Research Information System
Thesis Type: Doctorate
Institution Of The Thesis: Gazi University, Fen Bilimleri Enstitüsü, Turkey
Approval Date: 2024
Thesis Language: Turkish
Student: Gonca KETHÜDAOĞLU
Supervisor: Nureddin Dinler
Abstract:
In this study, the performance and emission parameters of HCCI (Homogeneous Charge Compression Ignition) engines using n-heptane fuel were investigated. The effects of parameters such as engine speed, equivalence ratio, EGR (Exhaust Gas Recirculation) rate, compression ratio, and intake air temperature on the HCCI combustion process were evaluated. The aim of the study is to improve the efficiency of HCCI engines and minimize emission levels by numerically analyzing the effects of these parameters on the combustion process, as well as proposing solutions to expand the operating range of these engines. Numerical analyses were performed using AVL FIRE™M software and compared with findings in the literature. In the study, engine speeds of 1000 rpm, 1400 rpm, and 1800 rpm were selected, with equivalence ratios ranging from 0,22 to 0,29. Intake air temperatures were set at 293,15 K (20°C), 313,15 K (40°C), 353,15 K (80°C), and 393,15 K (120°C). The EGR rate varied between 0% and 30%, and the compression ratios of 15, 16, and the existing compression ratio of 17,5 were analyzed. For each case, pressure, heat release rate, temperature, combustion duration, and emission values were calculated. A reduction in engine speed resulted in an increase in cylinder pressure and temperature, as well as a shorter combustion duration. The decrease in engine speed contributed to an expansion of the operating range. While 20% EGR extended the operating range, negative effects were observed at 30% EGR. Although increasing the intake air temperature expanded the operating range, it also led to a decrease in IMEP and maximum cylinder pressure. Increasing the compression ratio improved combustion efficiency. In all operating conditions, NOx emissions remained below 5 ppm. In conclusion, the performance and emission parameters of HCCI engines under different operating conditions were successfully analyzed, and the operating range was determined. This study aims to contribute to the identification of the necessary approaches to evaluate the potential of HCCI engines across a wider operating range, while improving combustion efficiency and minimizing emissions.
Key Words : HCCI engine, combustion, engine performance, numerical modeling