Biodiesel Production Using Modiﬁed Direct Transesteriﬁcation by Sequential Use of Acid-Base Catalysis and Performance Evaluation of Diesel Engine Using Various Blends

: Biodiesel is a seemingly suitable alternative substitute for conventional fossil fuels to run a diesel engine. In the ﬁrst part of the study, the production of biodiesel by modiﬁed direct transesteriﬁcation (MDT) is reported. An enhancement in the biodiesel yield with a considerable reduction in reaction time with the MDT method was observed. The required duration for diesel and biodiesel blending was minimized including glycerol separation time from biodiesel in the MDT method. The development in the automotive sector mainly focuses on the design of an efﬁcient, economical, and low emission greenhouse gas diesel engine. In the current experimental work Ceiba pentandra / Nigella sativa and diesel blends (CPB10 and NSB10) were used to run the diesel engine. A variety of approaches were implemented to improve the engine performance for these combinations of fuels. The fuel injector opening pressure (IOP) was set at 240 bar, the torriodal re-entrant combustion chamber (TRCC) having a six-hole injector with a 0.2 mm oriﬁce diameter each, provided better brake thermal efﬁciency (BTE) with lower emissions compared with the hemispherical combustion chamber (HCC) and trapezoidal combustion chamber (TCC) for both CPB10 and NSB10. CPB10 showed better performance compared with NSB10. A maximum BTE of 29.1% and 28.6% were achieved with CPB10 and NSB10, respectively, at all optimized conditions. Diesel engine operation with CPB10 and NSB10 at 23 ◦ bTDC fuel injection timing, and 240 bar IOP with TRCC can yield better results, close to a diesel run engine at 23 ◦ bTDC fuel injection timing, and 205 bar IOP with HCC.


Introduction
In the perspective of green emissions, biodiesel was regarded as a supplement to diesel as fuel [1,2]. Being a renewable fuel with low emission characteristics, biodiesel production has spiked. Biodiesel is produced by the transesterification of triglycerides with methanol using a catalyst [3]. There are rigorous technological proliferations to make

Materials and Methods
The Ceiba pentandra (Kapok) and Nigella sativa (black cumin) crude oils were purchased from Java, Indonesia, and Bangladesh, respectively. The other chemical reactants such as boron trifluoride (BF3), methanol, sodium methoxide (0.1 N), spectroscopic grade petroleum ether 60-80 • C, H 2 SO 4 , KOH, anhydrous sodium sulphate (Na 2 SO 4 ), etc. were locally bought at Kuala Lumpur, Malaysia. The background of both feedstocks was provided in our previous work [33].

Production of Biodiesel Using Direct Transesterification (DT)
The usual method of esterification-transesterification has acute drawbacks of delayed duration of reaction and reduced yield of biodiesel. Glycerine separation from biodiesel is another disadvantage associated with the esterification-transesterification method. These vital reasons motivated the devising of a direct transesterification, which involves the sequential use of acidic and basic catalysts. An intense detailing of which was discussed in our earlier research work [5].
The DT method had some disadvantages especially while using petroleum ether. The method described was not economical and was consuming more time while evaporation and condensation of petroleum ether occurred. It was decided to avoid usage of petroleum ether itself. After a reaction time of 120 min an upper methyl ester layer with fatty acids and a glycerol lower layer were produced in the reaction mixture. Next, distilled water (1 L) was used to wash the reaction mixture, without using petroleum ether. The biodiesel was separated from water. A total of 250 gms of sodium sulphate (Na 2 SO 4 ) was added to remove the moisture contents. The mixture was filtered. Finally, biodiesel was obtained. However, in this method the separation of biodiesel from water was difficult and biodiesel yield was not appreciable. There was wastage of biodiesel during separation. Hence, the method further improved with some modifications. The details of the modified method are explained in Section 2.2.

