meter Manometer Pressure pickup Crank angle encoder
0.01 vol% 1 ppm 1 ppm 0.02 mg m−3 1 °C 10 rpm 0.1 kg 0.1 cc 1 cc 0.1 MPa 1 °CA
Fig. 6. Variations of exhaust gas temperature as a function of load. Fig. 5. Variations of ignition delay as a function of load.
combustion chamber. Addition of DTBP increases the cetane number and lessens the ignition delay period resulting in reduced premixed burning stage [44]. Further, higher swirl associated with TSG helps in better mixing and evaporation of fuel and air.
3.3. Ignition delay Fig. 5 shows period of ignition delay as a function of load comparing among the test fuels. Period of ignition delay is lower for TSG than HCC for all fuels at all loads of operation and in specific; period of ignition delay for TSG with WPOCA is considerably lower than TSG with WPO. Cetane number of WPOCA is higher than WPO which ensue short ignition delay period and better diffusion part of combustion. Also as load increases the retainment of heat produced by past cycles, wall temperature of combustion chamber and exhaust gas dilution tends to decrease ignition delay period [45].
3.4. Exhaust gas temperature (EGT) EGT, which is obtained from the tail pipe gives an indication of inefficiency to extract work from the working fluid and incorrect heat release distribution. Fig. 6 shows EGT as a function of load comparing among the test fuels. TSG profiles of all test fuels recorded higher EGT. Better atomization and vaporization of fuel accounts to the result acquired. Amount of fuel injected is meant to increase in order to maintain constant speed of engine, as the load on engine increases. In this regard, heat produced by engine takes an increasing trend for all fuels [46].
Fig. 7. Brake thermal variations as a function of load.
3.5. BTE Fig. 7 shows BTE variations with load for HCC and TSG with all test fuels. It demonstrates that BTE increments with increment in load for all test fuels. BTE for WPO is lower than WPOCA and diesel with HCC and TSG. The reduction in BTE with WPO may be due to more molar mass of WPO, which needs more energy to break [47]. TSG profile showed higher BTE for all test fuels than HCC. Increased swirl in TSG prompts better ignition and along these lines, BTE increases [46]. In case of WPOCA, BTE for WPOCA with TSG is 3.24% higher than WPOCA with HCC. Substantial increase of 8.03% in BTE is found using WPOCA with TSG than WPO with TSG. While, marginal decrease in BTE is found with WPOCA than diesel in both HCC and TSG. The presence of phospho lipids in soy lecithin and
Please cite this article as: P. Bridjesh, P. Periyasamy and N.K. Geetha, Combined effect of composite additive and combustion chamber modification to adapt waste plastic oil as fuel on a diesel engine, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/ 10.1016/j.jtice.2019.02.022
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Fig. 8. Brake specific fuel consumption variations as a function of load.
Fig. 10. Carbon monoxide emission variations as a function of load.
Fig. 9. Hydrocarbon emission variations as a function of load.
higher amount of oxygen in WPOCA supports combustion by better mixing of fuel with encompassing air thus improving BTE [40].
Fig. 11. Oxides of nitrogen emission variations as a function of load.
3.8. CO 3.6. BSFC BSFC as a function of load is presented in Fig. 8. Usually, BSFC decreases with increase in the load [48]. Fig. 8 illustrates that BSFC for WPOCA has a reducing trend as compared to that of WPO for HCC and TSG. Experimental results show increase of BSFC on an average for TSG with WPO by 3.23% than TSG with WPOCA. On the other hand, BSFC of TSG with WPOCA decreased by 0.62% than TSG with diesel. It may be attributed that dissemination rate of fuel enhanced with composite additive brought about advancing the combustion. Reduction in viscosity of WPOCA than WPO can also be attributed to improved atomization to attain high combustion efficiency [37,41]. 3.7. HC The HC emission for HCC and TSG using WPO and WPOCA are compared with diesel and are shown in Fig. 9. The factors that influence HC emission are properties of fuel along with fuel air mixing and operating conditions of engine [49]. HC emission for HCC and TSG has reduced over the whole range of loads when operated with WPO and WPOCA. This may be due to availability of excess oxygen in WPO and WPOCA. It is also observed that HC emission reduced by 8.62% with HCC and 15.72% with TSG for WPOCA than diesel. Better mixing of WPOCA and air along with enhanced swirl might have led to complete combustion [31,33]. Besides, oxygen present in composite additive likewise increases combustion process subsequently decreasing HC emission.
