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Analysis of Improved Combustion Characteristics and NOx Emission of an SI-HCNG Engine

Pohang Univ of Science and Technology-Heesik Yoo, Dongkyu Lee, Kang Huh
Published 2012-04-16 by SAE International in United States
The purpose of this study is to analyze the performance of a spark ignition (SI)-HCNG (Hydrogen Compressed Natural Gas) engine by KIVA-3V. Turbulent premixed combustion is modeled by an independent transport equation for the mean reaction progress variable. The turbulent burning velocity is given by a phenomenological correlation in terms of laminar flame speed and turbulent intensity. The resulting flame speeds are validated against measured data in literature with parametric variation of turbulent intensity and H₂ fraction. Results showed good agreement with measured efficiencies and NOx emissions for varying air/fuel ratios and hydrogen fractions in CNG fuel. It is shown possible to satisfy the target of improved efficiency and reduced NOx of the test SI-HCNG engine due to enhanced lean flammability limits of CNG premixture with hydrogen.
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Prediction of Number Density, Volume Fraction and Size Distribution of Soot Particles in a Diesel Engine under Various Operating Conditions

Pohang Univ of Science and Technology-Jaeseo Lee, Kang Y. Huh
Published 2012-04-16 by SAE International in United States
Computation is performed to predict number density, volume fraction and size distribution of soot particles in typical operating conditions of a diesel engine. KIVA has been integrated with the CMC routine to consider turbulence/chemistry coupling and gas phase kinetics for heat release and soot precursors. The compositions of soot precursors are estimated by tracking Lagrangian particles to consider spatial inhomogeneity and differential diffusion in KIVA. The soot simulator SWEEP is employed as a postprocessing step to calculate conditional and integral quantities of soot particles. There are larger particles produced at a higher load or a lower rpm, but no consistent trend for injection timing in the conditional size distribution at the mixture fraction of 0.12. The integral results are obtained for number density, total mass and size distribution by summing up the histories of all tracked particles in the cylinder. They show similar overall trends as the conditional results, while the size distribution shows an opposite trend with respect to rpm due to the competing effects of time for particle growth and the degree of…
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