Article Cite This: Energy Fuels 2017, 31, 11362-11376
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Combined Effect of Compression Ratio, Injection Pressure, and Injection Timing on Performance and Emission of a DI Compression Ignition Engine Fueled with Diesel−Aegle Marmelos Oil−Diethyl Ether Blends Using Response Surface Methodology M. Krishnamoorthi* and R. Malayalamurthi Department of Mechanical Engineering, Government College of Technology, Coimbatore 641013, Tamil Nadu, India ABSTRACT: Renewable energy research in support of the generously developing choice for diesel fuel automobiles has been concentrated because of environmental causes and hurly burly into petroleum combat. The test has been conducted in a lightduty single cylinder variable compression ratio (VCR) naturally aspirated multifuel research engine. Three input parameters, compression ratio (CR), injection pressure (IP), and injection timing (IT), are taken as input amends. In this study parameters are taken as 16, 17, and 18 for CR and 210 bar, 230 bar, and 250 bar for IP and 21°, 23°, and 25° before top dead center (bTDC) for IT. Experimental trials have been planned via statistical tool like design of experiments (DoE) to outline the resulting output, such as performance and emission. Better performance and lesser exhaust pollution are the desirable output factors by optimizing the injection system and compression ratio parameters by factorial design. The confirmatory tests validated that the models developed using response surface methodology (RSM) are adequate to describe the effects of CR, IP, and IT on the performance and emission characteristics using all test fuels. The error in prediction using RSM is within 5%.
1. INTRODUCTION Renewable fuels such as biodiesel and vegetable oil are earning popularity for compression ignition engines due to emission effects on the environment and fossil fuels depleting nature.1,2 Since vegetable oils have similar properties and are a renewable source, they are considered a promising diesel oil alternate.3 Among a few alternative fuels, surplus quantities of straight vegetable oils (SVOs) are accessible copiously in several nations.4 SVOs derived from plant seeds/harvests can be utilized significantly in diesel engines.5 Vegetable oils and alcohols derived from biomass are renewable fuels for diesel engines.6 Studies on vegetable oils as fuel in diesel engines have been conducted by many researchers.7 Diesel engines fuelled with vegetable oils result in almost the same power output and slightly lower thermal efficiency.8,9 The main obstructions for commercialization of biodiesel are an elevated cost for its production from nonedible or edible oils.10 The cost of biodiesel production accounts for 70% of its feedstock and also the rapidly increasing vegetable oil cost in the market.11,12 Fuel with blends of 20−30% vegetable oil with diesel gave better performance over other blend ratios, and this is confirmed by many researchers.13 Pandian et al.14 concluded that a nozzle tip protrusion of 2.5 mm, an injection pressure of 225 bar, and 30° before the top dead center (bTDC) produce lower brake specific fuel consumption (BSFC), hydrocarbon (HC), smoke opacity and higher brake thermal efficiency (BTE) and oxides of nitrogen (NOx) emissions. The effect of change of CR on the emissions of the diesel engine was investigated by Sivaramakrishnan et al.,15 and the results demonstrate that either increase of IT or reducing CR values greatly reducing opacity and NOx emissions; there was also a small reduction in CO and HC emissions. The investigations were made by Raheman et al.,16 in diesel engines operated with different CR © 2017 American Chemical Society
and biodiesel as fuel. The results depicted that exhaust gas temperature and BTE increased and a decrease in BSFC was observed. Hirkude et al.17 investigated the influence of CR, IT, and IP in compression-ignition (CI) engines. The results conclude that CR of 17.99, IT of 27°bTDC, and IP of 250 bar were found to be optimum values for CI engines while fuelled with waste fried oil biodiesel blended with mineral diesel.18 The change in IT and CR leads to enhancement in engine performance and reduced emissions. Diethyl ether (DEE) is an oxygenated additive that can be added to diesel/biodiesel/ vegetable oil fuels to stifle the NOx emission, and it is an excellent ignition enhancer as it has a low autoignition temperature.19,20 The extensive use of factorial designs with several input parameters potentially affects the quality behavior or performance of the system.21 Several physical and chemical processes are used for factorial design optimization.22 For optimization of engine behaviors, linear