Fig. 10 shows CO emission with load for HCC and TSG for all test fuels. The formation of CO is essentially because of inadequate combustion which is aggravated due to insufficient oxygen and equivalence ratio. CO emission diminishes with increment in load up to 75% for all fuels and suddenly increases beyond 75% load. This may be due to the consumption of excess amount of fuel to meet the load and speed conditions. Wherein, sufficient time may not be available for the fuel to burn completely at these operational conditions [50]. Under full load conditions, WPO emits lower CO emission by 6.34% with HCC and 10.6% with TSG than diesel. The local rich and lean mixture formed in the combustion chamber has led to the reduction in CO [49]. As more amount of oxygen is available in WPO, this improved the conversion of CO into CO2 [47]. It can be interesting to note that for WPOCA, CO emission decreased by 13.55% with HCC and 17.74% with TSG than diesel respectively. This can be attributed to the surfactant action of composite additive for better atomization and vaporization of fuel along with swirl motion all through the combustion chamber bringing about complete combustion [40]. 3.9. NOX Fig. 11 shows NOx variations with respect to load using HCC and TSG for all fuels. Formation of NOx relies upon combustion temperature and amount of oxygen [51]. WPO shows an increase of 11.97% of NOx emission with HCC and 12.56% with TSG than that of diesel. It can also be seen that NOx emission using WPOCA re-
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diesel. It is also noticed that HC emission reduced by 8.62% with HCC and 15.72% with TSG for WPOCA than diesel. 5. Smoke emission has significantly reduced (14.5% than diesel) with the use of composite additive in WPOCA for TSG than that of other test fuels. Thus, the test results suggest that for the long term running, the addition of composite additive to neat WPO lead to smooth running of the engine without any trouble. The results also suggest that improvements in engine-out emissions as well as increase thermal efficiency along with adequate fuel consumption may be obtained from current diesel engine by careful matching of combustion system geometry and fuel modifications. More engine operating parameters such as injection timing, injection pressure and compression ratio need to be explored in order to obtain optimum engine performance. Fig. 12. Smoke emission variations as a function of load.
duced by 8.72% with HCC and 16.79% with TSG than WPO. The reduced HRR and shorter ignition delay period causes drop in peak combustion temperature, accordingly cutting down NOx emission. When compared with diesel, NOx emission for WPOCA increased by 4.28% with HCC and 5.75% with TSG. The presence of nitrogen content in soy lecithin and DTBP of composite additive also add to increase in NOx formation [40]. Be that as it may, improved mixture formation leading to increased combustion temperature in TSG along with the availability of oxygen in WPO and WPOCA may be attributed for increased NOx emission [42,33]. 3.10. Smoke Smoke emission is unequivocally identified with diffusive combustion which for the most part happens in rich zone at high temperatures [52]. Fig. 12 shows smoke emission variations for HCC and TSG with all test fuels. Smoke emission for WPO and WPOCA is found to be lower than diesel for both HCC and TSG. The presence of excess oxygen in WPO and WPOCA makes the fuel air mixture leaner consequently combustion occurs by making use of oxygen in rich zones resulting in a decreased smoke formation [49]. Smoke emission for WPOCA with TSG is lower than other test fuels which might be credited to adequate combustion because of better mixing of fuel with air and the availability of oxygen in composite additive along with that in WPO [40,42]. 4. Conclusions An experimental contemplate is lead to analyze diesel engine combustion performance and emission characteristics using HCC and TSG combustion chambers with neat WPO, WPOCA and are compared with diesel. Following conclusions can be drawn: 1. The chemical and physical properties of WPO and WPOCA are sufficient and ideal to be used as fuels on diesel engine. 2. In TSG, due to the geometry, improved air motion has improved mixture formation of WPOCA with air resulting in increase in BTE and decrease in BSFC. BTE for WPOCA with TSG is higher by 3.24% than WPOCA with HCC. Whereas, BSFC for WPOCA with TSG is lower by 2.86% than WPOCA with HCC. 3. NOx emission using WPOCA reduced by 8.72% with HCC and 16.79% with TSG than WPO. 4. Higher oxygen content in WPO and WPOCA, better air fuel mixing as a result of increased swirl in TSG, the CO and HC emissions are lower than diesel. For WPOCA, CO emission decreased by 13.55% with HCC and 17.74% with TSG than
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Combined effect of composite additive and combustion chamber modification to adapt waste plastic oil as fuel on a diesel engine Pappula Bridjesh a,b,∗, Pitchaipillai Periyasamy a, Narayanan Kannaiyan Geetha c a
Department of Mechanical Engineering, St. Peter’s Institute of Higher Education and Research, Chennai 600054, India Department of Mechanical Engineering, MLR Institute of Technology, Hyderabad 500043, India c Department of Science and Humanities, Sri Krishna College of Engineering and Technology, Coimbatore 641008, India b
a r t i c l e
i n f o
Article history: Received 7 November 2018 Revised 20 January 2019 Accepted 15 February 2019 Available online xxx Keywords: Waste plastic oil Pyrolysis Composite additive Toroidal spherical grooves
