5. Indicated pressure, HRR, and effect of blends on (TDI) CI engine

In combustion studies, the CN measures the ease with which a fuel auto-ignites. The CN is therefore a measure of a fuel's auto-ignition delay, the period between the start of injection and the first identifiable pressure increase during the combustion of the fuel. The heat release is the net heat of combustion generated by chemical reactions of the fuel affected by the fuel's physical and chemical properties in the combustion process of the fuel. The fuel is injected timely and periodically in the combustion chamber by means of fuel injectors. The mean pressure developed due to the heat released each cycle is termed as the IP, which is the pressure reading on an indicator diagram.

which is not desirable as it results in a hard start of the test engine. When comparing the CNs, it was found that the CN for RMEs was 55 whereas for DF was 51. The CN for n-butanol was approximately 25 and CN for ethanol was approximately 8. Therefore, increasing the shared volume of n-butanol above 20% in Diesel fuel displaces richer components of CN in DF than in n-butanol prolonging start of combustion SOC and prompting the hard start of the engine. Therefore, this limits how many fractions of n-butanol can be blended with DF. A blend of greater than 20% shared volume of n-butanol in DF further reduces the CN of the blend. Therefore, the

n-Butanol-Diesel (D2) Blend Fired in a Turbo-Charged Compression Ignition Engine: Performance and Combustion…

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45

limiting point would be when the final CN of the blend is too low for the engine to start.

restrict the fuel flow of the blends when not modified (see Section 4.3).

needle-valve lifting pressure on the injectors was set to 17.5 0.5 MPa.

5.1. Analysis

These results concur with the findings of past study conducted by [19], who obtained a prolonged ID by adding an alcoholic admix of E10 to BD30 and the ID was shortened by reducing the alcohol fraction. In the previous study, the engine used was a type T40 M, D-144 diesel engine, which was newly acquired for research in 2003 and was used throughout the period 2004–2008 [22]. Further details of the engine include the following: (a) mechanical power of 37 kW on 1600 rpm, (b) naturally-aspirated; (c) direct-injection, (d) four-cylinders; (e) diameter of 110 mm; (f) stroke of 120 mm, (g) compression ratio was 16.5:1, (h) dished-piston; and (i) compression ignition engine. The fuel was delivered by a single-plunger, fuel-pump, and type: ND 21/4, through three-hole injection-nozzles; with initial fuel delivery starting at 25 1 BTDC. The

Both biodiesel and n-butanol fractions in DF reduces the combustion duration of the blend. However, n-butanol has a limitation and may not be increased any further than 20% (v/v) in

The combustion characteristics of blend B20 in the author's study is compared with Bu20 (nbutanol 20%, biodiesel 40%, and diesel 40%) by others [20]. In the latter study, B50 (biodiesel 50% and diesel fuel 50%) was the preferred fuel type over Bu20 in terms of maximum pressure and heat release rate. The operating conditions were: single cylinder, four strokes, direct injection, air cooled, TecQuipment TD212 diesel engine, naturally aspirated, maximum power 3.5 kW at 3600 rpm and maximum heat release rate (HRR) 15.5 J/deg. In the author's study using B20, the maximum HRR was 43.5 J/deg. for four cylinders, four strokes, direct injection, turbo-charged diesel engine as specified in section (1). In a study by others, B50 was recommended as the most suitable blend fired in a diesel engine. Combustion duration for DF is higher (within the range for the indicated power of 1.2 and 1.6 kW) than Bu20. Combustion duration in the author's study using B20 (n-butanol 20%, DF 80%) was reduced as observed by a steeper profile of the heat curve in comparison with DF (D2) see Figure 5a–c. Figure 5a–c illustrate the mean IP which did not change much in terms of peak pressure for the increase of HRR at lower speeds for all test fuels. The IP and HRR were evaluated at 2500, 3000, and 3500 rpm for the entire test fuels at full load respectively. The operating BMEP for the blends are presented in Table 3. It was observed that at 3500, 3000 and 2500 rpm within 5 CAD the premixed heat release was within 17–24 J/deg., 15–23 J/deg., and 10–20 J/deg., respectively. In the study by others [20], the maximum pressure was obtained by DF followed by B50 and then Bu20 [20] at a constant speed of 1500 rpm. This could be attributed to the effect of the EDC which could

