23
Utilization of biofuels in diesel engines
Abstract
The chapter summarizes some experimental findings on the use of biofuels in conventional diesel engines conducted in ASEAN region. A number of biofuels such as vegetable crude oil, pure plant oil and biodiesel in different forms, which are derived from many types of raw materials such as jatropha, coconut, palm, kapok nut and cat-fish, are investigated to find impacts of these biofuels on engine's combustion characteristics, performance, exhaust emissions, and durability. The concept of using biofuels on engines is also mentioned to determine the ways of utilization of biofuels in engines that match both the demand of biofuels usage and the design of the engines.
Keywords
Biofuels; Combustion visualization; Diesel engine; Durability; Engine performance; Exhaust emissions; Vegetable oils23.1. Introduction
Biofuels are currently recognized as the most suitable alternative fuels for engines which were originally designed to use fossil fuels. Although the process of formation of fossil fuels still continues through the effect of underground heat and pressure, the current rate of consumption is higher than the rate of formation. Consequently, fossil fuels are considered to be nonrenewable; that is, they are not replenished as fast as they are consumed. Biofuels, including ethanol, biodiesel, and several other liquid and gaseous fuels, constitute a very promising renewable energy resource with the potential to displace the consumption of a substantial amount of petroleum worldwide during the next few decades (Demirbas, 2008; Bandivandekar et al., 2008; Gadesmann and Kuhnert, 2007; Reksowardojo and Soerawidjaja, 2009). A clear trend in that direction is already in process.
Research on the production and utilization of biofuels in engines is therefore regarded as a priority not only for developed nations but also for developing countries. Although the use of biofuels is currently low, the amount is continuously increasing in every country. However, due to the fact that biofuels are produced from many different sources, characteristics and quality also vary, so the utilization of different biofuels in internal combustion engines must be carefully investigated to determine the effects on engine performance and material components.
In this chapter, the utilization of biofuels in conventional diesel engines is considered. The use of crude jatropha oil (CJO), degummed jatropha oil (DJO), pure plant oils (PPO), and biodiesels produced from crude palm oil, jatropha curcas, coconut oil, kapok nut oil, and cat-fish fat in neat form (100% biodiesel) together with various blends of biodiesel with conventional diesel are described. In addition, the use of mixed biodiesel derived from different raw materials is also considered as a possible solution for improving the quality of biodiesels.
Findings regarding the utilization of biofuels in diesel engines are presented from case studies conducted in ASEAN (Association of Southeast Asian Nations) countries, especially Indonesia, Thailand, and Vietnam, where high priority has been given to the development and use of biofuels.
23.2. Utilization of vegetable pure plant oil and crude oil in diesel engines
23.2.1. Introduction
Early in the research stage, Crude Jatropha Oil (CJO) was considered to be suitable as a fuel oil based on its visual properties. The greatest difference between CJO and diesel oil is in viscosity. The high viscosity of CJO may contribute to the formation of carbon deposits in compression ignition engines (CIE). Incomplete fuel combustion results in reduced engine life. Reducing the viscosity of CJO oil by preheating or dilution with diesel fuel was studied in engine tests (Reksowardojo et al., 2006a; Project Report to New Energy Development Organization (NEDO), 2006). To investigate the suitability of CJO oil as an alternative fuel and examine emissions, two tests of performance and exhaust gas emission, and a long-term durability test of CIE in a direct injection (DI) engine were conducted. In performance and exhaust gas emission tests, JO10 (blend of 10% CJO and 90% diesel) was similar to diesel fuel. Its oxygen content is an advantage in improving combustion. Exhaust gas emission increased slightly because its slightly higher viscosity influences fuel atomization. JO10 is a promising alternative fuel because its performance and exhaust gas emission are similar to diesel fuel. JO100 gave lower performance and higher emission compared to diesel fuel because of its high viscosity. Using JO100 the engine was difficult to operate. The long-term durability test indicated that JO10 resulted in operational problems including increased exhaust gas emission (HC, particulate matter), injector coking, piston, and liner erosion. Maintenance frequency would be increased substantially including changing or cleaning of the injector nozzles at 125-h intervals, thus increasing the cost of operation. Dilution of lubricating oil and friction caused by ring sticking and deposits in the combustion chamber would reduce the lifetime of engine components. The main concern is the fuel quality and composition. The content of phosphorous compounds in JO10 was found to be significantly affecting the combustion process and exhaust emission. A degumming process to reduce the phosphorous level is therefore required to improve the fuel quality of crude jatropha oil.
Diesel engines can be operated on either pure plant oil (PPO) or biodiesel. The biodiesel process increases the cost of production as many processes are needed, whereas PPO only needs degumming to decrease phosphorous content and deacidification decreases the acid number. Potential resources of PPO in Indonesia include coconut, palm, and jatropha, because they are tropical plants that are common throughout the country. Various PPOs have been investigated (Reksowardojo et al., 2009b; Project Report to Ministry of Energy and Mineral Resources, 2007). Test fuels includes pure coconut oil (PCO), pure palm oil (PPaO), pure jatropha oil (PJO) (Reksowardojo et al., 2008c), and diesel fuel for comparison. Each PPO was blended with diesel fuel with composition 50%-volume and heated to 60°C, to decrease the viscosity by 1/10. Trials using a small DI diesel engine for 17 h endurance tests under various operating conditions were conducted according to engine test bed procedures for DI diesel and engine injector nozzle coking test. PPOs are characterized by high viscosity, low volatility, and low energy content. All PPOs had higher brake-specific fuel consumption (BSFC) before the endurance test by comparison with diesel fuel, but at the end of the test all PPO had BSFC similar to diesel fuel due to decreased friction between engine components. However, combustion of PPOs was not as complete as that of diesel fuel because of poorer spray characteristics, evidenced by low CO2 and high UHC, CO, O2, and opacity emissions. The phosphorus content, unsaturated fatty acid content, and low combustion quality of PPO, result in higher engine deposits than for diesel fuel. Even though the PPOs had been degummed the residual phosphorous content contributed to deposit formation. Deposits from PPOs were between 140 and 290% more than from diesel. However PPOs exhibited antiwear properties on the plunger and injector due to the lubrication effects of the fatty acid content. PCO had the best antiwear property of the test fuels.
