<p>A diesel engine modified for eucalyptus oil direct injection (EuDI) has been tested to study eucalyptus oil behavior. Since the eucalyptus oil possesses low cetane number fails to auto ignite, the test engine was modified to supply hot air during suction stroke which helps to auto-ignite the injected eucalyptus oil. The engine with this facility was operated using eucalyptus oil under various load conditions and at various intake temperatures. The results of the investigation were proved that eucalyptus oil could be direct injectable in a regular diesel engine after little engine modification. This method showed almost same brake thermal efficiency (BTE) at full load compared to standard diesel operation. Except NO_x emission other emissions were found closer to diesel baseline operation. This mode offered almost 50% smoke free operation at all loads compared to standard diesel operation. Also this method successfully proved the complete replacement of diesel fuel by eucalyptus oil.</p>