【作者】 赵佳佳；

【导师】 刘忠长；

【作者基本信息】 吉林大学 ， 动力机械及工程， 2007， 博士

【摘要】 随着柴油机市场占有率的逐步增加及其排放控制要求的越来越严格,从燃烧过程的角度探索柴油机有害排放物生成及转化机理进而寻求其排放控制策略是很有必要的研究。为此开发了一套基于接触碰撞机理的全气缸取样系统,并利用该系统在柴油机上进行了有害排放物生成历程的研究。设计了基于高速A/D数据采集卡和MCS-51单片机控制的试验测量与控制系统,实现了在瞬态条件下对柴油机排放物按循环及燃烧位置的取样。开发了基于接触碰撞机理的全气缸取样机构,简化了系统构成,实现了在发动机非停机状态下的取样。对碰撞式全气缸取样系统进行的性能测试表明:取样系统延迟时间的均方差为2.179ms。当柴油机转速为1500r·min-1时,在0～35°CA ATDC区间的取样率为50%～80%,在0～60°CA ATDC区间的压力半衰期约为10～20°CA。进行了有害排放物缸内生成历程的取样试验。大量的取样试验过程表明碰撞式全气缸取样系统具有较高的可靠性。稳态试验结果表明:柴油机的PM和DS质量生成历程具有单峰形式,DS随燃烧的开始而产生并在20°CA ATDC左右达到峰值;CO和HC的体积浓度生成历程具有单峰形式,CO随燃烧的开始而产生并在15～20°CA ATDC区间达到峰值;NOx的体积浓度生成历程呈类“S”形,大部分NOx都在燃烧开始后20°CA内生成;采用EGR后,DS的最大生成量有所减小而后期生成量有所增加,并且DS趋于稳定排放对应的曲轴转角也有所提前;GTL燃料的微粒生成量要低于柴油;微粒的生成过程中还伴随着不完全氧化作用,导致微粒总粒数浓度生成历程的峰值点滞后DS生成历程峰值点约10°CA。在0.01～1.0μm的区间内,在燃烧中期生成的微粒对应各粒径下的浓度值普遍高于燃烧前期和燃烧后期生成的量。瞬态试验结果表明:瞬态工况下由于边界条件滞后,DS的最大生成量要低于相应的稳态工况,而DS的后期生成量要高于相应的稳态工况;气体排放物的生成量略小于相应的稳态工况。边界条件的差异对瞬态工况前期的影响较后期大。更多还原

