Comparative performance and emissions of IDI-turbo automobile diesel engine operated using degummed, deacidified mixed crude palm oil–diesel blends

Fuel 90 (2011) 1487–1491

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Comparative performance and emissions of IDI-turbo automobile diesel engine operated using degummed, deacidified mixed crude palm oil–diesel blends q T. Leevijit ⇑, G. Prateepchaikul Department of Mechanical Engineering, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand

a r t i c l e

i n f o

Article history: Received 10 June 2010 Received in revised form 8 October 2010 Accepted 12 October 2010 Available online 23 October 2010 Keywords: Diesel substitute Mixed crude palm oil Engine performance Engine emission

a b s t r a c t The performance and emissions of an indirect injection (IDI)-turbo automobile diesel engine operated with diesel and blends of degummed-deacidified mixed crude palm oil in diesel at portions of 20, 30, and 40 vol.% are examined and compared at various loads and speeds. Although fuel properties of the tested blends do not exactly meet all regulations of Thailand, they are all able to operate the engine. Comparing this with diesel, especially at full loads, shows that all blends produce the same maximum brake torque and power. A higher blending portion results in a little higher brake specific fuel consumption (+4.3% to +7.6%), a slightly lower brake thermal efficiency (–3.0% to –5.2%), a slightly lower exhaust gas temperature ( 2.7% to 3.4%), and a significantly lower amount of black smoke ( 30% to 45%). The level of carbon monoxide from the 20 vol.% blend is significantly lower ( 70%), and the levels of nitrogen oxides from all blends are little higher. Ó 2010 Elsevier Ltd. All rights reserved.

1. Introduction Due to the fast depletion of fossil fuels and worsening environmental pollution related to fossil fuel usage in recent years, vegetable oils (VOs) have come across as a good potential feedstock for producing diesel substitutes [1–3]. In Thailand, palm is currently shown to be the highest potential feedstock. Research is being conducted intensively in order to develop various grades of diesel substitute from palm oil. Because mixed crude palm oil (MCPO) can be easily produced with a screw-press of whole dried palm fruits, it has become of interest as another form of feedstock for diesel substitute production, especially for farmers living in or near sufficient economic communities. MCPO is a viscous liquid containing gum and high free fatty acid (FFA). Through ester and transesterification with methanol, methyl ester (ME) is produced [4]. Properties of ME are comparable to diesel. Studies on short- and long-term usage of ME show promising results when compared with diesel in terms of engine performance, emission, and wear [1–3,5], but the cost is quite high. Currently, seeking and developing lower cost diesel substitutes from MCPO is very important for sustainable development in Thailand. Although the cost of VOs is low, the direct use of VOs is unsatisfactory, especially for long-term use [1–3]. Regarding MCPO, maq Some preliminary results were presented in ME-NETT22, 15–17 October 2008, Pathumthani, Thailand ⇑ Corresponding author. Tel./fax: +66 74 558830. E-mail address: [email protected] (T. Leevijit).

0016-2361/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2010.10.013

jor drawbacks are from gum, FFA, and high viscosity. Gum causes to filter and injector nozzle plugging and increases viscosity. High FFA corrodes engine parts, increases viscosity, and tends to increase deposit [6]. High viscosity leads to poor atomization, incomplete combustion, injector choking, ring carbonization, and accumulation of fuel in the lubricating oil. Thus, to utilize MCPO as a diesel substitute, the above drawbacks must be examined further and improved. It is possible to reduce gum and FFA. Through consecutive reactions with phosphoric acid and sodium hydroxide solutions, gum and FFA are eliminated. The obtained product, called degummeddeacidified MCPO (Dg-aMCPO), mainly consists of triglycerides (TG). Through esterification with methanol, FFA and some parts of TG are changed to ME while gum is eliminated. The obtained product, called esterified MCPO, mainly contains of TG and ME. Separate experiments in the present study show that the costs of ME and Dg-aMCPO are higher than the cost of esterified MCPO at about 25% and 100% due to the cost of methanol and the loss of FFA, respectively. Thus, in term of economics, esterified MCPO is very interesting for low cost diesel substitute production. However, in terms of composition and fuel property, esterified MCPO can be roughly accounted for as the blend of Dg-aMCPO with ME. Due to the fact that ME shares similar fuel properties as diesel, esterified MCPO can then be roughly accounted for as a blend of DgaMCPO with diesel. Based on these assumptions, Dg-aMCPO has been selected as the base fuel, as the worst case of TG derived from MCPO, for the present study. If the potential use of Dg-aMCPO is known and satisfactory, then the use potential of esterified MCPO at various degrees of ME can be estimated.