or nonlinear optimization tools such as genetic algorithm, response surface methodology (RSM), artificial neural network, the Taguchi method, and factorial design are employed.23 From the literature survey CR, IP, IT, and fuel influence the engine behavior. However, no literature study was done for bael oil (straight vegetable oil) blends in the IC engine for their better working condition (CR, IT, and IP) at trade-off engine loads. In this paper, the RSM based desirability approach has been employed for optimization of CR, IP, and IT for the observed response of BTE, BSFC, HC, NOx, CO, and smoke opacity. Minitab’17 software has been used to carry out the optimization analysis by dimensionless desirability reReceived: May 29, 2017 Revised: July 13, 2017 Published: August 25, 2017 11362
DOI: 10.1021/acs.energyfuels.7b01515 Energy Fuels 2017, 31, 11362−11376
Article
Energy & Fuels
of fuel additive.12 The bael oil has the acidic property that may lead to corrosion in the fuel line systems when their blends have higher concentration or the engine is purely powered by vegetable oil.31 The ignition performance of fuel is of crucial importance for CI engines as insufficient ignition quality can lead to higher emissions.5,11 The cetane number (CN) indicates ignition performance and is determined with the following formulas according to the volumetric concentration of each constituent:19
sponse.24,27 Depending on the problem in nature the output response has been set either maximum, minimum, in the range, target, and/or equal.26
2. MATERIALS AND METHODS The aegle marmoles (bael) tree is cultivated all over India, predominantly within sanctuary gardens due to its position as a sanctified tree; this is likewise true in northern Malaya and Srilanka. The properties of bael oils are as follows: iodine value, 94 mg iodine/g (it belongs to the family of monounsaturated vegetable oils); higher heating value (HHV), 40040 kJ/kg; saponification value, 0.205g/ KOH; lower heating value (LHV), 36300 kJ/kg; acid value, 8.02 mg KOH/g.27,28 It copes among a wide variety of soil conditions (pH range 5−10) and is tolerant water sorting and has exceptionally wide temperature flexibility (0 to 50 °C).3 The bael oil has 12.5% of 12 hydroxyoctadec-cis-enolic acids along with normal fatty acids. The DEE of 99% purity was purchased from a neighborhood business enterprise agent. The microemulsion is an undulate realistically, not as much of time-consuming technique which lessens the viscosity technique compared in the direction of transesterification, and possibly applies to uniformly mix the diesel with vegetable oil and alcohols/solvents.12,17 With the aid of a mechanical expeller appliance, the bael oil was extracted from aegle marmoles (Bael) seed. Bael oil became mixed with diesel and DEE fuel in a blender device and stirred in an electromagnetic agitator at 500 rpm for 20 min and left for 30 min to accomplish thermal equilibrium with ambient temperature before the experimental trial.3 2.1. Fuel properties. The flash and fire point, density, and kinematic viscosity are determined for different fuel blends according to ASTM D-93, ASTM D-1298, and ASTM D-445, respectively. The flash and fire points are determined with a closed cup fire point apparatus.3 The kinematic viscosity is measured by the redwood viscometer. The properties of diesel, bael oil, and DEE and its blends are given in Table 1 and Table 2. Three test fuels taken for the
Cetane number CNH =
property
Diesel
Bael oil
DEE
C16H34 830 2.7 200−400 50 −20 180−330 0.35 42800 14.9
C18H36O2 896 24.3 >370 51.7 −5 298 8.02 36300 12.4
C2H5OC2H5 713 0.23 160 >124 −110 35 1.39 33900 11.1
Calorific value CVH =
s. no
blend
1 2 3
F0 F1 F2
6.81 7.99 10.11
density (kg/m3) at 32 °C
cetane number
acid value (mg KOH/g)
calorific value (kJ/kg)
831 849 876
50 53.9 57.8
0.35 1.53 2.70
41218 40476 39734
∑ CVX i i
(2)
i
where CNH and CVH are the equivalent cetane number and calorific value of the blended fuel, while CNi is the cetane number of each constituent, Xi is the percentage of constituents and CVi is the calorific value of each constituent. 