Further investigation of the combustion and exhaust gas emissions of a DI CIE using Jatropha curcas L. oil as CJO (JO) and PJO/Degummed Jatropha Oil (DJO) were studied (Reksowardojo et al., 2007b). Of all the tested fuels, DJO10 was found to be closest to diesel fuel in performance, exhaust gas emission, and its combustion process (ignition delay).
In addition, a study of combustion of Jatropha curcas Linn. oil (crude; degummed; fatty acid methyl ester) as a fuel in a direct injection diesel engine was done (Reksowardojo et al., 2008a, 2009a). The summary of conclusions drawn from the experimental data were as follows:
JO100 and DJO100 have low cetane indices and very high viscosity. Lower engine performance and high exhaust gas emission were found. However, these fuels can be used in emergencies.
Blends of JO10 and DJO10 improve engine performance, and reduce exhaust gas emissions at low engine load. However, NOx emission tends to increase.
23.2.2. Combustion visualization
23.2.2.1. Combustion bomb study
The study on the spray combustion characteristics of 10% CPO blended with diesel fuel was conducted in a constant-volume combustion chamber. With the fixed experimental conditions such as spray ambient pressure and injection events, the effects of 10% CPO diesel at the injection line pressure of 100 MPa on spray combustion and flame structure were investigated using a photo diode and ICCD camera. Two-color method was also employed to predict combustion flame temperatures and KL factors.
Fuel specification
Many properties of the 10% CPO diesel fuel can be attributed directly to the thickening effect of the CPO on the diesel fuel. In this study, blending 10% of CPO by volume in diesel can meet the Thai diesel fuel specification. The primary properties of both the baseline diesel and the crude palm diesel blend are shown in Table 23.1. The higher density and higher viscosity of CPO, comparing to diesel fuel, resulted in a slight increase in these properties in the resulting crude palm diesel blends. The blend also has roughly 5% less energy per volume and less cetane value than diesel fuel. The 10% CPO diesel shows the slightly reductions in T90 point that may affect the poor long-trip economy. The addition of CPO to diesel fuel will degrade the cetane number of the resulting 10% CPO diesel blend. The flashpoint of 10% CPO diesel is controlled by high flashpoint of the CPO. The flashpoint of 10% CPO diesel is higher than that of diesel fuel.
Table 23.1
Comparative diesel and 10% CPO diesel properties (Ha et al., 2009c)
| Properties | Unit | Test method | Reference diesel | 10% CPO diesel | Thailand diesel specification |
| Specific gravity at 15.6/15.6°C | ASTM D1298 | 0.8266 | 0.8360 | 0.810–0.870 | |
| Cetane index | ASTM D976 | 58.9 | – | 47 min | |
| Cetane number | ASTM D613 | 59.3 | 55.5 | 47 min | |
| Viscosity at 40°C | CST | ASTM D445 | 3.10 | 3.910 | 1.8–4.1 |
| Pour point | °C | ASTM D97 | −3 | −6 | 10 max |
| Distillation | ASTM D86 | ||||
| IBP | °C | – | – | – | |
| 10% Recovered | °C | – | – | – | |
| 50% Recovered | °C | – | – | – | |
| 90% Recovered | °C | 350.6 | 346.2 | 350 max | |
| Lubricity by HFRR | μm | CEC F-06-A-96 | 522 (+LA = 398) | 209 | 460 max |
| Total acid number | ASTM D974 | 0.04 | 1.02 | – | |
| Gross heating value | J/g | 45,968 | 44,982 | 44,500 min |
Experimental apparatuses and procedure
The injection system used in this research was an electronically controlled accumulator-type fuel injector system (Azetsu et al., 2003; Matsui et al., 1979). With a 0.2-mm diameter single-hole injector, driven by a piezoelectric actuator via an extended pressure pin, we could control the needle lift and fuel injection rate shaping. The schematic diagram of the injector and details are shown in Fig. 23.1.
The experiments were conducted in the constant volume 2.2-L vessel with 80 mm diameter quartz observation window on the side, gas mixing propeller on the bottom and injector on the top, as shown in Fig. 23.2. The ambient condition inside the vessel was made to be high temperature and pressure by igniting hydrogen in an enrich oxygen and air mixture. The oxygen concentration after the hydrogen combustion was approximately 21% by volume (Azetsu et al., 2003; Matsui et al., 1979).
The rectangular injection rate shaping was selected in this experiment, as shown in Fig. 23.3. Fuel injection mass was set at approximately 15 mg for all experiments. Injection pressure was 100 MPa. The fuel was injected in the vessel at the ambient conditions of 3.0 MPa, temperature around 900°C, as shown in Fig. 23.4. The calculated compositions of ambient gas are O2 20.9%, N2 70.8%, and H2O 8.3%.
After the hydrogen combustion, the fuel was injected into the vessel and then combusted. Fuel spray combustion flame photographs were taken by ICCD camera. Light emission of flame was measured using two photo sensors; a photo multiplier tube with a band-pass filter center on a wavelength of 310.3 nm (FWHM: 16.3 nm) used for measuring the intensity of OH-radical emission and two photo diodes (used for measuring the luminous light intensity) at the upper and the middle of observation window. The start of spray was detected by the combination of the use of He–Ne laser with photo sensor. Using photo diode data, the ignition delay and combustion period were evaluated.
Figure 23.1 Schematic diagram of injector systems (Matsui et al., 1979).
Figure 23.3 Fuel injection rate shaping at injection pressure 100 MPa (Romphol and Wattanavichien, 2006).