Figure 5a–c illustrates the effect of the mean pressure and the heat release rate at different speeds of 2500, 3000, 3500 rpm on blends compared with DF. The operating conditions depicted by brake mean effective pressure (BMEF) for the blends is given in Table 3. It is observed that there are very little differences in the peak pressures obtained at the different speeds. After the Ignition delay, there exists a rapid combustion phase that causes a steep rise in the in-cylinder pressure and heat release. This is known as the premixed phase where after atomization of the fuel, the fuel droplets are evaporated and ignited by the heated air from the compression process prior to the start of injection. The peak pressure is controlled by the ignition delay, the rate of fuel injection, the speed of the engine and including the compression ratio for the engine. The remaining oxygen of the air charge limits the final phase slowing down the combustion rate (see Figure 5a–c heat release curve) as the crank angles advance toward the beginning of exhaust process. Increasing the shared volume of n-butanol in DF as well as the engine speed coupled with the molecular oxygen content of the oxygenated fuel improves the mixing quality of the blend. This phenomenon is observed in the increasingly distinguishable premixed combustion phase with an increase of engine speed (see Figure 5b and c heat release curve). The premixed phase is similar for B5 and B10 at 2500 and 3000 rpm. Higher heat release rate is observed at 2500 rpm because of the more resident time (s) allowed for the mass of fuel to burn than at higher speeds of 3000 and 3500 rpm. The mixing controlled combustion or final phase just after the premixed stage indicated a steeper slope on the heat release curve for the blends than DF with increasing the shared volume of n-butanol in the blend. By this, the combustion efficiency of the blends was better than DF and the combustion duration shortened.

In past studies conducted by Ref. [19], the effect of using BD30 (30% biodiesel or methyl ester, from rapeseed oil (RME) blended with 70% diesel fuel) alone shortened the ignition delay (ID). By adding E10 (10% ethanol and 90% diesel fuel) in other words, BD30 + E10 prolonged the ID,


Table 3. Operating BMEP (bars) for Figure 5a–c [21].

which is not desirable as it results in a hard start of the test engine. When comparing the CNs, it was found that the CN for RMEs was 55 whereas for DF was 51. The CN for n-butanol was approximately 25 and CN for ethanol was approximately 8. Therefore, increasing the shared volume of n-butanol above 20% in Diesel fuel displaces richer components of CN in DF than in n-butanol prolonging start of combustion SOC and prompting the hard start of the engine. Therefore, this limits how many fractions of n-butanol can be blended with DF. A blend of greater than 20% shared volume of n-butanol in DF further reduces the CN of the blend. Therefore, the limiting point would be when the final CN of the blend is too low for the engine to start.

The combustion characteristics of blend B20 in the author's study is compared with Bu20 (nbutanol 20%, biodiesel 40%, and diesel 40%) by others [20]. In the latter study, B50 (biodiesel 50% and diesel fuel 50%) was the preferred fuel type over Bu20 in terms of maximum pressure and heat release rate. The operating conditions were: single cylinder, four strokes, direct injection, air cooled, TecQuipment TD212 diesel engine, naturally aspirated, maximum power 3.5 kW at 3600 rpm and maximum heat release rate (HRR) 15.5 J/deg. In the author's study using B20, the maximum HRR was 43.5 J/deg. for four cylinders, four strokes, direct injection, turbo-charged diesel engine as specified in section (1). In a study by others, B50 was recommended as the most suitable blend fired in a diesel engine. Combustion duration for DF is higher (within the range for the indicated power of 1.2 and 1.6 kW) than Bu20. Combustion duration in the author's study using B20 (n-butanol 20%, DF 80%) was reduced as observed by a steeper profile of the heat curve in comparison with DF (D2) see Figure 5a–c. Figure 5a–c illustrate the mean IP which did not change much in terms of peak pressure for the increase of HRR at lower speeds for all test fuels. The IP and HRR were evaluated at 2500, 3000, and 3500 rpm for the entire test fuels at full load respectively. The operating BMEP for the blends are presented in Table 3. It was observed that at 3500, 3000 and 2500 rpm within 5 CAD the premixed heat release was within 17–24 J/deg., 15–23 J/deg., and 10–20 J/deg., respectively. In the study by others [20], the maximum pressure was obtained by DF followed by B50 and then Bu20 [20] at a constant speed of 1500 rpm. This could be attributed to the effect of the EDC which could restrict the fuel flow of the blends when not modified (see Section 4.3).

