**4.1. Birrea seed oil yield**

The oil yield of birrea seeds regarded as the actual oil content in this study is the one deter‐ mined using solvent extraction method and not mechanically extracted, as the latter is de‐ pendent on machine efficiency. After running four soxhlet extractions, the average oil content of birrea seeds was determined to be 58.56% by mass. Table 4 compares oil yield lev‐ el of birrea seeds with that of mostly studied plant species obtained from literature.

y = 0.1919x - 0.0072 R² = 0.9997

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Concentration (ppm)

The composition analysis of birrea biodiesel was done using a combination of AMDIS (Au‐ tomated Mass Spectral Deconvolution and Identification Software) and Data Analysis Soft‐ ware at a minimum match factor of 70%. The total number of compounds identified is fortyfive (45), of which thirty-six (36) are esters (appendix 1). The peak areas of the compounds were used to establish the ester content of the biodiesel sample. Using analysis data shown in appendix 1, ester content was computed to be 82% according to equation 4. This is about 15% below the requirements of the European standard EN 14214. The American Standard, ASTM D 6751-02, has no specification for this property. The ester content may however be

improved by modifying the biodiesel conversion process as discussed in section 3.3.

<sup>∑</sup> (Peak areas of all compounds) ×100 (4)

Ester content (%) <sup>=</sup> <sup>∑</sup> (Peak areas of all esters)

0

**Figure 4.** Methyl palmitate calibration curve for the standard sample

0.02

0.04

0.06

Peak area ratios (Analyte/IS)

0.08

0.1

0.12


**Table 4.** Oil yield levels of birrea seeds and common oil seed species.

#### **4.2. Birrea biodiesel chemical composition**

The chemical composition of birrea biodiesel was analysed according to the procedure de‐ scribed in section 2.3. Standard (Reference) samples supplied by AccuStandards were ana‐ lyzed to confirm that sample composition matched the composition listed on technical data sheets that accompanied the samples. To draw calibration curves for each ester identified in the standard samples, peak area ratios (Analyte/IS) were plotted against actual ester concen‐ tration in parts per million (ppm) for different gross concentrations of standard samples. Ac‐ tual concentration of an ester was calculated as a percentage of the same ester's concentration (as per standard sample data sheets) multiplied by gross concentration of the standard sample at varying dilution levels. Figure 4 shows a typical calibration curve for methyl palmitate for the standard sample.

To quantify the methyl palmitate detected in birrea biodiesel, the peak area ratio of the ester (Analyte/IS) was calculated and used in the calibration curve above to interpolate the actual concentration of the compound. The concentration value was validated by substituting the peak area ratio value for the y-value in the equation of the straight line graph and calculat‐ ing the value of x, which represents the concentration of Methyl palmitate in birrea biodie‐ sel. The R2 value, also called the goodness of fit, is a correlation value which indicates how closely a function fits a given set of experimental data.

**Figure 4.** Methyl palmitate calibration curve for the standard sample

**4. Results and discussion**

196 Advances in Internal Combustion Engines and Fuel Technologies

Sclerocarya birrea 58.56

The oil yield of birrea seeds regarded as the actual oil content in this study is the one deter‐ mined using solvent extraction method and not mechanically extracted, as the latter is de‐ pendent on machine efficiency. After running four soxhlet extractions, the average oil content of birrea seeds was determined to be 58.56% by mass. Table 4 compares oil yield lev‐

The chemical composition of birrea biodiesel was analysed according to the procedure de‐ scribed in section 2.3. Standard (Reference) samples supplied by AccuStandards were ana‐ lyzed to confirm that sample composition matched the composition listed on technical data sheets that accompanied the samples. To draw calibration curves for each ester identified in the standard samples, peak area ratios (Analyte/IS) were plotted against actual ester concen‐ tration in parts per million (ppm) for different gross concentrations of standard samples. Ac‐ tual concentration of an ester was calculated as a percentage of the same ester's concentration (as per standard sample data sheets) multiplied by gross concentration of the standard sample at varying dilution levels. Figure 4 shows a typical calibration curve for

To quantify the methyl palmitate detected in birrea biodiesel, the peak area ratio of the ester (Analyte/IS) was calculated and used in the calibration curve above to interpolate the actual concentration of the compound. The concentration value was validated by substituting the peak area ratio value for the y-value in the equation of the straight line graph and calculat‐ ing the value of x, which represents the concentration of Methyl palmitate in birrea biodie‐

value, also called the goodness of fit, is a correlation value which indicates how

el of birrea seeds with that of mostly studied plant species obtained from literature.

