In the present work, liquefied petroleum gas (LPG) is premixed with air for combustion in a compression ignition engine, along with neat rubber seed oil as the direct injected fuel. The LPG is injected directly into the intake manifold using an electronic gas injector. The variation in the LPG flow rate is from zero to the maximum tolerable value. The engine load was varied from no load to full load at regular intervals of 25% of full load. Experimental results indicate a reduction in thermal efficiency at low loads, followed by a small improvement in the thermal efficiency at 75% and 100% loads. Premixing of LPG prolongs the delay in the ignition with a simultaneous decrease in the duration of combustion. With an increase in the LPG flow rate, the maximum in-cylinder pressure increased at high outputs, whereas it decreased at low outputs. The heat release rate shows that the combustion rate increases with LPG induction. Carbon monoxide (CO) and hydrocarbon (HC) levels reduced at high outputs, whereas at all loads, the oxides of nitrogen (NOx) levels increased. The NOx level at full load increased from 6.9 g/kWh at no LPG induction to 10.36 g/kWh at 47.63% LPG induction. At all loads, the smoke level decreased drastically. The smoke level at full load decreased from 6.1BSU at no LPG induction to 3.9BSU at 47.63% LPG induction.