We have developed an accelerated multi-zone model for engine cycle simulation (AMECS) of homogeneous charge compression ignition (HCCI) combustion. This model incorporates chemical kinetics and is intended for use in system-level simulation software. A novel methodology to capture thermal stratification in the multi-zone model is proposed. The methodology calculates thermal stratification inside the cylinder based on a single computational fluid dynamics (CFD) calculation for motored conditions. CFD results are used for tuning zone heat loss multipliers that characterize wall heat loss from each individual engine zone based on the assumption that these heat loss multipliers can then be used at operating conditions different from those used in the single CFD run because the functional form of thermal stratification is more dependent on engine geometry than on operating conditions. The model is benchmarked against detailed CFD calculations and fully coupled HCCI CFD chemical kinetics calculations. The results indicate that the heat loss multiplier approach accurately predicts thermal stratification during the compression stroke and (therefore) HCCI combustion. The AMECS model with the thermal stratification methodology and reduced gasoline chemical kinetics shows good agreement with boosted gasoline HCCI experiments over a range of operating conditions, in terms of in-cylinder pressure and heat release rate predictions. The computational advantage of this method derives from the need for only a single motoring CFD run for a given engine, which makes the method very well suited for rapid HCCI calculations in system-level codes such as GT-Power, where it is often desirable to evaluate consecutive engine cycles.

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A study of the reforming rates, heat transfer and flow through a methanol reforming catalytic microreactor fabricated on a silicon wafer are presented.Comparison of computed and measured conversion efficiencies are shown to be favorable. Concepts for insulating the reactor while maintaining small overall size and starting operation from ambient temperature are analyzed.

A general formulation for surface chemical reactions is used with a nite element heat conduction code to compare computations of the ablated mass ux from carbon bodies experiencing conditions representative of Earth reentry. Several credible models for the surface chemical kinetics are exercised with the formulation and are compared both to each other and to test data obtained by the Passive Nosetip Technology program in the mid-1970s. Sublimation of C 5 and C 7 is shown to be a concern for surface temperatures greater than about 3900 K. The best match between measurements and the calculations is obtained with surface chemical models that use the usual CO formation reactions and the sublimation of C 1 -C 3 but that also include CN formation and the sublimation of C 5 and C 7 . For surface temperatures above 3500 K and for similar assumptions for the equilibrium vapor pressure and evaporation coef cients of the sublimated species, the net reaction rate approach and the surface site occupation approach give similar ablated mass uxes. Nomenclatureenergy, J/kg F = Gibbs free energy, J/gmol F = radiation view factor f = kinetic rate factor, 1=m 2 s or nondimensional H 0 298 = enthalpy of formation at 298 K, J/gmol h = enthalpy, J/kg h = Planck's constant, J ¢ s k = Boltzmann's constant, J/molecule ¢ K k = reaction rate constant, 1=m 2 s L = number of surface species l = surface species index M = molecular weight, kg/kmol m = mass per molecule, kg P m = mass ux, kg/m 2 s N 0 = Avogadro's number, 1=kmol P = pressure, N/m 2 P 0 = reference pressure, atmosphere, 0.101325 MPa p = pressure, N/m 2 Q = number of surface reactions q = chemical species index P q = heat ux, J/m 2 s R = linear correlation coef cient R u = universal gas constant, J/kmol ¢ K or J/gmol ¢ K r = forward reaction rate, m 2 s S = surface kinetic factor, 1/m 2 s or nondimensional T = temperature, K W = number of gaseous species w = gaseous species index X = mole fraction of gaseous species 125. Senior Member AIAA.°= concentration,kmol/kg " = emissivity " = parameter in surface species reaction constant = stoichiometric coef cient of surface reactants µ = surface species population fractioņ = stoichiometric coef cient of surface products ¹ = stoichiometric coef cient of gaseous products º = stoichiometric coef cient of gaseous reactants ¾ = Stefan-Boltzmann constant, J/m 2 s ¢ K 4 8 = modi cation factor in heat transfer relation Subscripts a = activation ab = ablation abspec = ablated species blow = blowing cw = cold wall diff = diffusion emittradn = emitted radiation eq = equilibrium er = erosion f = forward f = formation condn = uid conduction HAL = heating augmentation level i = mass species index incradn = incident radiation k = element index m = reaction index p = pressure pyrgas = pyrolysis gas q = reaction index r = recovery ref = reference re radn = re ected radiation s = species index s,l = solid to liquid solcondn = solid conduction stag = stagnation T = temperature und = underside u = universal v = volume w = wall º = vibrational 508 Downloaded...

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