A Study On Multi-component Petroleum Based Surrogate Fuel And Its Application To Internal Combustion Engine

The practical petroleum based fuel (gasoline and diesel) composition is very complexity and variability; the mechanisms suitable to be used under engine conditions are not very comprehensive; the chemical characterization data from the fundamental experimental reactor are still very scarce; the methods for mechanism reduction are also too empirical. So the above difficult problems hinder the pace for further research. Meanwhile, the trend of merging the traditional gasoline and diesel engine technology is also being paid more and more attention, and gasoline direct injection compression ignition engine is a very interesting field worthy of exploring study. Therefore, this present study takes the petroleum based surrogate fuel model development and the compression ignition engine fueled with gasoline fuel as a starting point, specially focus on the low temperature oxidation pathway of detailed mechanism; the construction approaches for multi-component surrogate fuel; the comparison study of different DRG-based methods; systematic and automatic multi-stage mechanism reduction strategies; the four-component gasoline surrogate fuel with olefin; the three-component diesel surrogate fuel with cycloalkanes; gasoline compression engine with fast thermal management(cold and hot intake air mixing). The main results and conclusions of this dissertation are listed as follows:[1] Firstly the paper systematically summarizes the gasoline and diesel surrogate fuel model and fundamental experimental data, and points out the research challenges and future development trends; the mechanisms reduction methods are reviewed and the reduction concept of each method is analyzed; the GCI combustion mode concept are expounded and some representative engine test results are elaborated. Then, the paper discusses the characteristics of low temperature oxidation pathway for different hydrocarbon fuels, including alkanes, alkenes, cycloalkanes and aromatics. The cross reactions between different hydrocarbon fuel are also summarized. Lastly, the basic thermodynamic and chemical kinetic theory of CHEMKIN software, and the computer numerical simulation of the shock tube, rapid compression engine and practical engine are described in detail. So this background knowledge can provide a solid foundation for development of the detailed and reduced gasoline and diesel surrogate fuel model.[2] DRG, DRGEP, DRG-max and PFA, which is most representative relation graph methods for large mechanism reduction, are selected for comparison study. And then an innovative method is proposed and named as "blocked relation graph" methods, which combined with original DRG, DRGEP, DRG-max and PFA methods to form the new BDRG, BDRGEP, BDRG-max and BPFA methods. By comparing the different methods under the same blocked strategy, the results show that the blocked relation graph methods include the relation graph methods. The blocked relation graph methods further explain the cause of the threshold mutation is due to remove the relative large-scale species blocks at one time. So we can improve the blocked strategies to further improve the accuracy of the reduction methods.[3] A systematic multi-stage mechanism reduction strategy for performing skeletal reductions of gasoline four-component surrogate fuel is presented. The approach includes the directed relation graph with error propagation, peak concentration analysis, linear isomer lumping, principal component analysis, temperature sensitivity analysis and rate of production analysis. The final reduced mechanism comprises 149 species and 414 reactions with embedded cross-reactions, which is suitable for homogeneous charge compression ignition (HCCI) engine application. Comparisons between computational and experimental data including the shock tube and rapid compression machine, indicate that the new reduced mechanism can provide good predictability of the ignition delay over extensive parameter space. Applying the reduced mechanism to the HCCI single zone model also shows satisfactory combustion and emission characteristics of the boosted HCCI combustion.[4] An improved surrogate diesel fuel composition has been proposed to simulate the autoignition time of diesel fuel under homogeneous charge compression ignition (HCCI) engine conditions. The surrogate fuel is modeled as a blend of n-heptane, toluene, and cyclohexane. Detailed mechanisms consisting of 1140 species and 4590 reactions were constructed by merging well-developed available chemical kinetics substructures for each chemical species. The optimal ratio of the selected diesel surrogate fuel components, n-heptane/toluene/cyclohexane= 8:1:1, was determined using trial-and-error blend methods. Numerically, the modeled heat-release rate obtained from a zero-dimensional single-zone code for the proposed new model was intensively validated against detailed single-and two-component kinetic models together with the referenced experimental engine data. The obtained results show that the new model provides a remarkable agreement with the obtained experimental data and can capture the auto-ignition angle and the whole combustion process effectively.[5] In order to make the GCI engine auto-ignition and operate steadily at low load, a scheme to control the inlet temperature by fast mixing the cold and hot air is put forward. Bench test was carried out on a modified single-cylinder direct-injection diesel engine with gasoline fuel. Results show that at 50° C of intake temperature GCI engine can be successfully operated, and single-stage heat release, the fast combustion velocity as well as relatively short combustion duration are clearly observed. When excess air ratio is kept constantly and engine operates steadily, with the increase of intake temperature, phase of ignition occurs earlier, and maximum cylinder pressure, peak of heat release and indicated thermal efficiency are increased, HC and CO emissions are decreased, but NO emission is increased. When intake temperature is kept constantly, with the increase of excess air ratio, the indicated mean effective pressure and indicated thermal efficiency are decreased, CO emission shows an increase and then a decrease, HC emission increases remarkably, NO emission decreases.