Predicting the Concentration and Specific Gravity of Biodiesel‐diesel Blends Using Near‐infrared Spectroscopy

Biodiesel made from different source materials usually have different physical and chemical properties and the concentration of biodiesel in biodiesel‐diesel blends varies from pump to pump and from user to user; all these factors have significant effects on performance and efficiency of engines fueled with biodiesel. To address these challenges, regressions based on near‐infrared spectroscopy were developed for relatively inexpensive and rapid on‐line measurement of the concentration and specific gravity of biodiesel‐diesel blends. Methyl esters of five different oils — soybean oil, canola oil, palm oil, waste cooling oil, and coconut oil — and two different brands of commercial‐grade No. 2 on‐highway diesel and one brand of off‐road No. 2 diesel were used in the calibration and validation processes. The predicted concentration and specific gravity of the biodiesel‐diesel blends were compared with the actual values. The maximum and average root‐mean‐square errors of prediction (RMSEP) of biodiesel concentration were 5.2% and 2.9%, respectively, from the biodiesel type‐specific regression. For the general regression, the RMSEP were 3.2% and 0.002 for biodiesel concentration and specific gravity predictions, respectively.