Figure 23.4 Temporal variation of gas pressure inside the vessel (Romphol and Wattanavichien, 2006).
The two-color method was applied to estimate two-dimensional (2D) contour of temperature and KL factor (KL factor is the factor used to indicate soot) distribution in the combustion flame. This two-color pyrometry system was set up by placing Vari lens that has the two different band-pass filters 488 nm in center wavelength (FWHM: 11.3 nm) and 634 nm in center wavelength (FWHM: 8.5 nm) for separating images to be two in front of an ICCD camera lens. The intensity data of both filters were used to calculate the true temperature and KL factor.
The data obtained from He–Ne laser and OH-radical were used to calculate ignition delay. It was found that 10% CPO gave a shorter ignition delay compared with diesel as shown in Fig. 23.5.
The data 10% of peak intensities obtained from the two photo diodes were selected to be the start and end of the combustion. The result showed that the observed combustion period of 10% CPO diesel at injection pressure of 100 MPa was slightly shorter than diesel as shown in Fig. 23.6.
The amount of injection fuel became slightly smaller and the injection period became slightly shorter with the 10% CPO diesel due to the higher viscosity of 10% CPO diesel.
The exposure time of ICCD camera was set at 10 μs (micro-seconds). The spray combustion flame intensity data were complied with a two-color method (Wattanavichien, 2004). Some of calculated results of true temperature are shown in Fig. 23.7.
The calculated data obtained from spray combustion flame true temperature were used for calculating the KL factor, the factor for indicating amount of combustion soot in flame, the calculated results are shown in Fig. 23.8.
Figure 23.5 Fuel combustion ignition delay (Romphol and Wattanavichien, 2006).
Total KL factor is the summation of KL factor over the spray combustion flame area. This factor could be used to estimate the total soot of the combustion.
It was found, as shown in Fig. 23.9, that the difference in total KL factor between diesel and 10% CPO was very small.
The average KL factor, which could be used to estimate the soot concentration of the spray combustion, was calculated from the total of KL factor divided by spray combustion flame area at all flame areas. The results showed that the difference of average KL factor between diesel and 10% CPO was also very small.
Histogram of temperature and KL factor were calculated by evaluating the value from the counted number of spray combustion flame pixels and converting them to flame area (mm2). The interval of temperature and KL factor were selected at 50K and at 0.005 AU, respectively. The results are shown in Fig. 23.10.
It was found from temperature histogram that spray combustion of 10% CPO was started with a lower temperature than diesel. Spray combustion temperature had increased close to diesel during the mid-range of the combustion period. Then it became lower by the end of combustion. However, the differences were very small.
The KL factor histogram of Thai palm 10% CPO had no significant difference compared to diesel. Hence, it could be concluded that the difference in soot emission would be very small.
23.2.2.2. Combustion engine study
This study aims to investigate comparative results of using crude palm diesel (blending 10% of CPO in diesel, 10% CPO diesel, properties of this fuel are presented in Table 23.1) on engine combustion of a CI IDI swirl chamber engine. The experiments, conducted on a Ford Ranger WL81 2.499 L engine (Table 23.2), were composed of two parts. First, measure and analyze in-cylinder pressure and fuel injection line pressure by using crude palm diesel and diesel fuel. Second, study combustion phenomena of both fuels in the swirl chamber by means of engine visioscope. Results show detailed phenomena of spray and flame propagation. Two-color method was also employed to evaluate flame temperature and distribution of soot in flame. Finally, results of visualized combustion phenomena with heat release that were estimated from in-cylinder pressure information were compared.
Figure 23.9 Total KL factor of palm diesel 60% and diesel fuel at injection pressure 100 and 60 MPa.
Figure 23.10 Flame temperature and KL factor histogram of palm diesel 60% and diesel fuel at injection pressure 100 and 60 MPa.
Table 23.2
Specifications of the test engine Ford Ranger WL81
| Engine type | WL 81 |
| Prechamber | Swirl pre-chamber |
| Displacement | 2499 cm3 |
| Bore × stroke | 93 × 92 mm |
| Compression ratio | 21.6:1 |
| Injection pump | Rotary distributor type |
| Injector starting pressure | 11.4–12.1 Mpa |
Experimental apparatus
The engine under study is a commercial IDI, water-cooled four cylinders, inline, natural aspirated engine. The following chart displays the main dimensions.
The engine was connected to an AVL alpha 40 eddy-current dynamometer. In-cylinder pressure was taken by AVL piezoelectric pressure transducer model GU12P. Fuel line pressure was taken by a KISTLER 607C1 pressure transducer.
Indicating data were captured with Cussons P4503 shaft encoder and Cussons P4500 autoscan. Direct photography was taken with an AVL Engine Visioscope. The system consists of a PixelFly VGA Color CCD camera (resolution 640 × 480 pixels), an AVL control unit, AVL 364C crank angle encoder, an optical linkage to the camera, and the endoscope. The optical access for the endoscope to the swirl chamber of the fourth cylinder was prepared through the cooling system of the cylinder head. The visioscope software controls the triggering of the digital camera within a crank angle tolerance of 0.1°CA. The endoscope has a viewing angle of 30 degrees forwarded view. To capture the spray images, the light source unit with fiberoptic (40 mJ/flash with 20 μs duration at frequency of 10 Hz) was used.
The schematic arrangement of the experimental set up is shown in Fig. 23.11.
Experimental procedure
The experiments were carried out at constant speed, steady state conditions at selected high probability operating points along ECE 15 driving cycle, as shown in Table 23.3. For the combustion analyses, images of simultaneous complex spray, inflammation, and combustion processes in the swirl chamber were taken. Speed, torque, fuel consumption, engine operating pressure, and temperature for both fuels were recorded during each test.
Figure 23.11 Schematic arrangement of the experimental system (Ha et al., 2009c).