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T. Leevijit, G. Prateepchaikul / Fuel 90 (2011) 1487–1491

To improve viscosity, VOs can be heated or blended with diesel. Although the satisfactory uses of preheated crude palm oil (CPO) are reported [7–9], Yankaew [5] found that the wear of agricultural engine due to long-term operation with preheated Dg-aMCPO is significantly higher than when it is operated with diesel. Thus, blending of Dg-aMCPO with diesel seems to be unavoidable. Some studies report acceptable results for using the blends of CPO and refined palm oil with diesel, especially for short-term uses [10,11], but there are no reports regarding the short- and longterm use potentials of Dg-aMCPO-diesel blends in both agricultural and automotive diesel engines. In the present study, however, the objective is focused on examining and comparing the performance and emissions of the indirect injection (IDI)-turbo automobile diesel engine when it is operated in a short term at various loads and speeds using diesel and blends of Dg-aMCPO in diesel at the selected portions of 20, 30, and 40 vol.%.

2. Materials and methods The tested blends were prepared using the following procedure. First, the MCPO containing FFA with about 15 g of NaOH/l oil reacted with a phosphoric acid solution (acid 0.0025 vol.% oil in water 10 vol.% oil) at 80 °C for 0.5 h and settled for 2 h. The separated upper phase reacted with a sodium hydroxide solution (17.9 g of NaOH/l oil in water 10 vol.% oil) at 80 °C for 2 h and settled for 8 h. The upper phase was separated and purified through water washing, gravity settling, and heating to remove the water. Finally, the Dg-aMCPO was obtained and blended with high-speed diesel (HSD). Important properties of the tested fuels are shown in Table 1. Thailand’s HSD regulation is provided for comparison. According to the ASTM standard, a suitable fuel used in compression ignition (CI) engines should have a cetane number within the range limits of 40–65 [12]. However, Thailand requires a cetane number of HSD P 47. The current literature explains that cetane numbers of HSD are in the range of 45–52 [9,13,14] and cetane numbers of CPO to ME fall within the range of 42–61 [1,7,9,15]. Although cetane numbers of all tested fuels are not actually measured, the above sufficient data can reliably indicate that they are expected to fall within the applicable range for CI engines. The viscosity of Dg-aMCPO was high. The viscosities of all blends were significantly lower; however, they still did not absolutely meet the regulation. The specific gravity at 15.6 °C for Dg-aMCPO was higher than the specific gravity of diesel (+10.7%) but the specific gravities of all blends met the requirement. The heating value of Dg-aMCPO was slightly lower than the heating value of diesel ( 5.5%). The acid values were also reported for all blends although this additional information is not regulated for HSD. The flash point of Dg-aMCPO was much higher than the flash point of diesel. The

Table 2 Test engine specifications. Engine type Displacement volume Number of cylinder Cylinder arrangement Bore/stroke Method of charging Compression ratio Maximum power (new engine) Maximum torque (new engine) Injection type Fuel supply system Cooling type

4-Stroke compression ignition 2446 cm3 4 Vertical in-line 92 mm/92 mm Turbocharged 21:1 69 kW at 4000 rpm 215 Nm at 2400 rpm Indirect injection mechanically controlled Distribution pump Water

flammable hazards of the blends tended to be lower, but this may be attributed to lower volatility characteristics. The second-hand automobile diesel engine of TOYOTA 2L-turbo, which its details are listed in Table 2, was used in the test. The engine was tested on an ESSOM dynamometer model MT504 using a constant speed test at 2400 rpm under loads in the range of 5– 37.5 kW, and it was also tested with a full-loaded variable speed test for speeds in the range of 2000–2800 rpm. Ambient temperature, relative humidity, air and fuel flow rates, brake torque, engine speed, and exhaust gas temperature (EGT) were recorded using the data acquisition system of the dynamometer. Black smoke was measured with a BOSCH smoke detector model ETD 020. Carbon monoxide (CO), nitric oxide (NO), nitrogen dioxide (NO2), carbon dioxide (CO2), and oxygen (O2) were measured using a TESTO flue gas analyzer model 350 M/XL.

