Abstract:To study the nonlinear dynamic characteristics of high-speed rolling bearing-rotor coupling system in maneuvering flight, the mathematical model of bearing-rub-impact rotor system with time-varying rigidity of rolling bearings in climbing-diving maneuvering flight was established by using finite element method, and the dynamic equation of the system was solved by Newmark-β integral method. The interaction between the time-varying stiffness of rolling bearings and the non-linear dynamic characteristics of rotor is considered in this model, as well as the influence of the eccentricity of rotor and the radial clearance of rolling bearings. By solving the model, the time-domain diagram, frequency-domain diagram and bifurcation diagram of the system under different states are obtained. Based on these, the time-varying characteristics of the stiffness of high-speed rolling bearings, the interaction between the stiffness of bearings and the dynamic state of rotor, the non-linear characteristics of the bearing-rotor system, the influence of the maneuvering flight state on the system and the dynamic response of rotor system with rub-impact fault in maneuvering flight are analyzed. The results show that the time-varying characteristics of bearing stiffness, which is one of the factors restricting the maximum speed of the rotor system, is closely related to the dynamic characteristics of the rotor system. Because of the maneuvering load, the complex non-linear dynamic characteristics will be generated in the rotor system, but when the speed of the system is low, the stability of the system will be improved to some extent due to the introduction of maneuvering loads. The stable motion interval decreases with the increase of rub-impact stiffness.

Abstract:To study the frictional heat of the asperity on friction pair of the inner and outer rings of spherical plain bearing during relative sliding process, the model of a hemispherical asperity sliding relative to a smooth plane is established. The steady-state temperature rise of the inner and outer rings in the asperity contact zone is calculated with integrating the temperature rise caused by point heat source. The temperature rise distributions of the contact zone under elastic contact and plastic contact were calculated respectively, and then the temperature rise along the velocity direction under different angular velocities and loads was examined. The maps of the maximum flash temperature in the contact zone of two different types of spherical plain bearings are presented. The results show that the temperature rise of the asperity in contact zone is symmetrically distributed, and the maximum temperature rise is at the center point. The temperature rise at the trailing edge of the outer ring is greater than that at the leading edge, and the maximum temperature rise appears at the position of trailing edge. The higher the angular velocity or load, the higher the temperature rise. Under low-speed and heavy-load conditions, the maximum flash temperature of the asperity is low, and in case of high-speed conditions, the maximum flash temperature is high. To prevent the spherical plain bearing from being damaged due to excessive heat generation caused by asperities, the control of loads and angular velocities should be noticed.

Abstract:Considering the friction between bump foil and surrounding structure and the interaction between bumps in bump foil, the bending moment of the bump foil including a rounding between bump and bridge was established based on the elastic deformation energy theory. The foil deformation and stiffness of single bump was obtained and the validity of the proposed model was verified by comparing with previous foil models. The effects of the rounding radius on the structural stiffness of gas bearing and the anisotropy performance are studied by simulating gas film force distribution with triangular load distribution. The simulation results show that with the increase of the rounding radius the number of pinned-down bumps decreases in a step-like manner, and the stiffness of pinned-down bumps first increases and then decreases whereas the stiffness of the sliding bumps decreases. There is an optimal rounding radius at which the mean stiffness of the bump foil has a maximum value. With the increase of friction coefficient, the stiffness of foil arch presents a non-linear upward trend, which effectively reduces the anisotropy of structural stiffness. With the increase of rounding radius, the anisotropy of the stiffness of the structure increases, but the influence degree is not as severe as the friction coefficient. The results above can provide theoretical reference for structural design of gas foil bearing.