Experimental results
Engine indicating information
Comparison of in-cylinder pressure, fuel line pressure, fuel injection rate, heat release rate, net heat release, and mass fraction burned is shown in Fig. 23.12. The measurement of in-cylinder pressure and fuel injection line pressure has indicated that 10% CPO diesel has approximately 1 degrees of early injection timing compared with diesel. The 10% CPO diesel also has longer ignition delay and higher amount of fuel injected mass (mf) due to its lower energy density. The maximum in-cylinder pressure of 10% CPO diesel is similar to diesel. Net heat release and mass fraction burned of 10% CPO diesel are also lower than diesel.
Figure 23.12 Comparison of in-cylinder pressure, fuel line pressure, fuel injection rate, heat release rate, net heat release, and mass fraction burned as engine operate with diesel and 10% CPO diesel at 2000 rev/min, 30 Nm (Wattanavichien and Traiphopphoom, 2006).
Table 23.4
Comparison of maximum in-cylinder pressure (Pmax), SOI, ignition delay, and fuel injected mass (mf) as engine operate with diesel and 10% CPO diesel (Wattanavichien and Traiphopphoom, 2006)
| Test point | Pmax (bar) | SOI (°CA) | Ignition delay (ms) | mf (mg/cycle) | ||||
| Diesel | 10% CPO diesel | Diesel | 10% CPO diesel | Diesel | 10% CPO diesel | Diesel | 10% CPO diesel | |
| Idle | 53.26 | 53.31 | −4.0 | −4.0 | 2.08 | 2.2 | 6.22 | 7.04 |
| 1000 rpm, 30 Nm | 58.45 | 59.45 | −10.5 | −11.5 | 2.08 | 2.17 | 9.63 | 10.77 |
| 2000 rpm, 30 Nm | 61.48 | 61.84 | −11.0 | −11.5 | 1.54 | 1.50 | 9.99 | 10.88 |
| 2000 rpm, 50 Nm | 61.72 | 61.74 | −10.0 | −10.0 | 0.46 | 0.46 | 12.64 | 13.97 |
| 2250 rpm, 20 Nm | 64.98 | 64.97 | −10.5 | −11.0 | 0.78 | 1.04 | 8.72 | 9.81 |
| 2750 rpm, 20 Nm | 63.90 | 64.66 | −9.0 | −9.0 | 0.21 | 0.21 | 9.56 | 10.46 |
Comparison of maximum in-cylinder pressure (Pmax), SOI, ignition delay, and fuel injected mass (mf) as engine operated with diesel and 10% CPO diesel are summarized in Table 23.4.
Spray formation
The images of spray formation at selected operating points of reference diesel and 10% CPO diesel are shown in Fig. 23.13(a,b), respectively. The figures show that 10% CPO diesel has approximately 1–2 degrees of early injection timing compared with diesel. The early injection timing is probably due to the higher isentropic bulk modulus and higher viscosity of CPO compared to diesel resulted in slightly increasing these properties in the resulting blends (Tat and Van Gerpen, 2003). The comparison of the observed spray formation between reference diesel and 10% CPO diesel is summarized in Table 23.5. It was found that, using OEM injection pump and standard injector in a prechamber, with 10% CPO diesel the observed sprays were wider than those of reference diesel. The difference in spray angle tends to reduce with increasing speed. The observed spray penetration with 10% CPO diesel is also longer than reference diesel in low to medium engine speed range. The higher the engine load, the longer the spray penetration was observed.
Figure 23.13 (a) and (b) Images of liquid fuel spray in the prechamber for reference diesel and 10% CPO diesel respectively. The crank angles at which the images were acquired are written on the left of the images: (a) reference diesel spray; (b) 10% CPO diesel spray.
Table 23.5
Maximum spray penetration (mm) and spray angle (degree)
| Test point | Max penetration (mm) | Max spray angle (degree) | ||
| Diesel | 10% CPO diesel | Diesel | 10% CPO diesel | |
| Idle | 23.0 | 27.8 | 25.5 | 24.1 |
| 1000 rpm, 30 nm | 27.9 | 25.6 | 24.1 | 26.4 |
| 2000 rpm, 30 nm | 29.8 | 27.1 | 36.8 | 41.4 |
| 2000 rpm, 50 nm | 28.3 | 28.7 | 36.3 | 39.3 |
| 2250 rpm, 20 nm | 25.6 | 28.4 | 36.4 | 39.4 |
| 2750 rpm, 20 nm | 28.5 | 33.7 | 36.4 | 40.8 |
Figure 23.14 Images of luminous spray combustion in the prechamber for reference diesel and 10% CPO diesel showing the start of luminous flame, the position for maximum area of over 2400K and end of luminous flame. The crank angles at which the images were acquired are written under the images: (a) diesel flame; (b) palm-diesel flame.
Spray combustion phenomena, flame temperature, and soot distribution
Summarizing the results of these sections, as shown in Fig. 23.14, it can be noted that the visible combustion course in a swirl chamber occurs without any starting aids. The visible inflammation appears above the fuel jet. From there the flame engulfs the whole swirl chamber very quickly. This process needs some delay time. The comparison of the observed luminous spray combustion between reference diesel and 10% CPO diesel is shown in Table 23.6. It was found that 10% CPO diesel has a longer ignition delay period than diesel. The combustion for both fuels tends to start faster with increasing speed. After this ignition delay, the burning area rotates under the influence of the swirl. This motion can be observed for nearly all the burn duration after complex luminous inflammation occurred. In the low speed and load range, 10% CPO diesel combustion duration tends to have a slightly shorter period than diesel. This may be due to the benefit of oxygen content in the fuel.
