| Since the last century, the rapid development of automobile industry leads the automobile possession of the world has increased dramatically. However, automobile brings traffic convenience and social prosperity as well as environment great harm. By the 1970s, automobile emissions have already become the main air pollution source of cities. Meanwhile, a surge of automobile possession cause world oil energy consumption increases. Excessive consumption must cause the energy crisis while the global oil reserves are limited. This makes automobile become a top priority of the focus of energy saving and emission reduction.Cold start gets more and more attention by every vehicle manufacturers and large research institutions as a special and important engine operation condition. According to the current emission regulations, new cars must pass the cold start test before sales. Vehicles start reliability and comfort performances are problems that vehicle manufacturers must face and solve. Therefore, carry out the related research work about engine start performance has the practical significance for the development of new engine and car.Based on the above reasons, research of start performance about a developing engine is carried out in this paper. The related literature and report at home and abroad were referred to, and the research methods, research devices, research emphases, important conclusions, the latest research results were analyzed and summed up. The ME7 management system which is applied to this engine is also analyzed in detail, including the comprehension of important sensors and actuators and the analysis of control strategy about cold start. Besides, the calibration tool matching the management system is analyzed, including the comprehension of its function characteristics and use method about hardware device and software INCA. Based on the above mentioned work, the sensors and actuators installation are achieved, and the management system is integrated with the calibration system, and the whole vehicle test system is constructed which including measure, control, calibration. In the end, the experimental research plan and the start performance evaluation standard are determined. The experimental research content in this paper includes:1. The influence of end start mark speed to start time and emission is analyzed through experimental research, and a suitable value is determined.2. The influence of intake valve open timing and outtake valve close timing to start performance is researched, and the influence regulation of valve timing to start time and emission are analyzed, and the reasonable valve timing is determined.3. The start fuel correction coefficient is changed to obtain different values, and the influence to gasoline engine start performance is analyzed, and the optimal control parameter is determined.4. The influence of ignition timing to start time and emission is researched through experiments, an ignition timing that makes start comprehensive performance optimum is determined.5. The start performance calibration experiment is carried out, including winter cold start, restart and warm start calibration experiment. Finally, the ideal start performance is obtained.Above-mentioned experiment results show that:1. Along with the increase of the end start mark speed, start time and emission present the increasing trend, but not linear. The reason is the end start mark speed increases, so the time to reach the speed value increases, therefore the operation time of the engine under the rich mixture increases, consequently the start time and emission tend to increase. But considering the start reliability, start time and emission,600r/min is set for the end start mark speed in this paper.2. Along with the advance of the intake valve open timing, start time presents increase tendency on the whole. There is an optimal intake valve open timing, which makes the HC and CO emissions lowest. In addition, the research found:the negative intake advance angle, the intake valve opens after the intake stroke has began, is beneficial to decrease emission and shorten start time, but not the more the better. The reason is the piston is down and away from valve while the intake valve opens in the intake stroke. It effectively reduces the quench effect caused by the fuel mixture bump the piston top. Secondly, since the intake valve open timing is delayed a vacuum is formed in the cylinder. When the intake valve opening, the mixture flow speed is increased and the mixture is easy to form disturbance. It is helpful for fuel evaporation and atomization, so the formation quality of the mixture is improved. Additionally, the formation of the vacuum is beneficial to the evaporation of the fuel film that adsorbed and condensed in the previous cycle, and the low pressure in the cylinder is also helpful to the evaporation of the fuel. As a result of above factors, it is beneficial to decrease emission and shorten start time that the intake valve opens in the intake stroke.3. Along with the delay of the outtake valve close timing, start time first increases then decreases, and the HC and CO emissions both present increasing trend. The research found that it is useful to decrease the emission that the outtake valve close timing is advanced appropriately, but not the more the better. The reason is with the advance of the outtake valve close timing the residual gas amount is increases which is closed in the cylinder, so the emission is reduced to some degrees. Also the residual gas contains a lot of fuel steam and incomplete combustion product which have great influence on the excess air coefficient of the next cycle. The residual gas causes the mixture change rich and improves the engine ignition performance at cold-state. Secondly, the temperature of residual gas is higher than the new mixture, so it has strong thermal effect. Therefore the initial temperature of the new mixture is increased, and then the temperature and pressure at the end of compression stroke are greatly improved. Consequently the ignition and combustion performance are improved, and the speed of combustion is accelerated. All the above reasons make combustion more thorough.4. Along with the increase of start fuel correction coefficient, start time first decreases then increases. And there is an optimal value makes the HC and CO emissions lowest. The start fuel correction coefficient is an important parameter. The high coefficient will cause the mixture thick then hinder combustion, and also the low coefficient will cause the mixture thin then make the engine miss fire. A calibration value that makes the start comprehensive performance optimum is determined through experiment in this paper.5. Along with the advance of the ignition timing, start time increase, and the HC and CO emissions first decreases then increases. Research shows:it is beneficial to decrease the emission that the ignition timing is delayed appropriately, but not the more the better. The reason is the mixture obtains more compression before igniting, so the pressure and temperature are relatively high. Thus the flame travels fast after igniting and the combustion is more thorough. Besides, the portion of the later period of combustion is big and the exhaust temperature is high. That is beneficial to oxidize the mixture in the later period. Furthermore, the ignition timing is delayed appropriately, so the pressure in the cylinder is lower and the crack effect is reduced.6. The engine temperature is very low at cold start operation, so the engine is basically in the missing fire condition for the first cycles. Once the burning begins, it will cause the mixture too thick, which will hinder the combustion progress. According to the actual condition, the relevant control module was calibrated through multiple experiments. Simultaneously, the control parameters for example, throttle position and ignition timing, were optimized. Eventually, the expected start comprehensive performance is obtained.
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