3. Results and discussion 3.1. General engine operation Although fuel properties of all tested blends are not exactly shown to completely meet each regulation requirement, general observations reveal that the engine can be normally operated using all blends as same as using diesel. There were no serious problems, such as fuel pumping and injection, cold starting, harmful knocking, and immediately piston ring sticking found in the present study. Although engine operation characteristics in terms of air and fuel flow rates are not explicitly shown, significant notes are as follows. Volumetric flow rates of inducted air, particularly for mass flow rates of dry air, were the same for all tested fuels at any point in the tested range, and the inter-relative differences were within ±1.2%. The engine had to supply a slightly higher mass flow rate of fuel when operating with the blend at a higher portion of Dg-aMCPO. The fuel–air mixture was richer for constant speed

Table 1 Important fuel properties of diesel, Dg-aMCPO, and blends of Dg-aMCPO in diesel. Property

Test method

Thailand’s regulation high-speed diesel

Diesel

Dg-aMCPO

Dg-aMCPO-Diesel Blends (vol.% of Dg-aMCPO)

Cetane number Viscosity at 40 °C (mm2/s) Specific gravity at 15.6 °C Specific gravity at 40 °C Lower heating value (MJ/kg) Acid value (mgKOH/g) Flash point ( °C)

ASTM D613 ASTM D445 ASTM D4052

P47 1.8–4.1 0.81–0.87 – – – P52

45–52a 3.10 0.840 0.828 41.6 – 69

42b 46.7 0.930 0.916 39.3 5.2 >240c

In applicable range for CI engine 5.28 7.11 8.93 0.858 0.867 0.876 0.845 0.852 0.860 41.1 41.0 40.8 1.0c 1.6c 2.1c – – –

20

a b c

ASTM D240 ASTM D664 ASTM D93

Refs. [7,13,14]. Refs. [1,9]. The actual value is not determined.

30

40

1489


operation at a high load, and it was leaner for full load operation at a high speed. 3.2. Engine performance All fuels provided the same maximum brake torque corresponding to the same maximum brake power at any speed within the tested range, and the inter-relative differences were within ±2% (experimental graphs are not shown). Altun et al. [16] also stated the same findings when testing the blend of sesame oil with diesel. The brake specific fuel consumption (BSFC) of the engine is shown in Fig. 1, and the corresponding brake thermal efficiency

Engine Load (kW): Constant Speed Test at 2,400 rpm 0

5

10

15

20

Brake Specific Fuel Consumption (g/kW-h)

600

25

30

35

40

Diesel Dg-aM CPO 20 vol% in Diesel Dg-aM CPO 30 vol% in Diesel Dg-aM CPO 40 vol% in Diesel

500

400

300 Part-a

200 350

Part-b

250

150 1800

2000

2200

2400

2600

2800

3000

Engine Speed (rpm): Full-Loaded Variable Speed Test Fig. 1. Brake specific fuel consumption.

