Performance and Emission Analysis of Watermelon Seed Oil Methyl Ester and n-Butanol Blends Fueled Diesel Engine

source to the standard diesel due to similar characterization. The n-butanol additive was added in small proportions as an oxygenated fuel for reducing emissions, improving thermal efficiency, and accelerating the combustion process. N-Butanol is blended with watermelon methyl ester in the form of emulsions in two different proportions (5% and 10% volume basis). Experiments were conducted with three different emulsions fuels, WME20, W20Bu5D75, and W20Bu10D70, and compared vis-`a-vis standard diesel. Investigations revealed that the addition of n-butanol as an enhancer with WME20 improved characteristics owing to its inherent nature of oxygen content. The blending of WME with n-butanol improves brake thermal efficiency when compared to WME20 and slightly matches with standard diesel. The max BTE was recorded 32.79% for WME20Bu10D70 at the crest load. The peak BSFC was 0.26 kg/kWh for W20Bu10D70 at the crest load. The emissions such as CO, smoke opacity, and HC were significantly reduced, vis-`a-vis diesel, and the oxides of nitrogen (NO X ) and carbon dioxide (CO 2 ) were decreased, relative to WME20. The maximum EGT was 354.98 ° C for W20Bu10D70 at the crest load. The peak CO emissions were 0.078% for W20Bu5D75 at the crest load. The blending of n-butanol with WME20 reduces the ignition delay while the combustion duration increases with an increase at full load conditions. The emulsion fuels tested in an unmodified engine did no negative impact on the engine stability.