Modified Direct Transesterification (MDT)
In the modified direct transesterification method, instead of petroleum ether, direct diesel was mixed. By using the diesel in place of petroleum ether, usage of petroleum ether was avoided. Hence, the evaporation and condensation time of petroleum ether was eliminated. It was known from the DT method that the biodiesel yield was 92% for NSME and 93% for CPME. Knowing the yield of biodiesel in the reaction mixture, the quantity of biodiesel present in the mixture was determined. Now, a proportionate volume of diesel was added to the reaction mixture instead of petroleum ether to form the B10 biodiesel-diesel blend. The reaction mixture, which contains B10 biodiesel-diesel blend, was separated from the glycerol layer. A total of 100 gms of potassium carbonate (K 2 CO 3 ) was added to the biodiesel-diesel blend to minimize the formation of moisture contents. The cleaning and filtering processes remained the same as in case of DT method. It is important to note that the MDT method produces the required biodiesel-diesel blends directly by mixing diesel into the reaction mixture containing biodiesel. However, this was not the case with the DT method. The DT method required the biodiesel be separated first from the reaction mixture and then cleaned. Further, the required quantity of diesel was added to obtain the required biodiesel-diesel blends.
The encompassed MDT method substantially removes the problems of evaporation, condensation, biodiesel-diesel blending time and segregation time involved with the use of petroleum ether. The fuel properties of the B10 biodiesel-diesel obtained by DT and MDT exhibited no significant variation.

Experimental Procedure and Set Up Used
The engine testing was carried out for the biodiesel-diesel blend (10%) produced by the MDT method of Nigella sativa and Ceiba pentandra feedstocks. Nigella sativa is a new feedstock which deserves to be tested, on the engine to establish its authority as a potential biodiesel feedstock. The other oil considered for engine testing is Ceiba pentandra because there is not much work published on this oil with respect to its behavior in the engine due to variations in injection parameters. Four stroke single cylinder diesel engine specifications are specified in Table 1. Experiments for various parameters were conducted as shown in Figure 1. Smoke meter and exhaust gas analyzer were incorporated to measure exhaust emissions. Further performance and emission testing of the engine were carried out for the biodiesel-diesel blends of Ceiba pentandra and Nigella sativa. The biodiesel-diesel blends of CPB10 and NSB10 were obtained from the modified direct transesterification method. Owing to similar fuel properties in contrast with diesel, 10% blends of Ceiba pentandra and Nigella sativa with diesel were selected. The experiments were conducted at the rated speed of 1500 rpm. Measurements were noted at stable operating conditions of the engine and exhaust gas analyzer. The DELTA 1600 S exhaust gas analyzer shown in Figure 2 works on nondispersive infrared technology (NDIR). Exhaust emissions such as CO, HC as n-Hexane equivalent: C 6 H 14 , CO 2 were recorded by allowing an infrared light to pass through the sample cell up to the optical block. The sample cell temperatures were controlled so that a measurement compensation for the sample gas temperature and pressure variances was provided. Infrared rays penetrate through (four optical band pass), each filter for the target gases (one filter being the reference filter). Voltage proportional to light intensity were obtained through four pyroelectric detectors that collect light passing through these filters and then digital values were obtained with ADC. The microprocessor samples the ADC and thereby provides the required data that are HC in ppm and CO in % volume. Electrochemical (fuel cell) sensors provide an electrical response proportional to oxygen and NO X concentration. Sensors are self-powered, diffusion limited, metal air battery type and consist of an anode, electrolyte, and an air cathode. Smoke level was obtained with a Hartridge smoke meter [ Figure 3]. It consists of two dimensionally similar tubes which are optically identical. Clean air is drawn into the reference tube through a damper connected to an air blower. The other tube (smoke) is connected to a pipe where the smoke is to be measured. The inlet manifold consists of a temperature sensor and moisture trap besides a pressure-controlled outlet. Smoke level in the sample gas was compared with clean air by recording a reading through the clean air tube to set the zero. After this, the light and photoelectric cell were moved through the smoke tube. Both values were compared.
The engine was fueled with diesel, CPB10 and NSB10. Diesel was run with ideal injection timing and pressure of 23 • bTDC and 205 bar. The engine was operated with CPB10 and NSB10 at an IOP range varying 220-250 bar keeping a normal fuel injection timing of 23 • bTDC. The fuel injection pressure was set using the fuel injection tester provided in Figure 4.
At every crank angle the HRR was tabulated employing the first law analysis of mean pressure against the variation in crank angle acquired considering 100 cycles. An AD-converter was used to record the sensor signals, indicating the pressure and TDC position of the cylinder. Table 2 provides information about measurement accuracy and variations in the calculated parameters.       The engine was fueled with diesel, CPB10 and NSB10. Diesel was run with ideal injection timing and pressure of 23° bTDC and 205 bar. The engine was operated with CPB10 and NSB10 at an IOP range varying 220-250 bar keeping a normal fuel injection timing of 23° bTDC. The fuel injection pressure was set using the fuel injection tester provided in Figure 4. At every crank angle the HRR was tabulated employing the first law analysis of mean pressure against the variation in crank angle acquired considering 100 cycles. An ADconverter was used to record the sensor signals, indicating the pressure and TDC position of the cylinder. Table 2 provides information about measurement accuracy and variations in the calculated parameters.  The engine was fueled with diesel, CPB10 and NSB10. Diesel was run with ideal injection timing and pressure of 23° bTDC and 205 bar. The engine was operated with CPB10 and NSB10 at an IOP range varying 220-250 bar keeping a normal fuel injection timing of 23° bTDC. The fuel injection pressure was set using the fuel injection tester provided in Figure 4. At every crank angle the HRR was tabulated employing the first law analysis of mean pressure against the variation in crank angle acquired considering 100 cycles. An ADconverter was used to record the sensor signals, indicating the pressure and TDC position of the cylinder. Table 2 provides information about measurement accuracy and variations in the calculated parameters.