Table 23.6
Comparison of the first appearance of luminous flame, end of luminous and luminous flame duration between reference diesel and crude palm diesel in an IDI engine (°CA)
| Test point | First appearance of luminous flame (°CA) | End of luminous flame (°CA) | Luminous flame duration in prechamber (°CA) | |||
| Diesel | 10% CPO diesel | Diesel | 10% CPO diesel | Diesel | 10% CPO diesel | |
| Idle | 3.5 | 5.0 | 28.5 | 25.5 | 25.0 | 20.5 |
| 1000 rpm, 30 nm | 0.5 | 2.0 | 32.5 | 31.0 | 32.0 | 29.0 |
| 2000 rpm, 30 nm | −0.5 | −0.5 | 30.5 | 28.5 | 31.0 | 29.0 |
| 2000 rpm, 50 nm | 0.5 | −0.5 | 27.5 | 31.0 | 27.0 | 31.5 |
| 2250 rpm, 20 nm | −0.5 | −0.5 | 25.5 | 27.0 | 26.0 | 27.5 |
| 2750 rpm, 20 nm | 1.0 | −1.0 | 27.5 | 26.5 | 26.5 | 27.5 |
Using the “Thermovision” software from AVL List GmbH (AVL List GmbH, 1998), the temperatures of radiating soot particles were calculated from the three spectral intensities in the flame images using the two-color method. In the temperature images, shown in Fig. 23.15, purple–blue–green–yellow–red–white denote the temperatures ranging from 1800 to 3000K.
The difference in combustion is much more obvious when looking at the flame. The in-cylinder combustion temperature of 10% CPO diesel combustion is lower than diesel combustion. From Fig. 23.16, the flame areas of temperature above 2400K for diesel and 10% CPO diesel at 2000 rev/min, 30 Nm, are compared. It was found that diesel fuel showed a greater amount of flame areas of temperature above 2400K.
In the soot distribution images, the same color scale denotes soot densities ranging from thin to dense soot. The appearance of luminous combustion flame comes from the radiation of soot particles occurring in the fuel mixture oxidation zone. Prediction of soot density distribution at selected operating points of diesel and 10% CPO diesel are shown in Fig. 23.17. It is noted that soot density in 10% CPO diesel combustion flame tends to be slightly lower than that in diesel.
Figure 23.15 Flame temperature images of spray combustion in the prechamber for reference diesel and 10% CPO diesel. The crank angles at which the images were acquired are written on the top of the images: (a) diesel flame temperature distribution; (b) crude palm diesel flame temperature distribution.
23.3. Utilization of biodiesel-based palm oil, jatropha oil, coconut oil, and kapok nut oil in diesel engines
Palm (Elaeis guineensis) has the most potential of the edible oils. Palm oil is now already produced and marketed in very large quantities, because it is edible and high-yielding (around 3.5–5.0 ton/hectare/year). Direct injection (DI) diesel engine performance, exhaust gas emissions, and some fuel properties have been studied for biodiesel from crude palm oil (CPO) and refined bleached deodorized palm oil (RBDPO), and these fuels blended with diesel fuel (Reksowardojo et al., 2004a). It was found that both of the biodiesel fuels and their blended fuels with diesel oil had increased brake-specific fuel consumption (BSFC) levels, while the exhaust emissions (CO, CO2, HC, and smoke) were better than for diesel fuel. Both DI and IDI (Reksowardojo et al., 2004b) engines were used for this research. These fuels were also used for a 2200 km fleet road test with two passenger cars and two trucks and compared with the performance of neat petrodiesel fuel (Reksowardojo et al., 2005b). Parameters evaluated before and after road testing were fuel consumption, exhaust gas emissions, fuel injection equipment, and engine lubricant.
Physic nut (Jatropha curcas) is one of the most potential sources of nonedible plant oil. Physic nut seed oil is practically unexploited commercially, although it has the potential to replace or substitute for palm oil as the raw material for biodiesel during periods of high food sector demand.
The effect of biodiesel fuel from Jatropha curcas oil in DI diesel engines on the components of the engine influenced by fuel before (injection pump, injector) and after the combustion process (piston crown, cylinder head) were studied (Reksowardojo et al., 2005a,c). The test bed procedure used was that commonly used for injection cleanliness evaluation adopted by World-Wide Fuel Charter (December 2002) (ACEA, 2002). Exhaust gas emissions such as nitrogen oxides (NOx), carbon monoxide (CO), brake-specific fuel consumption (BSFC), and engine lubricant before and after the test were also measured.
Figure 23.17 Soot concentration distribution images of spray combustion in the prechamber for reference diesel and 10% CPO diesel. The crank angles at which the images were acquired are written on the top of the images: (a) diesel soot concentration distribution; (b) crude palm diesel soot concentration distribution.
A single cylinder direct injection diesel engine fueled with pure biodiesel from physic nut oil and blends (B10, B20, B50) with diesel fuel was used to compare engine performance and engine exhaust gas emission by comparison with diesel fuel (Reksowardojo et al., 2007a). The results from this research show that biodiesel fuel from physic nut oil and its blends with diesel can give comparable engine performance for parameters, torque (T), fuel volumetric consumption (FVC), BSEC, and thermal efficiency (ηe). Engine exhaust gas emissions of total hydrocarbon (THC), CO, and smoke emissions were reduced significantly when engine was run with biodiesel fuel. Biodiesel use resulted in slight increases in NOx emission.
Much research has been focused on the use of biodiesel and its blends in stationary DI diesel engines. Only a few studies using biodiesel and its blends in automotive diesel engines or indirect injection diesel engines have been done. The effects of biodiesel and its blends on an automotive IDI diesel engine by comparison with local commercial diesel fuel (Reksowardojo et al., 2008b) were studied in an experiment. Jatropha curcas methyl-ester (JCME) and its blends had slightly lower torque, power output, and thermal efficiency, but slightly higher brake-specific fuel consumption than diesel fuel. In exhaust gas emission tests JCME and its blends significantly reduced HC, CO, and Bosch Smoke Number but NOx emission slightly increased. The results indicated that B10 was the optimum fuel for the test engine.