**Plant species Yield (%Weight) References**

Jatropha curcas 163.16; 246.27; 350-60 1[32]; 2[33]; 3[21]

Linseed 133.33 1[34]

Palm 144.60 1[34]

**Table 4.** Oil yield levels of birrea seeds and common oil seed species.

**4.2. Birrea biodiesel chemical composition**

methyl palmitate for the standard sample.

closely a function fits a given set of experimental data.

sel. The R2

Soybean 118.35; 220.00 1[34]; 2[35]

**4.1. Birrea seed oil yield**

The composition analysis of birrea biodiesel was done using a combination of AMDIS (Au‐ tomated Mass Spectral Deconvolution and Identification Software) and Data Analysis Soft‐ ware at a minimum match factor of 70%. The total number of compounds identified is fortyfive (45), of which thirty-six (36) are esters (appendix 1). The peak areas of the compounds were used to establish the ester content of the biodiesel sample. Using analysis data shown in appendix 1, ester content was computed to be 82% according to equation 4. This is about 15% below the requirements of the European standard EN 14214. The American Standard, ASTM D 6751-02, has no specification for this property. The ester content may however be improved by modifying the biodiesel conversion process as discussed in section 3.3.

$$\text{Ester content} \left( \% \right) = \frac{\sum \text{(Peak areas of all customers)}}{\sum \text{(Peak areas of all compounds)}} \times 100 \tag{4}$$

Some of the most abundant esters identified in birrea biodiesel are presented in table 5, together with their concentrations, while the complete list of constituent compounds is appended.


1

**Figure 5.** Viscosity variation with temperature

**4.4. Acidity of birrea biodiesel fuel**

20 25 30 35 40 45 50 55 60

Temperature (0C) Birrea B100 Petroleum Diesel ASTM Limits EN Limits

From figure 5, it is evident that birrea biodiesel largely meets quality requirements of both ASTM D-6751 and EN 14214 standards, while petroleum diesel (used in this study) viscosity profile is significantly lower than the requirements of the European standards. The kinemat‐

and is likely to have a better combustion profile when used as a fuel in a diesel engine. The low viscosity of petroleum diesel may not provide sufficient lubrication for the precision fit of fuel injection pumps, resulting in increased wear or leakage. Leakage will, under normal circumstances, correspond to a power loss for the engine as mentioned earlier. The birrea biodiesel fuel was therefore found to be suitable for use in compression ignition (CI) engine.

Analytical tests were conducted in a study to establish acidity levels of birrea biodiesel and petroleum diesel fuels. The experimental data were recorded as described in section 3.5. Af‐ ter running five titrations on birrea biodiesel sample, computation of the mean revealed an acid value of 0.62 mgKOH/g and a free fatty acid value of 0.31%. The acidity of birrea bio‐

These results indicate that the level of acidity of birrea biodiesel meets specifications of ASTM D 664 (0.8 mgKOH/g maximum), and is marginally out of specifications of EN 14214 biodiesel standard (0.5 mgKOH/g maximum). Acid value is a direct measure of free fatty acids (FFAs) in the biodiesel. Free fatty acids are undesirable in the fuel because they may cause corrosion of the fuel tank and engine components. The free fatty acids in the biodiesel could be reduced by neutralising birrea parent oil with an alkaline solution prior to transes‐ terification, and two-stage processing, for example, acid esterification followed by alkaline

diesel fuel closely compares with that of petroleum diesel (section 3.2).

