Study of a Pneumatic Hybrid aided by a FPGA Controlled Free Valve Technology System
Sammanfattning: Urban traffic involves frequent acceleration and deceleration. During deceleration, the energy previously used to accelerate the vehicle is mainly wasted on heat generated by the friction brakes. If this energy that is wasted in traditional IC engines could be saved, the fuel economy would improve. Today there are several solutions to meet the demand for better fuel economy and one of them is the pneumatic hybrids. The idea with pneumatic hybridization is to reduce the fuel consumption by taking advantage of the, otherwise lost, brake energy. In the work presented in this study a heavy duty Scania D12 engine has been converted to work as a pneumatic hybrid. During pneumatic hybrid operation the engine can be used as a 2‐stroke compressor for generation of compressed air during vehicle deceleration (compressor mode) and during vehicle acceleration the engine can be operated as an air‐motor driven by the previously stored pressurized air (air‐motor mode). The compressed air is stored in a pressure tank connected to one of the inlet ports. One of the engine inlet valves has been modified to work as a tank valve in order to control the pressurized air flow to and from the pressure tank. In order to switch between different modes of engine operation there is a need for a fully variable valve actuation (FVVA) system. The engine used in this study is equipped with pneumatic valve actuators that use compressed air in order to drive the valves and the motion of the valves are controlled by a combination of electronics and hydraulics. Since the pneumatic VVA system, used in the work presented in this thesis, was still under development, the need to evaluate the system before any extensive use was more than necessary. The evaluation of the pneumatic VVA system verified its potential and a stable function was noticed together with great flexibility to manipulate both valve timing and valve lift to fit the desired purpose. Initial testing concerning the different pneumatic hybrid engine modes of operation was conducted. Both compressor mode (CM) and air‐motor mode (AM) were executed successfully. Optimization of CM and AM with regards to valve timing and valve geometry has been done with great improvements in regenerative efficiency which is defined as the ratio between the energy extracted during AM and the energy consumed during CM.
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