Introduction
Relative to any temporal phase in human history, the twenty-rst century is forecasted to register the highest energy intensity and resource consumption, by virtue of increased demand driven by hitherto unprecedented prosperity. Over the course of the succeeding decades, a transition of substantial segments of the population, especially in Asia and Africa, from poverty to the middle class, with the concomitant change in consumption patterns, will exponentially exacerbate the contemporaneous energy crisis, unless structural changes are undertaken in the energy ecosystem. e utmost salience, vis-à-vis structural changes, is the substitution of fossil fuels, which are inimical to the environment, with sustainable alternatives [1,2]. Prudential policy-making for India, which is portended to triple its energy demand by 2040, according to its Petroleum Ministry, must focus on the vital issue of replacing fossil fuels with renewables.
e Indian government's commitment under its Intended Nationally Determined Contribution (INDC) target of generating 175 GW of renewable energy by the year 2022 is a positive step in this direction, but further substantive efforts are necessary, especially in a nation where previous brushes with crises of sovereignty, such as the Balance of Payments crisis of 1990, were a direct consequence of petrol addiction. In this scenario, biodiesels have emerged as a promising prospect to achieve India's renewable energy targets [3,4]. Multitudinous factors serve as strong arguments for renewed attention to biodiesel research, particularly in the context of its potential to substitute petroleum-based fuels. e considerable engine modification and retrofitting of vehicles constitute two of the foremost reasons for dissuasion, with reference to gravitation away from conventional petrol/diesel-based vehicles. Biodiesels obviate the need for engine modification, thus resolving a major impediment to switchover from dirty fuels, that is, upfront investment associated with migration. Additionally, the superior emission characteristics of biodiesels do not come at the cost of engine performance. Prior research with various biodiesel stocks has established the comparability of biodiesels and petroleum-based fuels, in terms of engine performance [5,6]. Furthermore, biodiesel research is mandated by their nontoxicity, biodegradability, and ease of creating symbiotic ecosystems of agricultural production and feedstock generation. e higher BTE for butanol-diesel blends (up to 40% v/v) related to reference diesel, and BTE improved with increasing butanol content [7,8].
e oxygen content of n-butanol improves combustion during the diffusion combustion phase [9,10], whereas the lower CN of the blends lengthens the ignition delay, burning a larger amount of the fuel during the premixed combustion phase [9,11]. Similar conclusions were obtained by Campos. Besides, the laminar burning velocities of butanol are higher than those of fossil diesel and contribute to higher BTE values [9,12]. Watermelon seeds are nowadays used for oil extraction. e seeds are dried, and oil is extracted by pressing them. is practice is common in West Africa, and the watermelon seed oil is popularly known as Ootanga oil or Kalahari oil. Oil is used as frying oil in various African nations. Watermelon seed contains about 40% of oil with a high amount of unsaturated fatty acids (about 80%) predominantly linoleic acid or omega 6 fatty acid (about 45-73%). Oleic, palmitic, and stearic acid are also present in small quantities. Various researches report the positive effect of watermelon seed oil on the skin. e oil is light and consists of humectants and moisturizing properties. It is easily absorbed by the skin and helps in restoring the elasticity of the skin. Due to these attributes, this oil can be used in the cosmetic industry for the production of skincare products. e watermelon seed oil can also be used as an anti-inflammatory agent [13][14][15][16][17]. Methyl ester of cotton seed oil was blended with diesel and enhancer (iso-butanol) for improving the performance and reducing the emissions. CSOME10B5D95, CSOME10B10D80, CSOME20B5D75, and CSOME20B10D70 were tested along with CSOME10 and CSOME20, which further compared with standard diesel. CSOME20B5D75 and CSOME20B10D70 were tested along with CSOME10 and CSOME20, which were further compared with standard diesel. e BTE of all the blends with iso-butanol as additive was observed to be a better performer than biodiesel blends. e blend CSOME10B10D80 was found to be the higher performer with a 3% improvement in performance. e fuel consumption for the rated power output was lower for the CSOME20B10D80 blend, and more fuel was consumed for all the blends mixed with iso-butanol. EGT for all the blends was observed to be lower due to its lower calorific value. During combustion, peak pressure was recorded for CSOME20B10D80. HC emissions reach maximum when iso-butanol content was increased. CSO-ME20B5D80 blend was recorded with a higher value than all other blends. CSOME20B10D80 was observed to be reduced when compared with standard diesel and other blends.
e addition of the iso-butanol reduces the carbon mon oxide emission. CO 2 emission was found to be decreased with an increase in the blending of methyl ester and iso-butanol. CSOME20B10D80 seems to be emitting low intensity of CO 2. Joy et al. studied emission characteristics of C.I engine using esterified palm oil and octanol blends. e fuels (POME100, O10POME90, O20POME80, O30POME70, and diesel) tested in the diesel engine show reduction in emission of exhaust gases. HC emission of all the test fuels of methyl ester was observed to be reduced when compared with standard diesel. Oxides of nitrogen for all the blends recorded lower values relative to pure methyl ester of palm oil whereas every fuel was comparably higher than diesel. CO and smoke opacity emissions were found to be lower for methyl ester and octanol blends. Based on the past decades, limited research work has been carried out on the watermelon seed oil methyl ester compared with diesel and butanol. In the current research work, investigations were conducted in a diesel engine without making any modifications for evaluating the performance and emission characteristics of the best blended fuel of watermelon methyl ester (WME20) by mixing with n-butanol additive in various proportions (5% and 10%) and compared with standard diesel with a same rated power of 5.2 KW at a constant speed of 1500 rpm. e additive (n-butanol) was mixed with a methyl ester-diesel blend for improving performance and reducing emission concentrations. e fuels tested in the diesel engine are WME20Bu5D75 and WME20Bu10D70 along with blend WME20. is work highlights the significant potential of watermelon seed oil for use as a bio-diesel blend.
is could have the dual benefit of helping increase the value of by-products of the watermelon industry and decreasing the amount of agricultural waste from the watermelon consumption.

Watermelon Seed Oil.
e seeds on a large scale from watermelon fruits were gathered and dried under the influence of sunlight for over a week for removing traces of moisture content. e dried seeds were finally allowed into the mechanical expeller for the extraction of oil. A small proportion of water, organic matter, and impurities were removed by adding 5% hexane to the raw oil and subjected to stirring for around 30 min by supplying heat at 90°C. e unwanted proportion of impurities and gum particles will reach the bottom surface of the oil and can be separated. e purified raw oil was tested for physical and chemical properties that were represented in Table 1.

