ABSTRACT
A conventional in-line piston engine was modified to reduce friction power loss and heat loss. The modification was achieved by including roller bearings, rack and pinion in the power train of piston engine. The components for the proposed modification were designed for strength using existing physical laws. Results obtained from the performance analysis at the main bearings of the proposed engine at 4000rpm reveal a friction power of 766.77W as against 1916.93W for a conventional in-line engine. Also the main bearing fuel consumption and carbon (iv) oxide emission were established as 8.5197×10–5m3/hr and 0.2215kg/hr, respectively for the proposed engine as against values of 2.1299×10–4m3/hr and 0.5538kg/hr, respectively for the conventional in-line engine. The stroke to bore ratio were evaluated as 1.97 and 1.00 for the proposed and conventional engines respectively. Furthermore, correlation between the connecting rod and friction established using Pearson’s product moment reveals a strong negative relationship between connecting angularity and friction power at the piston skirt of a conventional in-line piston engine. The above results therefore reveal the high potential of the proposed engine as a means of improving piston engines efficiency.
TABLE OF CONTENTS
Title Page
Declaration i
Certification ii
Dedication v
Acknowledgements
List of Tables iii
List of Figures x
Nomenclature
Abstract ii
CHAPTER 1: INTRODUCTION
1.1 Background of the Study
1.2 Statement of Problem
1.3 Aim and Objectives of the Study
1.4 Scope of the Study
1.5 Justification for the Study 3
CHAPTER 2: LITERATURE REVIEW
2.1 Heat Engine
2.1.1 Effect of stroke to bore ratio on thermal efficiency
2.1.2 Effect of stroke to bore ratio on engine friction
2.2 Crankshaft of Piston Engine
2.2.1 Crankshaft design
2.2.2 Connecting rod
2.2.3 Roller bearings
2.2.4 Gear
2.3 Correlation Analysis
2.4 Summary of Literature Review
CHAPTER 3: MATERIALS AND METHODS
3.1 Materials
3.2 Methods
3.2.1 Description of the novel piston engine
3.2.2 Centre crankshaft design for the novel engine
3.2.3 Connecting rod design for the novel engine
3.2.4 Pinion arm and pinion shaft design
3.2.5 Gear design for the novel engine
3.2.6 Roller bearing design for the novel engine
3.2.7 Viscous power estimation at main bearing
3.2.8 Model for volume of automotive gas and emission per hour 31
3.2.9 Correlation between connecting rod angle and
mechanical efficiency of conventional piston engine
3.2.10 regression analysis
CHAPTER 4: RESULTS AND DISCUSSION
4.1 Results
4.2 Dimensions Specification of the OCPE and IPE
CHAPTER 5: CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion
5.2.1 Contributions to knowledge
5.2 Recommendations
References
Appendices
LIST OF TABLES
2.1: Crankshaft Proportion in relation with diameter of cylinder bore 11
3.1: Specification of the in-line piston engine (IPE)
3.2: Number of bearing friction surfaces
4.1: Comparison of existing in-line engine and novel engine parameters 37
4.2: Mechanical efficiency of crank mechanism at various crank angle 42
4.3: Generated data for computation of correlation coefficient between mechanical efficiency and connecting rod angle of conventional piston engine 43
LIST OF FIGURES
3.1: Schematic diagram of novel opposed cylinder piston engine
3.2: Schematic diagram of conventional piston engine
3.3: Centre crankshaft at dead centre
3.4: Schematic diagram of connecting rod
3.5: Typical I-section for connecting rod in piston engines
3.6: Schematic diagram of crank mechanism of conventional piston engine 32
4.1: Pictorial view of oppose cylinder piston engine (OCPE)
4.2: Pictorial view of conventional in-line piston Engine (IPE)
4.3: Main bearing viscous power of IPE and OCPE
NOMENCLATURE
A = surface area
b = face width of gear teeth
BDC = bottom dead centre
c = distance of the neutral axis of circular shaft
D = cylinder bore diameter
d = diameter of the shaft
darm = diameter of pinion arm
dcp = diameter of crankpin
ddp = pitch circle diameter
di = internal diameter of the hollow shaft
dmB = diameter of the main bearing
do = external diameter of shaft
dy = oil film thickness
WB = buckling load of connecting rod
Fcr = force in connecting rod
Fgp = combustion force on piston
FN = normal reaction
Fthr = normal component of piston force on cylinder
I = moment of inertia
ICE = internal combustion engine
Ih = area moment of inertia for hollow circular shaft
IPE = inline piston engine or (conventional piston engine)
Is = area moment of inertia for solid circular shaft
l = length of connecting rod
L = stroke of piston
lcp = length of crankpin
M = bending moment
m = module
Mw = bending moment at crank web
ncr = connecting rod length to crank radius ratio
N = crankshaft speed, normal reaction
OCPE = opposed cylinder piston engine or (Novel engine)
Pbr = viscous power at crankshaft bearing
r = crank radius of crankshaft
R1 = reaction at bearing 1
rp = Pearson’s product-moment correlation
rsB = stroke-to-bore ratio
SV = swept volume
tfw = thickness I-section flange and web
T1 = belt tension at the slack side
T2 = belt tension at the tight side
TDC = top dead centre
T = torque
tw = web thickness
V = vertical component of force on the bearing
w = web width
WT = load transmitted by pinion teeth
x = independent variable
y = dependent variable
Y= tooth form factor of pinion
z = number of gear teeth
Z = sectional modulus
Zw = sectional modulus of web
η = mechanical efficiency
θ = angle between crankpin and cylinder axis
μ = friction coefficient, the viscosity of lubricating oil
σb = bending stress
φ = friction angle (angle between connecting rod and cylinder axis)
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND OF THE STUDY
This study is an attempt to reduce friction which originates at the crankshaft of a modern piston engine. Crankshaft bearings drain a substantial percentage of fuel energy in a traditional piston engine because of numerous bearing surfaces of the crankshaft.