(BTE) is shown in Fig. 2. It could be seen from Part-a of Figs. 1 and 2 that the engine could convert the supplied fuel to work efficiently when it operated at high loads of P25 kW. This is the general aspect of the internal combustion engine. However, the lowest BSFC and highest BTE were obtained at a full load. For full load operation (Part-b of Figs. 1 and 2), the BSFC significantly increased and the BTE significantly decreased when operating at high speeds of P2200 rpm. This is due to the significant increases in friction and heat loss. Over the tested range, the BSFC of all blends was slightly higher compared to diesel, while the BTE was slightly lower. Regarding the average for all speeds under the full load operation, the BSFCs of the 20, 30, and 40 vol.% blends were higher than diesel at about +4.3%, +5.9%, and +7.6%, respectively, while the BTEs were lower at about 3.0%, 4.1%, and 5.2%, respectively. This is importantly due to the lower heating value of Dg-aMCPO. 3.3. Exhaust gas emissions The emissions of EGT, black smoke, CO, and nitrogen oxides (NOx) in the exhaust gas are shown in Figs. 3–6, respectively. The emissions of CO2 and O2 of all tested fuels were similar at any point over the tested range, and the inter-relative differences were within ±2% (experimental graphs are not shown). It could be seen from Part-b of Figs. 4–6 that the concentrations of black smoke, CO, and NOx slightly decreased with increasing speeds. This is mainly due to the dilution effect of more excess air. In Fig. 3, the EGT significantly increased with increasing loads in the case of the constant speed operation and slightly decreased with increasing speeds in the case of full load operation. These results are in agreement with the fact that the combustion temperature and the corresponding EGT of the diesel engine increases when operating it with the richer mixture. The EGT of all blends was slightly lower than the EGT of diesel. The average for all speeds under the full load operation, EGTs of the 20, 30, and 40 vol.% blends were lower than diesel at about 2.7%, 3.0%, and 3.4%, respectively. Black smoke is produced mainly during the diffusive combustion phase, especially in locally rich zones. Sufficient fuel–air mix-


5

10

15

20

25

30

35


0

45

500 Part-a

400

25


15

5 45

Part-b

35

25 1800

Exhaust Gas Temperature (°C)

Brake Thermal Efficiency (%)

35

5

10

15

20

25

30

35

40


300

200 Part-a

100 550

Part-b

450

2000

2200

2400

2600

2800

3000

Engine Speed (rpm): Full-Loaded Variable Speed Test Fig. 2. Brake thermal efficiency.

350 1800

2000

2200

2400

2600

2800

Engine Speed (rpm): Full-Loaded Variable Speed Test Fig. 3. Exhaust gas temperature.

3000

1490



5

10

15

20

25

30

40

Part-a

350

NO x in Exhaust Gas (ppm)

Black Smoke (BSU)

0.8

0.4

0.0 Part-b

1.0

0.6

5

10

15

20

25

30

35

40


250

150 Part-a

50 450 Part-b

350

0.2 1800

2000

2200

2400

2600

2800

3000

Engine Speed (rpm): Full-Loaded Variable Speed Test

5

10

15

20

25

30

35

40

600 Diesel Dg-aM CPO 20 vol% in Diesel Dg-aM CPO 30 vol% in Diesel Dg-aM CPO 40 vol% in Diesel

Part-a

450

300

150

0 300 Part-b

150

0 1800

2000

2200

2400

2000

2200

2400

2600

2800

3000

Fig. 6. NOx in exhaust gas.


250 1800

Engine Speed (rpm): Full-Loaded Variable Speed Test

Fig. 4. Black smoke.

CO in Exhaust Gas (ppm)

0 450


1.2

Engine Load (kW): Constant Speed Test at 2,400 rpm

35

2600

2800

3000

Engine Speed (rpm): Full-Loaded Veriable Speed Test Fig. 5. CO in exhaust gas.

ing is necessary for preventing black smoke formation. The results in Fig. 4 (Part-a) indicated that black smoke was quite constant within the load range of 5–30 kW, and it increased significantly at higher loads of >30 kW. Increasing the temperature in the cylinder enhances fuel–air mixing, but it becomes insufficient with such a high load range when compared to the increase of supplied fuel. The black smoke from all blends was significantly lower in quantity than the black smoke from diesel. The average for all speeds under full load operation, the amounts of black smoke from the 20, 30, and 40 vol.% blends were lower than the amount of black smoke from diesel at about 30%, 40%, and 45%, respectively. The higher blending portion of Dg-aMCPO resulted in a lower amount of black smoke due to the oxygen content in Dg-aMCPO. This finding is in agreement with the conclusion from Ren et al.

