Ice d-1 to 15 fundamentals

1. FOUR STROKE vs TWO STROKE
Characteristics 4 Stroke Engine (equal hp)
One Cylinder
2 Stroke Engine (equal hp)
One Cylinder
1. Number of major
moving parts
Nine Three
2. Power strokes One every two revolutions
of crankshaft
One every revolution of
crankshaft
3. Running
temperature
Cooler running Hotter running
4. Overall engine size Larger Smaller
5. Engine weight Heavier construction Lighter in weight
6. Bore Size equal hp Larger Smaller
7. Fuel and oil No mixture required Must be premixed
8. Fuel consumption Fewer gallons per hour More gallons per hour
9. Oil consumption Oil re-circulates and stays
in engine
Oil is burned with fuel
10 Sound Generally quiet Louder in operation
11 Operation Smoother More erratic
12 Acceleration Slower Very quick

2. Characteristics 4 Stroke Engine (equal hp)
One Cylinder
2 Stroke Engine (equal hp)
One Cylinder
13. General maintenance Greater Less
14. Initial cost Greater Less
15. Versatility of
operation
Limited slope operation
(Receives less lubrication
when tilted)
Lubrication not affected at
any angle of operation
16. General operating
efficiency (hp/wt
ratio)
Less efficient More efficient
17. Pull starting Two crankshaft rotations
required to produce one
ignition phase
One revolution produces
an ignition phase
18. Flywheel Requires heavier flywheel
to carry engine through
three non-power strokes
Lighter flywheel
FOUR STROKE vs TWO STROKE

3. COMPARISION OF SI & CI ENGINES
SI ENGINE CI ENGINEE
1. Premixed charge drawn into cylinders Only air drawn into cylinders
2. Mixture formed in intake system Fuel injected into cylinder prior to
combustion
3. Load control by throttling Load control by fuel metering; no throttling
in diesel engines
4. Ignition by spark Spontaneous ignition of mixture; no
external ignition source
5 Generally volatile fuel (gasoline); does
not ignite spontaneously at lower
temperatures.
Generally distillate oil. Must ignite at Lower
temperatures.
6. Lower compression ratio (knock
limited)
Higher compression ratio (as high as 25,
no knock limitation).
7. Turbocharged in high performance Usually turbocharged (except engines in
smaller size engines) to increase power.
8. Lighter construction; higher rpm Heavier construction; limited rpm
9. Higher fuel consumption Lower fuel consumption

4. Pumping Loss
• The major cause of loss of efficiency at low power is
"pumping loss". When the engine is slowed down the
flow of air into the cylinders is restricted by closing a
"throttle" valve. This forces the engine to drag the air
through a narrow opening, creating a partial vacuum in
the inlet manifold.
• As the air entering the cylinder during the intake
stroke is below atmospheric pressure, there is less of
it. A smaller amount of fuel is injected and the
resulting smaller fuel/air "charge" causing the engine
to run at lower power, as desired.

5. Pumping Loss
• But, as well as having this intended effect, maintaining
a partial vacuum in the inlet manifold wastes energy.
As the piston moves down during the intake stroke,
normal pressure below it and a partial vacuum above
cause drag on the crankshaft's rotation.
• This also reduces power output, which is what we
want, but at the expense of wasted fuel, which we
want to avoid.
• Cars suffer from pumping losses even at highway
speeds. The throttle is wide open only when
accelerating or climbing hills.

6. Pumping Loss
• Diesel engines do not have this problem
because there is no throttle. Low power is
achieved by simple injecting less fuel.
• This is one of the reasons why diesel engines
achieve higher efficiency. This technique
cannot easily be used by gasoline engines
because the burn temperature becomes too
high and damages the cylinder

7. Volumetric efficiency
Volumetric efficiency is a ratio (or percentage)
of what quantity of fuel and air actually enters
the cylinder during induction to the actual
capacity of the cylinder under static
conditions.
Therefore, those engines that can create
higher induction manifold pressures - above
ambient - will have efficiencies greater than
100%.

8. Volumetric efficiency
• Volumetric efficiencies can be improved in a
number of ways, but most notably the size of the
valve openings compared to the volume of the
cylinder and streamlining the ports.
• Engines with higher volumetric efficiency will
generally be able to run at higher RPMs and
produce more overall power due to less
parasitic power loss of moving air in and out of
the engine.

9. Volumetric efficiency
• There are several standard ways to improve
volumetric efficiency as follows:-
• Larger valves. Larger valves increase flow but
weigh more.
• Multiple valves. Multi-valve engines combine
two or more smaller valves with areas greater
than a single, large valve while having less
weight, but with added complexity.

10. Volumetric efficiency
• Porting. Carefully streamlining the ports
increases flow capability. This is referred to as
porting and is done with the aid of an air flow
bench for testing.
• Crossflow cylinder head. Another major aspect
of design is to use a crossflow cylinder head,
which has become the standard configuration in
modern engines.

12. Volumetric efficiency
• Many high performance cars use carefully
arranged air intakes and tuned exhaust systems
to push air into and out of the cylinders, making
use of the resonance of the system.
• A more modern technique, variable valve
timing, attempts to address changes in
volumetric efficiency with changes in speed of the
engine: at higher speeds the engine needs the
valves open for a greater percentage of the cycle
time to move the charge in and out of the engine.

13. Volumetric efficiency
• Volumetric efficiencies above 100% can be
reached by using forced induction such as
supercharging or turbo charging.
• With proper tuning, volumetric efficiencies above
100% can also be reached by naturally aspirated
engines.
• The limit for naturally aspirated engines is about
137%; these engines are typically of a DOHC
layout with four valves per cylinder.

14. Double Overhead Camshaft
(DOHC)

15. Double or Dual Overhead Camshaft
(DOHC)