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Engine modification for alternative fuels usage in diesel engine 373

13.3 Results and discussion

13.3.1 Evaluation of model for waste frying methyl ester
The biodiesel experiments were conducted based on the design matrix as given by
design expert software and obtained biodiesel yield is mentioned in Table 13.1.
The maximum biodiesel yield of 97.44% was obtained in a conventional heating trans-
esterification reaction at 55°C temperature, 150min of time, 6:1molar ratio, 1.5wt%
of catalyst concentration, and 975rpm of stirrer speed. Biodiesel yield increased with
a further increase in the molar ratio of methanol to oil and then the biodiesel yield was
reduced after a certain point due to a backward reaction in the presence of excess
methanol [38, 39]. The ANOVA table provides the information about the P-value
as shown in Table 13.8; P-value .0001 (P-value <.05) indicates that model is signif-
icant. The significant process parameters were A, B, C, D, E, AB, AC, AE, BC, BD,
2
2
2
2
CD, CE, B ,C , and D and the insignificant process parameters were BE, AD, A ,
2
2
2
and E . Coefficient of determination (R ) and adjustable (R ) were 0.98 and 0.96,
2
respectively. The R value indicates the numbers of process variables are significant
2
under the 95% of confidence level, whereas adjusted R value describes the number of
predictors available in the model.
13.3.2 The effect of process parameters in biodiesel synthesis
Fig. 13.6A shows the biodiesel yield response surface plot with respect to temperature
and molar ratio. The molar ratio was the most influential parameter, followed by tem-
perature to obtained maximum biodiesel yield. The biodiesel yield decreased with an
increase in molar ratio, and increased with increase in temperature. The reaction con-
dition of molar ratio 6:1 and temperature 55°C obtained the maximum biodiesel yield.
The biodiesel conversion was reduced by further increasing the molar ratio of meth-
anol and oil [40]. The response surface plot of temperature and time on biodiesel yield
is depicted in Fig. 13.6B. When the reaction time is increased from 60 to 150min, the
biodiesel yield increased. However, when the reaction temperature increased from 40°
Cto55°C, the yield increased. When the reaction temperature was increased above
55°C, the yield reduced. Beyond the optimum reaction temperature, the percentage
conversion of biodiesel was decreased [41]. Initially, the transesterification reaction
was slow for minutes due to mixing and dispersion of methanol in oil. Fig. 13.6C
shows the effect of catalyst concentration with respect to molar ratio on biodiesel
yield. From the figure, it was inferred that the yield of biodiesel was quite minimum
at lower catalyst concentrations. The reaction rate increased with an increase in weight
percentage of the catalyst progressively from 0.5 to 2.0wt%. However, by increasing
the catalyst concentration beyond 2wt%, the yield of biodiesel was decreased. The
higher amount of catalyst increases the viscosity of the mixture which causes poor
mass transfer between methanol and oil results in biodiesel yield was decreased
[42].The influence of the catalyst amount with the stirrer speed on the yield of biodie-
sel is presented in Fig. 13.6D. Stirrer speed is a significant parameter on the trans-
esterification process. Fig. 13.6D shows that biodiesel yield decreased at lower