These results concur with the findings of past study conducted by [19], who obtained a prolonged ID by adding an alcoholic admix of E10 to BD30 and the ID was shortened by reducing the alcohol fraction. In the previous study, the engine used was a type T40 M, D-144 diesel engine, which was newly acquired for research in 2003 and was used throughout the period 2004–2008 [22]. Further details of the engine include the following: (a) mechanical power of 37 kW on 1600 rpm, (b) naturally-aspirated; (c) direct-injection, (d) four-cylinders; (e) diameter of 110 mm; (f) stroke of 120 mm, (g) compression ratio was 16.5:1, (h) dished-piston; and (i) compression ignition engine. The fuel was delivered by a single-plunger, fuel-pump, and type: ND 21/4, through three-hole injection-nozzles; with initial fuel delivery starting at 25 1 BTDC. The needle-valve lifting pressure on the injectors was set to 17.5 0.5 MPa.

#### 5.1. Analysis

5. Indicated pressure, HRR, and effect of blends on (TDI) CI engine

pressure reading on an indicator diagram.

44 Improvement Trends for Internal Combustion Engines

duration shortened.

Table 3. Operating BMEP (bars) for Figure 5a–c [21].

In combustion studies, the CN measures the ease with which a fuel auto-ignites. The CN is therefore a measure of a fuel's auto-ignition delay, the period between the start of injection and the first identifiable pressure increase during the combustion of the fuel. The heat release is the net heat of combustion generated by chemical reactions of the fuel affected by the fuel's physical and chemical properties in the combustion process of the fuel. The fuel is injected timely and periodically in the combustion chamber by means of fuel injectors. The mean pressure developed due to the heat released each cycle is termed as the IP, which is the

Figure 5a–c illustrates the effect of the mean pressure and the heat release rate at different speeds of 2500, 3000, 3500 rpm on blends compared with DF. The operating conditions depicted by brake mean effective pressure (BMEF) for the blends is given in Table 3. It is observed that there are very little differences in the peak pressures obtained at the different speeds. After the Ignition delay, there exists a rapid combustion phase that causes a steep rise in the in-cylinder pressure and heat release. This is known as the premixed phase where after atomization of the fuel, the fuel droplets are evaporated and ignited by the heated air from the compression process prior to the start of injection. The peak pressure is controlled by the ignition delay, the rate of fuel injection, the speed of the engine and including the compression ratio for the engine. The remaining oxygen of the air charge limits the final phase slowing down the combustion rate (see Figure 5a–c heat release curve) as the crank angles advance toward the beginning of exhaust process. Increasing the shared volume of n-butanol in DF as well as the engine speed coupled with the molecular oxygen content of the oxygenated fuel improves the mixing quality of the blend. This phenomenon is observed in the increasingly distinguishable premixed combustion phase with an increase of engine speed (see Figure 5b and c heat release curve). The premixed phase is similar for B5 and B10 at 2500 and 3000 rpm. Higher heat release rate is observed at 2500 rpm because of the more resident time (s) allowed for the mass of fuel to burn than at higher speeds of 3000 and 3500 rpm. The mixing controlled combustion or final phase just after the premixed stage indicated a steeper slope on the heat release curve for the blends than DF with increasing the shared volume of n-butanol in the blend. By this, the combustion efficiency of the blends was better than DF and the combustion

In past studies conducted by Ref. [19], the effect of using BD30 (30% biodiesel or methyl ester, from rapeseed oil (RME) blended with 70% diesel fuel) alone shortened the ignition delay (ID). By adding E10 (10% ethanol and 90% diesel fuel) in other words, BD30 + E10 prolonged the ID,

