Abstract
In this study, an in-cylinder steam injection method is introduced and applied to a turbocharged diesel engine for waste heat recovery and NOx emission reduction. In the method, cool water was first heated into superheated steam by exhaust. Then the superheated steam was directly injected into the cylinder during the compression stroke. The potential for fuel savings and NOx emission reduction obtained by this method was investigated. First, a two-zone combustion model for the baseline engine was established and calibrated with the experimental data. Based on the model, the effects of steam injection mass, temperature, and timing on engine performance and NOx emission were investigated. The results demonstrate that in-cylinder steam injection can improve engine performance and reduce NOx emissions significantly at all engine speeds. Optimal steam injection mass is obtained under full load at engine speed from 1000 rpm to 1900 rpm when the steam injection timing and temperature are −30° and 550 K, respectively. Under those conditions, engine torque is increased by 9.5–10.9%, brake-specific fuel consumption (BSFC) is reduced by 8.6–9.9%, and NOx emission is decreased by 83.4–91.8%. Steam injection mass and injection timing are the main parameters that significantly affect engine performance and NOx emission.
Highlights
At present and in the short to medium term, internal combustion engines are major power sources for various mechanical devices
According to Reactions (15)–(17), in-cylinder temperature and O2 concentration are the major factors that influence the formation of nitrogen oxides (NOx) emissions, and both are impacted by steam injection
According to the generation mechanism of nitric oxide (NO) x emission described by the extended Zeldovich model, NOx emission is mainly affected by the peak in-cylinder temperature and the O2
Summary
At present and in the short to medium term, internal combustion engines are major power sources for various mechanical devices. Various technologies have been proposed to achieve this goal, such as turbocompounding [3], Miller cycle [4], exhaust gas recirculation (EGR) [5], waste heat recovery [6,7], use of alternative fuel [8], and so on Water injection, another useful technology to improve engine performance and reduce emissions, has been widely researched. The effects of pre-turbine steam injection on engine performance were studied by Zhu et al [33,34] In their method, the water was heated into superheated steam by engine waste heat and injected at the pre-turbine to increase the boost pressure of the fresh air. In order to make effective use of waste heat to further reduce fuel consumption and NOx emissions, injection method is proposed and applied to a turbocharged diesel engine in 4 ofthe present study.
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