The Leakage Discrimination of LPG on Ignition Engine WANG Zhensuo, DENG Baoqing, LI Liguang, XIAO Zongcheng, WANG Huiping 1 (1. College of Automotive Engineering, Jilin University, Changchun 130025, China; 2. School of Mechanical and Power Engineering, Shanghai Jiaotong University, Shanghai 200030) Ming: Torque fluctuation , Rotational speed fluctuations, HC emission and HC increase rate are all affected by the air-fuel ratio, and their changing trends have better consistency; With the change of air-fuel ratio, the speed fluctuation does not change significantly, subject to engine structural parameters and operation The influence of the parameters is more difficult to determine the HC emission value that is used to determine the lean limit. Therefore, it is reasonable to consider the torque fluctuation and the HC increase rate as the conditions for determining the lean limit.
The lean-burn technology has the advantages of improving economy and reducing harmful emissions. Combining advanced technologies such as direct injection in the cylinder and timing of variable gas distribution, it has been applied to the ignition engine, and the key to the lean combustion technology is the scarcity. The method for determining and controlling the air-fuel ratio within a limited range. In foreign countries, many researchers have conducted in-depth analysis and experimental research on the scarcity. Quader proposed the definitions of combustion leanness, ignition leanness, and misfire limit; eywood pointed out that the average indicating effective pressure's coefficient of variation can be used to judge the fire leanness and HC emission value to determine the most practical significance of the leanness. At present, there are few studies in this field in China. Therefore, it is very necessary to study the determination of the rarity. In this paper, the relevant experiments of LPG thinning discrimination are carried out based on the application research of LPG lean combustion, trying to find a simple and accurate thinning detection method suitable for engine bench testing.
1 Definition of the scarcity limit and analysis of its criteria 11 Definition of scarcity According to Quader's formulation, there are three definitions of the lean burn limit, namely, the combustion scarcity, the ignition scarcity, and the fire scarcity.
Flammability Limit: The lowest lean air-fuel ratio that ensures flame propagation is a function of mixture temperature and pressure. The effect of temperature on combustion leanness can be calculated using the following formula: Ignition Scaling: The leanest air-fuel ratio at which the external energy reaches the lowest ignition temperature of the mixture. It is related to the fuel, the mixture speed and the temperature and pressure of the mixture gas at ignition of the spark plug, and also related to the parameters of the ignition system (spark duration, energy release rate, electrode material, and spark plug gap).
Fire misalignment: The air-fuel ratio at which the mixture does not ignite, does not burn completely, or the flame is extinguished before the combustion is completed because the flame propagation speed is too low. Quader has qualitatively analyzed the effects of ignition and flame spread on fire scarcity.
In practical applications, the engine lean limit can be divided into stable operation and limited application and application. When the unburned mixed-fuel project of a spark-ignition engine is funded by the National Teacher's Fund of the Ministry of Education, and the National Technology Innovation Fund-funded project (National Economic and Trade Technology (1998) No. 345) is too thin, the period of flame expansion, rapid combustion, and The fluctuations of the combustion process will increase during the cycle, and eventually reach a certain point. The engine operating conditions will deteriorate and become unstable, and the hydrocarbon emissions will increase rapidly. The occurrence of these phenomena defines the stable operation of the engine, and it is also called the lean operating limit. . The application of the lean limit refers to comprehensive consideration of the output power and emissions of the engine, which is compensated by increasing the throttle opening degree so as to reduce the power of the engine, and achieve reduction of emissions and improvement of fuel economy.
1.2 The identification of the scarcity When the engine exceeds the lean operation, there will be a series of problems such as combustion variation and emission deterioration. The determination of the lean limit is to determine whether the engine operates within a limited range by detecting whether these phenomena occur. The discriminating methods are divided into two categories. One is to install sensors directly in the combustion chamber to measure the combustion changes of the engine, and the other is to indirectly determine the combustion changes by detecting the output variables.
In the early research process, there were many methods for identifying the rarefaction, such as the misfire rate, the crank angle fluctuation when the cylinder pressure increase rate was the largest, and the fluctuation of the cylinder pressure map area. Each scheme can make different judgment results according to different judgment conditions. For example, Quader used the 0.5% misfire rate as the discriminating boundary of fire scarcity. He thought that the drivability of the vehicle at that time was very bad2; and Ryan et al. considered that when the misfire rate was 5%, the power loss and HC emission rose sharply, and should be taken as Scarcity of judgment limits. SAEPaper Wang Zhensuo. Study on Lean Burning of LPG Engines . Changchun: College of Automotive Engineering, Jilin University, 2000. Wang Zhensuo. LPG is used for the performance optimization and lean combustion of small ignition engines. Journal of Jilin University (Engineering Science) 2002, Li Xinghu. Study on the Change of Propane Engine Combustion. Journal of Internal Combustion Engines, 1999(1)
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