Study On The Diffusion Flame Combustion Characteristics Of Methanol Biodiesel Combined Fuel

Biodiesel and methanol are carbon-neutral fuels,both of which are important choices for fossil energy transitions under the"double carbon"goal.Additionally,the physical and chemical properties of biodiesel and methanol are complementary to a certain extent,so the research on the combined combustion of methanol and biodiesel in engines has attracted more attention from the academic circle.There are two main methods of dual-fuel combined compression combustion:（a）Multi-fuel pre-doping;（b）Active fuel is injected through the intake port to form an active atmosphere,and the other fuel is directly injected into the cylinder.In this thesis,the numerical calculation method is used to study the combustion characteristics of biodiesel jet flames with methanol active atmosphere and the generation characteristics of harmful formation based on the laminar counterflow flame frame of fuel flow vs air flow,and compared with the jet flame where methanol is directly doped into biodiesel（Methanol fuel side doping）.In this thesis,methyl-decanoate（MD）is used as a substitute for biodiesel,and the combustion mechanism is composed of the simplified MD mechanism developed by the CRECK combustion group and the corresponding harmful formation mechanism coupling.For ease of expression,the counterflow flames in which methanol is directly doped on the fuel side are defined as FA series,the counterflow flames in which methanol is formed into an active atmosphere on the air side are defined as AA series,and the basic flame without adding methanol is defined as BF0%flame.The main work and conclusions of the thesis are as follows;（1）The MD jet flames in which methanol forms an active atmosphere and methanol is directly doped are compared,and it is found that there are some similarities and differences in the changes of the global flame parameters of two flames.With the increase of the proportion of methanol,the heat release and the reactivity of the active components in the NPZ of the FA and AA flames are weakened,but the premixed flame on the methanol addition side is significantly enhanced and gradually shifts towards the methanol addition side.Therefore,the overall variation trend of the heat release laws of the AA and FA flames is positive.In the AA flame,the methanol oxidation zone is isolated on the right side of the SP,and gradually forms a stable LPZ with the increase of methanol addition,which is significant for the expansion of the high-temperature reaction zone.For the FA flame,the oxidation temperature range of methanol and MD is different,and the oxidation of methanol occurs in the downstream of MD pyrolysis region,which affects the transition from MD consumption to the rapid chain reaction stage.To summarize,the introduction of methanol on both sides has little effect on the pyrolysis and oxidation of MD,and the most significant effects are concentrated on the flame structure and the generation tendency of active radicals.（2）The effect of methanol oxidation on benzene formation in FA and AA flames was explored in comparison,and it was found that the concentration and formation tendency of benzene in both flames were significantly reduced.Whether AA or FA flame,A1formation is strongly related to reaction temperature and reaction behavior of C₃H₃radical.In the AA flame,the active atmosphere formed by methanol on the air side has no substantial material influence on A1,and the reduction of A1 is mainly related to the radial leakage of components.For FA flames,the direct doping of methanol will inhibit the formation tendency of high soot-prone components through dilution and chemical effect,and the dilution effect is better than the chemical effect.（3）The effects of the fuel-side and air-side introduction methanol on the NO distribution were comprehensively analyzed,and it was found that the NO generation in AA flame was significantly lower than that in FA flame.The formation of NO mainly occurs near local hot spots such as non-premixed and premixed reaction zones,and is dominated by the prompt NO and thermal NO routes in the high temperature region,which has little relationship with whether methanol is introduced.In both FA and AA flames,the introduction of methanol will significantly weaken the reactivity of carbon-containing groups such as C₂ and C₁,and accordingly balance the effect of active groups and flame temperature on the formation of NO.However,in the AA flame,the intervals between the reaction zones gradually increase with the increase of the methanol addition,and these intervals are the concentrated places of NO consumption.Moreover,the introduction of methanol in both flames will significantly stimulate the low-temperature formation route of NO,making the distribution of NO transition from"concentrated"to"uniform".The difference is that the O₂ concentration in the lean premixed reaction zone in the AA flame is significantly higher than that in the rich premixed zone,accordingly the NO output in the low temperature zone of the AA flame is dozens of times that of the FA flame in the same zone.