A similar study carried out using both palm oil methyl-ester (POME) and JCME with a DI engine yielded similar results (Reksowardojo et al., 2006b).
Coconut oil (Cocos nucifera) is an edible oil, but because it is widely distributed all over Indonesia in areas where it is often difficult to provide fossil fuels which are consequently high in price, it even becomes feasible to use coconut oil for fuel. Coconut methyl ester (CME) was field-tested in vehicle and fishing boat engines as a fuel for use in remote areas (PT LAPI Project's Report to Ministry of Industry, 2006). In the vehicle the road test, B30 CME was used as a fuel for 15,000 km, and in the fishing boat engine B100 CME was used for 200 h. Results indicated that as long as the biodiesel quality was according to Indonesian biodiesel standard SNI 04-7182-2006, there were no significant differences in engine operation during the test by comparison with diesel.
Kapok nut (Ceiba pentandra L.) is a nonedible oil. Kapok trees are also widely distributed throughout Indonesia but not utilized as an energy source (Mesra, 2007). Biodiesel from kapok seed oil was tested with a DI diesel using standard test procedures including engine injector nozzle coking test CEC F-23-A-01. Fuel consumption and smoke emissions increased. Nozzle tip deposits were very thick, presumably caused by the content of cyclopropenoid. Hydrogenation would be required to crack the cyclopropenoid structure before transesterification to solve this problem.
There is considerable potential for ASEAN to produce and supply various biodiesel products to the rest of the world due to its natural resource base. However, the use of biodiesel still presents a number of problems which need to be resolved, especially the high price of raw materials and the quality of biodiesel fuels. In view of these limitations, seeking ways to combine various biodiesel raw materials (eg, edible and nonedible oils) is one strategy that could be used to solve the problems: reducing the economic cost, utilizing the availability of raw materials and improving the quality of biodiesel fuels particularly cetane number, oxidation stability, and cold flow properties. In this study, four biodiesel fuels were mixed to create three biodiesel fuel mixtures in differing weight ratios as follows: (1) 70% Jatropha curcas oil methyl-ester (JME) with 30% palm oil methyl-ester (PME), (2) 70% JME with 30% coconut oil methyl-ester (CME) and (3) 75% soybean oil methyl-ester (SME) with 25% PME. Three kinds of mixed biodiesel fuels in the form of B10 and B100, together with conventional diesel fuel have been tested in a direct-injection diesel engine. Via an analyzing process based on the in-cylinder pressure data and the rate of heat release, the obtained results showed that biodiesel fuel mixtures had similar cetane number to diesel fuel; this is the main factor to explain why three biodiesel fuel mixtures were selected to simulate the currently used fuel—diesel fuel. Moreover, all mixed biodiesel fuels were comparable with conventional diesel fuel in performance and combustion efficiency and exhaust gas emissions were reduced significantly (eg, THC, CO, and PM). The reduction of NOx is an interesting issue in this study especially; this reduction could be explained by the rate of heat release obtained and the use of antioxidant BHA.
23.4. Utilization of biodiesel B5-based cat-fish fat in diesel engines
In Vietnam, the master plan of biofuels production until 2015, a vision to 2025, was approved by decision 177/2007/QD-TTg of the government (Decision No. 177/2007/QD-TTg, 2007). According to this decision, in 2015, biofuel production would be enough for 5 million tonnes of gasohol E5 and biodiesel B5; and until 2025, ethanol and biodiesel production will be 1.8 million tonnes, meeting 5% of the national fuel requirement.
In order to complete the biodiesel production process and to utilize biodiesel B5 (blend of 5% biodiesel and 95% market diesel) in engines, a national research project, code DTDL.2007G/19, was set up and run by the Vietnamese Institute of Industrial Chemistry. The School of Transportation Engineering, Hanoi University of Science and Technology, was one of the collaborative institutions that took care of the engine tests. The project was aimed at biodiesel-based cat-fish fat production and application of B5 fuel in diesel engines (United States Environmental Protection Agency, 2002).
23.4.1. Properties of biodiesel-based cat-fish fat
Properties of biodiesel B100 produced under industrial pilot scale at Institute of Industrial Chemistry are given in Table 23.7. It is shown in this table that the produced biodiesel B100 meets all requirements of Vietnam standard on biodiesel B100 (TCVN7717-07) (TCVN 7717-07, 2007). The cloud point of 10°C of biodiesel B100 requires an additive to reduce for storage of biodiesel in “neat” form, however within the pilot scale production, the fuel is stored in B5 form, so this matter was not mentioned.
