Optimization Of Valve Timing And Cam Profile For Heavy-duty LNG Engine

The LNG engine in this paper derives from a diesel engine. The valve timing of the diesel engine no longer fits due to the fuel supply difference between LNG engine and diesel engine, considering the using of pre-mixed intake mode for the LNG engine.Otherwise, a portion of CH4 will be discharged into atmosphere directly, which will lead to excess consumption of fuel and invalidation to meet the emission regulations, as a result of the using of the larger valve overlap.To solve this question, the overall performance of LNG engine simulation and the cam profile of the valve train optimization were carried out basing on AVL BOOST and AVL TYCON software in this paper. The impact of valve timing on the overall performance of LNG engine was analyzed detailedly, and the changed cam profile was optimized to meet the requirement of valve train. The main work is summarized as follows:(1) The LNG engine model was established with AVL BOOST software, and was verified by speed characteristcs test at full load. Basing upon the mode, an optimization proposal was recommended by analyzing the impact of intake delayed angle, exhaust advanced angle and valve overlap on the performance of the engine.(2) The kinematic and dynamic simulation models of intake and exhaust valve train were set up using AVL TYCON software. First, the performance of the original cam profile and the phase-optimized cam profile was compared, then an optimization direction of the phase-optimized cam profile was put forward and the cam profile was optimized according to simulation results.Finally, the optimized cam profile was evaluated according to requirement of dynamic performance through the dynamic simulation.Overall performance results of LNG engine show that the valve overlap reduction will reduce sharply the power of LNG engine with the other phase nochange. Therefore, the intake delayed angle and exhaust advanced angle optimization, is nece -ssary to reduce the fuel consumption and constrain CH4 emission without effecting the power of engine. It can conclude that the value of jerk of the phase-optimized valve train is large and the fullness coefficient is not enough large from the simulation results of the kinematics and the dynamics model of valve train. In order to solve this problem, optimization design on the cam profile was carried out to improve the performance, and the dynamic performance requirement was met.