**3.2. Birrea biodiesel preparation**

tained at that temperature using ice blocks. This process should ideally extract all the sol‐

double bond). However, to ensure that no trace of solvent remains in the oil sample, the oil was purged with nitrogen gas (nitrogen drying) for approximately 40 minutes. Nitrogen is

To ensure that properties of the oil are not distorted, mechanical extraction was done to yield crude oil for subsequent analyses. The mechanism for the extractor consists mainly of a piston, a multi-perforated cylindrical stainless steel compression chamber of approximate‐ ly 0.15m diameter and 0.3m high, and a hydraulic jack system. The schematic diagram of the

Eight kilograms (8kg) of birrea nuts were charged into a multi-perforated stainless steel compression chamber, with stainless steel discs placed at intervals of 2kg of birrea nuts. The piston was located to keep the top disc into position. The hydraulic system was then operat‐ ed manually to lift up the platform upon which the multi-perforated stainless steel compres‐ sion chamber sits, thereby compressing the seeds and forcing the oil out of the kernel and through the 1mm diameter perforations of the compression chamber. The hydraulic system was operated to a maximum pressure of 30 bars to ensure maximum oil extraction while

C) and then iso-propyl alcohol (due to the

vent, starting with hexane (boiling point of 40–600

190 Advances in Internal Combustion Engines and Fuel Technologies

mechanism is shown in Figure 2.

**Figure 2.** Schematic of mechanical oil extraction mechanism

used because it is inert and does not react with oil components.

Birrea biodiesel was produced through an alkali catalyzed transesterfication process in the laboratory under strict observation and controlled conditions. Alkaline transesterification was preferred since the oil sample had free fatty acid content below 2% [29]. One litre of crude birrea plant oil was filtered, pre-heated to approximately 105o C to eliminate water. The oil was allowed to cool to approximately 58o C and then charged to a 2 litre transparent reaction vessel. A solution of methanol of 99.5% purity and 7.5g of potassium hydroxide pel‐ lets of 98% purity as catalyst was prepared and charged to the reaction vessel. The molar ratio of methanol to oil was fixed at 1:6, which is optimal ratio for the transesterification of vegetable oils [23]. The reaction vessel was tightly closed and contents agitated using a me‐ chanical shaker for one hour. The reaction vessel was then set up-side down and allowed to cool for a further 3 hours. Two distinct layers were formed, the upper layer being the methyl ester and the lower layer was glycerol (due to its higher specific gravity). Glycerol was drained off from the bottom of the reaction vessel until only biodiesel (and possibly traces of unreacted methanol) remained. The biodiesel was then water washed twice with distilled water to ensure removal of all traces of glycerol. A rotary vacuum evaporator was used to recover the unreacted alcohol from the biodiesel.

The petroleum diesel used for comparison was purchased from a Shell petrol Station and had properties including boiling point of 422 K, vapour pressure of 53 Pa, density of 871Kg m-3, viscosity of 2.3 mm2 /s at 400 C, acidity of 0.2 mgKOH/g, calorific value of 50.4 MJ/Kg and cetane number of 48.

## **3.3. Chemical analysis**

Chemical analysis was done to identify esters present in the birrea biodiesel sample. The method involved analysing standard (reference) samples, generating calibration curves for esters identified in the standard samples, and identifying and quantifying esters present in the birrea biodiesel sample.

To establish the chemical composition of the standard samples, Methyl Arachidate was in‐ jected into the standard mixtures as an internal standard (IS) and the samples were run ten (10) times through the Gas Chromatograph - Mass Spectrometry (GC-MS) system at ten (10) concentrations of equal interval from 10ppm (parts per million) to 1ppm. At each concentration, peak areas and retention times for all esters present were captured from the chromatogram. Peak area ratios (Analyte/IS) were calculated for all esters present at all concentrations, and these were used to generate calibration curves for each ester in the standard samples. The birrea biodiesel sample was also run through the GC-MS system under similar conditions. Peak area ratios (Analyte/IS) were calculated for each ester de‐ tected in the biodiesel sample and ester concentration was then determined by interpola‐ tion from a calibration curve of corresponding compounds. The instrument used for composition analysis is the Waters GCT premier Time of Flight (TOF) mass spectrometer (MS) coupled to the Agilent 6890N gas chromatograph (GC) system. In addition, the Na‐ tional Institute for Standards and Technology (NIST) developed Automated Mass Spectral Deconvolution and Identification System (AMDIS) software package, (chemdata.nist.gov/ massspc/ amdis) was used for peak identification. The Automated Mass Spectral Deconvo‐ lution and Identification System extracts spectra for individual components in a GC-MS data file and identifies target compounds by matching these spectra against a reference li‐ brary, in this case the NIST library.

**3.5. Acid value determination**

of free fatty acids using equation 3.

Where, 56.1 = molecular weight of KOH

N = molarity of the base

**3.6. Energy content**

*3.6.1. Calorimeter conditions*

each experiment was 8.2 minutes.

**3.7. Engine performance analysis**

W = weight of sample in grams

Acid value, AV= 56.1 <sup>×</sup> *<sup>N</sup>*

Acid value measurements of diesel sample extracts were carried out by titration technique according to ASTM D664 standard test method [30]. Based on the same standard 125 ml of solvent, consisting of 50% isopropyl alcohol and 50% toluene was prepared in a 600 ml beaker. 5 g of sample was then added to the beaker, followed by 2 ml of phenolphthalein indicator. The solutions were titrated with 0.1M KOH to the first permanent pink colour. Three titrations were carried out for each of the four sample extracts and the average titra‐ tion values determined. The acid values were determined using equation 2 and percentage

The calorific values of birrea biodiesel and petroleum diesel (for comparison purposes) sam‐ ples were determined using the IKA C200 Calorimeter system whose main components in‐ clude the basic device, decomposition vessel, ignition adapter, combustion crucible and oxygen filling point. The system has automatic data acquisition through the CalWin calo‐

To determine the heating values of samples, 3ml of sample extract were weighed and placed in a combustion crucible at a temperature of approximately 22. The crucible was then closed up inside a decomposition vessel, which in turn was filled with oxygen at a pressure of 30 bars for 30 seconds to ensure adequate oxygen for combustion processes. The cooling water

filled decomposition vessel was inserted into the measuring cell that is equipped with a magnetic stirrer. The cell cover was then closed for the test to commence. Total run time for

The engine performance test was conducted on a TD43F engine test rig. The test rig is water cooled four-stroke diesel engine that is directly coupled to an electrical dynamom‐ eter as demonstrated by figure 3. The dynamometer was used for engine loading. In ad‐ dition to the conventional engine design, the engine incorporates variable compression

rimeter software which handles calculations for the calorific values of samples.

in the tank fillers was kept at initial temperature of within 180

*<sup>W</sup>* × *Average Titration Value* (2)

C – 240

C range. The oxygen-

Free Fatty Acids (%)=0.5× *AV* (3)

Sclerocarya Birrea Biodiesel as an Alternative Fuel for Compression Ignition Engines

http://dx.doi.org/10.5772/54215

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