M20 Stroker Engine Design for Improved Performance

This report seeks to describe the background and operation of the M20 stroker for the BMW automobile race car. The report determines the engine design for improved performance. The report has been drafted following a request by the engine development company on the upgrade of the stroker version of the M20 baby-six engine. The upgrade uses the same components for the engine design but each part is designed to result in either higher speeds or better use of fuel.

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EXECUTIVE SUMMARY
This report seeks to describe the background and operation of the M20 stroker for the BMW
automobile race car. The report determines the engine design for improved performance. The
report has been drafted following a request by the engine development company on the upgrade
of the stroker version of the M20 baby-six engine. The upgrade uses the same components for
the engine design but each part is designed to result in either higher speeds or better use of fuel.
The report uses the MATLAB software for analysis and the computation section is defined using
the dynamic analysis. The initial section of the report seeks to provide a proper overview of the
M20 stroker by defining the functions of the different components that make up the system. The
engine design company has tasked us with a number of problems to solve. We need to solve each
of the problems with the available resources and using the same changes system payload
parameters. The management requires us to determine which connecting rod length is
appropriate for the M20 out of a number of options. They also require that we determine the
maximum side loading that is appropriate for the piston and cylinder wall. The analysis section
seeks to express the change in length with regards to the dramatic change based on the maximum
force at the gudgeon pin.
The designers require the team to determine the most suitable connecting rod length to determine
the effective velocity and acceleration of the piston for the different cycles and baby six engine.
The super eta engine seeks to operate at 700 revolutions per minute while recommending a
maximum rpm built at 2.5i and M3 rods. The paper uses graphical illustrations to output the
results of the system based on the analysis of the internal combustion engine.
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INTRODUCTION
The car industry has progressed from using steam propellers to using the internal combustion
engine. With the advent need for green economies and the conservation of the environment, the
car industry is thinking of the next model of cars to ensure that they use renewable energy and
they do not pollute the environment. Currently, the best the car industry can achieve is to
improve the efficiency while reducing the pollution. Due to their high use of vehicles shortage or
fuel and rise in cost was eminent. So, the BMW upgraded their engine from a M20 to a more
efficient version. They named the project as ‘Super Eta’. The engineers decided to increase the
2.5l engine’s stroke from 75mm to 8mm. As the first design the engine was built to produce high
torque. But for the new ‘Super Eta’ Project the designs were required to produce low torque of
4800RPM. The vehicle needs a higher revving and large capacity engine that provides more
power. The M20, like the M10, is fairly well tuned from the factory.
There is not a lot of hidden horsepower just waiting for you to tease out. There are a few things
that can be done to make the engine run better and make a little more power, on the order of 5 to
10 percent at the wheels. The piston main function is to determine the thermal energy created by
the ignition of the fuel and the air which the system transforms into the linear motion. The linear
motion seeks to act on the crankshaft journal and becomes rotary motion. The piston is made up
of the domed, flat top, recessed valve reliefs, and the dished piston heads that form the crown of
the internal combustion engine. The piston pin is offset toward the major thrust surface. The
engine rotation and rod angle during the power stroke causes the engine to press harder against
one side of the cylinder so as to create the major thrust surface. The clockwise-rotating engine is
viewed from the front of the engine while the major thrust surface is on the side.
The connecting rod may be designed to utilize the spit holes or the bleed host. They are made of
the cast iron whose form is of the general duty or the forged steel which provides a stronger and