a b s t r a c t In order to compensate energy demand using fossil fuels, the development of alternative energy sources is the order of the day. The production of fuel from plastic wastes will indeed tackle the environmental pollution problem of waste plastic management in the landfills along with overcoming fuel crisis. This experimental investigation is an endeavor to substitute diesel with waste plastic oil (WPO) as fuel on a diesel engine. Enhancing the physiochemical properties of WPO or hardware modifications on engine could not improve the performance. However, physiochemical properties of WPO are enhanced using composite additive, which is a mixture of soy lecithin and di-tert-butyl peroxide and to improve the in-cylinder air motion; subsequently to increase the swirl and turbulence, standard hemispherical open type combustion chamber is modified to toroidal combustion chamber with spherical grooves. The results of combined effect of addition of composite additive and modifying the combustion chamber suggest that improvements in brake thermal efficiency, brake specific fuel consumption and engine-out emission shall be obtained from current diesel engine by careful matching of combustion chamber geometry and physiochemical properties of fuel. © 2019 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
1. Introduction The exhaustion of petroleum holds and consistently expanding concern about nature has quickened the quest for utilization of alternative fuels. Waste management policies and global warming can be addressed simultaneously by producing fuel from plastic wastes [1,2]. The oil produced from plastic wastes is termed as Waste Plastic Oil (WPO). As the raw material cost for production of WPO is zero, it is acclaimed to be a promising alternative fuel. The demanding topic of research across the nations is the production of fuel from plastic wastes. Methods widely used to produce oil from plastic wastes are hydrocracking, thermochemical conversion and catalytic conversion [3]. In hydrocracking, the large hydrocarbons are cracked into smaller hydrocarbons of desired fuel-range at elevated temperatures in the presence of hydrogen [4]. Catalytic hydrocracking using catalyst such as zeolites, alumina and silica–alumina is much more effective to convert polymers into hydrocarbon. However, unfavorable circumstances with hydrocracking are the poisoning effect of poly vinyl chloride if at all present in the plastic wastes, high cost of hydrogen and
∗ Corresponding author at: Department of Mechanical Engineering, MLR Institute of Technology, Hyderabad 50 0 043, India. E-mail address: [email protected] (P. Bridjesh).
high instrument and operating costs [5,6]. Thermo chemical treatment deals with breaking of large polymers into smaller fuel-range hydrocarbons in an inert environment [7,8]. The yield of thermo chemical treatment is influenced by type of plastic degradation temperature, time and type of catalyst used. However, this method is highly effective with organic non-biodegradable matter having less moisture content. Lest, more energy should be consumed in pre-treatment of raw plastic wastes. Pyrolysis is thermal degradation of long chain and complex organic material into smaller and less complex material in inert atmosphere in the presence of catalyst by regulating heat and pressure [9–11]. Pyrolysis yields liquid after condensation and solid residue. Addition of catalyst not only reduces pyrolysis temperature but also influences the production of hydrocarbons on lower range i.e., between C3 and C5. The parameters that influence pyrolysis are operating temperature, residence time, type of catalyst, polymer to catalyst ratio, type of reactor, type and size of raw material, rate of waste heating, initial moisture, mineral matter content and method of contact of catalyst with raw material (liquid phase contact or vapor phase contact) [12]. A high pyrolysis temperature is favorable for production of gaseous products as in case of fast pyrolysis where as medium temperatures are favorable for liquid oil yield at short residence time [13,14]. Plastics have high viscosity and low thermal conductivity which refrains the mass and energy transfer during pyrolysis
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and these are affected by the type of reactor and prevailing operating conditions in reactor. Addition of solvents tends to reduce viscosity of plastic wastes [15]. Reactors that have been used for pyrolysis are batch and semi-batch reactor, fixed and fluidized bed reactor and conical spouted bed reactor. Batch reactors are widely used as lab scale in which high conversion of plastic waste into oil could be achieved [16]. However, batch reactors are not desirable for large scale production and the yield variability in batch to batch is also observed apart from high labor costs. To increase the yield selectivity also, catalysts are used. The rate of reaction speeds up with reduced optimum temperature in catalytic pyrolysis process. Needless to say, significant improvement in hydrocarbon distribution could also be achieved using catalyst. Widely used catalysts in pyrolysis are AlCl3 [17], Zeolites like silica-alumina, HZSM-5, HUSY, HMOR [18–20]. Temperature has significant effect in pyrolysis. The energy needed to break C–C bond in the polymer chain is called thermal degradation temperature, which depends on the type of plastic waste used. For HDPE, degradation initiated at 378–404 °C and completed at 517–539 °C [21]. Whereas, high liquid yield from LDPE was obtained at 410 °C [22]. The desired yield of plastic wastes i.e., liquid, gas or char is regulated by the pyrolysis temperature. For liquid yield (automobile range) temperature range from 300 to 500 °C is required whereas, temperature above 500 °C is favorable for gas or char [23]. Many researchers have proclaimed that chemical and physical properties of WPO are close to mineral diesel [24,25]. Further they have investigated WPO as fuel on diesel engine either by blending or by adding additives. In this regard, utilization of neat WPO in diesel engine drives into an imperative area of research. The utilization of neat WPO and WPO blends with diesel