Abstract:To get the particle impact characteristics of the water wall, numerical simulations on a 660 MW supercritical tangentially coal-fired boiler were performed based on Ansys Fluent. The impact mass flow value on the water wall in burner area was gotten by using Fluent erosion wear model. By using the Sample function of Fluent and Excel data processing function, how much the maximum velocity and how the velocity of particles distributes were obtained. The result indicates that the maximum mass flow value of particle impacting contralateral water wall area of burner nozzle is 6 kg·m^-2·s, the maximum velocity of particles impacting the water wall in burner area can exceed 30 m·s^-1 at a rate of 3%, the subject of velocity value is 5 ~ 20 m·s^-1, and particles with a speed from 20 m·s^-1 to 25 m·s^-1 may accounts for 10% of the total. It also shows that the 6 kg·m^-2·s high impact mass flow value and the 25 ~ 29 m·s^-1 high impact velocity coexists on the back wall in the second burner group area, where severe erosion wear may occur.

Abstract:To investigate the effect of nonuniform axial heat flux distribution and uneven radial heating and inlet throttling on density wave oscillations in reactors, RELAP5/MOD4.0 code is applied to conduct numerical simulations of a parallel channel system in forced circulation loops. The results obtained from the combination of non-homogeneous non-equilibrium model and semi-implicit numerical method in the code agree well with experimental data. Flow instability boundaries of linear and cosine axial heat flux distribution are compared and integral of axial heat flux along the channel is plotted to analyze the detailed mechanism. Besides, the critical phase change numbers of system and each channel under different nonuniformity of radial heating and inlet throttling are calculated. The results show that the system stability depends on the location of boiling boundary and the integral of axial heat flux along channel. Increasing or decreasing axial heat flux linearly has stabilizing or destabilizing effect compared with uniform axial heat flux respectively. Cosine heat flux increases system stability at low inlet subcooling. However, system stability could either be strengthened or weakened at high inlet subcooling. Inlet-peaked heat flux decreases system stability while outlet-peaked heat flux increases system stability compared with cosine heat flux. The influence of uneven radial heating on system stability is not significant. System stability decreases with nonuniformity of radial inlet throttling and it increases if the inlet throttling of one channel is increased.

Abstract:Aiming at improving the anti-swing effect of automated rail mounted container gantry crane(ARMG) during its unmanned hoisting and handling work at the automated terminal, an active anti-swing method using the spreader auxiliary wire rope as traction was proposed. By the auxiliary wire rope, the traction is used to restrain the swing of spreader and consume its swing kinetic energy, thus the swing amplitude of the spreader can be reduced to the safe ranges to realize the anti-swing target. Firstly, the dynamic model of the active anti-swing can be set up, then the traction force of auxiliary wire rope is equivalent to the damping of spreader, and the actual traction force can be calculated by obtaining the equivalent damping. Throughout the simulation of the active anti-swing process of different trolley travelling schemes and different typical heave height, the swing response of spreader and the size of traction force applied by the auxiliary wire ropes could be acquired and it verified the effectiveness of the anti-swing strategy and the correctness of the equivalent damping calculation. Finally, taking a certain ARMG produced by Shanghai Zhenhua Heavy Industries Company(ZPMC) as an experimental object, experimental verification was carried out at typical heave height, and the output moment of the auxiliary motor obtained by experiment verified the feasibility of the active anti-swing method and its practicability in the actual application.

Abstract:In order to solve the problem of load expression of transmission test bench under non-stationary random cyclic load conditions, a parameterized test load model for typical shifting condition reconstruction was proposed. Taking the transmission drive shaft of the typical shifting condition of loader as research object, the non-stationary random load data was decomposed into non-stationary deterministic component (trend term) and stationary random component (random term) based on the wavelet transform series decomposition method. The trend items with non-stationary random characteristics were parameterized by piecewise functions fitting with RMS weighting. The random term with stationary random characteristics was based on Parseval theorem to establish the expression of random harmonic function, and the two component expression functions were reconstructed to realize the expression of its parameterized test load model. Through the test data of small sample loader, the validity of the parameterized test load model for typical shifting condition reconstruction and its non-stationary random characteristics and non-stationary random correlation were verified, which can be used as a load expression for the transmission drive shaft bench test of the typical shifting condition of the loader. The modeled method had engineering value for test bench load reconstruction under non-stationary random cyclic loading conditions.