Conventional engines exhibit problems such as piston side thrust that causes increase in friction and accelerated cylinder liner wear, high heat loss to cooling water through the cylinder liner with a resultant to low efficiency of the engines. A reasonable fraction of heat energy which is available in a piston engine is lost to the atmosphere while friction made part of the power unusable by converting it to heat. These situations made the efficiency achieved in conventional engines to be far lower than the theoretical efficiency limits.
Losses incurred in an engine include; incomplete combustion, cooling, exhaust, friction, and pumping losses. Friction force plays a significant role in the wear and overall efficiency of engines. According to Wong et al., (2006), mechanical losses due to friction account for between 4 and 15 percent of the total energy consumed in modern internal combustion engines. Zweiri et al., (1999) and Wong et al., (2006) believed that friction losses, especially at the piston and its assembly affect the economy, performance and durability of the reciprocating internal combustion engine significantly. Much of the cylinder friction occurs between the cylinder liner and piston skirt. The behaviour of the skirt-to-cylinder contact is a function of connecting-rod angle, gas loading, oil film thickness, and piston velocity (Wong et al., 2006). The reduction of piston friction losses is necessary in order to increase engine efficiency (Betz et al., 1989).
Many efforts to modify and develop better piston engines have been made. Some attempts were aimed at improving the combustion efficiency of the piston engine and include variable valve timing, compression ratio, exhaust gas recirculation, supercharging, turbo charging and inter-cooling. Others tried to control the friction between engine components through piston pin offset from piston axis, crankshaft offset from the cylinder centerline and the use of long connecting rod while some aimed at reducing the heat loss to cooling water and lowering exhaust temperature as found in the six-stroke engine. Also, the improved design of engine components, finishing and material selection was to reduce engine weight and inertia loss all with the overall aim of achieving better piston engine performance.
1.2 STATEMENT OF PROBLEM
The efficiency of conventional piston engine is low; the order being between 15 and 35 percent. This is primarily due to losses in form of heat and friction during operation. The increased friction results from the connecting rod angular thrust on the cylinder surface via the piston skirt and the numerous crankshaft bearings while the high heat loss is attributable to the bore to stroke relation. Reducing the friction and heat losses will therefore increase the efficiency of piston engine. This work therefore seeks to address this problem by proposing a novel engine configuration that will reduce friction and heat losses in a conventional engine.
1.3 AIM AND OBJECTIVES OF THE STUDY
The aim of this work is the design modification of a conventional in-line four stroke engine. The specific objectives are:
i. To propose a modification to the conventional in-line engine and carryout appropriate engineering design of the components of the new engine.
ii. To estimate the friction power at the bearings of this proposed engine and compare it with that from a similar in-line engine.
iii. To establish a correlation between connecting rod angle and cylinder friction in a Conventional piston engine.
1.4 SCOPE OF THE STUDY
The study is limited to geometry modification of four-cylinder piston engine crankshaft and piston skirt. The cylinder head and other engine peripherals of a complete engine are not treated under this study.
1.5 JUSTIFICATION FOR THE STUDY
The reduction of friction and heat rejection to the cooling system in piston engine improves the conversion efficiency of fuel power to mechanical power thereby reduces the depletion rate of fossil fuel and air pollution.
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