Different techniques adopted for converting vegetable oils to biodiesel are (a) degumming of vegetable oils, (b) transesterification by acid or alkali, and (c) enzymatic transesterification.

5.2.1 Degumming of vegetable oils

Degumming is an economical chemical process involving acid treatment to improve the viscosity and cetane number up to a certain limit so that the blends of nonedible oils with diesel can be used satisfactorily in a diesel engine. It is a very simple process by which the gum of the veg­etable oil is removed to decrease the viscosity of oil by using an appro­priate acid that can be optimized for reduction in viscosity. The quantity of acid and the duration of the process are very important to obtain optimum results. Compared to transesterification, the process of degum — ming is simple, very easy, and less costly, and the reduction in viscosity of vegetable oil is very small.

Nag et al. [25] degummed karanja, putranjiva, and jatropha oils by phosphoric acid treatment. Before degumming the oils, the fuel properties of three oils have been measured and compared with diesel (Table 6.1). Acid concentrations of 1%, 2%, 3%, 4%, and 5% were used at 40°C with vigorous stirring. The stirring was continued for 10 min after adding the acid. After stirring, the mixtures were held for 1 week to complete the reactions and to settle the gum materials. Then the mixtures were filtered through a packed bed filled with charred sawdust. Viscosities of the fil­trate were then measured.

Performance and emission measurement. After studying the properties of the jatropha, karanja, and putranjiva oils, they were degummed. In this context, the Ricardo variable-compression engine (Ricardo & Co. Engineers Ltd., England, single cylinder, 3-in bore, 35/8 in stroke) was run with 10%, 20%, 30%, and 40% blends of degummed karanja, jatropha, and putranjiva oils with diesel at different loads (0-2.7 kW) and different timings (45°, 40°, 35°, and 30° bTDC [before top dead center]). To meas­ure emissions, an automotive exhaust monitor (model PEA205) and smoke meter (model OMS103, Indus Scientific Pvt. Ltd., India) were used.

Degumming by acid treatment lowers the viscosity. Viscosities of karanja, jatropha, and putranjiva oils degummed at 40°C and at various acid concentrations are shown in Fig. 6.1. Karanja oil with 4% acid treatment had the lowest viscosity, whereas jatropha and putranjiva oils both had the lowest viscosities with 1% acid treatment.

Effect of timing. By observing the performance data at various timings (45°, 40°, and 35° bTDC) in Fig. 6.2, it was concluded that at 45° bTDC timing, the nonedible karanja, jatropha, and putranjiva oils gave the highest yields, whereas at 40° bTDC timing, diesel gave the highest yield. That may have been due to the different ignition temperatures of the nonedible oils from diesel.

40
30
25
0 1 2 3 4 5
Acid concentration (%)
Figure 6.1 Viscosity versus acid concentration of jatropha, karanja, and putranjiva oils at 40°C.
Diesel Jatropha Karanja Putranjiva Oils Figure 6.2 Brake thermal efficiency at various timings of diesel and 20% vegetable oil blends at 1-kW brake power, 1200 rpm, and 20 compression ratio.

Performance of various blends. Performances of blends of degummed vegetable oil with diesel are shown in Figs. 6.3 and 6.4. The 20% blends of jatropha, karanja, and putranjiva oils with diesel gave quite satis­factory performance related to BSFC and brake thermal efficiency (^bt). Beyond the 20% blends, the cetane numbers and viscosities of the blends were not so effective.

Comparison of the performance of blends. As per Figs. 6.5 and 6.6, engine performance using jatropha and karanja oils was better than diesel but the use of putranjiva oil gave reverse results at all loads, although the results were more or less the same. Degummed karanja oil blends gave better performance, but at high loads, the performance of jatropha oil blends was better in comparison to the performance of karanja oil blends. The performance data showed that all three vegetable oils could be used as alternative fuels for diesel engines.

Effect of loads on emissions of vegetable oil blends and comparison. As per

Figs. 6.7 and 6.8, it is interesting to note that for the karanja, jatropha, and putranjiva oils, in every case, smoke and particulates decreased, which was very favorable in terms of their environmental impact on human beings. The rate of increase in smoke and particulate generation with the load of jatropha oil, in comparison to karanja and putranjiva

Diesel

IWWl 10% blend 20% blend 30% blend

Figure 6.6 Brake thermal efficiency versus brake power of diesel, 20% karanja oil, 20% jatropha oil, and 20% putranjiva oil blends at 1200 rpm, 45° bTDC, and 20 compression ratio.

oils, was very low. It is very interesting to observe that although the par­ticulates and smoke for all the oils decreased, jatropha oil blends gave the highest reduction.

In Figs. 6.9 and 6.10, the CO, CO2, NOx, and HC (hydrocarbon) emis­sions for the three nonedible oils were less in comparison to diesel at high loads. However, at low loads, emissions from the nonedible oils are almost parallel to diesel. Because of the higher ignition temperature of nonedible oils than diesel, the better combustion of these oils gave less exhaust emissions.

Thus, degumming is an economic chemical process for a 20% blend of karanja, jatropha, and putranjiva oils with diesel to have very satisfactory results. The degumming method, therefore, offers a potential low-cost method with simple technology for producing an alternative fuel for CI engines. Out of the three nonedible oils, jatropha oil was the most prom­ising to yield good performance and emissions at high loads in all respects. Comparing CO, CO2, NOx, HC, smoke, and particulate emis­sions from using the three nonedible oils, jatropha oil was very encour­aging (see Fig. 6.11). Considering the above-mentioned points, it can be concluded that the diesel engine can be run very satisfactorily using a 20% blend of vegetable oil with diesel at 45° bTDC, 1200 rpm, and 20 compression ratios. Any diesel engine can be operated with a 20% blend

of degummed vegetable oils as a prime mover for agriculture purposes without any modification of the engine.