Abstract:To improve the pass ability of heavy-duty tractors, a hydraulic hybrid heavy-duty tractor is equipped with a hydraulic hub motor auxiliary drive system on front axle based on the traditional structure. On this basis, an engineering control strategy is developed to achieve time-sharing all-wheel-drive control. The strategy ensures the smooth switching of the system mode by identifying the working states of the two sets of power systems and the driving intention, and the controlling of hydraulic system to intervene and exit at the right time. In each mode, the pump displacement is controlled rationally, and a good wheel speed tracking in the assist mode is achieved. The actual vehicle test results of the control strategy show that the driver's operation intention is accurately identified, the mode switching and shift smoothness are good. The two systems work in harmony and do not interfere with each other, and the driving safety is guaranteed. The variable pump displacement response reasonably in each mode, and the wheel speed tracking method is effective. The actual vehicle test verifies the feasibility of the hub hydraulic hybrid system and the rationality of the strategy proposed.

Abstract:To research the structural characteristics of 3A molecular sieve and Al₂O₃ mixed carrier catalyst and the catalytic characteristics of catalyst for toluene, a series of nickel-based catalysts were prepared by equal volume impregnation, and γ-Al₂O₃ and 3A molecular sieve were mixed as carriers. The catalysts were characterized using XRD, H₂-TPR and BET, and the catalytic performance of nickel catalyst for toluene was investigated in a fixed-bed reactor. The results indicated that the active species Ni mainly exists as NiO and Ni₃Fe iron-nickel alloy in the catalysts. The specific surface area and pore volume of catalysts went down for the Al₂O3 catalysts, and then the toluene conversion rose with the increase of temperature, while the conversion rate of toluene increased firstly and then decreased as the load amount of Fe increased. For the mixing catalysts, the specific surface area and pore volume of catalysts increased, while the activity of catalysts and the conversion of toluene increased firstly and then decreased with the increase of γ-Al₂O3 proportion. It has the highest toluene conversion rate, when the reaction temperature is at 700 ℃, the water/carbon ratio is 2, and the residence time is 0.6 s, at same time the mixing ratio of γ-Al₂O3 is 60%.

Abstract:To analyze the effect of performance dependence caused by interaction among units on the reliability of multi-state system, the function-motion-action (FMA) theory is used to decompose a multi-state system into meta-actions. By using the non-homogeneous Markov model, the multi-state evolution process of the meta-action unit is described. By setting the state transition coefficient to associate the state transition rate with the dependency property, a new state transition matrix is constructed. The Kolmogorov differential equation is used to obtain the probability. The model considering the performance-dependent characteristics of the units is established by the vector universal generation function. The index turntable system is used as an example to verify the influence of the unit dependence characteristics on the system. The results show that the state transfer rate will change with the performance degradation of the free cells. Compared with the multi-state system with independent units, when the unit is in a high performance state, the multi-state system with unit-dependent characteristics is more reliable. On the contrary, the system is more vulnerable. The results provide theoretical basis for the reliability design and the product maintenance cycle setting.

Abstract:To realize the ultra-precision diamond cutting of micro-structured single germanium components, the vibration assisted diamond cutting was adopted to increase the critical undeformed chip thickness (CUCT) of brittle germanium, and the theoretical equations were derived for calculating chip thickness of micro groove. By micro cutting tests with micro arc shaped diamond tool, the influence of vibration amplitude on CUCT was analyzed, and the surface roughness of micro groove and morphology of chip were also studied according to the experimental results. Accordingly, the machining quality was evaluated during cutting cross-shaped groove and rectangular boss with depths of 4.5 μm and 10.0 μm. For the sake of removing damage near the edge of groove, a technological process was adopted and conducted by applying cutting-depths decreased gradually and cross feed together. According to the experimental results, the cutting depth of micro groove was suggested to measure directly because of the higher values calculated by theoretical equations. The CUCT was found to increase with the increase of vibration amplitude and reached 704 nm, which is almost 5.2 times of that without vibration assistance. It was also observed that the surface roughness could be decreased when applying vibration assisted cutting. Moreover, vibration assisted cutting was proved to have excellent performance on machining micro structures with high accuracy under large cutting depth. The adopted technological process was able to remove the surface damage and generate smooth surface with R_a 3.09 nm.

