Optical Study On Spray Combustion And Soot Formation Of Pentanol/Dodecane Blends

As a traditional power plant,internal combustion engine is widely used in national defense construction,engineering machinery,transportation and other fields.It plays an important role in the development of national economy.In the face of increasingly stringent emission regulations and carbon peak and carbon neutral development goals,achieving ultra-low emissions in the whole life cycle of internal combustion engine has become the main goal of internal combustion engine technology development.New combustion technology coupled with clean and renewable alternative fuel has become one of the effective technical ways to solve the above problems.Pentanol is an ideal renewable alternative fuel because of its oxygen-containing,renewable,volatile,low polarity and stable mutual solubility with diesel and biodiesel.However,it has high latent heat of vaporization,poor cold start performance,low cetane number and poor ignition performance,so it needs to be blended with highly active fuel to make up for its shortcomings.As a traditional highly active fuel,diesel can be blended with pentanol to effectively solve the above problems.However,the complex components of diesel fuel pose a great challenge to the combustion model construction.The dodecane as a single substance can provide a more accurate characterization of the physicochemical properties of diesel.Therefore,based on the concept of fuel design,the model fuel of pentanol/dodecane two element was constructed.The optical diagnosis technology was used in the constant volume combustion bomb system to carry out visualization research on the spray,ignition,combustion and soot generation characteristics of pentanol/dodecane binary fuel,providing experimental data support for the establishment of pentanol/dodecane binary fuel combustion model.The main contents of this paper are as follows:（1）The gas-liquid phase characteristics of pentanol/dodecane binary fuel and dodecane were compared by schlieren method and Mie scattering method.The results show that:because binary fuel has lower distillation range and smaller surface tension,spray cone angle and spray volume is significantly improved.The entrainment ability of pentanol/n-dodecane binary fuel to air was enhanced.In addition,due to the higher fuel density and latent heat of vaporization of binary model fuel,the liquid length of binary model fuel is longer,which increases the risk of wet wall.Particle tracking velocimetry（PTV）was developed to explore the spray velocity distribution of pentanol/dodecane binary fuel,and the axial and radial distribution characteristics of fuel spray velocity of binary fuel were obtained.（2）Based on the constant volume combustion bomb system,a synchronous measurement platform of schlieren method,natural broadband luminescence method and OH*chemiluminescence method is established.The first stage ignition delay and total ignition delay has the same trend with the change of ambient temperature and injection pressure,The lower reaction activity of pentanol increases the ignition delay and the lift-off length of binary fuel,which provides sufficient time for the oil gas mixing before combustion,reduces the local equivalent ratio and avoids the occurrence of"injection in fire".Because of the high latent heat of vaporization of pentanol,the vaporization latent heat V_a is introduced to fit the empirical formula about the length of binary fuel liquid length and the first stage ignition delay,The influence of latent heat of vaporization on the liquid length and first stage ignition delay is revealed.（3）The temporal and spatial distribution of CH₂O group,an intermediate product of combustion,was studied by laser-induced fluorescence（LIF）.It was found that the time interval between the initial time of CH₂O and high temperature reaction was shortened with the increase of ambient temperature.The initial formation position of CH₂O is near the upstream of the lift-off length of the flame,and the fast consumption of CH₂O strengthens the steady-state flame structure.The addition of pentanol prolonged the initial time and position of CH₂O.The high frequency background light extinction method was used to explore the soot generation characteristics of two kinds of fuel.The experimental results show that the addition of pentanol reduces the fuel air ratio of binary fuel and the soot generation quality.At the same time,due to the oxygen-containing characteristics of pentanol,the net soot generation rate of binary fuel is greatly inhibited.In high temperature environment,with higher injection pressure,the difference between the lift-off length and the liquid length,LOL-LL,increases gradually,which makes the soot generation of binary fuel maintain at a low level.