Four grades of gasoline fuel – obtained from Iraqi oil refineries – are used in this research to investigate their performance in spark-ignition (SI) engines. These grades are RON 77, RON 82, RON 87, and RON 93. We used a four-stroke, four-cylinder SI engine laboratory rig to conduct the experiments and calculate the engine performance for each gasoline grade. We compared the experimental results with the predicted numerical simulations carried out using a well-known commercial software called Lotus Engine Simulation (LES). The numerical results obtained using LES show good agreement with experimental findings. A higher gasoline grade shows better engine performance than lower grades owing to its superior quality and purity, better combustion characteristics and performance, and lower amount of gasoline inclusions. Gasoline fuel RON 93 provided the best engine performance in comparison to the remaining grades. The variation between the numerical and experimental results in all tested conditions was below 3%.

Variable valve timing (VVT) is an advanced modern technique applied in internal combustion engines by altering the valve lift event timing. This work aims to contribute to the continuing industrial VVT development to improve engine efficiency, fuel consumption and performance. To observe the influence on the spark-ignition (SI) engine’s performance, four valve timing strategies are selected carefully by varying the intake and exhaust valve timing. Lotus Engine Simulation, a simulation engineering software, is adapted in this study. The engine characteristics used in this modelling are spark engine, multicylinder, four strokes, port injection fuel system and constant compression ratio. A comparison between a conventional standard exhaust/intake valve timing and three other different timing cases is carried out. Results reveal that the overlap case of 98° showed a good brake-specific fuel consumption by approximately 3% less than the conventional case. An improvement of 6.2% for volume efficiency and 2.9% in brake thermal efficiency is also reported.

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