Thermo-Mechanical (Vibration & Noise) Performance of CNG Converted Petrol Engine

This study investigates the overall thermal and mechanical performance of a single cylinder four- stroke engine using gasoline and CNG as fuel. The main reason for undertaking this study is comparing the vibration and noise emitted from an engine run with CNG to those generated from an engine run with gasoline. The analysis of vibration measurement on external surfaces is used to deliver information correlated to the internal combustion processes. A four-stroke single cylinder variable compression engine was used as a test unit. The engine was fully equipped with necessary instruments and measuring devices such as ICP® accelerometer, data acquisition card (DAQ) and signal conditioning. The signals were conditioned and stored in the computer using DAQ system. Thermal performance parameters were measured before and after the conversion process. The maximum brake thermal engine efficiency and maximum engine output power conditions were identified for vibration measurements. Additionally, the different sources contributing to the vibration and noise of SI engines and pressure time history were explained. This study clarifies the impact left by the conversion process on engine noise and vibration and on its relation to the physical processes of combustion when the engine is operated with liquid or gaseous fuels. The effect of load on vibration and noise is obtained by the comparison of full load and no load conditions using two different fuels. Results show the difference in vibration spectrums and noise levels to be related to the type of fuel, the variation of air flow, combustion and cycle-to-cycle variation.