Required time response of a variable valve actuator equiping a hybrid pneumatic–combustion engine

Abstract

This work is a part of a research program that aims to modify a conventional internal combustion engine and turn it into a hybrid pneumatic–combustion engine. The hybrid pneumatic–combustion engine should be able to convert mechanical energy into compressed air and convert compressed air back into mechanical energy. The potential application for the concept is any use of the internal combustion engine where the load oscillates between a negative and a positive value, such as automobiles and hybrid wind diesel systems for remote area power generation. In the first application, during vehicle decelerations, an excess of power occurs, and a negative load could be applied to the engine, whereas during vehicle accelerations, a positive load is applied. In the second application, if the generated wind power is higher than consumption demand, then the load applied to the engine could be negative, and if the generated wind power is lower than consumption demand, then the load is positive. In previous work, we exposed an optimization followed by a fuel-saving evaluation of a new hybrid pneumatic–combustion engine concept that uses a variable valve actuator system. The optimization of the valve actuation was based on ideal thermodynamic cycle modeling, assuming therefore an instant response of the variable valve actuator system. In the present work, a more realistic analysis of the system is provided by taking into consideration the dynamic response of the variable valve actuator system. Variable valve actuators have been widely studied for optimizing performance and fuel consumption of the internal combustion engine, especially in spark-ignition engines. For these engines, it is possible to reduce the pumping losses and to optimize the engine filling by controlling the intake and exhaust valve opening and closing angles, as well as their lifts. However, the variation of valve actuation crank angles required in a conventional internal combustion engine is significantly smaller than the one required in the hybrid pneumatic–combustion engine. This paper describes, through simulation, how the valve time response affects the performance of the hybrid pneumatic–combustion engine and recommends a required valve time response.