Thermal Efficiency of a Combined Turbocharger Set with Gasoline Engine

Abstract

Problem statement: The technology of turbocharger has been used with internal combustion engines since 1905 to increase intake air pressure prior to putting it into the cylinders to increase thermal efficiency of the engine. Based on previous researches and uses of turbochargers, the pattern of turbocharger installation remains the same, either in series or in parallel. Therefore, this research aims to study installation of the combined turbocharger. The combined turbocharger set comprised two turbochargers of the same size having exhaust turbine connected in parallel to let both turbochargers work simultaneously and having intake air compressor connected in series for two stage compress. Approach: This research aimed to study the thermal efficiency of a combined turbocharger set with gasoline engine. The study was done by comparing the thermal efficiency between the combined turbocharger set and the parallel turbocharger set. The variation of both temperature and pressure of the intake air and exhaust gas were also investigated. The engine used in the study was TOYOTA engine model 1JZ-GTE with six cylinders and a total displacement volume of 2,491 cc. The engine was already installed with parallel turbocharger from the factory, therefore, the thermal efficiency test of the parallel turbocharger case was conducted first. Then, the engine was modified to be a combined turbocharger set and tested by the same procedure. The test was run under the speed of 2,000-5,000 rpm. Results: According to the test, the combined turbocharger set gave higher thermal efficiency than the parallel turbocharger set in all range of speed. At the speed of 2,500, 3,000, 3,500, 4,000, 4,500 and 5,000 rpm, the thermal efficiency of the combined turbocharger set was equal to 39.37, 57.73, 79.30, 67.66, 60.63 and 55.05%, respectively. Meanwhile, the thermal efficiency of the parallel turbocharger set was equal to 15.40, 22.61, 44.96, 55.21, 56.38 and 52.24%, respectively. Conclusion: It could be seen that the thermal efficiency of the combined turbocharger set was higher than that of the parallel set by 2.55 times at the speed range of 2,500-3,000 rpm. The efficiency of the combined turbocharger would be equal or higher than that of the parallel set by 1.05 times at the speed of 5,000 rpm.