Effects of supercharging on combustion and NOx emission characteristics under various relative air-to-fuel ratios in a hydrogen DISI engine
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The focus of this study is an experimental analysis of the effects of increasing the intake pressure on combustion characteristics and NOx emissions under various relative air-to-fuel ratios with a hydrogen direct injection spark ignition (DISI) single-cylinder engine. The engine speed was set to 1500 rpm, and the relative air-to-fuel ratio was changed by controlling the amount of injected hydrogen. The intake pressure was changed from 0.10 MPa to 0.14 MPa with an interval of 0.2 MPa using a supercharger. The results revealed that increasing the intake pressure from 0.10 MPa to 0.14 MPa decreased the coefficient of variation in the gross mean effective pressure from 5.79% to 1.02% at λ=3.5 because of faster flame development. Owing to higher combustion stability for an intake pressure of 0.14 MPa, the operable relative air-to-fuel ratio toward lean conditions was extended, resulting in 47.13% gross thermal efficiency with 4 ppm NOx emissions at λ=4.0. In addition, the gross mean effective pressure increased with increasing intake pressure under various relative air-to-fuel ratio conditions. Specifically, the maximum gross mean effective pressures were 0.80, 0.95, and 1.02 MPa for intake pressures of 0.10, 0.12, and 0.14 MPa, respectively.
Abstract
The focus of this study is an experimental analysis of the effects of increasing the intake pressure on combustion characteristics and NOx emissions under various relative air-to-fuel ratios with a hydrogen direct injection spark ignition (DISI) single-cylinder engine. The engine speed was set to 1500 rpm, and the relative air-to-fuel ratio was changed by controlling the amount of injected hydrogen. The intake pressure was changed from 0.10 MPa to 0.14 MPa with an interval of 0.2 MPa using a supercharger. The results revealed that increasing the intake pressure from 0.10 MPa to 0.14 MPa decreased the coefficient of variation in the gross mean effective pressure from 5.79% to 1.02% at λ=3.5 because of faster flame development. Owing to higher combustion stability for an intake pressure of 0.14 MPa, the operable relative air-to-fuel ratio toward lean conditions was extended, resulting in 47.13% gross thermal efficiency with 4 ppm NOx emissions at λ=4.0. In addition, the gross mean effective pressure increased with increasing intake pressure under various relative air-to-fuel ratio conditions. Specifically, the maximum gross mean effective pressures were 0.80, 0.95, and 1.02 MPa for intake pressures of 0.10, 0.12, and 0.14 MPa, respectively.