Fuel Preparation.
e measured watermelon oil of 3000 ml possessing an acid value of 1.13 is made to flow into the vessel of the biodiesel plant. e pictorial view of the biodiesel plant is shown in Figure 1. e oil is allowed into the vessel to get heated above 100°C for around 30 min for removing moisture content and left undisturbed for reducing temperature [18][19][20]. e calculated quantity of catalyst KOH is dissolved in the methanol and then added to the vessel containing watermelon oil. e chemical mixture is subjected to proper stirring over the period of 90 minutes for the reaction to happen. KOH dissolved in the yield of methanol increases with an increase in watermelon oil ratio up to 9 : 1 due to an increase in driving force for methanol adsorption. Maximum yield was found at 96.8% with 9 : 1 methanol to watermelon oil molar ratio. Beyond the molar ratio of 9 : 1, the excess amount of methanol had no substantial change in watermelon oil yield. Finally, the completed reaction is allowed into a funnel for cooling and separation of layers as top strata (methyl ester) and bottom strata (glycerol). e top strata are parted away from the lower strata. e methyl ester was held for water washing to remove entrained methanol, small traces of KOH, and glycerol.

N-Butanol.
N-butanol, a colorless renewable fuel procured from propylene, is having a better solvency behavior and higher calorific value. e straight-chain isomer of n-butanol is having a molecular formula of C 4 H 9 OH [21,22]. In recent times, n-butanol is considered as a partial substitute for diesel blends due to the presence of more oxygen content, higher cetane number, and higher miscibility than ethanol with lower corrosion. Characteristics of n-butanol are illustrated in Table 2. is investigation employs n-butanol having a purity level of 99%.

Engine Setup.
e photographic view of the engine setup is shown in Figures 2 and 3, which illustrate the schematic diagram of the CI engine. e engine is initially made to run with standard diesel as a fuel for about half an hour to attain steady conditions. After warming up, the engine is operated with standard diesel and then switched over to watermelondiesel blends. e time taken is calculated using a stopwatch for 10 cc of fuel consumption presented in a burette. e fuel combinations present in the fuel tank; fuel line and filter fuel pump are completely removed before switching over to start the experiment with new fuel combinations. e engine test was conducted for investigating the characteristics using standard diesel for comparison. e specification is listed in Table 3.

Uncertainty Analysis.
e variation between the predefined result and actual value could calibrate the uncertainty. e analysis of uncertainties and errors in the test conducted during experimentations may probably arrive from reading, working conditions, observations, instruments selection, and changes in ambient conditions [23,24].

Brake ermal Efficiency (BTE)
. BTE is defined as the ratio of mechanical work produced to the heat energy obtained when fuel is injected. Figure 4 depicts the variation of BTE w.r.t load for WME20, W20Bu5D75, and W20Bu10D70 along with standard diesel at all conditions of load. BTE of W20Bu5D75 and W20Bu10D70 blends was improved when compared with WME20 whereas the efficiencies of all the blends are lower than standard diesel. e addition of the nbutanol additive with the WME20 diesel reduces the viscosity and calorific value of the fuel [24,25]. e peak BTE was 32.79% for WME20Bu10D70, 34.14% for standard diesel, 32.24% for WME20Bu5D75, and 31.81% for WME20 at the crest load.

