Generally the biodiesel contains ten percent oxygen content and it might be the reason for lowering calorific value.. any possible route to enhance the calorific value of biodiesel.
Well, oxygen content is not related to CV. Petro-diiesel has no oxygen but it has higher calorific value. Calorific value can be increased by adding additives. It should be the first target to produce biodiesel which has less viscosity and FFA with higher FAAE. During optimization, you can do some experiment on the parameters to increase the CV.