气门间隙自行变化的原因与危害

1.气门间隙变化的危害 各种型号发动机的气门间隙都有一个规定数值。当发动机工作较长时间后,气门间隙就会发生变化,需要进行检测调整。气门间隙变化情况大致分为三种:一是气门间隙变大;二是气门间隙变小;三是气门间隙时大时小。     

气门二次调整法在多缸V型发动机中的应用

正确的气门间隙对发动机正常运转、保持良好的性能是非常重要的。由于发动机的各气缸分布不同,做功的间隔角不同,使其气门间隙的调整各有差异。为此,结合多缸V型发动机曲轴配角、做功间隔角以及发火顺序等基本工况和原理,通过实例分析,探讨了二次调整法在多缸V型发动机气门间隙调整中的应用。     

气门摇臂的损伤形式及检修措施

气门摇臂是发动机气门传动组的一个关键零件，采用可锻铸铁制成。气门摇臂活套在摇臂轴上，它实际上是一个杠杆，以摇臂轴为回转中心，头部一端与气门杆接触，尾部一端通过气门间隙调整螺钉与气门推杆活络连接。气门摇臂由凸轮轴、挺杆和推杆驱动，进而打开气门。气门摇臂的损伤主要有以下4种：摇臂头部磨损、摇臂衬套间隙过大、摇臂尾部螺纹损伤以及气门摇臂折断。现对各种损伤的产生原因及防治措施分析如下。     

多缸发动机气门间隙简易调整法

调整多缸发动机气门间隙比较复杂,笔者在实践中采用看“进气门动”的方法确定调整某缸气门,简便易行,效果不错,机手朋友不妨一试。 具体方法是:①四缸发动机,看一调四,看四调一;看二调三,看三调二。②六缸发动机,看一调六,看六调一;看二调五,看五调二;看三调四,看四调三。     

WY156FMI-5四气门发动机的开发

摩托车发动机的动力性、经济性及可靠性决定了摩托车的整机性能。为适应市场竞争，开发的WY156FMI-5四气门发动机，围绕“两提高、两降低”（提高转速、提高压缩比，降低机械损失、降低热负荷）进行了系统结构的优化设计研究。试验表明，该四气门摩托车发动机比两气门机的动力性提高12%～18%，经济性从低速到高速均具有明显优势；综合技术性能大大提高。     

柴油机废气再循环电控系统设计

以DL190-12型柴油机为样机,设计了EGR电子控制系统.硬件设计包括控制单元、数据采集信号处理电路、执行机构驱动电路和显示电路.控制软件采取模块化设计方法.发动机台架实验表明DL190-12型柴油机匹配EGR电子控制系统后,掺烧15%乙醇的NOx排放量比原柴油机下降50%～90%.     

凸轮轴损伤及检修

凸轮轴是气门驱动组中最主要的零件,用来驱动和控制各缸气门的开启与关闭,使其符合发动机的工作顺序、配气相位、气门开度变化规律的要求。凸轮轴多用优质钢模锻而成,有的采用合金铸铁或球墨铸铁铸造而成。 一、凸轮轴损伤 1.凸轮磨损 如图1所示,凸轮顶部附近磨损最大。凸轮磨损后,使气门开启时刻由原来的C点延后一个角度转移到C点,气门升程减小,造成气门开启的时间断面积减少,使气体通过阻力增大,造成进气不足,排气受阻,发动机功率下降,燃油消耗增加。     

气门间隙自行变动的原因与危害

1.气门间隙变动的危害 新购的发动机在其使用说明书中规定了该机的气门间隙数值,当发动机工作较长时间后,气门间隙会发生变化,需要进行检测调整,如果该台发动机的气门间隙调好后,因种种原因发生了变化,其变化情况大致可分为以下3种:一是气门间隙越来越大;二是气门间隙越米越小;三是气门间隙时大时小。     

连续可变气门驱动装置的设计研究

介绍了一种连续可变气门驱动装置。该装置通过油路控制系统使滑移螺母在丝杠上左右往复移动,促使连接滑移螺母的正时链轮与连接丝杠的凸轮轴相对往复转动,进而实现凸轮轴上的凸轮相位连续可变,使发动机气门开启时间始终处于理想状态,兼顾发动机低速及高速不同工况,以降低发动机的燃油消耗及排放,提高发动机的动力输出。     

调整气门间隙一妙法

调整气门间隙一妙法４１２５和４１１５发动机，可用二、三缸排气门压开量来调整其气门间隙。通过计算，４１２５和４１１５发动机的二、三缸排气问弹簧座各压下４．８７毫米和５．０４毫米时，恰是一、四缸活塞到达上止点位置。用此法调整气门间隙，省事、准确、可靠，同...     