in engine demonstrated very much clashing outcomes in performance combustion and emission along with engine lifespan. Research established by Ananthakumar et al. [26] and Devaraj et al. [27] with diethyl ether (DEE) as additive to WPO-diesel blends resulted in decrease in oxides of nitrogen (NOx ), carbon monoxide (CO) and smoke emissions along with decrease in brake thermal efficiency (BTE) and increase in brake specific fuel consumption (BSFC). Addition of alcohols can decrease sulphur content and aromatics of fuel. There can be beneficial reduction in harmful emissions with n-butanol as additive to WPO-diesel blends [28]. With addition of n-butanol, not only the spray characteristics, but also the performance of engine has improved. However, NOx emission increased rapidly with increase in volume of n-butanol. With addition of methoxyethyl acetate to diesel favored in lessening of smoke, hydrocarbon (HC) and CO penalty in NOx [29]. Use of dimethoxymethane with diesel demonstrated a decrease in soot but, BTE of engine has deteriorated [30]. Challenges in using WPO as fuel are low cetane number, low calorific value, poor atomization, high aromatic content and high viscosity along with injector hole deposits. Apart from that, the delay period is increased during combustion with neat WPO. And these challenges unfavorably influence the performance and emissions. Despite the higher efficiency, diesel engines emit higher NOx and soot emissions. In an attempt to mitigate these emissions, tradeoff between NOx and HC props up that always influenced the design of engines. The injected fuel has to atomize vaporize and mix properly with air so as to attain better combustion which can be achieved either by modification of geometry of combustion chamber or by increasing fuel injection pressure. In employing high pressure injector, major modifications are needed on the engine. Superior choice to create turbulence is to use high swirl induced pistons [31]. It is inevitable that the combustion quality is significantly influenced by the charge motion inside the engine cylinder. Accordingly, the combustion chamber geometry has been considered as an incredible plan in incrementing efficiency and emission lessening. Numerical investigation carried out by
Subramanian et al. [32] revealed that better squish and high heat release rate (HRR) can be acquired with smaller bowl size. However, engine performance was adversely affected by increasing the bowl radius. Out of the various combustion chamber profiles like toroidal combustion chamber, Mexican hat combustion chamber, double lip combustion chamber and bow combustion chamber it was investigated numerically that turbulence was greatly enhanced with toroidal combustion chamber profile [33]. It is clear from the above literature that either enhancing physiochemical properties of WPO or hardware modifications on engine could not improve performance of engine with neat WPO. These issues motivated authors to look for composite additive to enhance those properties of WPO which are inferior to diesel and also to modify the geometry of combustion chamber to enhance the charge turbulence. The goal of this study is to explore combined effect of addition of composite additive i.e., mixture of soy-lecithin and di– tert–butyl peroxide (DTBP) to WPO, Waste Plastic Oil – Composite Additive (WPOCA) and modifying combustion chamber i.e., the standard hemispherical open type combustion chamber (HCC) is modified to toroidal combustion chamber with spherical grooves (TSG) to analyze performance emission and combustion characteristics of a single cylinder diesel engine. 2. Materials and methods 2.1. WPO extraction WPO is produced from plastic wastes constituting polyethylene (75% in weight) with high and low density, terephthalate polyethylene (15% in weight) and polypropylene (10% in weight) using pyrolysis process. Plastic wastes are cut into little bits of size 1–2 cm2 and washed incessantly with water and then dried. Those bits are taken into a laboratory scale batch reactor, with an inner diameter of reactor shell as 494 mm outer diameter as 500 mm, height of reactor is 476 mm and the capacity of reactor is 91 l approximately to undergo pyrolysis in the presence of nitrogen gas which acts as a fluidizing agent. Fluid catalytic cracking catalyst, ZSM5 (Zeolite Socony Mobil-5) was used not only to reduce the optimum temperature of pyrolysis but also to enhance hydrocarbon dissemination in pyrolysis. Catalyst to polymer ratio of 20 wt% was used in the process for higher yield. ZSM-5 was subjected to mild steaming at 750 °C for 5 h to increase the production of diesel fraction in WPO. Proportional integral derivative controller maintains temperature in reactor between 300 and 450 °C at a heat rate of 5 °C min−1 . Degradation of plastic bits initiated around 325–352 °C and maximum of it has occurred at 419 °C. The vapors are passed through condenser and collected as WPO. Utmost care was taken to aloof polyvinyl chloride waste in this pyrolysis process as it produces harmful and toxic gases like hydrogen chloride [34]. The vital chemical compounds of WPO as analyzed by GC/MS are presented in Table 1 and the physiochemical properties of WPO are presented in Table 2. 2.2. Composite additive Many types of fuel additives like oxygenates, antioxidants, organic compounds, antiknock agents, combustion improvers etc., have been used along with diesel and alternative fuels either to lessen emissions or to improve engine performance. Based on comparison of physiochemical properties of WPO with diesel, those properties of WPO which are inferior to diesel cannot be improved with single additive [35]. In this regard, a composite additive which is a mixture of soy lecithin and DTBP is used. Soy lecithin, CAS No.:8002-43-5 is extracted from soybeans and is a bio-additive known for its surfactant and emulsifying properties.
