Numerical study of Intake Manifold Water Injection on Performance and Emissions in a Heavy-duty Nature Gas Engine 2019-01-0562
The performance of heavy-duty nature gas engines has been limited by combustion temperature and NOx emissions for a long time. Recently, water injection technology has been widely considered as a technical solution in reducing fuel consumption and emissions simultaneously in both diesel and gasoline engines.
This paper focuses on the impacts of intake manifold water injection on characteristics of combustion and emissions in a heavy-duty nature gas engine through numerical methods. A detailed numerical model was established and validated with experimental data of pressure traces in CFD software coupled with detailed chemical kinetics. The simulation was mainly carried out under low speed and full load condition, and knock level was also measured and calculated by Logarithmic Knock Intensity (LKI).
The results show that intake manifold water injection is an efficient way to reduce high NOX emissions in nature gas engines without deteriorating other emissions characteristics. Compared with original engine emissions, a decrease of 40% in NOX emissions can be achieved under 0.6 water-gas mass ratio. Moreover, the knock in nature gas engines can be suppressed when water is injected into intake manifold. The simulation results illustrate that, at the same LKI index, spark timing can be advanced from 16°CA BTDC to 22°CA BTDC with a relative low level of NOX emissions, and thermal efficiency increases by 1.5% while 0.5 water-gas mass ratio is applied. Furthermore, the analysis of specie concentrations presents that injected water does not have a remarkable effect on low temperature reactions, but fuel combustion is impacted by the generation and consumption of HO2 in the stage of high temperature reactions considerably. These numerical results can be helpful for the application of water injection technology in practical heavy-duty nature gas engines to reduce emissions and increase thermal efficiency in the future.