Combustion characteristics of hydrogen-enriched gasoline in homogeneous SI-engines

Authors

Enrico Conte and Konstantinos Boulouchos, LAV-Aerothermochemistry and Combustion Systems Laboratory at ETH-Swiss Federal Institute of Technology, Zurich, Switzerland

Year

2005

Summary

Addition of H2-rich gas to gasoline allows stable operation of the engine under extreme conditions, such as ultra-lean air-fuel mixtures, or at very high rates of exhaust gas recirculation. Under these conditions engine-out emissions are dramatically reduced to near-zero levels, which could be easily brought down to zero by means of a simplified catalyst. The efficiency gain measured in the engine seems to be enough to compensate or even overcome the energy losses occurring in the reforming process. The analysis of the heat release rate shows a global shortening of combustion when adding hydrogen to gasoline, but a deeper analysis reveals a dominant effect of hydrogen on the early phase of combustion (0-5%), which is shortened much more than the remaining phases. Use of a Quasi-Dimensional Model allowed calculating the flame speed out of the heat release rate, revealing how in the laminar phase of combustion hydrogen addition increases up to more than three times the laminar flame speed of pure gasoline, while such increase is smaller in the rest of combustion, after transition to turbulence. By means of the Chemkin software the laminar flame speed of hydrogen-enriched gasoline blends has been calculated, and the influence of hydrogen-rich gas composition, degree of enrichment, pressure, temperature and stoichiometry has been investigated. Correlations have then been inferred, opening the perspective of implementing them in a 3D-CFD simulation of the engine combustion process.

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