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Table 1 Vital components in waste plastic oil. Compound name
Molecular Formula
Composition (%)
2,2,9-Trimethyldec-5-ene-3,8-dione Ethyl dodecyl ether 1-Dodecanol, 3,7,11-trimethyl-1-ol 1-Hexadecanol, 2-methyl-1-ol 3-Chloropropionic acid, octadecyl ester 4-Octadecanal 2.5-Dimethyl-4-benzyl-pyridine 2-Hexadecanol 4-[1,5-Dimethylhexyl]-1-Cyclohexane carboxylic acid Z-5-Methyl-6-heneicosen-11-one Oleyl chloride 1-(Triethylsiloxy)−3,7-dimethyl-2,6-octadiene Spiro(3H-cyclopenta(a)pentalene-3,2 -oxiran)−2(1H)-one, 1,7a-epoxyoctahydro-4,7-dihydroxy-3a,5,5-trimethyl-, stereoisomer Xylofuranose, cyclic 1,2:3,5-bis[butylboronate] Toluene-4-sulfonic acid, 2,7-dioxatricyclodec–10-yl ester
C13 H22 O2 C14 H30 O C15 H32 O C17 H36 O C21 H41 ClO2 C18 H36 O C14 H17 N C16 H34 O C15 H26 O2 C22 H42 O C18 H35 Cl C16 H32 OSi C15 H20 O5
5.9 4.5 10.8 2.5 3.3 11.0 10.7 5.1 7.4 8.0 3.5 4.3 9.7
C13 H24 B2 O5 C15 H18 O5 S
9.2 3.8
Table 2 Properties of test fuels. Property
Diesel
WPO
WPOCA
ASTM method
Density @15 °C (kg m−3 ) Calorific value (MJ kg−1 ) Kinematic viscosity (cSt) Flash point (°C) Boiling point (°C) Self ignition temperature (°C) Cetane index (calculated)
0.835 45.4 2.15 49 180–330 210 45
0.782 38.2 3.12 58 120–375 261 31
0.786 38.1 2.78 56 – 252 42
D4052 D240 D445 D93 D7169-16 D1929-16 D4737
Phospholipids present in soy lecithin are the principal surface active agent and also an excellent emulsifier apart from dispersing agent [36]. The amount of soy lecithin was optimized as 0.2% using critical micelle concentration method. Another property that is inferior in WPO to diesel is cetane number. The delay period in the combustion process is greatly influenced by the cetane number. The shorter ignition delay period during combustion leads to better combustion which in turn reduces engine noise and exhaust gas emissions. As such, the delay period is longer with WPO. In this study DTBP with CAS No.:110-05-4 is chosen from among various cetane number improvers. DTBP is an organic compound with peroxide group and bonded to two tert–butyl group. Chemical analysis shows that DTBP undergoes homolysis at temperature greater than 100 °C and thus it acts as a radical initiator. The produced free radicals accelerate the combustion rate when mixed with free radicals of fuel [37].
Fig. 1. Piston bowl (a) standard HCC, (b) modified TSG.
2.3. Piston bowl 2.4. Experimental setup and procedure The shape of combustion chamber is one of the decisive factors for creating air turbulence that determines the quantity and quality of combustion. To enhance the turbulence effect in combustion chamber, the HCC is modified to TSG. Piston bowl volume was kept consistent for both configurations with the goal that compression ratio should be same. It is understood that TSG geometry of piston bowl helps to allow more fuel and air with high velocity over the grooves. While the piston compresses the charge, the squish velocity takes over the flow for the duration of fag end of compression stroke. Some part of charge remains on piston land is forced into the bowl directly that helps to create whirl flow to get more atomization. The increase fuel air motion may effect to develop high turbulence. HCC and TSG profiles are presented in Fig. 1(a) and(b), respectively.
