Optimization of performance and thermal efficiency in HCCI engines using blended fuel strategies for renewable energy transitions
摘要
Homogeneous Charge Compression Ignition (HCCI) engines offer enhanced fuel efficiency and lower emissions, but their performance is highly sensitive to fuel composition and combustion parameters. This study investigates the optimization of HCCI engine performance using blended fuels composed of iso-octane and n-heptane. A 0-D combustion model implemented in CHEMKIN-PRO is used to analyze the effects of various fuel blends (0%, 25%, 50%, 75%, and 100% iso-octane) on combustion characteristics, peak pressure, temperature profiles, and Heat Release Rates across different engine speeds. The results indicate that 100% n-heptane yields the highest peak temperature (approximately 1700 K) and peak pressure (8.5 MPa) at 2000 rpm, while higher iso-octane content delays ignition and reduces combustion intensity. Blends with more n-heptane exhibit earlier combustion phasing, particularly at lower speeds, with peak pressure occurring 5 to 10 crank angle degrees (°CA) earlier than in high iso-octane blends. At 3000 rpm, peak pressure reduces to 7.2 MPa for pure n-heptane and 5.6 MPa for pure iso-octane, highlighting the speed-dependent nature of combustion performance. The Heat Release Rate (HRR) analysis shows that n-heptane-dominant blends produce sharper and higher HRR peaks (85 J °CA−1 at 2000 rpm) compared to iso-octane-rich blends (50 J °CA−1 at the same speed). The study concludes that optimizing fuel blends is critical for achieving balanced performance, with pure n-heptane delivering the highest efficiency at 2000 rpm, while increasing iso-octane content deteriorates combustion quality. These findings contribute to fuel selection strategies for improving HCCI engine operation under varying load and speed conditions.