Abstract:To investigate the effects of pressure side winglet on aerodynamic performance of high subsonic compressor cascade at different Inlet Mach Number, the experimental study has been carried out to explore the original cascade and cascades with different pressure side winglets at different Inlet Mach Number(Ma=0.5,Ma=0.6 and Ma=0.7). The results show that the pressure side winglet not only weakens the pressure gradient on both sides of the blade, but also obstructs flow into the tip clearance. At the same time the pressure side winglet can inhibit the tip leakage flow and reduce the flow loss under the condition of high subsonic, thus the tip clearance flow is improved. With the increase of pressure side winglet width, the improvement degree is increased, and the change of Mach number is proportional to the control effect. The most effective pressure side winglet is PW2.0 at inlet Mach number of 0.7, which provides the most significant aerodynamic loss reduction by 6.53% compared to the original cascade at the same inlet Mach number .

Abstract:To simulate the low-temperature environment required for the friction performance test of polar deck machinery, the German Julabo expert type ultra-low temperature heating refrigeration circulator FP89-HL was used as the cold source, and a light and sturdy aluminum alloy was used to make the chambers, then two cryogenic chambers for reciprocating friction and wear tester and rotating friction and wear tester were developed respectively. The physical and mathematical models of air flow and heat transfer in the chamber were established and simulated using FLUENT software. The experimental results show that the lowest temperature in the reciprocating cryogenic chamber can reach -64 ℃ and the lowest temperature in the rotating cryogenic chamber reaches -70 ℃ under the condition of the ambient temperature of 18 ℃. The simulation results are in good agreement with the cavity temperature test results. The environment design, simulation and implementation of the combination of low temperature cycle system and friction and wear testing machine broaden the operating temperature range of friction and wear testing machine. Compared to the traditional test environment which is only cooling the sample to low temperature, the new environment which is simulating real low temperature friction conditions through ambient cooling has the advantage of being closer to the actual working conditions.

Abstract:To explore the influence of lightweight of hydrodynamic torque converter on its working characteristics and working parts, the hydrodynamic torque converter three-dimensional flow lightweight platform was developed based on the three components hydrodynamic torque converter prototype. By using the Bessel curve, the parameterized modeling of cascade system and the inner and outer ring surfaces was performed to define the thickness coefficients of the blades and the inner and outer rings. Design of experiment method (DOE) was used to establish each wheel with different thickness parameter of single flow channel model, and computational fluid dynamics software was used to calculate the single flow channel model for flow field simulation. The simulation results were used to analyze the unidirectional flow solid interaction calculation of wheels after thickness variation and its influence on the external characteristic and strength. The performance of lightweight torque converter was tested and the results show that with the decrease of thickness, the torque converter can withstand the stress increasing on structure, and the expandance of flow passage and circulatory flux will significantly improve the efficiency and torque values of pump and turbine wheels.

Abstract:Chemical plating method is one of the most common manufacturing techniques of IPMC (Ionic polymer-metal composites) electrode. But the preparation period of conventional chemical silver plating method is about 32 h, which is very time consuming. Thus, the electrophoretic deposition method was proposed in this paper. MCNT (multiwalled carbon nanotube) was introduced in the electrophoretic deposition method. In considering the poor combination of MCNT and Nafion membrane, an electroless silver plating reaction was first carried out before the electrophoretic deposition method. Finally, MCNT-Ag-IPMC was successfully prepared. In addition, the influences of electrophoresis voltage and deposition time, two important parameters in electrophoretic deposition method, on the actuating performance of IPMC were also studied. As a result, the preparation period of electrophoretic deposition method was half of that of the conventional chemical silver plating method. In addition, the actuating performance of prepared IPMC was fully superior to that of conventional chemical silver plating method. It could be concluded that the electrophoretic deposition method is a promising method for the preparation of IPMC electrode.

