A COMPARISON OF DIESEL AND JATROPHA METHYL ESTER (JME) SPRAY CHARACTERISTICS: EFFECT OF NOZZLE ENTRY RADIUS

In the present article, diesel and Jatropha methyl ester (JME) sprays are compared in a detailed manner in terms of their macroscopic and microscopic spray characteristics. The comparison is made at injection pressures of 500, 1000, and 1500 bar by injecting the fuels through a nozzle having a single hole of 200 mu m diameter and 70 mu m entry radius into a spray chamber (with optical access). From the measurements of macroscopic spray structure, it is observed that the spray tip penetration is faster and spray cone angle is narrower by approximately 10% for JME than those of diesel, indicating that the JME spray atomization is poor. Droplet sizes are measured for diesel and JME sprays at 4 ms after the start of injection using particle/droplet image analysis, which showed that the Sauter mean diameter (SMD) of JME sprays is higher by around 5% as compared to that of diesel. Subsequently, a nozzle with a hole diameter of approximately 200 mu m having an entry radius of 10 mu m is studied to understand the effect of nozzle entry radius on breakup of diesel and JME sprays. Computational fluid dynamic modeling of inner-nozzle flow showed that there is significant inner-nozzle cavitation for this nozzle. A comparison of spray structure at injection pressures of 500 and 1500 bar showed that the spray tip penetration is slower and spray cone angles are wider by approximately 5% to 12% for sprays from the cavitating nozzle than those from the noncavitating nozzle. Droplet size comparison showed that SMD of spray from the cavitating nozzle is lower by approximately 5% as compared to that from the noncavitating nozzle. Thus improvement in spray atomization due to inner-nozzle cavitation may be able to compensate for the inferior atomization of JME, although with an associated penalty in the coefficient of discharge