Study On Bio-butanol Application In High Speed Gasoline Engine And Its Laminar Flame Speed

Biofuels are receiving increasing public and scientific attentions, driven by factorssuch as the shortage of fossil oil supplying, the continued global environmentalpollution, and the need for increased energy security and diversity. The governmentsof more than35countries, including the United States, Brazil and members of theEuropean Union, have established policies promoting the production and use ofbiofuels. Bio-butanol has been proposed as a next-generation biofuel for vehicles tosubstitute or supplement gasoline due to its superior physical and chemical propertiesin terms of the energy per unit weight, volatility, causticity and its compatibility to theexisting fuel storage and distribution infrastructures.There are two research parts in this paper, one is the study of effects brought bybutanol in a SI (spark ignition) engine’s application; two is the study of laminar flamespeed of butanol, iso-octane, and their blends.In the first part, the engine behaviors brought by butanol were revealed throughcombined method between experiment and simulation, and the influences of engineoperating parameters (such as sparked timing and valves timing) and conditions (suchas engine load) on engine performances were studied, the research contents andachievements are as follows:1. Firstly, the experiment and simulated model were set-up; and the measuredparameters were used as boundary conditions of model calculation, and thecalculated model was calibrated by measured results.2. The impacts of engine operating parameters and conditions on engine performacesand emissions were revealed and analyzed by combining experiment and modelsimulation.3. With the butanol addition, combined with using the optimum ignition timing,positive results are achieved in the power, energy consumption, and HC and COemissions. But it has deteriorated NOx emissions largely.4. The enlargement of overlap presents a good "trade-off" effect, such as decreasesin emissions (especially for NOx) without deteriorating the torque and BSEC toomuch.5. The HC and CO emissions depend more on the fuel properties. While, the powerand NOx emissions are more sensitive to the operating parameters (impact theengine combustion process). 6. The engine load is more influencing on combustion heat release than speed or fueltype.In the second part, several description methods of laminar flame speed, namely thechemical flame structure method, the experimental method, and the empiricalcorrection method, were introduced. Then, all the experimental data within theauthor’s best knowledge on the butanol’s laminar flame speed were collected, and thelimition of experiments was pointed out. The ChemKin-PRO model was set-up and6combustion chemistry mechanisms were initially chosen based on the widely reviewon the development of butanol’s combustion mechanism. Then, through thecomparison between predicted value and measured data, and for ensuring the samedata source of butanol, iso-octane and their blends, the Frassoldati mechanism wasfinally chosen for the next study (especially for the correction constants fitting).Combined with the collected experimental data and the predicted data, the impacts offactors, including equivalence ratio, pressure, temperature, diluent and the blend ratio,on laminar flame speed were investigated in detail. Some conclusions andachievements are:1. The influences on laminar flame speed by fuel-air composition and pressure aremainly through chemical kinetics (other fuels may have similar behaviors).2. While, the density ratio effect has comparative weight relative to chemical kineticeffect when considering the temperature influence, and the thermal effect has theweakest impact.3. Concerning the diluent effect, the diluent composition plays a key role in declineof fuel’s laminar flame speed, for example, the CO2has the strongest influence onlaminar flame speed, followed by H2O, and N2is the weakest one.4. The laminar flame speed is influenced by diluent effect mainly because the fuelconcentration is decreased and the specific heat capacity of combustion productsis increased as diluent addition, such that the flame temperature is declined,resulting in the lower laminar flame speed.5. While, in the aspect of chemical kinetic effect, CO2has negative effect, incontrary, H2O has positive effect, and N2’s kinetic effect can be neglected.6. In the aspect of blend ratio effect between alcohol fuels and iso-octane, theenergy rule and the Hirasawa rule show the similar excellent accuracies to capturethe experimental results, and they have been improved at fuel-rich range when acorrection factor was introduced. 7. For each effect, the correction model was extended or proposed, and the fittingconstants were resolved, and the combined correction, which considering allinfluential factors, was developed at last. In addition, the corrections proposed byvarious researchers were collected for comparing, the dispersion between themwas pointed out, this will help clarify the future research direction.The present work will largely extend the butanol application range (the engine typeand the operating condition range). This will be a demonstration effect and useful forpromoting the application of bio-fuel. Besides, the butanol’s combustioncharacteristic was investigated profoundly, providing the deepest explanation forbutanol as an alternative fuel, and building up a good base for the further turbulentcombustion modeling. Also, the present study can also serve as a special case andprovide good learning ideas and methods for the combustion mechanism study ofother bio-fuels.