C indicates that birrea biodiesel has better lubricity than petroleum diesel

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2

3

4

5

Viscosity (mm2/s)

ic viscosity at 400

6

7

8

**Table 5.** Ester composition of birrea biodiesel

The ester composition of birrea biodiesel indicates that the most abundant compounds include methyl palmitate, methyl oleate, methyl stearate and methyl linoleate. These are all long chain compounds that are largely saturated, with a small degree of unsaturation. The characteristic ester composition of birrea biodiesel depicted by the mixture of these compounds has a strong influence on its fuel properties. Fuel properties of plant oil and its derived biodiesel improve in quality with increase in carbon chain length and de‐ crease as the number of double bonds increase, except for cold flow properties as men‐ tioned in section 1. Thus the cetane number, heat and quality of combustion, freezing temperature, viscosity and oxidative stability increase as the chain length increases and decrease as the number of double bonds increase. A fuel whose constituent mixture of compounds is fully saturated will depict higher cetane number and better oxidative sta‐ bility, but poor cold flow properties. The small degree of unsaturation depicted by the presence of double bonds in compounds like Methyl Oleate and Methyl Linoleate is sig‐ nificant as double bonds inhibit crystallization, thus lowering the cloud point of the fuel. A low cloud point is a desirable fuel property as it ensures that a fuel remains in the liq‐ uid phase at low temperatures. Thus birrea biodiesel has a good properties trade-off be‐ tween cold flow properties, oxidative stability and cetane number. The viscosity analysis profile of birrea biodiesel is presented in section 4.3.

#### **4.3. Viscosity analysis of birrea biodiesel and petroleum diesel fuels**

It is integral to evaluate the viscosities of fuels in order to determine the feasibility of use in a diesel engine since viscosity influences fuel atomization and the combustion process. The viscosity profiles of birrea biodiesel and petroleum diesel fuels were analysed. Figure 5 shows profiles of viscosity variation with temperature for the two diesel fuels, with each da‐ ta point representing an average of three viscosity measurements. Viscosity limits for the American standard testing methods (ASTM-D6751) and the European standards (EN 14214) are also included in the same figure for quick assessment of conformance to major interna‐ tional biodiesel quality standards.

**Figure 5.** Viscosity variation with temperature

Some of the most abundant esters identified in birrea biodiesel are presented in table 5, together with their concentrations, while the complete list of constituent compounds is

The ester composition of birrea biodiesel indicates that the most abundant compounds include methyl palmitate, methyl oleate, methyl stearate and methyl linoleate. These are all long chain compounds that are largely saturated, with a small degree of unsaturation. The characteristic ester composition of birrea biodiesel depicted by the mixture of these compounds has a strong influence on its fuel properties. Fuel properties of plant oil and its derived biodiesel improve in quality with increase in carbon chain length and de‐ crease as the number of double bonds increase, except for cold flow properties as men‐ tioned in section 1. Thus the cetane number, heat and quality of combustion, freezing temperature, viscosity and oxidative stability increase as the chain length increases and decrease as the number of double bonds increase. A fuel whose constituent mixture of compounds is fully saturated will depict higher cetane number and better oxidative sta‐ bility, but poor cold flow properties. The small degree of unsaturation depicted by the presence of double bonds in compounds like Methyl Oleate and Methyl Linoleate is sig‐ nificant as double bonds inhibit crystallization, thus lowering the cloud point of the fuel. A low cloud point is a desirable fuel property as it ensures that a fuel remains in the liq‐ uid phase at low temperatures. Thus birrea biodiesel has a good properties trade-off be‐ tween cold flow properties, oxidative stability and cetane number. The viscosity analysis

**Compound Concentration (µg/ml)**

Methyl palmitate (C16:0) 1993.71

198 Advances in Internal Combustion Engines and Fuel Technologies

Methyl Oleate (C18:1) 2294.72

Methyl Stearate (C18:0) 1044.37

Methyl Linoleate (C18:2) 560.18

profile of birrea biodiesel is presented in section 4.3.

tional biodiesel quality standards.

**4.3. Viscosity analysis of birrea biodiesel and petroleum diesel fuels**

It is integral to evaluate the viscosities of fuels in order to determine the feasibility of use in a diesel engine since viscosity influences fuel atomization and the combustion process. The viscosity profiles of birrea biodiesel and petroleum diesel fuels were analysed. Figure 5 shows profiles of viscosity variation with temperature for the two diesel fuels, with each da‐ ta point representing an average of three viscosity measurements. Viscosity limits for the American standard testing methods (ASTM-D6751) and the European standards (EN 14214) are also included in the same figure for quick assessment of conformance to major interna‐

**Table 5.** Ester composition of birrea biodiesel

appended.