[13], which explains that smoke reduction is strongly related to the oxygen mass fraction in fuel that leads improvement of the diffusive combustion and promotion of the post-flame oxidation of black smoke in the late expansion and exhaust processes. Other researchers [7,14] also came to similar conclusions when testing different VOs and their blends with diesel. Diesel engines generally operate with lean mixtures. There is a sufficient O2 for complete combustion, but a small amount of CO can form due to poor mixing, locally rich zones, and frame quenching. In Fig. 5 (Part-a), CO gradually decreased with increasing loads. This is due to the increase of temperature in the cylinder. This enhances the fuel–air mixing, resulting in better combustion that is sufficient to reduce CO. Over the tested range, the CO emission of the 20 vol.% blend was significantly lower compared to diesel, at about 70% at full loads, while the emission of the 30 vol.% blend was similar and the emission of the 40 vol.% blend was slightly higher. This is due to the effects of two factors: (1) oxygen content in Dg-aMCPO promotes easier burning, (2) high viscosity makes it more difficult to be atomized, and the resulting locally rich mixtures cause more CO to be produced during combustion. It could be concluded that the oxygen content in Dg-aMCPO could overcome the adverse effects of high viscosity when the blending portion was 630 vol.%. Bari et al. [8] and Almeida et al. [9] also found that CO emissions of neat CPO and refine palm oil are higher than emissions from diesel. Although diesel engines operate with lean mixtures, much of fuel still burns close to stoichiometric, and almost all of NOx is produced in these flame-front zones. It is well known that NOx formation strongly depends on the combustion temperature and oxygen concentration; however, for CI engines, formation also depends on the amount of flame zone that is proportional to the mass of supplied fuel [17]. The results in Fig. 6 (Part-a) showed that NOx significantly increased with increasing loads, which was to be expected. This is due to the increase of temperature in the cylinder and the larger flame zones that were produced as more fuel was supplied. In Fig. 6 (Part-b), the NOx emission of the 20 vol.% blend was slightly higher than the emission from diesel, while its EGT was slightly lower (Fig. 3). This is possible because the effects of the larger frame zones due to the higher mass of supplied blend, and the


higher oxygen concentration in frame zones due to the oxygen content in Dg-aMCPO, overcome the effects of temperature change. For the blends with >20 vol.%, EGTs slightly decreased, and NOx emissions also slightly decreased. This is due to the fact that the decrease in temperature began to overcome the remaining effects. In total, the average for all speeds under full load operation, NOx emissions of the 20, 30, and 40 vol.% blends were higher than diesel at about +6.6%, +5.2%, and +2.9%, respectively. Kalam and Masjuki [7] and Bari et al. [8] also found that NOx emissions of esterified and preheated CPO are greater than the emissions from diesel. 4. Conclusion Performance and emissions of the IDI-turbo automobile diesel engine operated using diesel and blends of Dg-aMCPO in diesel at portions of 20, 30, and 40 vol.% are examined and compared at various loads and speeds. Although fuel properties of the tested blends are not exactly shown to absolutely meet all of Thailand’s regulations for HSD, all of them can operate the engine. Comparing this with diesel, especially at full loads, shows that all blends produce the same maximum brake torque and power. The higher blending portion results in a little higher level of BSFC (+4.3% to +7.6%), a slightly lower level of BTE ( 3.0% to 5.2%), a slightly lower level of EGT ( 2.7% to 3.4%), and a significantly lower amount of black smoke ( 30% to 45%). The CO emission of the 20 vol.% blend is significantly lower ( 70%), and the NOx emissions of all blends are little higher. In conclusion, blends of Dg-aMCPO in diesel up to 40 vol.% have been shown to be satisfactory for short-term usage in the IDI-turbo automotive diesel engine. Furthermore, comparative testes of 1000 h for automotive diesel engines and 5000 h for agricultural diesel engines have been conducted and are nearly complete at Prince of Songkla University in order to show that whether or not these blends are suitable for long-term use. Acknowledgments The authors would like to acknowledge the Chaipattana Foundation under the support of the King of Thailand for the research fund.

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Comparative performance and emissions of IDI-turbo automobile diesel engine operated using degummed, deacidified mixed crude palm oil–diesel blends

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