Effect of polyethylene glycol (PEG) 600 as ignition improver on performance and combustion characteristics of hydrous bioethanol under CI engine condition

Ethanol is widely used in spark ignition (SI) engines, but its application in compression ignition (CI) engines is limited by its low cetane number, necessitating the use of additives like cetane improvers. This study evaluates, for the first time, the performance of polyethylene glycol 600 (PEG 600) as an ignition improver for bioethanol in a CI automotive engine, based on laboratory-scale findings. Hydrous bioethanol with 10% (HEPEG10) and 15% (HEPEG15) PEG 600 by weight was tested as a diesel substitute under two compression ratios (CR) of 20:1 and 25:1. The study varied the start of injection (SOI) and throttle positions, measuring key performance parameters including power, efficiency, maximum pressure, indicated mean effective pressure (IMEP), heat release, and ignition delay. The results indicated that PEG 600 could be a viable additive for bioethanol. HEPEG15 demonstrated more stable combustion than diesel at higher loads. Specifically, at 2280 rpm and CR 20:1, HEPEG15 achieved an 8% higher efficiency compared to diesel, with 13 % lower maximum pressure and 33% lower IMEP covariance. At CR 25:1, the additized bioethanol performed better across all load conditions, with HEPEG15 showing a 9% higher efficiency than diesel. At CR 20:1, the additized bioethanol only outperformed diesel at higher loads. Overall, while additized bioethanol exhibited lower efficiency at lower loads and higher maximum pressure, it provided better combustion performance when the SOI was advanced close to top dead center, though this might impact engine integrity and durability.