heavier version of the connecting rod. The connecting rod is one of the most stressed
components of the engine. The combustion forces tend to compress it and when the piston stops
at the top of the cylinder, inertia forces try to pull it apart. The connecting rods are designed with
balancing bosses or pads on each end of the rod. The rod caps are unidirectional and they have to
be reinstalled in the same rod position. The chamfered side of the bore leads towards the
crankshaft side on the baby-six engine.
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AIMS OF THE TASKS
(i) To choose the connecting rod length change versus the maximum side loading
between piston and cylinder wall.
(ii) To choose the connecting rod length that may affect the forces at the gudgeon pin and
journal bearing.
(iii) To determine the velocity and acceleration relationship with the length of the
connecting rod.
ARITHMETIC PROBLEM
The system M20 stroker design and payload parameters are given as,
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ENGINEERS ANALYSIS
The heart of the reciprocating internal combustion engine is the piston assembly, forming a
critical linkage in transforming the energy generated by combustion of the fuel and air mixture
into useful kinetic energy. The piston assembly includes the ring pack, which is essentially a
series of metallic rings, the primary role of which is to maintain an effective gas seal between the
combustion chamber and the crankcase. The rings of the piston assembly, which form a labyrinth
seal, achieve this function by closely conforming to their grooves in the piston and to the
cylinder wall. The total load acting in the ring in radial direction due to the sum of the
hydrodynamic lubrication (FH) force and the solid-to-solid interactions along the asperities of the
surfaces.
CHR FFF 
ASSUMPTIONS & LIMITATIONS OF THE ANALYSIS
(i) It is assumed that there is negligible friction force between the piston and the
cylinder.
(ii) It is assumed that there is no force produced when the engine accelerates.
(iii) It is assumed that there is no force produced using gas at the combustion chamber
(iv) It is assumed that the angular velocity is set at 7000 revolutions per minute and the
angular acceleration of the engine is zero.
CALCULATIONS
Studying the kinematic dynamics of the system,
V B =V A + V B
A
The piston is the main part of the engine which transfers the force from the gas which expands in
the cylinder to the crankshaft and links to the connecting rod. The position of the piston using the
vector loop is obtained as,
x= ( l+r ) −s
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The schematic diagram for the crank mechanism components relationship illustrates the
connecting rod length, crank radius, and the instantaneous piston position from the piston pin.
The mean piston velocity for the 6 stroke engine is computed as,
vp = 2 ln
60
The relationship between the crank radius and the connecting rod length and distance from the
piston axis for the pin to the crank axis such that the variables of the crank mechanism are
formulated as,
s=lcos φ+r cos θ
¿ l sin φ=r sin θ
The values are rearranged to obtain the relationship with the angles as,
The values are factorized with a focus on the higher approaches such that,
The kinematics are used to formulate the piston instantaneous displacement in the crank
mechanism such that,
The system is able to manipulate the kinematics by expressing the equation by easily estimating
the variable based on the angle phi. The system is able to determine the angle theta which is the
crank angle,
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The piston instantaneous velocity is obtained from the piston on the crank mechanism,
Performing the first derivation of the equation with respect to the crank angle in the equation,
The connecting rod bolt stretch gauge is used to measure the amount the rod bolt stretches to
tighten the fastener to its ultimate strength. The total friction force Ff, acting on the ring in
tangential direction, is the sum of the friction force between the asperities and the shear force
about the HDL regime:
The friction coefficient is computed such that,
The components of force tend to show a strongly dependence on the minimal nominal distance
between the ring and the cylinder wall such that,
The friction force is directly proportional to piston velocity considering the coefficient of friction
takes into consideration the global frictional losses,
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pf Sf 