From figure 5, it is evident that birrea biodiesel largely meets quality requirements of both ASTM D-6751 and EN 14214 standards, while petroleum diesel (used in this study) viscosity profile is significantly lower than the requirements of the European standards. The kinemat‐ ic viscosity at 400 C indicates that birrea biodiesel has better lubricity than petroleum diesel and is likely to have a better combustion profile when used as a fuel in a diesel engine. The low viscosity of petroleum diesel may not provide sufficient lubrication for the precision fit of fuel injection pumps, resulting in increased wear or leakage. Leakage will, under normal circumstances, correspond to a power loss for the engine as mentioned earlier. The birrea biodiesel fuel was therefore found to be suitable for use in compression ignition (CI) engine.

#### **4.4. Acidity of birrea biodiesel fuel**

Analytical tests were conducted in a study to establish acidity levels of birrea biodiesel and petroleum diesel fuels. The experimental data were recorded as described in section 3.5. Af‐ ter running five titrations on birrea biodiesel sample, computation of the mean revealed an acid value of 0.62 mgKOH/g and a free fatty acid value of 0.31%. The acidity of birrea bio‐ diesel fuel closely compares with that of petroleum diesel (section 3.2).

These results indicate that the level of acidity of birrea biodiesel meets specifications of ASTM D 664 (0.8 mgKOH/g maximum), and is marginally out of specifications of EN 14214 biodiesel standard (0.5 mgKOH/g maximum). Acid value is a direct measure of free fatty acids (FFAs) in the biodiesel. Free fatty acids are undesirable in the fuel because they may cause corrosion of the fuel tank and engine components. The free fatty acids in the biodiesel could be reduced by neutralising birrea parent oil with an alkaline solution prior to transes‐ terification, and two-stage processing, for example, acid esterification followed by alkaline transesterification [36, 19]. The overall quality of birrea biodiesel is however deemed accept‐ able as it meets ASTM specifications.

## **4.5. Heat of combustion**

Heat of combustion is the thermal energy that is liberated upon combustion, and is com‐ monly referred to as energy content. A systematic study was conducted to analyse energy content levels of birrea biodiesel and petroleum diesel fuels. The experimental data were re‐ corded as described in section 3.6. After running four experiments for each of birrea biodie‐ sel and petroleum diesel fuel samples, computation of mean values revealed calorific values of 42.4 MJ/kg and 50.4 MJ/kg for birrea biodiesel and petroleum diesel fuels respectively. Unlike petroleum diesel, biodiesel fuels do not contain aromatics but fatty acids with differ‐ ent levels of saturation, and energy content decreases with increase in the degree of unsatu‐ ration [13]. Thus the lower energy content of birrea biodiesel relative to petroleum diesel fuel is to be expected. However, energy content of 42.4 MJ/kg for birrea biodiesel fuel com‐ pares favourably well with biodiesel fuels from other feed stocks. Ravi et al. [15] found that the gross heat of combustion for soybean biodiesel is 37.4 MJ/kg, while that of jatropha cur‐ cas was found to be 41.0 MJ/kg [21].

(a) Specific Fuel Consumption

20 30 40 50 60 70 80 90 100

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Load (%) Petroleum Diesel Birrea B100

(b) Engine Torque

20 30 40 50 60 70 80 90 100

Load (%) Petroleum Diesel Birrea B100

(c) Brake Power

20 30 40 50 60 70 80 90 100

Load (%) Petroleum Diesel Birrea B100

**Figure 6.** Variation of engine performance for birrea biodiesel and petroleum diesel fuels with engine load. *Legend:*

There are several clear findings to be drawn from the data profiles presented in figure 6. General‐ ly, the results clearly indicate that birrea biodiesel performs significantly better than petroleum diesel in terms of fuel consumption, engine torque and engine brake power. This is contrary to general knowledge from most research outputs that rank the performance of biodiesel fuels lower than that of petroleum diesel [17, 18]. This may partly be due to the higher thermal efficien‐

*Birrea B100 = 100% Birrea biodiesel.*

Brake Power (W)

0.2 0.4 0.6 0.8 1 1.2 1.4

Specific Fuel Consumption (kg/h)

Engine Torque (Nm)

#### **4.6. Engine performance analysis**

The performance of the variable compression ignition engine was evaluated in terms of spe‐ cific fuel consumption, engine torque and engine brake power. Some of the key properties of birrea biodiesel fuel used in this study are summarised in table 6.