【Abstract】 The human being’s society has been made progress with the development of world’s automobile industry powered by internal combustion engines, but automobiles also brought seriously environment problems. The automobile emission control regulations have become stricter than before to limit the emissions of pollutants. Diesel engines have been widely used because of its high power density, low fuel consumption, and high work reliability, the mostly attention have been paid on its particulate emissions. The performances of diesel engines under transient conditions are much different from that under steady operating conditions. The combustion process, the emission behavior and the performance improvement of diesel engines under transient operating conditions have been a very important research field.An important way to control emissions is to study the creation behavior of pollutants through combustion process of diesel engines. These techniques include in-cylinder sampling, optic measurements, CFD （Computational Fluid Dynamics）, and so on. The total in-cylinder sampling technique has several advantages than other techniques, such as lower cost, more reliability of the measuring results, more prior to be used to measure in-cylinder mass-averaged particulate histories. The sampling mechanism is the key of total in-cylinder sampling technique. The conventional sampling mechanism uses cutter and diaphragm to obtain samples which brought some flaws to this technique. The conventional total in-cylinder sampling system is more complicated and the experimental period has been prolonged by the replacing of diaphragm due to its broken after each sampling action. So improve the sampling mechanism is very meaningful to meet with the high requirements of convenience and efficiency of modern control and measure system.This research discussed on emission formation histories, such as particulate, nitrogen oxides and total hydrocarbon in a single direct injection （D.I.） diesel engine by using a developed total in-cylinder sampling system. The effects on emission formation histories by using GTL fuel and EGR technique were analyzed. The differences of emission formation histories under transient operating conditions and steady operating conditions were also discussed.The main study objects and achievements are as follows.1. Establishment of control and measure system for transient operating conditionsThe test system was composed of three components: parameter measure system, operating conditions control system and sampling control system.1) A high speed, real time data recording and monitoring system was developed. The data of in-cylinder pressure, speed of engine, et al, could be recording and displaying at the same time by software programming of an A/D converter board.2) A repeatable transient condition control system was realized by using SCP （Single Chip Processors） of MCS-51 series as the core control elements and a step motor as the actuator. Two kinds of typical transient operating conditions at constant speed or constant torque could be realized by a conventional eddy current dynamometer combined with the developed transient condition control system.3) The signals of engine cycles and crank angles obtained by sensors were identified by the ECU （Electronic Control Unit） to trigger the action of sampling mechanism. Before each sampling action, released determinate volume of nitrogen gas under NTP （Standard Conditions for Temperature and Pressure,NTP） into the flexible sampling bag to quench the chemical reaction of cylinder contents gathered latterly. 2. Development of sampling mechanismAn impact theory based total in-cylinder sampling mechanism was developed. The kinetic performances of the developed sampling mechanism were simulated by ADAMS software.1) The sampling mechanism was composed of electronic magnet, spring, impact anvil, sampling valve, and so on. This system was simplified by removing the intake and exhaust valve deactuators and injection system controller which indispensably in conventional sampling system. The sampling tube could be sealed and shut off timely by sampling valve, so the sampling process could be completed without shutting down the engine.2) The two key factors which affected the intensity of sampling mechanism were the structure of sampling valve and the impact energy.3) The smaller valve head’s diameter, the shorter valve length, the bigger valve staff’s diameter, and the heavier impact anvil were chosed, the higher reliability of the sampling mechanism could be obtained satisfied with three conditions: sampling more than 80% mass of cylinder contents, the maximal impact force less than the value that sampling valve could endure, and the maximal height during valve rising period more than 3mm.4) If the valve head’s diameter is 26mm, the valve staff’s diameter is 10mm, the valve length is 158.4mm, the impact anvil’s mass is 3kg, the gas’s pressure is 10MPa, the gas’s temperature is 2000K, the impact velocity is 2.1m·s^-1, then the safety factor of sampling mechanism is 2.1 according to the simulation results.3. Performance analysis of developed total in-cylinder sampling systemThe performances of the developed sampling system were obtained by two kinds of tests: simulative cylinder tests and engine bench tests. The simulative cylinder tests were operated with a fixed volume cylinder under atmosphere temperature. The engine bench tests referred to the sampling actions on diesel engine under the conditions of 1500r·min-1/30N·m and 1500r·min-1/50N·m. 1) The maximal difference of sampling system’s delay time is 9ms and the mean square error （MSE） is 2.18ms. They are 1.125 times and 1.5 times of the conventional sampling systems respectively.2) The results of simulative cylinder tests showed that the maximal height of valve rise, and the duration of valve open were enlarged with the decreasing of initial gas pressure under the conditions of same impact energy, but the duration of pressure drop to 50% and 80% of its initial pressure were almost steady, they were 1.4ms and 3.4ms respectively.3) The results of engine bench tests showed that the sampling process was different from simulative cylinder tests because of the changing cylinder volume and temperature during sampling process. The mass ratio of cylinder contents decreased from 80% to 50% when the blowdown angle increased from 0°CA ATDC （Crank Angle After Top Dead Center） to 35°CA ATDC. The half decay period of pressure drop was 10 to 20 degrees of crank angle when the blowdown angle just between 0°CA ATDC to 60°CA ATDC, it was 2～3 times of the conventional sampling systems.4) The sampling process had a little affect on engine’s speed. The speed dropped nearly 3% but could return to the same level a short time later.5) The tests proved the high reliability of the sampling system.4. Experiment study on emission formation historiesThe experimental study was carried out to produce cylinder histories of particulate, nitrogen oxides and total hydrocarbon.1) The mass-averaged histories of PM （Particulate Matter） and DS （Dry Soot） had the shapes of one peak value. DS appeared when the combustion starts. At about 20°CA ATDC, DS reached its peak value, then largely decreased after that. Compared to the fuel of 0# diesel, GTL （Gas to Liquid） diesel could produce less PM and DS emissions, but EGR （Exhaust Gas Recirculation） made the PM and DS emissions worse. Compared to the fuel of 0# diesel, the peak values of DS forming histories were both reduced when the GTL or EGR techniques were used.2) The histories of particulate quantity, surface area, and volume concentration had the shapes of one peak value. The position of the peak at about 30°CA ATDC. When engine’s load increased from 30N·m to 50N·m, the total particulate quantity, surface area, and volume increased 2.3, 1.7, and 1.7 times respectively.3) In this research, the distribution of particulate quantity had two peak values within 0.01～1.0μm. The first one was not evident, but the second one occurred when the particulate diameter was 0.133μm. The second peak value was much smaller than the first one. The distributions of particulate surface area and volume had one peak value within 0.01～1.0μm. The peak value of surface area occurred when the particulate diameter within 0.075～0.237μm, and the peak value of volume occurred when the particulate diameter was 0.237μm. The concentration of particulates which emerged in the metaphase of combustion was higher than that emerged in the prophase and anaphase of combustion. The concentration of middle-scale particulates which emerged in the anaphase of combustion was higher than that emerged in the prophase of combustion, while the concentration of large-scale particulates which emerged in the anaphase of combustion was on the contrary.4) The volume concentration of HC （Hydrocarbon） and CO （Carbon Monoxide） had the shapes of one peak value while NOx （Nitrogen Oxides） had the“S”shape. When the load was 30N.m, the emission value was about 9% relative to peak value of CO, while the load was 50N.m, the ratio was 11%. Most NOx were produced within 20°CA after the combustion began. The emission of NOx increased with the increasing of load.5) The mass-averaged histories of PM and DS were different between transient operating conditions and steady operating conditions. The peak values of PM and DS were lower while the emission of DS was higher at transient operating conditions than that of the corresponding steady operating conditions. The HC, CO and NOx emissions were reduced appreciably at transient operating conditions. The differences of boundary conditions had greater effects on prophase than anaphase of transient operating conditions.更多还原