Ethanol Effects on Combustion and Emissions in Partial HCCI Diesel Engines Under Variable Load and Speed Conditions

Ethanol, a cleaner fuel alternative in diesel engines, is used in certain proportions to modify engine performance and improve emissions in diesel engines. In this study, a series of experiments were conducted to determine the effect of different ethanol concentrations on engine performance and emissions in a single-cylinder, water-cooled partial homogenous charge compression ignition (HCCI) diesel engine. Partial HCCI combustion was achieved by port injecting ethanol to form a homogeneous ethanol–air mixture that entered the cylinder, followed by direct diesel injection near the end of the compression stroke to initiate combustion. Experiments were primarily conducted with diesel fuel to achieve performance and emission values of conventional diesel engines. Subsequently, tests were conducted for ethanol contents of 5%, 10%, 15%, and 20%, respectively, under different load and engine speed conditions. Analysis of the experimental results revealed that ethanol fumigation improved combustion and engine performance under all operating conditions. Compared with neat diesel fuel, the E20 blend increased the maximum cylinder pressure by approximately 10% and the peak heat release rate by nearly 38% under full-load conditions. Furthermore, ethanol fumigation improved brake thermal efficiency and reduced brake-specific fuel consumption. In terms of emissions, CO and CO2 emissions decreased by approximately 40% and 18%, respectively, whereas NOx and HC emissions increased by nearly 25% and 57%, respectively, with increasing ethanol content. Among the investigated fuels, E20 provided the most favorable overall balance between combustion enhancement, engine performance, and emission characteristics.