Table 23.7
Properties of produced biodiesel B100 in comparison with TCVN standard limits
| Properties | B100 limits TCVN7717-07 | B100 produced | Test method |
| Methyl ester, wt% | 96.5 min | 98.4 | EN 14103 |
| Density at 15°C, kg/m3 | 860–900 | 878.9 | TCVN 6594 (ASTM D 1298) |
| Flash point, °C | 130.0 min | 150 | TCVN 2693 (ASTM D 93) |
| Water and sediment, %vol | 0.050 max | 0.005 | ASTM D 2709 |
| Kinematic viscosity 40°C, mm2/s | 1.9–6.0 | 4.6 | TCVN 3171 (ASTM D 445) |
| Sulfated ash, wt% | 0.020 max | 0.001 | TCVN 2689 (ASTM D 874) |
| Sulfur, ppm | 500 max | 50 | ASTM D 5453/TCVN 6701 |
| Copper strip corrosion | No1 | 1a | TCVN 2694 (ASTM D 130) |
| Cetane number | 47 min | 51 | TCVN 7630 (ASTM D 613) |
| Cloud point, °C | Report | +10 | ASTM D 2500 |
| Carbon residue, 100% sample, wt% | 0.050 max | 0.019 | ASTM D 4530 |
| Acid number, mg KOH/g | 0.50 max | 0.35 | TCVN 6325 (ASTM D 664) |
| Iodine value, g/100g | 120 max | 44.3 | EN 14111/TCVN 6122 |
| Oxidation stability at 110°C, hours | 6 min | 6.2 | ASTM D 2274/EN 14112 |
| Free glycerin, wt% | 0.020 max | 0.018 | ASTM D 6584 |
| Total glycerin, wt% | 0.240 max | 0.184 | ASTM D 6584 |
| Phosphorus content, wt% | 0.001 max | 0.0006 | ASTM D 4951 |
| 90% distillation fraction temp, °C | 360 max | 337 | ASTM D 1160 |
| Sodium/potassium, combined, mg/kg | 5.0 max | 3 | EN 14108, EN 14109 |
Table 23.8
Properties of cat-fish fat-based biodiesel blend B5 fuel and Vietnamese standard limits for biodiesel B5 according QCVN 1:2009
| Properties | B5 | QCVN 1:2009 limits |
| Density at 15°C, kg/m3 | 844.2 | 820–860 |
| Flash point, °C | 77 | – |
| Water and sediment, %vol | 0.007 | 0.02, max |
| Kinematic viscosity 40°C, mm2/s | 3.91 | 2–4.5 |
| Sulfated ash, wt% | 0.0025 | – |
| Sulfur, ppm | 470 | 500 |
| Copper strip corrosion, 50°C, 3 h | 1a | – |
| Cetane number | 54 | 46, min |
| Cloud point, °C | −3 | – |
| Carbon residue, 100% sample, wt% | 0.0487 | – |
| 90% distillation fraction temp, °C | 346 | 360, max |
Following a specific blending procedure, biodiesel B5 blend (5% B100% and 95% market diesel) was produced. This biodiesel B5 meets almost all limits of the biodiesel B5 standard described in Table 23.8. In addition, due to the low percentage of biodiesel B100 in the mixture, the B5 fuel has quite close properties to those of market diesel and standard limits of petrodiesel given in TCVN 5689-2005 (TCVN 5689-2005, 2005) (now changed to TCVN 5689-2013 (TCVN 5689-2013, 2013)). The cetane number, flash point, and kinematic viscosity are, in turn, 54, 79, and 3.91—slightly higher than those of market diesel (51, 78, and 3.87, respectively). These properties of biodiesel B5 analyzed within the mentioned national research project have contributed remarkably to the Directorate for Standards, Metrology and Quality development of B5 fuel standard in Vietnam.
23.4.2. Experimental set up and apparatus
Many testing objects such as engines, passenger cars, and light-duty vehicles have been used (Le Anh et al., 2009; Ha et al., 2009a,b,c), the findings from testing engines are going to be presented in detail as following.
The testing objects include two similar diesel engines D243, Belarus-made. One used market diesel, the other used biodiesel B5. These engines are usually used on tractors and fishing boats; specifications of the test engines are shown in Table 23.9.
Comparative tests were conducted on load curves and speed curves to investigate impacts of B5 fuel on engine's performance.
To assess exhaust emissions, R49 driving cycles (equivalent to Euro 2 emission standard—the one currently applied for heavy duty vehicle engines in Vietnam) were used for the testing engines.
The two testing engines were also operated within 300 h durability tests to assess engine components, lubrication oil, as well as engine performance and exhaust emissions.
The test-cell used to conduct comparative tests and durability tests is the high dynamic engine AVL test-cell for heavy duty vehicle engines.
Emission bench CEBII was used for gaseous emissions analysis. Particulate matter was sampled by the AVL Smart sampler 743. The testing apparatuses are presented in Fig. 23.18.
23.4.3. Test results and discussions
23.4.3.1. Findings from performance tests
Engine power (P) and brake-specific fuel consumption (FC) at full load of the same engine running with market diesel (Do) and biodiesel B5 (B5) are given in Fig. 23.19. It is observed in Fig. 23.19 that engine power is higher and brake-specific fuel consumption is lower with B5 fuel at all measuring points, although the improvement is not much due to the low percentage of biodiesel in the blend. The averaged engine power was increased 1.34% while averaged brake-specific fuel consumption was reduced 1.29%. The detailed explanation of this effect is shown together with impacts of B5 on exhaust emissions below.
Impacts of biodiesel B5 fuel on exhaust emissions in comparison with those market diesel can be observed in Fig. 23.20.
It is shown in Fig. 23.20 that with use of B5 fuel the HC, CO, and PM were reduced 12.29%, 8.60%, 2.25% respectively, while NOx was increased 1.93%. The reduction of HC, CO, and PM, and the increasing of NOx emissions with biodiesel fuels have already mentioned by many researches. Those shown in Fig. 23.21 by US Environmental Protection Agency (EPA) (United States Environmental Protection Agency, 2002) are an example of these effects.
Average emission changes found by the EPA for B20 (a blend of 20% biodiesel with conventional diesel) also showed significantly lower levels of emissions of specific toxic compounds for biodiesel and biodiesel blends, including aldehydes, PAH (polycyclic aromatic hydrocarbons), and nitrated-PAH (United States Environmental Protection Agency, 2002). However, a number of factors, such as different fuel system designs, engine calibrations, fuel quality, and blending rate can cause biodiesel emissions to differ significantly from the average values.
Figure 23.21 US Environmental Protection Agency evaluation of biodiesel effects on pollutant emissions for heavy-duty engines (United States Environmental Protection Agency, 2002).
The increasing of NOx was shown to be related to a small shift in fuel injection timing caused by the different mechanical properties of biodiesel relative to conventional diesel. Because of the higher bulk modulus of compressibility (or speed of sound) of biodiesel, there is a more rapid transfer of the fuel pump pressure wave to the injector needle, resulting in earlier needle lift and producing a small advance in injection timing (Knothe et al., 2005).
