Research on combustion and emission characteristics of a hydrous ethanol/hydrogen combined injection spark ignition engine under lean-burn conditions

Ethanol, as one of the carbon-neutral fuels for spark ignition (SI) engine, has been widely used. Dehydration and purification of ethanol during production process will lead to high energy consumption. If hydrous ethanol can be directly applied to the engine, the cost of use will be greatly reduced. Due to the high latent heat of vaporization of ethanol and water, it is necessary to consider the performance of atomization, evaporation and com-bustion stability when hydrous ethanol is used in engine. As a zero-carbon fuel, hydrogen has excellent characteristics such as low ignition energy, fast flame propagation speed and wide combustion limit. The combination of hydrous ethanol and hydrogen can reduce the use cost and ensure better combustion performance. Therefore, this study explores the performance of hydrous ethanol/hydrogen in SI combined injection engine. The hydrous ethanol is injected into the intake port and the hydrogen is directly injected into the cyl-inder during the compression stroke. In this study, we firstly analyze the optimal water blending ratio (u) of hydrous ethanol, which including 0, 3%, 6%, 9% and 12%. The exper-imental results show that the hydrous ethanol with 9% water ratio has the best perfor-mance without hydrogen addition. Based on the 9% water ratio, the effects of hydrogen blending ratio (0, 5%, 10%, 15% and 20%) on the combustion and emission under different excess air ratio (l) (1, 1.1, 1.2, 1.3, 1.4). Hydrogen addition can increase the degree of con-stant volume combustion, so that the maximum cylinder pressure and temperature in-crease with the increase of the hydrogen blending ratio (HBR). When l = 1.3 and HBR = 20%, the maximum in-cylinder pressure can be increased by 108.64% compared to pure hydrous ethanol. Hydrogen effectively increases the indicated mean effective pres-sure (IMEP) and reduces the coefficient of variation of IMEP (COVIMEP). Adding hydrogen can reduce CO and HC emissions, while NOx emissions will increase. When l = 1.2 and HBR increasing from 0 to 20%, the NOx emissions increase by 106.75%, but it is still less than the NOx emissions of pure hydrous ethanol at l = 1. On the whole, hydrogen direct injection can improve the combustion performance of hydrous ethanol and achieve stable com-bustion under lean-burn conditions.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

Ethanol, a carbon-neutral fuel, is widely used in engines. Combining hydrous ethanol with hydrogen can reduce costs and improve combustion performance, especially under lean-burn conditions.