Test rig for this study has a 5.2 kW diesel engine of model TV1, Kirloskar make. This engine is coupled with an eddy current dynamometer. Instruments needed to measure combustion performance and emission characteristics such as AVL H12D pressure transducer, AVL 364 angle encoder, AVL Digas 444 gas analyzer, AVL make smoke meter are installed onto the test rig. AVL INDI MICRA-602-T10602A version V2.5 interfaces for online analysis. The detailed description of setup is presented in [38]. The photographic view of setup is presented in Fig. 2 and alongside specifications of test engine is presented in Table 3. Fuels used for test are diesel, neat WPO and WPOCA (97.8 vol% WPO+0.2 vol% soy lecithin+2 vol% DTBP). The chemical and physical properties of fuels for test are given in Table 2.
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Fig. 2. Single cylinder diesel engine test rig. Fig. 3. In-cylinder pressure variations as a function of crank angle at 100% load.
Table 3 Engine specifications. Make and model
Kirloskar, TV1
Number of cylinders Bore, mm Stroke, mm Piston bowl Compression ratio Rated power, kW Rated speed, rpm Fuel injection type No. of nozzle holes Injection pressure, Mpa Injection timing, °CA bTDC
1 87.5 110 Standard: Hemispherical Modified: Toroidal spherical groove 17.5:1 5.2 1500 Direct injection 3 22 23
Standard operating procedure has been followed in conducting experiments. Tests were conducted with diesel at various loads using HCC piston. These values are utilized as baseline all through for correlation. Then, tests were conducted with diesel, WPO and WPOCA using HCC and TSG pistons at 20%, 40%, 60%, 80% and 100% load. Engine was kept running for 20 min at all loads ensure that engine has stabilized and then readings have been taken. At each step of fuelling along with other fuels, engine continues to run for 30 min to utilize the fuel taken in fuel lines. Repeatability was ensured by repeating the experiments twice. The uncertainties [39] percentage of various parameters is presented in Table 4.
3. Results and discussion 3.1. Cylinder pressure In-cylinder pressure variations with crank angle at 100% load conditions for all test fuels with HCC and TSG are shown in Fig. 3. Maximum in-cylinder pressures of TSG with diesel, TSG with WPO and TSG with WPOCA are 5.67, 5.86 and 5.47 MPa respectively. The peak pressure for WPOCA with TSG is slightly lower than diesel with TSG by 1.93 MPa which could be due to shorter period of ignition delay; subsequently because of emulsifying and surfactant property of composite additive. Soy lecithin present in the composite additive being a surfactant tends to diminish surface tension of fuel which specifically relates to internal pressure and compressibility which leads to shorter period of ignition delay resulting in lower cylinder pressure [40]. Also, with addition of DTBP in composite additive to WPO, the peroxide molecules breakdown amid combustion and shape as free radicals prompting higher disintegration of fuel. The cetane index of WPOCA was enhanced with
Fig. 4. Heat release rate variations as a function of crank angle at 100% load.
DTBP, which accelerates the start of combustion [41] and similar enhancement in cetane number was observed with [37]. 3.2. HRR Variations of HRR using HCC and TSG for diesel, WPO and WPOCA at 100% load are shown in Fig. 4. HRR is affected by period of ignition delay and premixed combustion phase. It can be seen from figure that HRR with all test fuels for TSG is higher than that of HCC. TSG is likely to generate a stronger squish; subsequently a better and intense combustion to take place [42]. Under 100% load conditions, maximum HRR with TSG profiles for diesel, WPO and WPOCA are recorded as 53.13, 58.94 and 51.33 J °C A−1 , respectively, and with HCC profiles for diesel, WPO and WPOCA the maximum HR were recorded as 47.73, 49.51 and 46.36 J °C A−1 , respectively. The maximum HRR for WPO with HCC and TSG is higher than other test fuels. Higher viscosity of WPO deteriorates the spray atomization during premixed combustion phase and lengthens combustion delay [24]. Albeit, ignition delay is shortened by use of composite additive in WPOCA. The surface area and volume of droplets along with bulk modulus of fuel are of essential significance for evaporation of fuel and combustion which strongly influences ignition delay [43]. Soy lecithin in composite additive acts as surfactant bringing about speedier vaporization and atomization of fuel. Also, the higher volatility of DTBP increases dissemination rates of fuel vapor which accelerates the mixture preparation before the ignition and as well increases the rate of fuel burnt in the
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Table 4 List of instruments and their range, accuracy, and uncertainties. Instrument
Range
Accuracy
Percentage Uncertainty
Gas analyzer
CO: 0–10% HC: 0–20,0 0 0 ppm NOx : 0–50 0 0 ppm 0–31,999 mg m−3 0–10 0 0 °C 0–9999 rpm 0–100 kg 0–100 cc 0–50 cc 0–25 MPa 0–360 °CA
± ± ± ± ± ± ± ± ± ± ±
±0.5 ±5.0 ±10.0 ±5 ±0.15 ±0.1 ±0.2 ±1 ±1 ±0.1 ±0.2
Smoke meter Thermocouple (K type) Speed measuring unit Load indicator Volumetric fuel flow meter Manometer Pressure pickup Crank angle encoder
0.01 vol% 1 ppm 1 ppm 0.02 mg m−3 1 °C 10 rpm 0.1 kg 0.1 cc 1 cc 0.1 MPa 1 °CA
Fig. 6. Variations of exhaust gas temperature as a function of load. Fig. 5. Variations of ignition delay as a function of load.
