Hello I am back again with new
engineering concept related to engine. This time it is 8 stroke engine. Of course
you all have heard about 2 stroke engine and 4 stroke engine but 8 stroke seems
little confusing.
Actually there are 5 stroke and 6
stroke engines already developed. This engines are still under development and
there are many different cycles are available to fulfill 8 strokes.
Before we see study 8 stroke
engine lets brush up our concept on 2 and 4 stroke. So in 4 stroke engine there
are four strokes named suction, compression, power, and exhaust stroke. While in
2 stroke this 4 strokes mentioned before is grouped into two strokes.
This 8 stroke engine cycle is
developed by students of engineering as part of their project so all credit
goes to them there is also link of video of them at end of this article.
So why 8 stroke? This question
will surely arise on your mind while there are already plenty of engine
available in market then why another one? the answer is quite simple that all
that engines has high fuel consumption and lot of energy is wasted hence low
efficiency is major problem to overcome this limitation of conventional engine
this concept is developed
Following are 8 strokes of engine
cycle in which first 4 strokes are as same as our normal 4 stroke engine but I still
have mentioned for better understanding.
EIGHT STROKES OF ENGINE
1) Intake, induction or
suction:
The intake valves are open as a
result of the cam lobe pressing down on the valve stem. The piston moves
downward increasing the volume of the combustion chamber and allowing air to
enter in the case of a CI engine or an air fuel mix in the case of SI engines
that do not use direct injection. The air or air-fuel mixture is called the
charge in any case.
2) Compression:
PIn this stroke, both valves are
closed and the piston moves upward reducing the combustion chamber volume which
reaches its minimum when the piston is at TDC. The piston performs work on the
charge as it is being compressed; as a result its pressure, temperature and
density increase; an approximation to this behavior is provided by the ideal
gas law. Just before the piston reaches TDC, ignition begins. In the case of a
SI engine, the spark plug receives a high voltage pulse that generates the
spark which gives it its name and ignites the charge. In the case of a CI
engine the fuel injector quickly injects fuel into the combustion chamber as a
spray; the fuel ignites due to the high temperature.
3) Power
The pressure of the combustion
gases pushes the piston downward, generating more work than it required to
compress the charge. Complementary to the compression stroke, the combustion
gases expand and as a result their temperature, pressure and density decreases.
When the piston is near to BDC the exhaust valve opens. The combustion gases
expand irreversibly due to the leftover pressure—in excess of back pressure,
the gauge pressure on the exhaust port.
4) Exhaust
The exhaust valve remains open
while the piston moves upward expelling the combustion gases. For naturally
aspirated engines a small part of the combustion gases may remain in the
cylinder during normal operation because the piston does not
close the combustion chamber
completely; these gases dissolve in the next charge. At the end of this stroke,
the exhaust valve closes, the intake valve opens, and the sequence repeats in
the next cycle. The intake valve may open before the exhaust valve closes to
allow better scavenging.
5) Intake of water in H.P.
cylinder
The inlet valve of high pressure
cylinder is opened and water is introduced in the cylinder. Piston moves from
T.D.C to B.D.C. during this process. The water is converted into steam due to
heat stored by cylinder wall and volume of water is increased the exhaust valve
remains close.
6) Intake of exhaust gases in
L.P. cylinder
The gases expelled from high
pressure cylinder still contains some portion of energy. This gases are
introduced in the low pressure cylinder by opening the intake valve in low
pressure cylinder. Exhaust valve of low pressure cylinder remains closed.
Piston moves from T.D.C to B.D.C. during this process. The gases expand
adiabatically in cylinder.
7) Exhaust of heated steam
from H.P. cylinder(second Power Stroke)
The heated steam from H.P.
cylinder now expelled by moving piston T.D.C to B.D.C position. Inlet valve
remains close. Piston moves from B.D.C to T.D.C.
8) Exhaust of gases from L.P.
cylinder(Third power Stroke)
The energy from exhaust gas is
utilized by getting another power stroke in L.P. cylinder. Piston moves from
B.D.C to T.D.C. exhaust valve opens and inlet valve remains closed.
Line Diagram
As this engine has 3 power
strokes it has benefits of lower fuel consumption, lesser pollution, and better
thermal efficiency. But it also has some disadvantage as its construction will
be very complex and heavy.
Video URL:
thanks very good idea by your student through project
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