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Experiments were conducted on a four-cylinder direct-injection diesel engine with part of the engine load taken up by fumigation ethanol, which was injected into the air intake of each cylinder, to investigate the combustion and emissions of the engine under five engine loads at an engine speed of 1800 rpm. Fumigation ethanol was injected to top up 5, 10, 15, and 20% of the engine loads under different engine-operating conditions. In comparison to Euro V diesel fuel, fumigation ethanol gives a higher peak in-cylinder pressure and heat release rate. Increasing the fumigation ethanol would increase the ignition delay. More fuel is burned in the premixed mode, and less fuel is burned in the diffusion mode. The brake thermal efficiency decreases with an increase in fumigation ethanol at low and medium engine loads but does not change significantly at high engine loads. On the emission side, the application of fumigation ethanol results in a significant increase in hydrocarbon (HC), carbon monoxide (CO), and nitrogen dioxide (NO 2 ) emissions. However, there is a decrease in nitrogen oxides (NO x ), smoke, and particulate mass and number concentrations. The diesel oxidation catalyst is able to reduce the high emissions of CO and HC arising from fumigation ethanol and, in addition, further reduce the particulate emissions.

Currently, considerable attention has been given to the investigation of biofuels, including biodiesel, as alternative fuels for internal combustion engines. This study is aimed to investigate the effects of fumigation methanol on the emissions of a diesel engine fueled with biodiesel as the baseline fuel. The biodiesel used in this study was converted from waste cooking oil. Experiments were performed on a 4-cylinder naturally aspirated diesel engine operating at a constant speed of 1800 rev/min for three engine loads. The results indicate no significant change in brake thermal efficiency and carbon dioxide (CO 2 ) emission, an increase in both carbon monoxide (CO) and unburned hydrocarbon (HC) emissions, and a decrease in both nitrogen oxides (NOx) and particulate matter (PM) emissions. In particular, there is also an increase in nitrogen dioxide (NO 2 ) in the exhaust gas. The results obtained at a fumigation ratio of 0.1 are compared with those obtained with the engine operating on ultralow sulfur diesel: there is still an increase in CO and HC, by a factor of up to two, and an increase in NO 2 , by a factor of up to 5, while the NOx is reduced by up to 8% and the particulate mass is reduced by up to 50%, depending on the engine load.