Blended fuels of turpentine oil and castor oil, palm oil, and sunflower oil have been used as alternative fuels in compression ignition, pre-combustion chamber CI engines. The effect of these blended fuels on engine performance, exhaust emissions, and combustion process have also been investigated. Here, the effect of higher injection valve opening pressures with blended fuels was investigated, and the behavior of the fuel spray at the higher injection valve opening pressure were observed by a Liquid-Liquid Injection Technique. The fuel injection rate at the higher injection valve opening pressure was measured by the Bosch method.The experimental results showed that: 1) Blended fuels of turpentine oil and plant oils such as castor, sunflower, or palm oils displayed better thermal efficiencies and NOx emissions than turpentine oil, close to the values obtained with diesel oil. 2) With increasing fuel injection, valve opening pressure brake thermal efficiency improved and ignition lag was delayed, and then the combustion instability improves. 3) The Liquid-Liquid Injection Technique showed that spray penetration was longer and that the spray impingement at the wall of the pre-chamber increased with higher injection valve opening pressure and a part of the fuel escapes from the pre-combustion chamber into the main combustion camber before ignition.