Study On Dual-Spark Plugs For Rapid Combustion And Multi-state VVT System Of Small And High-speed Gasoline Engine

Small and high-speed gasoline engines below 250ml displacement are the main power of Chinese two-tyre motorcycles, but their performance is not very good at low and medium speed. These problems are small torque at low-speed, high fuel consumption at medium speed, small power at high speed and low speed at maximum power point. Therefore, it is necessary to improve the engine performance.In this paper, according to actual working condition and use characteristics of a normal 125ml gasoline engine, a VVT system of triple-form and rapid combustion with dual-spark plug ignition for multiple states is developed with advanced technologies of Variable Valve Timing and rapid combustion with dual-spark plugs.The main contents are illustrated as follows.①One multi-state VVT system of triple-form with dual-spark plug ignition is researched and designed, which adopts three admission cams and rockers, an automatic switching control system, an external switch oil system and dual-spark plugs set symmetrically to realize multi-state Valve Timing Optimization and single or dual-spark plug ignition in or out phase automatically according to the working condition to optimize intake and promote combustion.②Combining the structure characteristics of the VVT system of triple-form with dual-spark plugs, a small and high speed 125ml gasoline engine is retrofit with the auxiliary air injection system, the two-stage catalytic converter and a closed crankcase ventilation device to decrease exhausted pollutants in the GB14622-2007 emission limit to further control the emission.③A VL-TYCON software is used to analyze the kinematics and dynamics of the VVT system of triple-form and dual spark plugs including the simulation and calculation on the intake valve lift, speed and acceleration, force and stress of three intake cams and rockers at three different speeds, force of valve closed and movement and force of inside and outside valve springs. In addition, the finite elements of the key components as intake rocker arms at low, medium and high speed are analyzed with the ANSYS software to verify operation rationality of the system.④According to the treatment benchmark of the gasoline engine combustion model, a limited planar approximation method is created to calculate the combustion model with Monte Carlo principle. The limited planar approximation method is compared with the plane nodes method and spherical triangle method on calculation units, accuracy and amount, and the two latter are proved to be the special cases of the former to unify the three methods. Then the combustion conditions of the single and dual spark plug ignition in phase are calculated with the method.⑤The intake and the combustion processes of the small gasoline engine that is 125ml displacement with one cylinder are simulated and analyzed with the AVL-FIRE software of three-dimensional simulation to optimize the combustion controlling strategy.⑥The correctness of the analyzing method is proved by testing engine performance for wide open throttle and mode test cycle between the 125ml prototype engine with one cylinder and the VVT gasoline engine in different working conditions including the idle, low, medium and high speeds.