**Table 6.** Properties of birrea biodiesel fuel

Performance tests were conducted for compression ratios 14:1 through 18:1, but to enable the main findings of the study to be identified clearly, only performance results for compres‐ sion ratio 16:1 are presented and discussed. The results for birrea biodiesel were compared with results for petroleum diesel fuel, whose properties are presented in section 3.2. The ex‐ perimental data were collected as discussed in Section 2.5; leading to results presented in figure 6(a) to (c).

transesterification [36, 19]. The overall quality of birrea biodiesel is however deemed accept‐

Heat of combustion is the thermal energy that is liberated upon combustion, and is com‐ monly referred to as energy content. A systematic study was conducted to analyse energy content levels of birrea biodiesel and petroleum diesel fuels. The experimental data were re‐ corded as described in section 3.6. After running four experiments for each of birrea biodie‐ sel and petroleum diesel fuel samples, computation of mean values revealed calorific values of 42.4 MJ/kg and 50.4 MJ/kg for birrea biodiesel and petroleum diesel fuels respectively. Unlike petroleum diesel, biodiesel fuels do not contain aromatics but fatty acids with differ‐ ent levels of saturation, and energy content decreases with increase in the degree of unsatu‐ ration [13]. Thus the lower energy content of birrea biodiesel relative to petroleum diesel fuel is to be expected. However, energy content of 42.4 MJ/kg for birrea biodiesel fuel com‐ pares favourably well with biodiesel fuels from other feed stocks. Ravi et al. [15] found that the gross heat of combustion for soybean biodiesel is 37.4 MJ/kg, while that of jatropha cur‐

The performance of the variable compression ignition engine was evaluated in terms of spe‐ cific fuel consumption, engine torque and engine brake power. Some of the key properties of

**Property Value ASTM D-6751 EN 14214**

Performance tests were conducted for compression ratios 14:1 through 18:1, but to enable the main findings of the study to be identified clearly, only performance results for compres‐ sion ratio 16:1 are presented and discussed. The results for birrea biodiesel were compared with results for petroleum diesel fuel, whose properties are presented in section 3.2. The ex‐ perimental data were collected as discussed in Section 2.5; leading to results presented in

Density (kg/m3) 973 - 860 - 900

Viscosity, 400C (mm2/s) 3.95 1.9 – 6.0 3.5 – 5.0

Acidity (mgKOH/g) 0.62 0.8 max 0.5 max

Free Fatty Acids (%) 0.31 - -

Calorific values (MJ/kg) 42.4 - -

birrea biodiesel fuel used in this study are summarised in table 6.

able as it meets ASTM specifications.

200 Advances in Internal Combustion Engines and Fuel Technologies

cas was found to be 41.0 MJ/kg [21].

**4.6. Engine performance analysis**

**Table 6.** Properties of birrea biodiesel fuel

figure 6(a) to (c).

**4.5. Heat of combustion**

**Figure 6.** Variation of engine performance for birrea biodiesel and petroleum diesel fuels with engine load. *Legend: Birrea B100 = 100% Birrea biodiesel.*

There are several clear findings to be drawn from the data profiles presented in figure 6. General‐ ly, the results clearly indicate that birrea biodiesel performs significantly better than petroleum diesel in terms of fuel consumption, engine torque and engine brake power. This is contrary to general knowledge from most research outputs that rank the performance of biodiesel fuels lower than that of petroleum diesel [17, 18]. This may partly be due to the higher thermal efficien‐ cy of birrea biodiesel when compared to fossil diesel as shown in table 7. The improved thermal efficiency of biodiesel is attributed to the oxygen content and higher cetane number.