Contributing understanding of mitigation options for phosphorus and sediment to a review of the efficacy of contemporary agricultural stewardship measures

Experiences from the Mitigation Options for Phosphorus and Sediment (MOPS) projects, which aim to determine the effectiveness of measures to reduce pollutant loading from agricultural land to surface waters, have been used to contribute to the findings of a recent paper (Kay et al., 2009, Agricultural Systems, 99, 67-75), which reviewed the efficacy of contemporary agricultural stewardship measures for ameliorating the water pollution problems of key concern to the UK water industry. MOPS1 is a recently completed 3-year research project on three different soil types in the UK, which focused on mitigation options for winter cereals. MOPS1 demonstrated that tramlines can be the major pathway for sediment and nutrient transfer from arable hillslopes, and that although minimum tillage, crop residue incorporation, contour cultivation, and beetle banks also have potential to be cost-effective mitigation options, tramline management is the one of the most promising treatments for mitigating diffuse pollution losses, as it was able to reduce sediment and nutrient losses by 72-99% in four out of five site years trialled. Using information from the MOPS projects, this paper builds on the findings of Kay et al. to provide an updated picture of the evidence available and the immediate needs for research in this area.     

Poverty and biodiversity trade-offs in rural development: A case study for Pujiang county,China

Both, poverty reduction and preservation of biodiversity are high on the global agenda on sustainable development. The relationships between poverty, biodiversity of agro-ecosystems and agricultural development are complex and poorly understood. In this paper, we present an integrated framework for analysis of agricultural development and natural resource management options at agro-ecosystem level, using Pujiang county, in Zhejiang province, China as a case study area to perform the analysis. A regional linear programming (LP) model is applied, maximizing regional economic surplus, given production and labour market conditions in Pujiang. We use the model to examine the consequences for a set of regional poverty and biodiversity indicators, of four so-called poverty reduction strategies, i.e., (i) intensification of production, (ii) diversification towards livestock production, (iii) land expansion, and (iv) an exit from agriculture. The analysis indicates that diversification is the most promising poverty reduction strategy, but requires efficient use of animal manure in cropping systems to avoid environmental problems. Improved nutrient management in cropping systems is effective in reducing the regional nitrogen surplus, but less effective in increasing per capita income. The exit strategy is effective in reducing poverty and achieving biodiversity goals, but may have important social consequences that are not addressed in this study. Further reduction in rural poverty is hampered by labour constraints during the harvesting period in high value crops such as vegetables and fruits, which calls for research and development in the field of agricultural mechanization.     

Differential evolution – an easy and efficient evolutionary algorithm for model optimisation

Recently, evolutionary algorithms (encompassing genetic algorithms, evolution strategies, and genetic programming) have proven to be the best general method for the optimisation of large, difficult problems, including agricultural models. Differential evolution (DE) is one comparatively simple variant of an evolutionary algorithm. DE has only three or four operational parameters, and can be coded in about 20 lines of pseudo-code. Investigations of its performance in the optimisation of a challenging beef property model with 70 interacting management options (hence a 70-dimensional optimisation problem) indicate that DE performs better than Genial (a real-value genetic algorithm), which has been the preferred operational package thus far. Despite DE's apparent simplicity, the interacting key evolutionary operators of mutation and recombination are present and effective. In particular, DE has the advantage of incorporating a relatively simple and efficient form of self-adapting mutation. This is one of the main advantages found in evolution strategies, but these methods usually require the burdening overhead of doubling the dimensionality of the search-space to achieve this. DE's processes are illustrated, and model optimisations totaling over two years of Sun workstation computation are presented. These results show that the baseline DE parameters work effectively, but can be improved in two ways. Firstly, the population size does not need to be overly high, and smaller populations can be considerably more efficient; and second, the periodic application of extrapolative mutation may be effective in counteracting the contractive nature of DE's intermediate arithmetic recombination in the latter stages of the optimisations. This provides an escape mechanism to prevent sub-optimal convergence. With its ease of implementation and proven efficiency, DE is ideally suited to both novice and experienced users wishing to optimise their simulation models.     

节能温室环保材料使用性能评价体系研究

本文采用模糊分析法对我国节能温室中大量使用的保温薄膜进行了使用性能的评估,通过建立一套以保温性、经济性、力学性、环保性等主要评价指标的综合评价体系,从而为我国从事设施农业生产的众多农户在购买保温薄膜时提供一套行之有效的选择方案。      

Can irrigation be sustainable?

