| The fuit trees are perennials plants with less soil tillage,which results in serious soil compaction,and is not conducive to the growth of roots.Meanwhile,at present in the orchard fertilization process,the most widely used method is ditching and fertilizing method.However,orchard ditching and fertilizing technology has a series of problems,such as easy damage to tree roots and high energy consumption.The fertilizer is concentratedly applied in the trenches,and the diffusion is uneven,which is not conducive to the balanced absorption of the fruit tree roots.In order to solve the above problems,this paper proposes a gas explosion subsoiling and fertilizer injection method combining the theoretical analysis and experiment.In this paper,the mechanism of the gas explosion subsoiling is studied systematically,the diffusion effect of fertilizer injection is researched,the key components of the gas explosion drill pipe is optimized,and the gas explosion subsoiling and fertilizer injection machine is developed.The main work accomplished in this paper and the results achieved are as follows:(1)The stress relationship between gas explosion and soil was analyzed based on the circular hole expansion mechanics model,and the form and conditions of soil failure caused by gas explosion were studied.The gas explosion soil fissure extension model was introduced based on the Murdoch L C equations,the limitation of Murdoch L C model with soil fractures expansion in a two-dimensional plane was pointed out,and the establishment of a model for soil fractures expansion in the whole soil was proposed.The evaluation method of the soil disturbance was constructed..(2)The drill pipe mechanism was optimized by using soil mechanics model.The drill bit structure parameters was optimized with the minimum drilling resistance as the goal.The optimized drill cone angle was 60° and the drill cylinder radius was 12.5 mm.The outflow hole structure was optimized with the outflow effect as the goal by using FLUENT numerical analysis method.The optimized number of outflow holes was 4,the diameter was 7 mm,the structure was an inverted cone,and the cone angle was 60°.(3)The whole soil layer gas explosion soil fissures extension mathematical model was established based on air pressure leak attenuation equation and plane positive shock wave theory.The experiment of soil fissures and disturbance caused by gas explosion subsoiling was studied.The influence of gas explosion parameters(explosion depth H and gas explosion pressure P)on soil fissure extension was studied,the soil fissure trace equation and soil disturbance model were established,and then the gas explosion parameters were optimized.The above work provides a theoretical basis for the design of the whole machine.The area of soil disturbance caused by gas explosion in the entire soil layer is a parabolic object.The radius of the bottom circle of the paraboloid is the intercept of the fissure trace on the soil surface,and the height of the parabolic object is the maximum depth of the fissure trace.The soil was mainly subjected to pulling damage when the gas explosion depth was less than 25 cm,the soil surface tended to rise at the gas splitting force of 0.17 MPa and the disturbance coefficient of 50%,and the center of soil fissure was the gas explosion center.The soil was mainly subjected to shear damage when the gas explosion depth was more than 25 cm,the soil surface elevation was not obvious at the gas splitting force of 0.39 MPa and the soil disturbance coefficient of more than 50%.The data optimization results showed that 1 MPa gas explosion pressure and 30 cm gas explosion depth were more appropriate,and under the condition the soil subsoiling effect was remarkable with the soil disturbance coefficient of 79.5%.(4)The gas explosion subsoiling and fertilizer injection experiments were carried out,the changing rules of the gas explosion parameters on the soil compactness descent rate(SCDR)were studied,and the influence rules of the gas explosion parameters and liquid fertilizer concentration on the diffusion distribution of the fertilizer were revealed.After the gas explosion,the SCDR was distributed in a circular zone.The closer to the center of the gas explosion,the larger the SCDR,the better the subsoiling effect.The effect of P on the SCDR was significant,and the larger the P,the SCDR in the test domain increased in both the radial and longitudinal directions.When H was 30 cm and the P reached 0.8 MPa,the SCDR in the test domain was greater than 20%,and the soil disturbance depth below 45 cm,the subsoiling effect was significant.The effect of H on SCDR was as follows:When H<25 cm,the soil surface was easy to lift,and the SCDR was larger with the decrease of H,so that when H was 10 cm,the SCDR in the test area was all higher than 45%,which indicated that the soil disturbance effect was good;When H>25 cm,due to the increase of soil gravity stress,the SCDR decreased with the increase of H,the overall subsoiling effect was better when the His 30 cm.Before the fertilizer injection,the gas explosion subsoiling could promote the diffusion of the liquid fertilizer.The larger the P,the greater the soil porosity,and the more beneficial for the diffusion and flow of the liquid fertilizer.The gas explosion and fertilizer injection depth H determined the spread situation of liquid fertilizer in soil.When H ?20 cm,the liquid fertilizer easily overflowed from soil surface,which easily caused fertilizer waste.When H>20 cm,the fertilizer concentration range decreased with the increase of H,and the deeper the H,the soil fluid tended to radial flow diffusion due to soil gravity stress.The liquid fertilizer concentration determined the size of the diffusion radius.When the concentration was high,the viscous resistance of the liquid fertilizer and the soil was large,the fluidity of the liquid fertilizer was weak,the diffusion radius was small,and the diffusion effect was poor.When the concentration was low,the infiltration rate of the liquid fertilizer in the soil was faster,and the diffusion effect was general.On the whole,the diffusion effect of the liquid fertilizer with a concentration of 300 g/L was better.(5)The gas explosion subsoiling and fertilizer injection machine prototype was produced and the field experiments were carried out.The drill pipe mechanism with pneumatic chipping hammer excitation and hydraulic assistance was designed to drill the soil The dynamical model and kinematical equation of soil drilling by pneumatic chipping hammer with hydraulic assistance were established,and force analysis of drill pipe during soil drilling process was performed.Meanwhile,the drill bit structure parameters and hydraulic component were optimized,which made the pipe drill and lift rapidly.An economical multi-knob switch control system based on PLC was made to improve the equipment automation degree and reduce the intensity of labor operations,which could make the machine operations controlled manually and automatically.The working processes of soil drilling,gas explosion subsoiling,liquid fertilizer injection and drill pipe rebound were completed in a key operation.Field experiments results showed that soil fractures were created by gas explosion.Under the condition of 0.8 MPa gas pressure and 30 cm drilling depth,the maximum breadth of fractures was about 3-4 mm,the extension disturbance radius of fractures about 40 cm.The reduction of soil compactness was obvious with an average drop of 40.5%within a horizontal radius of 40 cm.In addition,the soil perturbation happened after gas explosion,and the soil disturbance coefficient was 72.17%,which was better than shovel subsoiling technology.The liquid fertilizer was sprayed in deep soil with no stoppage and diffused uniformly in the role of high pressure pump.The work efficiency was 0.048 hm2/h at least and would increase with different agronomic requirements.What's more,with simple operation and stable performance,the new designed machine can meet the agronomic requirements of orchard,garden and city greening fertilization. |
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