Mehmet Zencirkıran, Alper Calam, Fatih Aksoy, Hamit Solmaz, H. Serdar Yücesu
Homogeneous charge compression ignition (HCCI) is a promising low-temperature combustion concept that enables high efficiency and ultra-low emissions, but its operation is highly sensitive to fuel properties. This study experimentally investigated the effects of isopropanol–butanol–ethanol (IBE, 3:6:1 by vol.) and n-heptane blends on the combustion and emission characteristics of a port-fuel-injected single-cylinder HCCI engine. Tests were conducted at 800 rpm, intake air temperature of 353 K, and compression ratios of 11:1–13:1 over a range of lambda values. Three blends were evaluated: IBE20 (20 vol% IBE), IBE40 (40 vol% IBE), and IBE60 (60 vol% IBE) with n-heptane. Increasing IBE content reduced fuel reactivity, delayed combustion phasing, and shifted the heat release rate toward top dead center. Compared with neat n-heptane, the indicated mean effective pressure range increased from approximately 2.6–4.2 bar to 3.2–5.6 bar with IBE40, while IBE60 achieved up to 6.2 bar but within a much narrower lambda range. At a compression ratio of 13:1 and λ = 2.8, the start of combustion was retarded from − 23°CA for n-heptane to − 7.5°CA for IBE60. The knock limit of 10 bar/°CA occurred at λ = 2.8 for n-heptane, whereas it shifted to λ = 2.2 for IBE40, indicating improved knock resistance. IBE40 provided optimal combustion phasing, achieving CA50 within the desired 7–11°CA aTDC range over a wider operating region and delivering improved indicated thermal efficiency compared with the reference fuel. Although IBE60 achieved slightly higher peak efficiency, its stable operating range was significantly narrower and resulted by increased CO and HC emissions. Overall, the IBE40 blend offered the best compromise between combustion stability, load range, efficiency, and emissions, demonstrating its potential as a practical oxygenated fuel for controlled and efficient HCCI operation without complex control strategies.