Study On Mechanism Reduction For Detailed Chemical Kinetics Of IC Engine Fuel

Numerical simulation plays an important role in study, research and industry. Multi-dimensional CFD simulation provides directional instructions on understanding temperature field, pressure field and the formation and distribution of emissions. Considering that the detailed mechanism about engine fuel contains plenty of element reactions and species, it is difficult to carry out a multi-dimensional CFD simulation directly. The calculation efficiency about simulations involving combustion has quadratic relation about the number of species. Therefore, reducing the number of species will accelerate the calculation speed.Traditional CSP(Computational Singular Perturbation) method concerns only about one time or spatial point. For reactors, such as auto-ignition reactor or onedimensional, unstretched, premixed, laminar steady flame which is inhomogenous in time or space, traditional CSP method will encounter difficulties. Considering species with small concentration or rapid reaction rate will be deemed as quasi-steady state species. Meanwhile, heat release rate is a symbol evaluating the intensity of a reaction. Therefore, a new algorithm, named integral CSP, is proposed based on traditional CSP method. Integral CSP includes species concentrations, species production rates and heat release rates as integral weighting factors and obtains the overall radical pointers by integrating the radical pointers over time and spatial domain. With the help of overall radical pointers, overall radicals will be picked up and these radicals will not included in the final reduced mechanisms.The number of quasi-steady state species needs to be known before the integral CSP being implemented. A method used to determine this number is proposed: Reduced mechanisms are conducted corresponding to different number of quasisteady state species. Then, ignition delay is calculated with respect to these reduced mechanisms. The number of quasi-steady state species is determined with the help of user defined threshold value.A C++ program named I-CSP is developed based on integral CSP algorithm. ICSP uses linking file and calculation results generated in Chemkin and uses interface functions to read heat release rate, pressure and species concentrations to calculate net species production rate. Then, I-CSP calculates the radical pointers which are used to identify radicals and fast reactions which are used to find fast reactions corresponding to each radical. With radicals and fast reactions, the reduced mechanism will be readily generated. I-CSP is easy to modify and expand. Radicals and fast reactions can be assigned manually. Matrix calculation is adopted in I-CSP, which makes the source code more readable. The deducted reduced mechanism is compatible with Chemkin, which makes the validation more efficient.A reduced mechanism including 23 species and 18 lumped reactions was deducted after applying I-CSP to CH4 with threshold value 5%. The reduced mechanism was then validated in PSR, auto-ignition reactor and one-dimensional, unstretched, premixed, laminar steady flame over a wide range of pressure, temperature, equivalence ratio and mass flow rate. It turns out that the reduced mechanism shows high accuracy. Then, the recued mechanism was ‘trimming’ with a threshold 5%. Comparison with other mechanism shows that the ‘trimming’ can increase the calculation efficiency substantially.A reduced mechanism including 26 species and 20 lumped reactions was deducted after applying I-CSP to DME with threshold value 5%. The reduced mechanism was then validated in PSR, auto-ignition reactor and one-dimensional, unstretched, premixed, laminar steady flame over a wide range of pressure, temperature, equivalence ratio and mass flow rate. Three dimensional CFD simulation using software AVL Fire was carried out on 6114 diesel engine. Comparison between calculation and experimental results demonstrates the validation of the reduced mechanism.A reduced mechanism including 123 species and 117 lumped reactions and a reduced mechanism including 239 species and 234 lumped reactions were deducted after applying I-CSP to n-propanol and n-heptane with threshold value 5%. The reduced mechanisms were then validated in PSR and auto-ignition reactor over a wide range of pressure, temperature and equivalence ratio. Meanwhile, comparison of results from experiment and calculated in Chemkin about pressure, HC and CO demonstrates the validation of the reduced mechanism.Based on Fire software, according to the reduced mechanism of DME, the numerical simulation of in-cylinder combustion and emissions and experiments of DME engine are investigated to prove that the simulate results are basically consistent with the measured one. Also, the DME concentration, in-cylinder temperature and CO concentration distribution under different loads of engine speed of 1570r/min are simulated. Moreover, through the experiment of the in-cylinder WP6.210 electroniccontrolled DME engine, the in-cylinder pressure, pressure rising rate, in-cylinder temperature, heat release rate, combustion phasing and exhaust emissions are got to comprehensively analyzed.