2.2. Test engine and facilities. The tests were conducted in a single cylinder direct injection variable compression ratio (VCR) test engine. The engine used for the test was a Kirloskar VCR, and specifications are shown in Table 3. The engine was (Figure 1) connected to an eddy current dynamometer, and suitable arrangements were made to acquire all the controlling parameters. HC, NOx, and CO emissions were measured with the aid of an exhaust gas analyzer AVL DI 444 model (Table 4). Smoke opacity is measured with the aid of a smoke meter, model AVL437C (Table 5). The various temperatures are measured using a K-type thermocouple fitted on a respective position. The piezoelectric transducer is located in the cylinder head with the water-cooling system, and it is used to measure the cylinder gas pressure. Piezoelectric pressure transducers are appropriate for measuring dynamic and quasi-static, highly dynamic pressure curves or pulsations.3 The signals from the crank angle encoder and charge amplifier are acquired with a data acquisition system (DAQ). The apparatus is ideal for test, control, and design applications together with transportable data logging, field monitoring, and in-vehicle data acquisition.21 The combustion analyses data are usually represented on the basis of degree (deg) of crank angle. The crank angle encoder provides an angle and TDC correlation, essential for the calculation of any crank angle based consequence associated with a combustion cycle. The water flow was adjusted to 250 and 70 L per hour for engine cooling and the calorimeter, respectively, according to the information given by the engine manufacturer.3 2.3. Test procedure. All the experiments were performed under 80% engine load (trade off operating condition) and 25 rps.3,30 The standard IT of the test engine is 21°bTDC. The numbers of shims are used to adjust the static injection timing by mounting it under the seat flange of the fuel pump. For changing the injection timing, the TDC position is marked on the flywheel. The repeated operations have to be done to attain the exact IT by slowly rotating and stopping the flywheel rapidly. The shim is added and removed to vary the original IT to attain the required IT. The thickness of the shim is 0.4 mm which corresponds to a 2°CA advance of the IT.21 The shims are inserted and removed under the nozzle spring to vary the IP.14 The pressure gauge connected to the fuel injection line, which measures pressure ranges from 100 to 400 bar. In the beginning, the test engine was operated for 20 min without any load and after stabilization; the experiments were conducted at steady environment air intake temperature.17 2.4. Error analysis. Uncertainties and errors in the experimental analysis may occur due to instruments selection, calibration, working condition, observation, environment and method of the tests.3 The instruments for measurements are chosen with a view to keeping the experimental uncertainties as minimum as possible. The uncertainties has been calculated by eq 152;
Table 2. Properties of Blended Fuels kinematic viscosity (cS)
(1)
i
Table 1. Properties of Diesel, Bael Oil, and DEE Chemical structure Density (kg/m3) Viscosity (cS) Auto ignition point (°C) Cetane number (CN) Pour point (°C) Fire point (°C) Acid value (mg KOH/g) Lower heating value (kJ/kg) Chemically correct A/F ratio
∑ CNX i i
examination are neat diesel (F0), and two blended fuels are blends with diesel, bael oil, and diethyl ether (DEE) in the percentage of 80:15:5 (F1) and 60:30:10 (F2). The literature reports that the CN value of DEE is 124. Such a higher CN value of DEE indicates that it was determined using a constant volume bomb.43,44 The combination of above ternary fuels has been prepared based on their better performance from the literature study.3,20 The properties of the ternary blends have been calculated by Kay’s mixing rule.12 The increasing percentage of vegetable oil in the blends creates few operating problems, and it has been reduced by increasing the fraction
Δq = q 11363
⎡ Δx ⎤2 ⎡ Δz ⎤2 ⎡ Δu ⎤2 ⎡ Δw ⎤2 + ... + ⎢ ⎥ + ⎢ ⎥ + ... + ⎢ ⎣⎢ x ⎦⎥ ⎣ z ⎦ ⎣ u ⎦ ⎣ w ⎦⎥
(1)
DOI: 10.1021/acs.energyfuels.7b01515 Energy Fuels 2017, 31, 11362−11376
Article
Energy & Fuels Table 3. Technical Specifications of the Test Engine parameter
value
Type No. of cylinders/No. of strokes Rated power Bore (mm)/Stroke(mm) Type of ignition Compression ratio Injection pressure (standard) Injection timing (standard) Speed Diameter/no. of nozzle hole Dynamometer Cylinder pressure sensor Crank angle encoder Data acquisition system Fuel flow measurement Load cell Air flow measurement
KIRLOSKAR, VCR multi fuel, vertical, water cooled, direct injection, naturally aspirated engine 01/04 3.5 kW/diesel mode, 4.5 kW/petrol mode 87.5/110 CI 12 to 18 210 bar 21°bTDC 1500 Rev/min 0.3 mm/3 Eddy current dynamometer; Water cooled; Model, TMEC10; RPM 1500−6000; Make, Technomech Pvt., Ltd. Piezo electric sensor; Model, M111A22; Resolution, 0.1 psi; Sensitivity, 1 mV/psi. Make, Kistler; Model, 2614C11; Speed range, 0 to 12000 rpm; Crank angle signal, 720 × 0.5 degree. USB-6210; 16AI; 4DI; 4DO USB, multifunction I/O devive; Make, National instruments. Differential pressure transmitter; Make, Broiltech; Model, FCM. Make, Sensortronics; Model, 60001. Make, Wika; Model, SL1.