Brake Specific Fuel
Consumption. BSFC is considered as the ratio of quantity (mass stream rate) of the fuel to the unit-created brake power. Figure 5 depicts the BSFC w.r.t load for W20Bu5D75, WME20, W20Bu10D70, and standard diesel.
e BSFC of W20Bu5D75, WME20, and W20Bu10D70 recorded slightly higher values vis-à-vis standard diesel. e addition of the additive butanol with the  Figure 6 depicts the EGT w.r.t load for W20Bu5D75, WME20, W20Bu10D70, and standard diesel at full load. EGT of WME20, W20Bu5D75, W20Bu10D70registered higher values visa-vis standard diesel. e lower IDP, efficient combustion, and lower calorific value of the standard diesel could be the prevailing reasons for indicating a trend for the samples of watermelon [28,29]. e maximum EGT was 352.63°C for W20Bu5D75, 347°C for standard diesel, 351.19°C for WME20, and 354.98°C for W20Bu10D70 at the crest load. Figure 7 depicts the CO w.r.t load for WME20, W20Bu5D75, W20Bu10D70, and standard diesel at full load. CO emissions of WME20, W20Bu5D75, and W20Bu10D70 registered lower values relative to standard diesel. CO recorded lower values for WME20, W20Bu5D75, and W20Bu10D70 blends vis-à-vis standard diesel at all load conditions. e surplus availability of oxygen in WME and blends indorses lower emissions of CO [30,31]. e peak CO emissions were 0.078% for W20Bu5D75, 0.088% for diesel, 0.083% for WME20, and 0.075% for W20Bu10D70 at the crest load. Figure 8 depicts the HC w.r.t load for W20Bu5D75, WME20, W20Bu10D70, and standard diesel at full load. HC emissions of WME20, W20Bu5D75, and W20Bu10D70 recorded lower values relative to standard diesel. e lower IDP, efficient combustion, and lower calorific value of the standard diesel could be the prevailing reasons for indicating the trend for the samples of watermelon with additive n-butanol indorses lower HC emission [32,33]. e peak HC emissions were 45 ppm for W20Bu5D75, 49 ppm for standard diesel, 48 ppm for WME20, and 42 ppm for W20Bu10D70 at the crest load. Figure 9 depicts the CO 2 w.r.t load for W20Bu5D75, WME20, and W20Bu10D70 along with standard diesel at full load. CO 2 emissions of WME20, W20Bu5D75, and W20Bu10D70 recorded higher vis-à-vis standard diesel. e lower IDP, efficient     Figure 10 depicts the NO X w.r.t load for W20Bu5D75, WME20, and W20Bu10D70 along with standard diesel at full load condition. NO X emissions of W20Bu5D75 and W20Bu10D70 registered lower relative to standard diesel. Generally, methyl esters exhibit a rich amount of NO x relative to standard diesel owing to the enriched concentration of oxygen [37,38]. e peak NO X emissions were 2139 ppm for W20Bu5D75, 2140 ppm for diesel, 2183 ppm for WME20, and 2112 ppm for W20Bu10D70 at the crest load. Figure 11 depicts the smoke opacity w.r.t load for W20Bu5D75, WME20, and W20Bu10D70 along with standard diesel at full load. Smoke emissions of WME20, W20Bu5D75, and W20Bu10D70 recorded lower vis-à-vis standard diesel. e effective atomization for the droplets and better vaporization of methyl esters of watermelon along with additive n-butanol could be the reason for low recorded values vis-à-vis standard diesel. In addition, the rich content of oxygen in methyl esters of watermelon along with additive n-butanol indorses lower smoke emission [39,40]. e peak smoke emissions were 48.9% for W20Bu5D75, 63.4% for standard diesel, 50.5% for WME20, and 43.9% for W20Bu10D70 at the crest load.

In-Cylinder Pressure (ICP)
ICP predicts the cycle of combustion in the diesel engine. e variation of ICP for WME20, WME20Bu5D75, and WME20Bu10D70 along with standard diesel at full load with injection timing (23BTDC) is depicted in Figure 12. e peak cylinder pressure for WME20, W20Bu5D75, and

Mathematical Problems in Engineering
W20Bu10D70 along with standard diesel was recorded as 71.56, 74.02, 72.71, 72.52 bar, respectively. Standard diesel had a higher in-cylinder pressure amid stall tested fuels owing to its longer ignition delay and greater calorific value as compared to all other tested fuels. e addition of enhancers in 5% and 10% increased the ICP but slightly recorded lower visa standard diesel [41,42]. e combustion happened burning phase of diffusion for WME20, W20Bu5D75, and W20Bu10D70 owing to the innate contribution of oxygen available in both biodiesels and n-butanol vis-à-vis standard diesel. e significant causes for the high in-cylinder temperature with high butanol were better fuel atomization and better combustion of fuel.

