Experimental Investigation of Partial Laser Surface Texturing for Piston-Ring Friction Reduction

An experimental study is presented to evaluate the effect of partial laser surface texturing (LST) on friction reduction in piston rings. In a previous study, 30% friction reduction was obtained with full LST where the full width of the piston ring is textured with a very large number of microdimples that act individually as microhydrodynamic bearings. In partial LST, only a portion of the piston-ring width is textured with high dimple density, producing a “collective” effect of the dimples that provides an equivalent converging clearance even with nominally parallel mating surfaces. Experimental results obtained with flat and parallel test specimens with partial LST are presented, confirming a previously published theoretical model and the advantage of partial over full LST. Friction reduction by LST with actual production-crowned piston rings and cylinder liner segments is not straightforward and needs further investigation.     

Performance of an Al-Si-graphite particle composite piston in a diesel engine

Al-Si-graphite particle composite alloy pistons containing different percentages of about 80 μm uncoated graphite particles were successfully cast by foundry techniques. Tests with a 5 hp single-cylinder diesel engine show that Al-Si-graphite particle composite pistons can withstand an endurance test of 500 h without any apparent deterioration and do not seize during the running-in period. The use of the Al-Si-3% graphite particle composite piston also results in (a) up to 3% reduction in the specific fuel consumption, (b) considerable reduction in the wear of all four piston rings, (c) a reduction in piston wear, (d) a 9% reduction in the frictional horsepower losses of the engine as determined by the motoring test and (e) a slight increase in the exhaust gas temperature. These reductions (a)–(d) appear to be due to increased lubrication from the graphite particles which are smeared on the bearing surface, the higher damping capacity of the composite pistons and the reduced coefficient of thermal expansion of the composite pistons. Preliminary results indicate that aluminum-graphite particle composite alloy is a promising material for automotive pistons.     

内燃机缸套激光珩磨技术及其性能试验研究

激光表面微造型技术是改善摩擦副表面摩擦学性能的有效途径之一。基于声光调Q技术的二极管泵浦固体光源（DPSS）Nd:YAG激光器，采用“单脉冲同点间隔多次”激光微加工工艺，对CA6DF2-26型柴油机气缸套内孔表面进行激光珩磨加工。加工出的缸套网纹参数具有较好的一致性，达到了主机厂的技术要求。进行了激光珩磨缸套的台架综合性能试验研究，结果表明，采用激光珩磨缸套的发动机，其功率、扭矩、燃油消耗指标保持稳定，与采用传统平台珩磨网纹缸套的发动机相比，柴油机的机油油耗降低53％，漏气量降低近50％。     

Running-in wear of a compression ignition engine: Factors influencing the conformance between cylinder liner and piston rings

The conformance between the liner and rings of an internal combustion engine depends mainly on their linear wear (dimensional loss) during running-in. Running-in wear studies, using the factorial design of experiments, on a compression ignition engine show that at certain dead centre locations of piston rings the linear wear of the cylinder liner increases with increase in the initial surface roughness of the liner. Rough surfaces wear rapidly without seizure during running-in to promote quick conformance, so an initial surface finish of the liner of 0.8 μm c.l.a. is recommended. The linear wear of the cast iron liner and rings decreases with increasing load but the mass wear increases with increasing load. This discrepancy is due to phase changes in the cast iron accompanied by dimensional growth at higher thermal loads. During running-in the growth of cast iron should be minimised by running the engine at an initial load for which the exhaust gas temperature is approximately 180 °C.     

矿用防爆柴油机结构改造

在防爆柴油机上通过对排气迟闭角的调整、进气栅栏的改造和供油系统供油量的调整,同时增加扫气泵就可使防爆改造后的柴油机在动力性和尾气排放性能上接近改造前柴油机的性能,而且减小机体受热对缸盖、活塞、活塞环和缸筒的损伤.     

基于低摩擦的柴油机节能新方法研究

针对车用柴油机节能问题,提出一种基于低摩擦技术的柴油机综合节能方法。研究柴油机摩擦副低摩擦技术,采用涂层技术与润滑技术减少摩擦副磨损;搭建柴油机节能综合试验台,通过油耗仪和尾气分析仪检测节能减排效果。实验研究表明,采用涂层技术与耐磨润滑油,具有较好的节能效果,实现柴油机的节能,这为车用柴油机的节能减排提供了新的方法与思路。     

A study on effects of recirculated exhaust gas upon wear of cylinder liner and piston in diesel engines

The effects of recirculated exhaust gas on the wear of cylinder liner and piston were experimentally investigated by a two-cylinder, four cycle, indirect injection diesel engine operating at 75% load and 1600 rpm. For the purpose of comparison between the wear rates of the two cylinders with and without EGR, the recirculated exhaust gas was sucked into one of two cylinders after the soot in exhaust emissions was removed by an intentionally designed cylinder-type scrubber equipped with 6 water injectors (A water injector has 144 nozzles of mm diameter), while only the fresh air was inhaled into the other cylinder. These experiments were carried out with the fuel injection timing fixed at 15.3° BTDC. It was found that the mean wear rate of cylinder liner with EGR was greater in the measurement positions of the second half than those of the first half, that the mean wear rate without EGR was almost uniform regardless of measurement positions, and that the wear rate of piston skirt with EGR increased a little bit, but the piston head diameter increased, rather than decreased, owing to soot adhesion and erosion wear, and especially larger with EGR.     

高压直喷天然气发动机技术简介

缸内高压直喷(HPDI)天然气发动机是一款缸内喷入少量柴油、引燃直喷入缸内的天然气的1A型双燃料发动机。HPDI发动机可以保持同排量柴油机原有的性能;与传统点燃式天然气发动机相比,主要优势表现为动力强劲,燃气消耗低,可靠性高,排温低,响应快;与进气道喷射双燃料发动机相比,替代率高,经济优势明显,市场前景光明。     

Effects of piston shapes and intake flow on the behavior of fuel mixtures in a GDI engine

The purpose of this study is to investigate the stratification of fuel vapor with different in-cylinder flow, piston cavity and injection timings in an optically accessible engine. Three different piston shapes that are F(Flat), B(Bowl) and R(Re-entrance) types were used. The images of liquid and vapor fuel were captured under the motoring condition using Laser Induced Exciplex Fluorescence technique. As a result, at early injection timing of 270° BTDC, liquid fuel was evaporated faster by tumble flow than swirl flow, where most of fuel vapor were transported by tumble flow to the lower region and both sides of cylinder for the F-type piston. At late injection timing of 90° BTDC, tumble flow appears to be moving the fuel vapor to the intake side of the cylinder, while swirl flow convects the fuel vapor to the exhaust side. The concentration of mixture in the center region was highest in the B-type piston, while fuel vapor was transported to the exhaust side by swirl flow in F and Rtype pistons. At the injection timing of 60° BTDC, the R-type piston was better for stratification due to a relatively smaller bowl diameter than the others.     

内燃机活塞环组密封性能研究

为检验活塞环的密封性,进一步研究其摩擦学性能,建立内燃机环组密封数值仿真模型,模型中考虑气室体积、泄漏面积、内燃机运转工况和气室温度变化项等因素对活塞环密封性能的影响.以PA6-280柴油机为例,对活塞环组的密封性能进行仿真计算.结果表明,磨损对环组的密封性能影响很大,而工况对活塞环的密封性影响不是很明显;气室温度变化项对活塞环漏量影响较大,设计时不容忽视.