Study the influence of pre-heating on atomization of straight vegetable oil through Ohnesorge number and Sauter mean diameter

Abstract

Vegetable oil has been considered as one of the most promising alternative fuels for compression ignition engine in recent years. However, the atomization of vegetable oil seems to be different than that of diesel fuel because of having different properties. Atomization and vaporization of fuel are greatly influenced by physical properties of fuel and these properties are temperature dependent. Thus, impact of pre-heating on atomization of straight vegetable oil (SVO) needs to be examined. In the fluid mechanics literature, Ohnesorge jet disintegration classification is most commonly accepted to describe the atomization quality of water jet break-up. A water jet having higher Reynolds number in the atomization regime was considered to atomize quickly after discharge from downstream the nozzle as per this classification. This concept of Ohnesorge classification was used in the present work to study the atomization of SVO. The atomization quality of fuel is judged by the droplet diameter of fuel because it plays a vital role in a primary spray break up and formation process. The main objective of this study was to study the influence of pre-heating on atomization quality of non-edible karanj oil (Pongamia Pinnata) through Ohnesorge number and Sauter mean diameter (SMD). The focus was on atomization quality rather than atomization characteristics of fuel. In this study, effort was made to study atomization quality of SVO in a simplest, easiest and cost effective way by measuring only physical properties of fuel and fuel flow rate. The dimensionless Ohnesorge number and correlation given by Elkotb for SMD were used to predict the atomization quality of SVO with rise in temperature. The study showed that SMD of karanj oil decreases with increase in temperature which in turn improves the air-fuel mixing rate and thus atomization. The Ohnesorge classification showed improvement in atomization of karanj oil while moving from regime I to IV with pre-heating. It is concluded that smaller SMD and higher Reynolds number of karanj oil at 90 °C in regime IV leading to better atomization as compared to karanj oil at room temperature.