Erjiang Hu

Study on the effect of hydrogen addition to dimethyl ether homogeneous charge compression ignition combustion engine

The auto-ignition characteristics of dimethyl ether (DME)/H2/Air blends (hydrogen blending ratio ranging from 0% to 70%) in homogeneous charge compression ignition (HCCI) combustion engine are investigated by calculation method using zero-dimension single-zone model. All the simulated mixtures demonstrated a two-stage heat release phenomenon at different crank angles. The results show that the hydrogen addition can retard the auto-ignition timing of DME in HCCI combustion engine. The ignition timing at low temperature is retarded slightly with the hydrogen addition, and the ignition timing at high temperature is delayed significantly due to the increased negative temperature coefficient duration. Chemical kinetic analysis reveals that the competition of OH radicals between hydrogen and DME could be the reason why the low temperature reactions of DME are mitigated. H2O2 molecules decompose at about 1000 K and initiate the high temperature reactions of the mixtures.

Effect of Lewis Number on Nonlinear Extrapolation Methods from Expanding Spherical Flames

ABSTRACT Uncertainties in measurement of the laminar flame speed and Markstein length result from various aspects, in which the methodology of extrapolation is believed to be an important factor; the present work is focusing on reducing uncertainties associated with the extrapolations. A new nonlinear extrapolation method (NL4) is proposed though further derivation of the original model, and expressed in series form. Along with the available linear model (L) and three nonlinear models (NL1, NL2, and NL3), NL4 is numerically analyzed and results indicate that it is the most accurate for mixture of Lewis number larger than unity, while NL2 is most accurate for mixture of Lewis number apparently smaller than unity. To further assess the performance of different extrapolation equations, different experimental conditions are designed and conducted using outwardly expanding spherical flame, and the results convincingly demonstrate the validity of the numerical analysis. The application of NL4 on methane/air mixture serves as a support on the accuracy and reliability of NL4, implying that NL4 may be an alternative nonlinear extrapolation method.

Measurements and kinetic study on the ignition delay time of dimethyl carbonate/n-heptane/oxygen/argon mixtures

ABSTRACT Ignition delay time measurements of dimethyl carbonate (DMC)/n-heptane blends have been studied in a shock tube in the temperature range of 1100–1600K, at different equivalence ratios (0.5; 1.0; 2.0), pressures of 2.0 and 10.0 atm, and with mole fractions of DMC in the fuel blends varying from 0% to 100% (0%; 20%; 80%; 100%). A detailed model of DMC/n-heptane was constructed to simulate the ignition process of neat and blended fuels. The effect of equivalence ratio on the ignition delay time of fuel blends was found to be increasingly weak with an increase in DMC addition. Reaction path analysis was conducted to explain the equivalence ratio effect. The concentration of the radical pool increased during its buildup stage at higher temperatures as DMC addition increases, leading to an enhanced chemical reactivity in the reaction system. The opposite observation at lower temperatures was interpreted by the methyl ester moiety.