combustion chamber. Addition of DTBP increases the cetane number and lessens the ignition delay period resulting in reduced premixed burning stage [44]. Further, higher swirl associated with TSG helps in better mixing and evaporation of fuel and air.
3.3. Ignition delay Fig. 5 shows period of ignition delay as a function of load comparing among the test fuels. Period of ignition delay is lower for TSG than HCC for all fuels at all loads of operation and in specific; period of ignition delay for TSG with WPOCA is considerably lower than TSG with WPO. Cetane number of WPOCA is higher than WPO which ensue short ignition delay period and better diffusion part of combustion. Also as load increases the retainment of heat produced by past cycles, wall temperature of combustion chamber and exhaust gas dilution tends to decrease ignition delay period [45].
3.4. Exhaust gas temperature (EGT) EGT, which is obtained from the tail pipe gives an indication of inefficiency to extract work from the working fluid and incorrect heat release distribution. Fig. 6 shows EGT as a function of load comparing among the test fuels. TSG profiles of all test fuels recorded higher EGT. Better atomization and vaporization of fuel accounts to the result acquired. Amount of fuel injected is meant to increase in order to maintain constant speed of engine, as the load on engine increases. In this regard, heat produced by engine takes an increasing trend for all fuels [46].
Fig. 7. Brake thermal variations as a function of load.
3.5. BTE Fig. 7 shows BTE variations with load for HCC and TSG with all test fuels. It demonstrates that BTE increments with increment in load for all test fuels. BTE for WPO is lower than WPOCA and diesel with HCC and TSG. The reduction in BTE with WPO may be due to more molar mass of WPO, which needs more energy to break [47]. TSG profile showed higher BTE for all test fuels than HCC. Increased swirl in TSG prompts better ignition and along these lines, BTE increases [46]. In case of WPOCA, BTE for WPOCA with TSG is 3.24% higher than WPOCA with HCC. Substantial increase of 8.03% in BTE is found using WPOCA with TSG than WPO with TSG. While, marginal decrease in BTE is found with WPOCA than diesel in both HCC and TSG. The presence of phospho lipids in soy lecithin and
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Fig. 8. Brake specific fuel consumption variations as a function of load.
Fig. 10. Carbon monoxide emission variations as a function of load.
Fig. 9. Hydrocarbon emission variations as a function of load.
higher amount of oxygen in WPOCA supports combustion by better mixing of fuel with encompassing air thus improving BTE [40].
Fig. 11. Oxides of nitrogen emission variations as a function of load.
3.8. CO 3.6. BSFC BSFC as a function of load is presented in Fig. 8. Usually, BSFC decreases with increase in the load [48]. Fig. 8 illustrates that BSFC for WPOCA has a reducing trend as compared to that of WPO for HCC and TSG. Experimental results show increase of BSFC on an average for TSG with WPO by 3.23% than TSG with WPOCA. On the other hand, BSFC of TSG with WPOCA decreased by 0.62% than TSG with diesel. It may be attributed that dissemination rate of fuel enhanced with composite additive brought about advancing the combustion. Reduction in viscosity of WPOCA than WPO can also be attributed to improved atomization to attain high combustion efficiency [37,41]. 3.7. HC The HC emission for HCC and TSG using WPO and WPOCA are compared with diesel and are shown in Fig. 9. The factors that influence HC emission are properties of fuel along with fuel air mixing and operating conditions of engine [49]. HC emission for HCC and TSG has reduced over the whole range of loads when operated with WPO and WPOCA. This may be due to availability of excess oxygen in WPO and WPOCA. It is also observed that HC emission reduced by 8.62% with HCC and 15.72% with TSG for WPOCA than diesel. Better mixing of WPOCA and air along with enhanced swirl might have led to complete combustion [31,33]. Besides, oxygen present in composite additive likewise increases combustion process subsequently decreasing HC emission.
