But biodiesel undergoes oxidative degradation over time due to

6.8. Smoke
The variation of smoke density for the different blends of Kapok methyl ester and diesel against the engine load is shown in Fig. 7.
Fig. 7. Smoke density with respect to engine loads for Kapok methyl esters and diesel.Figure optionsDownload full-size imageDownload as PowerPoint slide
The unburned carbon NVP-AUY922 appear as smoke in the exhaust gases, or impinge on the combustion chamber wall and in the exhaust system. The smoke density has been reduced by 14%, 22%, and 16.6% for the blends B20, B40 and B60 respectively, compared to diesel.
The main reasons for lower smoke, are geographic isolation the lean blends of biodiesel have additional oxygen content, no aromatic substances, higher thermal efficiency, lower fuel consumption and shorter ignition delay. Moreover, the aforesaid facts enhance the combustion performance, and ensure complete combustion. But, the smoke density is slightly higher for the blends B80 and B100 than diesel at all the load conditions. This higher smoke may be due to incomplete burning of hydrocarbons, lower brake thermal efficiency at higher loads, sulfur content, and the water present in the rich blends of biodiesel.