UWE Bristol Engineering showcase 2015

Umberto Chmeit
Beng Motorsport Engineering
Project Supervisor
Dr. Changho Yang
Variable Compression Engine
Introducing new technologies in today’s world is getting more and more difficult as projects get more complicated, the variable
compression engine has been under development for the past 15-20 years and more companies evolve with new ways to make
transportation more fuel efficient and reduce emission without compromising power, Variable compression ratio has had a big impact
on today’s world, since the 1920’s designer such as Sir Harry Ricardo who due to irregular combustion (knocking or pinging) developed
the first variable compression engine to come up with the Octane rating system which manufactures still follow today. It is a challenge to
vary the compression ratio of an engine during running engine cycles, many tried attempts have been made but where never taken
forward.
Variable Compression engines
Even though methods and technology for variable engine compression has been around
since the early 1920’s no one thought that this concept would improve the efficiency of an
engine without compromising reliability, due to complexity of the design, there has been
various studies in the past regarding variable compression engine and many large motor
industry companies like Nissan, Saab, Peugeot and many others have involved themselves in
the research and development of this technology. Beside is a table with the most common
V.C.R. methods in todays world, each company have their own concept on how to develop a
new efficient internal combustion engine, the VCR concept consist of adapting the cylinders
compression to get the most optimal fuel burn rate hence giving the best efficiency and
reducing emissions.
Variable Connecting Rod
An example engine was designed using Solidworks, this engine uses the connecting rod of an
engine to alter the compression ratio, it increase or decreases in length to vary the ratio.
The Variable Con-Rod design concept is a new conceptual automated system which works using
hydraulic pressure from the oil lubrication passing through the crankshaft, this system is a twostage
variable compression method, this means the actuation of the Con-Rod is depended on
RPM and Turbo pressure, it is best suited for a high compression ratio at low RPM and low
compression ratio once the turbo starts boosting, it uses a pressure release valve to decrease
the oil pressure within the Con-Rod as the rpm increases (as the oil pressure from pump
increases with RPM) thus allowing the Con-Rod to shrink and decrease the compression ratio in
order for the pressure from the turbo to enter the combustion chamber without knocking
occurring. At lower RPMs the oil pressure decreases and the release valve shuts allowing the oil
to take up space in the con-rod’s turning chambers and therefore increase the con-rod’s length
and thus increasing the compression ratio, this system uses the help of the inertial forces of the
piston and crankshaft to increase or decrease the con-rod’s length.
Project summary
This project was produced to prove that a
variable compression ratio engine has
adequate improvement characteristics
compared to a Fixed compression engine.
Project Objectives
The objectives are to provide engine data
from a software simulation using different
results to analyze the performance of a VCR
engine.
Project Conclusion
After comparing various experimental data
with data which was produced on Ricardo
Wave Engine simulation software, a
conclusion was made that varying the
compression ratio of a fixed compression
ratio engine at low RPMs proves to have
greater efficiency in terms of Brake Specific
Fuel Consumption, BMEP and engine torque.