Fig. 10 shows CO emission with load for HCC and TSG for all test fuels. The formation of CO is essentially because of inadequate combustion which is aggravated due to insufficient oxygen and equivalence ratio. CO emission diminishes with increment in load up to 75% for all fuels and suddenly increases beyond 75% load. This may be due to the consumption of excess amount of fuel to meet the load and speed conditions. Wherein, sufficient time may not be available for the fuel to burn completely at these operational conditions [50]. Under full load conditions, WPO emits lower CO emission by 6.34% with HCC and 10.6% with TSG than diesel. The local rich and lean mixture formed in the combustion chamber has led to the reduction in CO [49]. As more amount of oxygen is available in WPO, this improved the conversion of CO into CO2 [47]. It can be interesting to note that for WPOCA, CO emission decreased by 13.55% with HCC and 17.74% with TSG than diesel respectively. This can be attributed to the surfactant action of composite additive for better atomization and vaporization of fuel along with swirl motion all through the combustion chamber bringing about complete combustion [40]. 3.9. NOX Fig. 11 shows NOx variations with respect to load using HCC and TSG for all fuels. Formation of NOx relies upon combustion temperature and amount of oxygen [51]. WPO shows an increase of 11.97% of NOx emission with HCC and 12.56% with TSG than that of diesel. It can also be seen that NOx emission using WPOCA re-
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diesel. It is also noticed that HC emission reduced by 8.62% with HCC and 15.72% with TSG for WPOCA than diesel. 5. Smoke emission has significantly reduced (14.5% than diesel) with the use of composite additive in WPOCA for TSG than that of other test fuels. Thus, the test results suggest that for the long term running, the addition of composite additive to neat WPO lead to smooth running of the engine without any trouble. The results also suggest that improvements in engine-out emissions as well as increase thermal efficiency along with adequate fuel consumption may be obtained from current diesel engine by careful matching of combustion system geometry and fuel modifications. More engine operating parameters such as injection timing, injection pressure and compression ratio need to be explored in order to obtain optimum engine performance. Fig. 12. Smoke emission variations as a function of load.
duced by 8.72% with HCC and 16.79% with TSG than WPO. The reduced HRR and shorter ignition delay period causes drop in peak combustion temperature, accordingly cutting down NOx emission. When compared with diesel, NOx emission for WPOCA increased by 4.28% with HCC and 5.75% with TSG. The presence of nitrogen content in soy lecithin and DTBP of composite additive also add to increase in NOx formation [40]. Be that as it may, improved mixture formation leading to increased combustion temperature in TSG along with the availability of oxygen in WPO and WPOCA may be attributed for increased NOx emission [42,33]. 3.10. Smoke Smoke emission is unequivocally identified with diffusive combustion which for the most part happens in rich zone at high temperatures [52]. Fig. 12 shows smoke emission variations for HCC and TSG with all test fuels. Smoke emission for WPO and WPOCA is found to be lower than diesel for both HCC and TSG. The presence of excess oxygen in WPO and WPOCA makes the fuel air mixture leaner consequently combustion occurs by making use of oxygen in rich zones resulting in a decreased smoke formation [49]. Smoke emission for WPOCA with TSG is lower than other test fuels which might be credited to adequate combustion because of better mixing of fuel with air and the availability of oxygen in composite additive along with that in WPO [40,42]. 4. Conclusions An experimental contemplate is lead to analyze diesel engine combustion performance and emission characteristics using HCC and TSG combustion chambers with neat WPO, WPOCA and are compared with diesel. Following conclusions can be drawn: 1. The chemical and physical properties of WPO and WPOCA are sufficient and ideal to be used as fuels on diesel engine. 2. In TSG, due to the geometry, improved air motion has improved mixture formation of WPOCA with air resulting in increase in BTE and decrease in BSFC. BTE for WPOCA with TSG is higher by 3.24% than WPOCA with HCC. Whereas, BSFC for WPOCA with TSG is lower by 2.86% than WPOCA with HCC. 3. NOx emission using WPOCA reduced by 8.72% with HCC and 16.79% with TSG than WPO. 4. Higher oxygen content in WPO and WPOCA, better air fuel mixing as a result of increased swirl in TSG, the CO and HC emissions are lower than diesel. For WPOCA, CO emission decreased by 13.55% with HCC and 17.74% with TSG than
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