Abstract:To study the mechanical properties of spatial thin-walled elastic extension bar, the change of energy, external load during leveling and flattening and stiffness are analyzed. Firstly, the stiffness of elastic extension bar is theoretically analyzed, and the parameters that affect the stiffness of elastic extension bar are found out. Then, the process of flattening and leveling the elastic extension bar is simulated by ABAQUS, and the influence of various parameters on the stiffness is analyzed by using the control variable method. The simulation results show that the energy variation in the leveling process is basically consistent with that in the flattening process, but the external load required for the flattening is relatively small. With the increase of the radius of arc section, the number of layers and the center distance, the deformation of the elastic extension bar will gradually decrease under the same load. By the analysis of the simulation results, it can be seen that the external load is smaller in the initial stage of flattening and leveling, and the peak value of the external load appears in the final stage of flattening and leveling, and the stiffness of elastic extension bar can be improved effectively by increasing the radius, center distance and the number of layers.

Abstract:The instantaneous velocity analysis of a 2R1T (R denotes rotation, T denotes translation) spherical parallel mechanism was performed. As the center of the moving platform of the mechanism and the center of the base are plane-symmetric about the three spherical joints, the position solution of the moving platform can be easily obtained by using geometric method, but the calculation of instantaneous velocity is relatively complicated. In particularly, the calculation of angular velocity is heavily dependent on the correct solution of the rotation matrix or the complete Jacobian matrix, and the calculation efficiency is low and error-prone. For this reason, the Riemann symmetric space theory method is used in this paper. Starting from the symmetry of the subchain screw system, the constraints on joint movement of each subchain are established and the calculation of instantaneous velocity is simplified. Instantaneous velocity forms a linear space of which the base just explains the instantaneous degree of freedom of the mechanism. Finally, an example is given to verify the correctness and effectiveness of the method. By comparing ADAMS (Automatic Dynamic Analysis of Mechanical Systems) software simulation with theoretical calculation, the angular velocity calculation error is within a range of -0.004 rad/s~0.006 rad/s; and the linear velocity calculation error is within a range of -0.01 mm/s~0.015 mm/s, the calculation time is 5.187 seconds by using the symmetric space theory.

Abstract:For the defects that the outlet pressure of condensate pump fails to meet the prescribed requirement during startup period of a marine feed water unit due to the fact that high temperature deoxidizing water enters the condensate pump and its suction pipeline during the standby state and the standby switching start-up, which leads to the cavitation of condensate pump, and on the basis of the head-volume flow rate-rotation speed model of each impeller obtained by Differential Evolution algorithm, the model of condensate system pipeline and valve, and the whole condensate system simulation model were established with SimuWorks simulation platform, and the changes of parameters such as enthalpy, pressure, temperature and the rate of vapor content with the switching process of the unit were obtained by simulation under the condition of different high temperature deoxidizing water leakage. The results show that the startup condensate pump will cavitate and its outlet pressure cannot be established in time when the condensate pump is filled with hot water before startup due to the leakage of suction gate valve, as well as the leakage of high temperature water from the startup unit and the outage unit which has lost drainage ability is large. Thermodynamics is used to reveal a special fault mechanism of marine condensate system, which has important reference value for system design improvement and fault detection.

Abstract:In this paper, considering the problem of multimodal time series modeling based robot safety surveillance, we present a fast, robust, and versatile measure for executing process identification and anomaly detection through Hierarchical Dirichlet Process Hidden Markov Model (HDPHMM). To effectively improve the robot safety surveillance, first the complex manipulation task into sequences of executing processes was decomposed and then the process identification could be achieved by comparing the log-likelihood value of cumulative observations during robot manipulation. After the process identification, the anomaly detection of each process could also be implemented by discriminating anomalies by the gradient of log-likelihood thresholding from the normal training executions.