Results and Discussions
The MDT method was applied to two non-edible feedstocks of Nigella sativa and Ceiba pentandra. The method was used to obtain the B10 blend of both respective biodiesels. Table  3 provides the fuel properties of B10 Nigella sativa (NSB10) and Ceiba pentandra (CPB10). The properties obtained by MDT applied to Nigella sativa and Ceiba pentandra specifically display scarce differences in the properties of fuel produced by DT and MDT methods. Thus, it can be confidently said that the MDT and DT are well-qualified to be adopted as biodiesel production techniques. A CI engine with a 17.5 compression ratio and 1500 rpm rated speed, powered with CPB10 and NSB10, was used in the experimental study. An injector with three holes, each of 0.3 mm diameter was incorporated in the initial experimentation.

Injector Opening Pressure (IOP) Effect on the CI Engine Performance
To obtain the best IOP for the maximum BTE, the diesel engine was run with different IOP ranging within 220-250 bar in increments of 10 bar at various brake power (BP). The normal combustion chamber (HCC) was used.
Engine Brake Thermal Efficiency Figures 5 and 6 show the IOP variation effect at different loads on the CI engine BTE. At the IOP of 240 bar, the BTE achieved was highest. Better fuel atomization and mixing with air can be attributed for the improved combustion resulting in high BTE [17,34]. Wall wetting can be the reason for the lower BTE reported at the IOP of 250 bar. Thus, for the diesel engine to run on CPB10 and NSB10, an optimum BTE can be achieved at the IOP of 240 bar. Henceforth, IOP of 240 bar will be used in experimental work.

Number of Nozzle Holes and Their Orifice Diameter effect on the Diesel Engine Performance
The effect of the number of nozzle holes and their orifice diameters on the performance of the diesel engine was studied considering six nozzle holes with an orifice diameter range 0.2 mm, 0.25 mm and 0.3 mm. At a load capacity of 80% the results obtained were compared with those achieved using three, four and five nozzle holes, each with 0.3 mm orifice diameter.