Speed [rpm] B0 B05 B10 B20 12.45 12.25 11.92 11.76 12.23 12.09 11.8 11.50 11.19 10.98 10.74 10.64

Both biodiesel and n-butanol fractions in DF reduces the combustion duration of the blend. However, n-butanol has a limitation and may not be increased any further than 20% (v/v) in DF due to its significantly low CN. Biodiesel, on the other hand, has a higher CN making it possible to increase fractions for blending in DF. Results obtained in the author's study involving only n-butanol in DF and comparing with a study by others [20] who included biodiesel in n-butanol/DF blend indicated enhanced combustion characteristics when biodiesel was added. It was observed that B50 performed better than Bu20.

blends were used as indicated in Figure 7. The soot concentration for the blends was always lower than that of DF in both the speeds: 1500 and 3000 rpm, when measured against BMEP. The soot emission reduction with increasing the shared volume of n-butanol to DF was 55.5, 77.8, and 85.1% for B5, B10, and B20, respectively in the 75% load with 1500 rpm. The reduction of soot emission for all the test fuels was higher in the engine tests with 3000 rpm than with 1500 rpm. The reduction of soot emission was highest in the 75% load. The small deviation exhibited by the blends from the trend in the 25 and 50% load with 3000 rpm is not well known: it might be caused by the temperature distribution during the combustion process, as temperature also plays an important role in the formation and oxidation of soot.

n-Butanol-Diesel (D2) Blend Fired in a Turbo-Charged Compression Ignition Engine: Performance and Combustion…

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A study was conducted to determine the performance and combustion characteristics of a mixture of n-butanol in diesel fuel in the ratios: 5,10, and 20% (B5:n-butanol 5% with diesel fuel 95%, B10 and B20) using a turbo-charged four cylinder compression ignition engine. The results were compared with studies by others using similar shared volumes of n-butanol (20%, v/v), including 40% (v/v) biodiesel. Combustion characteristics of B20 (n-butanol 20% and 80% DF) in the author's study improved when the study was compared with the study by others where 40% biodiesel was added to B20. A higher value of the standard deviation for DF than the blends was observed from the standard deviation diagram, indicating a more stable combustion process for the blends than DF. Soot emission was greatly reduced in both compared studies (in author's study and Ref. [19]). This was when bioethanol admix was introduced to BD30/DF blend in the other study [19]. In both cases, smaller proportions of bioalcohol were used. In the author's study, the soot reduction relative to DF at 1500 rpm at 75% load for B05, B10, and B20 mixtures was 55.5, 77.8, and 85.1% respectively. This reduction is a significant advantage of blending DF with smaller shared volumes of bioalcohol. The study has indicated a highly prospective fuel in n-butanol/DF bioalcohol to be promoted in the blending science to reduce particulate matter and improve combustion efficiency in the

application of the diesel fuel in reciprocating internal combustion engines.

Moreover, the results should be compatible with figures. I cannot understand how authors say, for example, about ID using pressure development figures, premixed combustion period using HRR or combustion stability which requires a cyclic analysis. Certainly, pressure development and HRR curves are a indicator for such parameters, but the author should define, first, the terms based on the related quantity for better understanding of a reader. Moreover, the results

The authors acknowledge and are greatly indebted for the financial support from the joint research collaboration between Hungary/South Africa Funding (UID 72384 and TET\_10-1- 2011-0005); for facilitation by the two universities, Tshwane University of Technology, Pretoria,

7. Conclusions

should be discussed more.

Acknowledgements

Figure 6 illustrates the standard deviation of pressure cycles. It can be deduced that blends have less deviation of pressure from the mean value than diesel. In other words, blends have a more stable combustion characteristic than the reference fuel. The blend B10 revealed a less stable combustion quality than the other blends by indicating a higher standard deviation at all speeds. A similar study by others [20] measured the thermodynamic cycle-to-cycle variations for the in-cylinder pressure using the coefficient of variation (COV) to determine combustion stability for the blends Bu20 and B50. They found that the COV for the blends was below 5% for the engine loads, which agrees with the author's study where the standard deviation of the mean in-cylinder pressure cycles was below that of DF. Figure 6 results should reconsider referring to other studies.