Abstract:Aiming at the complexity of the vibration mechanism of rolling bearing induced by compound fault under radial load, based on Hertz contact theory, a 4-DOF dynamic model of deep groove ball bearing with compound fault is proposed by considering compound fault, coupled excitation between the shaft and the bearing housing and the bearing, time-varying displacement excitation and rolling element sliding. The model describes the contact and movement of rolling element on the raceway surface, explores the compound fault excitation mechanism of the bearing, and analyzes the influence of rolling bearing compound fault on the system dynamic vibration response under three kinds of working conditions, which provides a theoretical basis for bearing condition monitoring and diagnose. The experimental and simulation results show that the vibration response of the compound fault is the result of the coupling of vibration response of single fault on the inner and outer ring. The fault characteristic frequency and multiple frequency components of the inner and outer ring can be clearly distinguished in the spectrum. Compared with a single fault, the vibration amplitude of the compound fault is higher than that of the single fault. The increasing of size, speed and load will increase the vibration amplitude of the bearing with compound fault and affect its operating state, which will accelerate the failure and reduce the service life of bearing.

Abstract:Side window clarity and its effect on side mirror visibility plays a major role in safe driving. In view of the problem of side window water pollution when a car is driving in rainy days, combined the aerodynamics and multiphase theory, the Boltzmann method and Lagrangian method are used to solve the transient external flow field and the droplet movement in this paper. Trajectory of the droplet and distribution of the water phase in the side window area are given, the mechanism of water pollution in the side window area is analyzed and the A-column surface is modified. Four different schemes are established, the effects of different schemes on the water film distribution in the side window area are compared and the image processing technology is used to quantify the pollution area. The results show that the four schemes all play a role in reducing water pollution in the side window area. The side window of scheme 2 is the best, the water film coverage is 38.2%, which is decreased by 19.2% compared with the basic model.

Abstract:To solve the global path for a biped wall-climbing robot in a 3D wall environment, a planning method combining wall transition analysis, searching of global wall sequences, and optimization of adhesion points when performing wall transitions is proposed. Firstly, to obtain the feasibility for the biped wall-climbing robot to transit between walls, the robot’s reachable workspace and the wall are simplified to transform the problem into a geometric intersection test. Then, the global wall sequence is found by using a graph search method. Finally, to obtain the optimal global path, a mathematical model is established to compute the optimal adhesion point for transiting between adjacent walls. A biped wall-climbing robot, named W-Climbot, is used for simulation. The simulation results show that the proposed method takes only 2ms on average to analyze the feasibility of transition between different walls and search the global wall sequence in a three-dimensional environment composed of 5 to 20 walls. The success rate to obtain the optimal global path is 95%, and the average time consumed is less than 4s. This method can provide optimized global paths for biped wall-climbing robots and lay a foundation for motion planning.

Abstract:When globe-cone sealing has long storage or working requirement, it is necessary to consider the effect of stress relaxation on the globe-cone seal performance. Based on this, a finite element model of globe-cone sealing considering stress relaxation is established, and the law of the nut residual preload force and the contact stress between globe and cone is obtained with increasing creep time by this model. Then the calculating formulas of globe-cone seal leakage rate are presented by the leakage model which is presented by Roth considering stress relaxation effect, and the law of leakage rate is obtained with increasing creep time under different working parameters. The effect of stress relaxation on globe-cone seal performance is analyzed in the paper, which would be practical in the engineering design, and also improve the theory system and method about globe-cone seal performance analysis in a certain extent.

Abstract:In this paper, the Error Motion in ISO 230-7:2015 is introduced to evaluate the radial rotation accuracy for the gas dynamic gyro motor. A measurement system of rotation accuracy is built up based on 3-points error separation method. The roundness error, eccentricity error of installation and motion error are separated, respectively. In addition, a method to measure the radial centrifugal deformation and thermal deformation is proposed. Finally, the experiment system is set up and the validity of separation accuracy is verified, which provides the basis for the quantitative evaluation of gyro motor rotation accuracy in production process.

