| With energy conservation and emission regulations being more strictly, the cylinder pressure of diesel increased to more than16Mpa. Thermal load and mechanical load in cylinder liner-piston group increased significantly. Cylinder liner and piston rings easily lead to deformation influenced by cylinder head bolt preload, piston high-speed periodic reciprocating, non-uniformity of cylinder block stiffness and thermal stress generated by non-uniform cooling. When the cylinder liner deformation and out-of-roundness can not be compensated by elastic force of piston rings, abnormal gap will emerge thus cause oil and gas leak. According to statistics,50%diesel particulate material (PM) emission is soluble organic matter produced by burning of lubrication oil fleeing into the combustion chamber. So it is significantly important for reducing oil consumption, emissions and improving friction properties that controlling cylinder and piston deformation and out-of-roundness, improving cylinder sealing performance. The engine used in this study was a turbocharged inter-cooled diesel, and the main purpose of the experiment was to get the principles and influencing factors about the cylinder liner installation distortion and deformation under working conditions. Some strategies and solutions in controlling the deformation of the cylinder liner were proposed. The following specific research works were carried out.(1) The study on characteristics of the cylinder liner installation deformation and influence factors under pre-tightening working conditionThe body cylinder head cylinder assembly coupling model was established. Static analysis was finished under preload condition. The experiment has researched the effects of structural and non-structural factors on the cylinder liner deformation with orthogonal design method, and cylinder structure was optimized. Studies have shown that for all cylinder liners, the shrinkage deformation was presented in cylinder upper section under preload conditions, and expansion deformation occurred in lower section. The maximum deformation was mainly occurred at the top of the cylinder liner. The deformation of four cylinder liners is non-uniform, cylinder liner1has larger deformation with cylinder liner4, and the deformation of cylinder liner2is smaller with cylinder liner3. The bolt preload in non-structural factors, the depth of countersunk and cylinder liner wall thickness have greater impact on cylinder liner deformation.2) The study on characteristics of the cylinder liner thermal deformation and influence factors under thermal load conditionBased on the engine bench test, the thermal load of cylinder head, cylinder block and liners, flow and cooling uniformity of the cooling jacket are studied by fluid-solid coupling heat transfer method. And the effect of cooling jacket structure on cooling uniformity and cylinder liner thermal deformation is studied. Studies have shown that the upper liners have larger thermal deformation value and gradient, the lower and central liners have relatively smaller thermal deformation value and gradient, the average thermal deformation of the cylinder liners under thermal load is16times of that under pre-tightening working condition. The regions between two cylinders have relatively smaller thermal deformation. At free areas of cylinder liner1and cylinder liner4have the largest thermal deformation. Due to each cylinder head, cylinder block and cylinder liner has non-uniformity distribution in temperature field, cooling water flow uniformity optimization scheme is different from cooling uniformity optimization scheme.(3) The study on characteristics of the engine cylinder liner thermal-mechanical coupling deformation and influence factors under working conditionWith considering the effect of mechanical load and heat load, the thermal-mechanical coupling analysis of cylinder block and liners assembly coupling model is made to research the different loading cases of the deformation features of the liners. Compared to pre-tightening working condition and thermal load working condition, the cylinder liner maximum main stress under working-load condition increases significantly, the cylinder liner deformation increases little and is similar to that under thermal load condition. In summary, the cylinder liner out-of-roundness of optimized case under pre-tightening working condition reduces more effectively than that of cooling uniformity optimized case. In addition, the deformation of cylinder liner2is symmetrical with that of cylinder liner3caused by the cylinder block stiffness, and the deformation law is pea-shaped, so is the deformation of cylinder liner1and the cylinder liner4. The cylinder block structure stiffness uniformity plays an important role in the liner deformation distribution.(4) The test and analysis of cylinder liner dynamic deformationThe cylinder liner dynamic deformation of TCI engine and naturally aspirated engine under full-load condition is tested by the strain test method, the liner circular and radial deformation of different engines is compared and analyzed. With the increase of engine speed, the deformation of cylinder liner thrust surface, anti-thrust surface and side surface increase. When the engine at a high speed, the cylinder liner deformation of the naturally aspirated diesel engine shows obviously random vibration characteristics, but the cylinder liner deformation of the TCI engine shows regular and maximum explosion pressure-related vibration characteristics, the deformation of cylinder liner thrust surface under maximum torque condition is larger than the deformation under any other condition.(5) The study on the effect of the cylinder liner deformation on piston dynamics characteristics, sealing performance and friction lossesOn the basis of the cylinder liner deformation, the effect of piston assembly structure and cylinder liner deformation uniformity on the piston secondary motion, oil consumption, blow-by and friction lose is studied. When the piston head gap, the gap between the piston and cylinder and piston pin offset increase, the piston average pendulum angle and peak striking power (KEP) increase. The top compression ring tangential elasticity has the greatest impact on the oil consumption, the second compression ring tangential elasticity has the greatest impact on the blow-by, and the oil ring tangential elasticity has the greatest impact on the friction lose. As each ring tangential elasticity increases, the oil consumption and blow-by decrease, the friction lose increases. As the engine speed increases, cylinder liner deformation non-uniformity, oil consumption, blow-by and friction ring average pressure increase.By studying the effect of pre-tightening working condition and cooling uniformity optimized case on the piston ring dynamics characteristics, each case has a little effect on the piston ring FMEP, and improves the oil consumption and blow-by greatly, the pre-tightening optimization scheme has great effect on reduction of the oil consumption.
|
PDF Full Text Request