Engine Brake Thermal Efficiency
The BTE variation at a load of 80% using an injector with six holes and a variety of orifice diameters is represented by Figure 7. The 0.2 mm orifice diameter of a six-hole nozzle was witnessed to provide higher BTE in comparison with other setups. The appropriate reason for a spike in BTE can be the improved mixing of the air-fuel and proper combustion of the same [35]. Another critical review can be the less wetting of combustion chamber walls, owing to the reduced mass flow rate of the fuel per hole. Contrary to diesel, CPB10 exhibited 28.1% and NSB10 showed 27.5% BTE.

Number of Nozzle Holes and Their Orifice Diameter effect on the Diesel Engine Performance
The effect of the number of nozzle holes and their orifice diameters on the performance of the diesel engine was studied considering six nozzle holes with an orifice diameter range 0.2 mm, 0.25 mm and 0.3 mm. At a load capacity of 80% the results obtained

Number of Nozzle Holes and Their Orifice Diameter effect on the Diesel Engine Performance
The effect of the number of nozzle holes and their orifice diameters on the performance of the diesel engine was studied considering six nozzle holes with an orifice diameter range 0.2 mm, 0.25 mm and 0.3 mm. At a load capacity of 80% the results obtained The BTE variation at a load of 80% using an injector with six holes and a variety orifice diameters is represented by Figure 7. The 0.2 mm orifice diameter of a six-ho nozzle was witnessed to provide higher BTE in comparison with other setups. The appr priate reason for a spike in BTE can be the improved mixing of the air-fuel and prop combustion of the same [35]. Another critical review can be the less wetting of combustio chamber walls, owing to the reduced mass flow rate of the fuel per hole. Contrary to di sel, CPB10 exhibited 28.1% and NSB10 showed 27.5% BTE.

CC Shapes Effect on the Performance of Diesel Engine Driven by CPB10 and NSB10
The experimental results with different CC shapes viz., HCC, trapezoidal combu tion chamber (TCC) and TRCC shapes are presented in Figures 8-16. The IOP of 240 b for blends, and a six-hole nozzle with orifice diameters of 0.2 mm was utilized for exper mentation as the BTE yielded under these conditions was better.

Performance of Engine Brake Thermal Efficiency
The BTE variation in a diesel engine driven by CPB10 and NSB10 with various C shapes and BP is represented by Figure 8. TRCC endowed diesel engine driven by blende fuel exhibited prominent results comparatively with various CC shapes selected. TRC prevents flame front propagation from spreading in the squish region; thereby, a bett mixture formation, on account of better air motion, increased the swirl and tumble flo that yielded enhanced BTE. Higher BTE with TRCC shape can be due to the ability guide the field of flow to the cylinder sub volumes.

CC Shapes Effect on the Performance of Diesel Engine Driven by CPB10 and NSB10
The experimental results with different CC shapes viz., HCC, trapezoidal combustion chamber (TCC) and TRCC shapes are presented in Figures 8-16. The IOP of 240 bar for blends, and a six-hole nozzle with orifice diameters of 0.2 mm was utilized for experimentation as the BTE yielded under these conditions was better.       of combustion was taken as the point where 90% of the heat release had occurred. Ignition delay (ID) is the time duration between the start of injection (SOI) and the start of ignition SOI is the static fuel injection timing.  of combustion was taken as the point where 90% of the heat release had occurred. Ignition delay (ID) is the time duration between the start of injection (SOI) and the start of ignition. SOI is the static fuel injection timing.    The graphs display a decreasing ID curve and an increasing CD trend at elevated BP and all CC shapes, which in the case of diesel as fuel are observed to be lower. The reason for this can be the rise in the temperature of gases inside the cylinder at higher BP. The ID and CD with diesel were lower compared with blends with all CC shapes. Proper air-fuel  The graphs display a decreasing ID curve and an increasing CD trend at elevated BP and all CC shapes, which in the case of diesel as fuel are observed to be lower. The reason for this can be the rise in the temperature of gases inside the cylinder at higher BP. The ID and CD with diesel were lower compared with blends with all CC shapes. Proper air-fuel

Performance of Engine Brake Thermal Efficiency
The BTE variation in a diesel engine driven by CPB10 and NSB10 with various CC shapes and BP is represented by Figure 8. TRCC endowed diesel engine driven by blended fuel exhibited prominent results comparatively with various CC shapes selected. TRCC prevents flame front propagation from spreading in the squish region; thereby, a better mixture formation, on account of better air motion, increased the swirl and tumble flow that yielded enhanced BTE. Higher BTE with TRCC shape can be due to the ability to guide the field of flow to the cylinder sub volumes.