Of the testing case, 5% of biodiesel in the blend did not affect the reduction of the energy content much compared with that of the market diesel, while the structural oxygen content of a biodiesel fuel improved its combustion efficiency due to an increase in the homogeneity of oxygen with the fuel during combustion. Because of this the combustion efficiency of biodiesel is higher than that of petrodiesel. The results were that, with the biodiesel B5 fuel, the engine power was increased, and CO, HC, and PM emissions were reduced. Because of the low energy content of the biodiesel, higher biodiesel blends may lead to lower engine power and higher fuel consumption.
23.4.3.2. Findings from durability test
Variance of engine power and fuel consumption in percent (%) compared with those parameters before 300 h durability test of each testing engine are depicted in Fig. 23.22. Where D243-B5 and D243-Do are in turn of the testing engine fueled with biodiesel B5 and market diesel; D243-B5-150h means the testing engine D243 fueled with biodiesel B5 after 150 h. The same definitions are applied for D243-B5-300h, D243-Do-150h, and D243-Do-300h.
As shown in Fig. 23.22 the engine power decreased and the fuel consumption increased after 150 h and 300 h durability tests. Although the differences are not much due to short period running time, there is a clear consensus in the changes of engine power and fuel consumption. The fact that the engine fueled with biodiesel B5 had lower changes of engine power and fuel consumption after 150 h and 300 h durability test is not relevant with other research results which showed higher engine wear when the engine was fueled with biodiesel (Ayhan Demirbas, 2008).
Exhaust emissions were measured before, after 150 h, and after 300 h durability test following R49 driving cycle. The results are given in Fig. 23.23.
It is shown in Fig. 23.23 that none of the emission components meets Euro 2 emission standard limits. This reveals somehow the current emission quality of the diesel engine in Vietnam. The emission components HC, CO, and PM were higher but NOx was depleted within the test period. These results match with the deflection of engine power and fuel consumption as mentioned above, again longer testing period is needed to have better evaluation of engine durability.
Principally, as the wear of engine parts increased after a certain time of operation, compression pressure reduced and more combustion products blew to crankcase, the combustion process of the engine deteriorated causing worse engine performance, high hydrocarbon, carbon monoxide, and particulate matter were formed, whilst nitrogen oxide reduced due to lower temperature.
There was no harm to the engine's components observed during 300 h durability test with biodiesel B5 fuel. The potential coking of the injector was not found as the kinematic viscosity of the biodiesel B5 fuel is almost equal to that of the market diesel. However this has to be considered with higher biodiesel blends because high viscosity of the biodiesel causes the larger fuel droplet sizes. The fuel droplet size is a function of surface tension, density, and viscosity. Since the viscosity of biodiesel is high, the fuel droplets are large and hence may not be fully burned. The remaining biodiesel may then decompose at high temperatures (430–480°C) and form the deposits.
23.5. The concept of using biofuel on engines (prime mover)
From long experience in research on the application of alternative fuels, it is clear that the strategy of technology to apply alternative fuels depends on the designed requirements of the prime mover to match the characteristic properties of the fuel used and the characteristic properties of possible alternative fuels. When the designed fuel requirement of the prime mover is matched with the characteristic properties of an alternative fuel, the prime mover will operate as designed. But when the properties of an alternative fuel do not match, the prime mover will be operated outside (off-design) designed operation conditions and naturally the output (performance: power, fuel consumption, efficiency, etc., emission: exhaust gas emission, noise, etc., life time) will also be affected.
There are two ways to solve this problem: Firstly the prime mover designed requirement for fuel characteristics may be converted (adapted) to match the characteristic properties of alternative fuel or the characteristic properties of alternative fuel may be converted (adapted) to match the design fuel requirements of the prime mover. This concept is illustrated in Fig. 23.24. The most important requirement for the interface is the standard which must be met to satisfy the requirements of both sides. Which choice to use and how far to convert each, depends on many factors, including technical, location, economic, social, and political aspects. For example, in the case of biofuel for a high-technology engine which has a designed requirement for high-quality fuel, fuel conversion (adaptation) to a vegetable-based oil may require transesterification to produce FAME to fulfill the high-quality standard of fuel needed. However, for a stationary diesel engine where the operation condition is relatively constant, the required level of fuel quality may be relatively low, so a PPO with a lower production cost may be a suitable fuel. However, adapting the engine to use the PPO fuel may require the addition of a fuel heating system, a second fuel tank and a switching system to enable starting of the engine on diesel to warm up the engine and heat the PPO fuel and switch back to diesel before stopping the engine to flush the fuel system with diesel.
Clearly, when an engine designed for a certain fuel is converted to run on an alternative fuel, it is very important to see that the designed need of the engine for the characteristic properties of the fuel are matched by the characteristic properties of the alternative fuel. Consequently, it is very important to establish effective standards for alternative fuels.
23.6. Conclusion and remarks
As the majority of ASEAN countries are located in a humid tropical region, many different plant oils and animal fats are available as sources of biofuel feedstock. Consequently the properties and quality of differing biofuels vary considerably. The strategy of technology to apply alternative fuels depends on matching the characteristic properties of the fuel for which the engine was originally designed with the characteristic properties of possible alternative fuels. When the designed fuel requirement of the engine closely matches the characteristic properties of an alternative fuel, the engine will operate as designed, whereas if the properties of an alternative fuel do not match, the engine will operate outside (off-design) designed operation conditions and naturally the output (performance: power, fuel consumption, efficiency, etc., emission: exhaust gas emission, noise, etc., life time) will also be affected.
There are two ways to solve this problem: Firstly, the engine designed requirement for fuel characteristics may be altered or adapted to match the characteristic properties of alternative fuels or the characteristic properties of alternative fuels may be adjusted or adapted to match the design fuel requirements of the engine. The most important requirement for the interface is the standard which must be met to satisfy the requirements of both sides. What choices are made and how far adjustments are made in either respect depends on many factors, including technical, location, economic, social, and political aspects.
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