Globally, about 10 Mha of agricultural land is lost annually due to salinisation, of which about 1.5 Mha is in irrigated areas. While some climate and management aspects are common to semi-arid regions, the detailed mechanisms and options to secure ecological sustainability and economic viability may vary considerably from case to case. This paper applies a whole of system-water balance to compare irrigation in three semi-arid regions suffering from similar sustainability issues: Rechna Doab (RD), Pakistan; the Liuyuankou irrigation system (LIS), China; and Murrumbidgee irrigation area (MIA), Australia. Soil salinity, lack of adequate water resources and groundwater management are major issues in these areas. The MIA and LIS irrigation systems also suffer from soil salinity and low water-use efficiency issues. These similarities occur in spite of very different climatic and underlying hydrogeological conditions. The key data used to compare these different regions are climate and soils, available water resources and their use, as well as components of the water balance. In addition, the history of water resource development in these areas is examined to understand how salinity problems emerge in semi-arid regions and the consequences for production. Based on the efficiency parameters and the definitions of sustainability, approaches are explored to solve common environmental problems while maintaining economic viability and environmental sustainability for irrigation systems.     

农机制造业战略投资决策的实物期权分析

农业机械化是实现农业现代化的根本保证,"三农"对农机制造业产品的需求具有较大的不确定性.为此,运用实物期权方法研究不确定条件下农机制造业的战略投资决策最佳投资时点选择问题,利用案例说明在净现值大于零时立刻执行投资决策未必是最优的,投资者具有延迟期权等,克服了传统的折现现金流投资估价方法的不足.同时,对影响投资阈值的相关影响因素与多项目条件下的实物期权决策进行了分析,对投资决策具有指导意义.     

多体式秸秆生物质气化炉的设计

生物质能是一种清洁、可再生的能源,秸秆生物质能的开发、应用具有广阔前景,而气化燃烧是秸秆生物质能利用的一种形式。针对小型家用生物质气化炉在使用中存在气化气中焦油、灰分含量多,物料连续添加工艺复杂,而物料间断供给使用不便等问题,提出一种多体式秸秆生物质气化炉的设计。通过3个气化燃烧炉体且内炉体可拆卸,空气气化剂预热、均布供给,焦油及灰尘杂质二级净化处置等结构设计,可使得生物质物料装填工况满足家用炊事需求、保证气化反应工艺要求、有效去除气化气中焦油及灰尘杂质。多体式秸秆生物质气化炉的使用推广,可实现对秸秆生物质能源有效利用,也有助于解决秸秆生物质资源浪费及污染问题。     

黑龙江省农机合作社存在问题及发展对策

农机合作社是实现农业机械化、农业现代化的有效形式,是解决"三农问题"、粮食增产增收的最优途径。通过对基层农机合作社的实地调研以及对2014年黑龙江省现代农机专业合作社相关统计数据整理分析,在总结目前黑龙江省现代农机专业合作社面临具体问题的基础上,提出了黑龙江省现代农机专业合作社发展对策。研究结论可为黑龙江省农机合作组织的建设和发展提供具体指导,同时对全国农业合作组织健康发展具有参考意义。     

Factors influencing the stability of salt affected soils in the UK—criteria for identifying appropriate management options

Changes in agricultural practices that brought about deflocculation problems on salt affected alluvial soils in eastern England are outlined. The spatial variation in the occurrence of problems is discussed. Exchangeable sodium percentage (ESP) was found to be the factor having greatest influence on soil stability as measured by the dispersion ratio. Changes in ESP had similar effects on the stability of soils from Essex and Kent. Threshold ESP of 5% for topsoils and 10% for subsoils are suggested, above which deflocculation problems can be expected. The use of these thresholds as part of the process for identifying future management options is discussed.     

Productive efficiency and allocative efficiency: why better water management may not solve the problem

It is commonplace for scientists and professionals who are not part of national and communal water discourses to have very clear views on what is economically and environmentally sound. They are certain of the fundamental principles which they claim should guide the development of policy. They believe that it will be possible to communicate the idea that `more can be achieved with less' and that `better water management' is something over which there can be a consensus. It will be demonstrated in the following analysis that only some ideal water allocation and management options are politically feasible. More importantly, it will be shown that the measures from which the most water use efficiency gains can be achieved are the ones for which `political prices' would have to be paid. These optimum options are, therefore, rarely addressed.