The exhaust emissions produced from the engine performance analysis are discussed in

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This section compares emission levels of unburned hydrocarbon (HC), carbon monoxide (CO), and carbon dioxide (CO2) when the engine under review runs on petroleum diesel and on birrea biodiesel fuel (B100). The experimental data recorded for the three pollutants are presented in

This section however focuses on HC, CO and CO2 only. Figure 7(a) shows the data on emis‐ sion levels of HC recorded when the engine was using petroleum diesel and birrea biodie‐ sel. One of the most discernible trends connected to the data in figure 7(a) is that combustion

The difference in magnitude of HC emissions between the two diesel fuels increases with increase in load in a near exponential relationship. Based on average values, combustion of birrea biodiesel provides a reduction of unburned HC of approximately 59.4% at the com‐ pression ratio of 16:1. The lower HC emissions may be attributed to the availability of oxy‐ gen and high cetane number in biodiesel, which facilitates better combustion. It is the view of the authors that the relatively low level of HC emissions recorded when the engine was run using birrea biodiesel is linked to the quality of the biodiesel in terms of kinematic vis‐ cosity profile which complies favourably well with more stringent international standards

Figures 7(b) and (c) show variation of CO and CO2 emission levels respectively with in‐

The data in figures 7 (b) and (c) should be viewed and discussed in parallel to enable the correlation between CO and CO2 emission levels to be identified and explained for the op‐

Considering the results in figures 7(b) and (c), it can be seen that CO and CO2 emissions of petroleum diesel tend to increase with increase in engine load, while the same emissions for birrea biodiesel tend to increase gradually with increase in load for low load ratings. How‐ ever, the data in figure 7(b) show that both diesel fuels recorded the same average value of 1.5% by volume of CO emissions, while figure 7(c) depicts a slightly higher average value of CO2 for birrea biodiesel. CO is one of the consequences of incomplete fuel combustion. Less CO is generated with biodiesels than diesel for engine load below 60%. Concentration of oxygen during combustion would enhance the oxidation rate of CO and lead to less CO for‐ mation. This is a major advantage of oxygenated fuels like biodiesel. However, at higher en‐ gine loads, the lower temperatures could hinder the conversion rate of CO to CO2, leading to higher CO emissions. These effects are mainly attributed to the complex interactions be‐ tween combustion dynamics and physicochemical properties of the fuel. The combustion ef‐

Fuel + Air (N2 + O2) =CO2 + CO + H2O + N2 + O2 + HC + O3 + NO2 (5)

figure 7(a), (b), and (c). Typical engine combustion reaction is summarised by equation 5.

of birrea biodiesel provides a significant reduction in unburned HC.

such as the European standard (EN 14214), as demonstrated by figure 5.

Section 4.7.

**4.7. Emissions analysis**

crease in engine load.

erational conditions under review.

The fuel consumption profiles shown in figure 6(a) indicate that birrea biodiesel performs bet‐ ter than petroleum diesel across all engine loads under review. The maximum variation be‐ tween the two fuels is 48% at engine load of 90%, and the minimum variation is 34% at engine load of 30%.The variation of specific fuel consumption also depicts birrea biodiesel to be a more economic fuel for the diesel engine than petroleum diesel. The changes in specific fuel con‐ sumption and power depend on engine design, speed and loading conditions. Engines with higher compression ratios would result in higher temperatures and pressures during combus‐ tion in the cylinder, promoting more complete combustion. Engine speed also affects the airfuel mixing process, with higher engine speed normally giving a better mixture and higher cylinder temperature and pressure. On the contrary lowering the engine speed would lower the cylinder temperature and this can lead to poor vaporization and atomization.

The economic value of birrea biodiesel as a fuel in CI engine is further validated by its re‐ markably high engine torque shown in figure 6(b). For both petroleum diesel and birrea bio‐ diesel fuels, torque increases steadily to maximum values of 20.1 Nm and 27 Nm respectively and then gradually decreases to minimum values of 10 Nm and 23.1 Nm re‐ spectively at engine load of 90%. The disparity in the generated torque can be attributed to the improved combustion processes caused by increased atomisation and spray characteris‐ tics for biodiesel fuel.

The brake power profiles shown in figure 6(c) indicates a gradual decrease with increase in engine load for both diesel fuels, with birrea biodiesel recording relatively high values when compared to petroleum diesel across the entire engine loads under review. This is consistent with the high torque shown in figure 6(b).

Overall, the results in figure 6 indicate that birrea biodiesel is a suitable fuel for the compres‐ sion ignition engine. A summary of engine performance using birrea biodiesel in compari‐ son with petroleum diesel and jatropha curcas biodiesel fuels at a speed of 2500rpm and engine load of 30% is presented in table 7.


**Table 7.** Engine performance using birrea biodiesel, petroleum diesel and jatropha biodiesel fuels.

The exhaust emissions produced from the engine performance analysis are discussed in Section 4.7.