Abstract:To make the numerical control machine precision design have quantitative theoretical values for reference, the kinematic accuracy mapping model of NC machine tools based on the meta-action unit is established from the perspective of motion. The functional decomposition method of "Function-Motion-Action, FMA" is used to obtain the meta-action unit, and the topology of the NC machine tool is described in combination with the multi-body system theory. Using the theory of spin quantity the error of NC machine tools is modeled, the spatial kinematic error model of NC machine tools is established, and the comprehensive value of spatial kinematic error by spiral theory is obtained. Based on the manufacturing cost, spatial kinematic error pitch and its size, the kinematic accuracy mapping model is constructed, and the NSGA-II genetic algorithm is used to map the kinematic precision of NC machine tools. Finally, the kinematic accuracy mapping of a domestic machining center is solved, and the feasibility and effectiveness of the model are illustrated.

Abstract:In order to perfect traditional electrochemical jet machining and improve the machining quality, a wire-preposed electrochemical jet machining(WPEJM) technology is proposed, in which a flexible electrode wire is fixed in the high-speed jet to concentrate the electric field and improve the localization of jet electrolysis. According to the processing principle of this technology, software COMSOL is used to conduct simulation analysis on the distribution of multiple physical fields in machining process, and an experimental platform is set up to verify its feasibility. The preliminary results show that under the same condition, compared with the traditional electrochemical jet machining, the proposed method increases the machining efficiency and the depth-diameter ratio of the pit. Furthermore, the inner surface quality of the pit is significantly improved.

Abstract:Based on the CHEMKIN PRO software, this paper selects the NUI 2016 mechanism to study methane-n-heptane dual fuel. The two-stage ignition characteristics of methane-n-heptane dual fuel under medium and low temperature conditions were investigated, and the corresponding chemical kinetic analysis was carried out. The results show that the two-stage ignition behavior occurs when the initial temperature is lower than 750 K, and the two-stage ignition process shows a certain NTC (negative temperature coefficient) behavior; with the increase of n-heptane content, the two-stage ignition delay time is reduced, and the effect is most significant when the n-heptane content below about 75%. The related chemical kinetic analysis shows that the methane is mainly consumed in the second stage, the n-heptane is oxidatively decomposed in the first stage and during the second stage it is completely oxidized. By the reaction path analysis, it is found that the radicals and intermediates produced by the first stage reaction increase the activity of the system and promote the ignition process of the dual fuel.

Abstract:In the design of scroll wrap profiles, aiming at the problem of lacking of simple and effective general geometric model and the preference of scroll profile geometric performance is not taken into consideration in practical engineering applications, a new method of constructing scroll wrap profiles applying the frenet moving frame was proposed. Firstly, a frenet moving frame was attached to the curve of scroll wrap profile to replace the fixed Cartesian Coordinate System. Then, using the curvature of the plane curve and frenet moving frame to express the intrinsic characteristics of the scroll wrap profiles, a general geometric model of scroll wrap profiles with curvature and frenet moving frame as parameters was established. Finally, the mapping relationship between the control coefficients and the geometric performance of the scroll wrap profiles was set up. On this basis, taking the engineering application of scroll compressor as the design goal, under the condition that the circumferential diameter of scroll plate as well as the tooth thickness were known respectively, by using the mapping relationship, a series of control coefficients were selected according to the preferences of the design requirements, then the scroll wrap profiles that satisfy the requirements were constructed. The results show that the scroll wrap profile constructed by frenet moving frame not only includes all types of scroll wrap profiles at present, but also reconstructs them according to the expected geometric performance, so as to design the scroll wrap profiles with the best performances. This method lays a theoretical foundation for the flexible design of scroll compressor profile.