Heat Release Rate (HRR)
e heat release profiles may provide numeric info about combustion development. HRR brings up the fuel release rate of chemical energy through combustion. e HRR basis on the pressure values of the cylinder [41][42][43][44]. Figure 13 depicts the HRR against crank angle diagram at full load condition for WME20, standard diesel, WME20Bu5D75, and WME20Bu10D70. e HRR for standard diesel registered a higher value among blends WME20, standard diesel, W20Bu5D75, and W20Bu10D70. is is due to a longer IDP and greater calorific value. W20Bu5D75 and W20Bu10D70 generate higher HRR than WME20. e addition of butanol at 5% and 10% volume improves the HRR relative to WME20. is is due to improved mixing and evaporation with reduced viscosity at increased inlet fuel temperature [23,28]. Due to duction in viscosity, the fuel was atomized into finer droplets which might have enhanced the combustion process resulting in higher peak HRR [45][46][47][48].

Numerical Validation
Model-based experimental design techniques are extremely reliable for rapid improvement and better process models. Also, numerical analysis helps in estimating the results and times and reducing experimental costs. Numerical simulations were created with the developed numerical model. It predicts the possible problems that may arise in the combustion of diesel engines. e numerical values are validated with the experimental results such as brake thermal efficiency. Figure 14(a) illustrates the comparison of p-V diagrams for diesel and biodiesel fuels. Figure 14(b) demonstrates the comparison of the charge change process for diesel and biodiesel fuels. e numerical method demonstrates the validity of this approach. e method that predicts the best results is identified for in-cylinder pressure and mass fraction burned. e experimental and numerical results for cylinder pressure and mass fraction burned are close to each other. It could be said that the difference is probably due to the difference in pumping losses, friction losses, and heat losses. Experimental and numerical results confirmed that the numerical model is consistent [49,50].

Conclusion
(i) e BTE for diesel is 34.22%, WME20 is 31.81%, W20Bu5D75 is 32.24%, and W20Bu10D70 is 32.89%. BTE was improved by adding 5% and 10% n-butanol when compared with WME20, and on the whole, the results obtained were recorded at lesser values relative to standard diesel.  Mathematical Problems in Engineering (ii) NO X emission for the blends W20Bu5D75 and W20Bu10D70 was greatly reduced when compared to standard diesel. e addition of 5% and 10% n-butanol in the blend of WME20 decreased it by 0.1% and 1.3%, respectively.
(iii) In this study, NO emissions show the same trend as NOX emissions and represent 93%, 95%, and 93% of the total NOX emissions observed. (iv) Smoke opacity, CO, and HC emissions are predominantly decreased when WME20 was blended with diesel along with n-butanol. (v) CO 2 emission for the blends W20Bu5D75 and W20Bu10D70 was 3.6% and 9.4% lower than the standard diesel. (vi) Exhaust gas temperature rises with an increase in the percentage blending of diesel in watermelon methyl ester. (vii) e pattern for in-cylinder pressure (bar) registered rise for the blends of watermelon along with additive n-butanol (bar). In-cylinder pressure (ICP) for standard diesel is 72.52 bar, and in-cylinder pressure for W20Bu5D75, W20Bu10D70, and WME20 is 74.02, 72.71, and 71.56 bar. (viii) e heat release rate (kJ/m 3 ) with respect to the crank angle (degree) for standard diesel is higher and followed by W20Bu10D70.
e blending of n-butanol as an enhancer in WME20 improves the performance and reduces the emissions. Normally, when biodiesels are used as fuels in diesel engine, it releases more NO X and CO 2 emissions. ese emissions were reduced significantly by adding n-butanol to the methyl esterdiesel blends. e blending of n-butanol with WME20 reduces the ignition delay while the combustion duration increases with an increase at full load conditions.

Data Availability
e data used to support the findings of this study are included within the article.

Conflicts of Interest
e authors declare that there are no conflicts of interest regarding the publication of this article.