Defining a waste vegetable oil-biodiesel based diesel substitute blend fuel by response surface optimization of density and calorific value

A blend fuel was optimized statistically using a response surface approach to substitute diesel. The waste vegetable oil biodiesel (WVO-BD) fraction in the blend, thermal exposure time of waste vegetable oil used to prepare the WVO-BD, and density of complementary fuel oil used in the blend were the factors optimized to produce a blend fuel having density equivalent to diesel. A response surface model was developed to predict the density of the blend. The model for blend density was extended to calculate the calorific value of the blend fuel. The optimum diesel equivalent blend was predicted to contain a 0.46 fraction of WVO-BD prepared from waste vegetable oil with 48 h of thermal exposure in fuel oil of density 0.80 g/ml. An experimental equivalent of the model-optimized blend recorded a density of 0.829 +/- 0.004 g/ml and a calorific value of 44.0 +/- 0.5 MJ/kg. The model was found to accurately predict the density and calorific value of the blend with less than 1% error. The model optimized blend was found to have density and calorific value comparable with standard diesel fuel. The blend showed an analogous performance but cleaner emission relative to diesel in an engine operation. A reduction of 43-46% in engine operating cost is achievable with the model-optimized blend relative to diesel. Thus, the present study successfully valorized WVO-BD and defined a diesel-substitute blend fuel.