Exhaust Emissions
The variations in the CI engine emission levels of hydrocarbons, smoke, carbon monoxide and NOx for varying CC shapes and BP are projected in Figures 9-12. Blends were observed to have higher HC, CO and smoke emissions in comparison with diesel with all CC shapes. Adverse to this, NOx emissions for blends were low with all CC shapes. Owing to proper air-fuel mixing resulted by high turbulence, complete combustion with TRCC displayed results better than the other CC shapes and all BP [36]. A combined effect of high PP and HRR during the premixing phase of combustion at higher temperatures can produce the noticed trend. Figure 9 provides the influence of the combustion chamber shape on smoke with both biodiesels. Diesel engine produced lower smoke emission with TRCC in comparison with other CC shapes used owing to a better mixing process inside the cylinder. Higher turbulence in the TRCC resulted in low heat losses and enhanced oxidation, thus reducing the combustion temperature and smoke emission. At 80% load, the engine exhibited approximately 5.1% to 9.5% lesser smoke with biodiesel in comparison with diesel operation.
The effect of CC shapes on HC and CO emissions are illustrated in Figures 10 and 11. TRCC resulted in lower HC and CO emissions owing to a lower ignition lag and higher HRR. The air motion in TRCC improved the mixture formation of both biodiesels and air, thus improving the overall combustion process and increasing both HC and CO emissions. Furthermore, owing to the better burning qualities, the CPB10 produced significantly reduced HC and CO emissions than the NSB10.
NOx changes with BP and different CC shape are provided in Figure 12. Diesel engine operation with both biodiesels showed elevated NOx at higher loads. Rapid combustion of fuel boosted the combustion process by reducing the ignition delay period that elevated the combustion temperature to yield higher Nox. The TRCC shape provided higher Nox emission, which may be caused by increased combustion temperatures owing to the enhanced combustion process as a result of improved mixture formation in TRCC. Furthermore, at 80% load the engine produced approximately 6% to 12% lower NOx with biodiesels contrasted with single (CI) mode [37].
Figures 13-16 specify the variation trend of ID, CD, PP and HRR at various CC shapes and BP. Static IT was used to calculate the ignition delay. The start of combustion was determined from the differentiated cylinder pressure variation time data where a sudden rise in the slope at the start of ignition on account of fast premixed heat release. The end of combustion was taken as the point where 90% of the heat release had occurred. Ignition delay (ID) is the time duration between the start of injection (SOI) and the start of ignition. SOI is the static fuel injection timing.
The graphs display a decreasing ID curve and an increasing CD trend at elevated BP and all CC shapes, which in the case of diesel as fuel are observed to be lower. The reason for this can be the rise in the temperature of gases inside the cylinder at higher BP. The ID and CD with diesel were lower compared with blends with all CC shapes. Proper air-fuel mixture ensures effective combustion, which contributes to the rise in temperature and pressure, thereby resulting in higher HRR [38,39]. Lower trends were observed in TRCC for ID and CD at high PP and HRR for various CC shapes. Blend exhibited lower HRR in comparison with diesel owing to poor combustion potentials.

Conclusions
The outcomes of the modified direct transesterification (MDT) method of biodiesel extraction followed by the experimental work carried out on diesel engine operation with blends with different operating parameters can be summarized as follows: Overall, it can be concluded that the engine operation with CPB10 and NSB10 at 23 • bTDC fuel injection timing, 240 bar IOP with TRCC can yield better results close to a diesel run engine at 23 • bTDC fuel injection timing, 205 bar IOP with HCC.