incomplete combustion due to insufficient atomization, and too much IP leads to fuel droplets wall quench and charge dilution problems. The retardation of IT positively affects the BSFC, and HC and CO emissions.34 The advancing of IT (more than 25°bTDC) leads to progressive combustion, lower NOx emissions, and opacity but reduces the maximum cylinder gas pressure and BTE.18,30 Among these factors, the fuel blend is treated as a nominal categoric factor which has no intrinsic ordering to the category. The other three factors, compression ratio, injection pressure, and injection timing are of numeric type among distinct values.21 In earlier studies, the CR has been varied to increase the efficiency and to optimize NOx emissions in a diesel engine, when fueled with vegetable oil−diesel blends. If using the higher CR (about CR18 and above), it could cause higher NOx, HC, and smoke opacity due to wall quench of the fuel particles.29 The increasing IP leads to better atomization of fuel particles, better air−fuel mixing, increasing the combustion efficiency, and reducing the ignition delay.17 For the injection timing, a standard and advanced injecting timing were chosen. The advancing of IT increases the NOx emissions with a reduction in CO, HC, and opacity, and further advancing of IT leads to an inefficient combustion process.14 2.5.1. Factorial design. Design of experiments is a nonlinear method for multivariable problems as to explore the combined effect of input response, and it is the most effective and economical technique. Factorial design is employed in the research work by modeling and analysis of response parameters in order to obtain the characteristics of the engine.21 This study adopts a four factor-three level factorial design to investigate the combined effect of CR, IP, and IT. The design matrix generated by minitab’17 factorial design contains 81 test experiments as shown in Table 8. The experiments were conducted as per run order, and the responses were changed as per response column. The coefficients and equations are generated by multiple regression analysis that can be used to predict the output response.25,30 2.5.2. Response surface methodology (RSM). RSM is a compilation of statistical and mathematical techniques that are helpful
Figure 1. Schematic diagram of experimental setup. The uncertainty examination was essential to confirm the precision of the experiments. The uncertainties of a few calculated and measured parameters are given in Table 6. Based on the above value, the calculated engine performance is believed to be accurate within ±3%.3 2.5. Experimental design. Table 7 shows the factors investigated in this study with their chosen level, such as compression ratio, injection pressure, injection timing, and fuel blends. The compression ratio (CR) is varied as 16:1, 17:1, and 18:1; the fuel injection pressure (IP) is varied as 210, 230, and 250 bar; and the fuel injection timing (IT) is varied in the range of 21°, 23°, and 25°bTDC, and the injector with three nozzle holes was located near the combustion chamber.26,30 The lower CR reduces the BTE and increases the HC and CO emissions, and higher CR could cause higher NOx.40 At higher CR, the fuel particles hit the combustion chamber walls due to lower clearance volume and contribute to HC emissions.29 Lower IP can cause
Table 4. Technical Specifications of Gas Analyzer AVL DI444 measuring range
resolution
accuracy
Carbon monoxide (CO) Hydrocarbon (HC)
measured quantity
0−10% vol 0−20000 ppm vol
HighiHi ⎛ Y − Low ⎞ wti di = ⎜ TH − Lowi ⎟ , when Ti > Yi > HighiHi ⎝ i i i⎠ Similar definitions of di were observed for other objectives such as “maximum”, “equal to”, and “in range”.14 Here Y is the value of the response, i indicates the response, high and low represent the higher and lower limits of the response, respectively, and T indicates the target value of the response. The weights wti are used to give more emphasis to the lower/upper bounds.17 Weight varies over the range 0.1 < wti < 10; a weight greater than 1 gives more emphasis to the objective, while weights less than 1 give less emphasis.21 The individual desirability of each response is then combined using the geometric mean to obtain an overall desirability objective function D that varies from 0 to 1, which is calculated by eq 3,
Table 6. Uncertainties of Some Measured and Calculated Parameters s. no
parameter
percentage uncertainties
1 2 3 4 5 6 7 8 9 10 11 12
NOx CO Kinematic viscosity CO2 HC Smoke opacity BSEC BTE Stopwatch Speed indicator Graduated burette scale Load cell (strain gauge)
±0.1 ±0.01 ±1.3 ±0.3 ±0.1 ±0.5 ±1.5 ±1 0.01 s 5 rpm 0.001 m 0.1 kg
Table 7. Factors Considered with Their Chosen Levels levels factors
factor type
1
2
3
fuel used CR IP (bar) IT (°bTDC)
categoric numeric numeric numeric
(F0) 16 210 21
(F1) 17 230 23
(F2) 18 250 25
n
D = (∏ diri)1/ ∑ ri i=1
In the desirability objective function, each response is assigned an importance (r) that is relative to the other response. Importance varies from the least important value of 1 to the most important value of 3.21 The high value of D indicates a desirable and optimum solution. The optimum value of factors is then determined from the values of individual desired functions that maximizes D.14 The various solutions obtained using the desirability approach is then validated by conducting confirmatory experimental trails based on the optimization criterion.17
for modeling and analysis of problems during which the objective is to optimize a response (output response) that is influenced by several factors (input factors).23 In this work, the RSM is employed to model and predict the response. The experimental data (Table 8) was analyzed via response regression, and second order polynomial models were developed using eq 2,25 3
Y = β0 +
3
n
∑ βi X i + ∑ βii X i2 + ∑ βij X iX j + ε i=1
i−1
i