 

 1
sin
cos
sin
60 22



R
LN
S p





 

 1
sin
cos
sin
60 22




R
LN
f f
The cyclic integral of the friction work is computed as,
2
22 1
sin
cos
sin
60 












 








R
LN
SfP fp
   

 dPW frictioncycle,
   
strokestroke
frictioncycle
mep V
dP
V
W
F 


,
The longer stroke increases the engine friction and it increases the stress on the crankshaft at
certain engine speeds. The piston force balance is given as,
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Engines can be classified per the type of ignition or the engine cycle. It can have a spark ignition
or a compression ignition while the engine cycle has a four-stroke cycle and a two-stroke cycle,
The initial section of the report seeks to provide a proper overview of the M20 stroker by
defining the functions of the different components that make up the system. The engine design
company has tasked us with a number of problems to solve. We need to solve each of the
problems with the available resources and using the same changes system payload parameters.
The management requires us to determine which connecting rod length is appropriate for the
M20 out of a number of options. They also require that we determine the maximum side loading
that is appropriate for the piston and cylinder wall. The rod ratio is estimated between the
connecting rod length and the stroke length of the motor which greatly affects the way it
performs and it shows how long it lasts. The rod length against the stroke determine the ration R.
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Further, the system requires that the designer performs a rod ratio versus the intake efficiency
where the value of R is set to 1.75 so that it is considered ideal for the performance of the design.
RESULTS & FINDINGS
The original eta connecting rod is of the length 130mm. The connecting rod from 2.5i engine is
given of the length 135 mm. The rod has an equivalent strength to the eta engine. The M3 and it
is quite modern as the geometry wise for the M3 for the 2.5i which is 10 percent greater in
strength.
To determine the velocity and acceleration for the mathematical solution in the piston design
where the engine pistons have no considerate differences. The system is concluded for the choice
of the connecting rod for the difference between the velocities of different engines.
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The system results in a sinusoidal output depicting the maximum velocity at 30m/s. The
acceleration has similar differences and there is need to determine the value of the choice to
connect the rod.
The graph illustrates that the maximum acceleration is 1.5meter per square seconds. The forces
are computed to determine Gudgeon pin forces for the three options tested in the matlab code
with the shorter rods.
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There is a gas force during the complete cycle they depend on the crankshaft position. The gas
forces produce a periodically variable torque value. In multiple cylinder engines, the torque
curve of the individual cylinders are superimposed with a phase shift dependent on the numbers
of cylinders, their configuration, crankshaft design and firing sequence. The resulting composite
curve is characteristics of the engine design and covers a full working cycle.
When the system implements bearing,
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Considering the Gudgeon pin for the shorter rod, the forces are expressed as,
The open loops for simulation results,
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RECOMMENDATIONS
The long rod ensures that more efficient combustion for the internal combustion engine at very
high speeds. The designer at this point may wish to measure the carbon monoxide or the carbon
dioxide value during the test. The power stroke for the piston is further down in bore for any
given rod/crank pin angle for any crank angle whose force is less on the crank pin than on the
shorter rod. The piston is observed to be higher compared to the given crank such that the
cylinder pressure is a bit higher.
The rod ratio is estimated between the connecting rod length and the stroke length of the motor
which greatly affects the way it performs and it shows how long it lasts. The rod length against
the stroke determine the ration R. Further, the system requires that the designer performs a rod
ratio versus the intake efficiency where the value of R is set to 1.75 so that it is considered ideal
for the performance of the design.
The long rod spends less time having the piston move upwards while it allows less time for the
exhaust to escape while the automobile is on power stroke. The connecting rod is exposed to
very severe loads. Combustion gas pressure acting downwards on the piston exerts very heavy
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forces along the connecting rod. Since the piston's speed is continually varying, the high
acceleration and deceleration forces which result must be withstood in the form of tensile and
compressive loads on the connecting rod. R is set to 1.75 for most of the automobiles unless
where the engine is built for a race car. The value of R is in the range of 1.45 to 1.75 requires
that the short connecting rods are used in the crankshaft to piston system in relation to the stroke.
To implement the long connecting rod in relation to the stroke, the value of ratio, R, is in the
range of 1.75 to 2.1.
REFERENCES
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and Analysis," Proc. 1987 ACC, pp. 332-340.
Borges, A. C. C., Oliveira, L. C., and Neto, P. S., 2012, “Stress Distribution in a Crankshaft
Crank Using a Geometrucally Restricted Finite Element Model”, SAE Technical Paper No.
2002- 01-2183, Society of Automotive Engineers.
Norton R.L., Kinematics and Dynamics of Machinery, Tata McGraw Hill Education (P) Ltd.,
New Delhi, 2012.
Prakash, V., Aprameyan, K., and Shrinivasa, U., 2008, “An FEM Based Approach to Crankshaft
Dynamics and Life Estimation,” SAE Technical Paper No. 980565, Society of Automotive
Engineers.
R. W. Weeks and J. J. Moskwa, "Automotive Engine Modeling for Real-Time Control Using
Matlab/Simulink," 2015 SAE Intl. Cong. paper 950417.
Shenoy, P. S. and Fatemi, A., 2016, “Dynamic analysis of loads and stresses in connecting rods,”
IMechE, Journal of Mechanical Engineering Science, Vol. 220, No. 5, pp. 615-624.
Shenoy, P. S. and Fatemi, A., "Connecting Rod Optimization for Weight and Cost Reduction",
SAE Paper No. 2005-01-0987, SAE 2005 Transactions: Journal of Materials and Manufacturing.
Zoroufi, M. and Fatemi, A., "A Literature Review on Durability Evaluation of Crankshafts
Including Comparisons of Competing Manufacturing Processes and Cost Analysis", 26th
Forging Industry Technical Conference, Chicago, IL, November 2005.
Xiaorong Zhou., Ganwei Cai., Zhuan Zhang. Zhongqing Cheng., 2009, “Analysis on Dynamic
Characteristics of Internal Combustion Engine Crankshaft System,” International Conference on
Measuring Technology and Mechatronics Automation.
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Yadav Vinod and Mittal N.D, Design and Analysis of Piston Design for 4 Stroke Hero Bike
Engine, International Journal of Engineering Innovation & Research, Vol. 2, page 148 – 150,
2013.
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