Study of a Pneumatic Hybrid aided by a FPGA Controlled Free Valve Technology System

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.