Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR OPERATING AND ARRANGEMENT
OF A PNEUMATIC PISTON ENGINE
Technical Field
The present invention relates to the field of engineering industry, in
particular
engine building, namely pneumatic piston engines (PPE). The invention can be
1o used at transport in power drives and in power generation.
Background Art
High power consumption is the main problem of present-day transport. That is
the reason why experts in the field of transport engineering face a task to
provide speeds being adequate to up-to-date requirements with simultaneous
increasing piston specific power of the engine and decreasing specific fuel
consumption.
2o Internal combustion engines (ICE) make up the bulk of the present-day
transport engines. Increase of transport speed requires increasing engine
power density. However, raise of engine power density in present-day ICEs is
obstructed by high temperature in the working chamber of the engine and
resulting thermo stress, as well as low reliability and low life of engine.
Among
other ICE disadvantages, one may point to its complex construction, in which a
fuel-delivery system, a cooling system, and a system of turbocharger for the
working chamber of the engine are needed.
Essential limitation of ship propulsion systems using ICEs (diesel engines) as
a
3o main engine is stopping of the main engine (diesel) when the ship power
plant
fails. It may cause wreck of a ship; and that is the reason why reliability of
the
ICEs is the factor of the vessel survivability. For the railway transport, the
role of
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the ICEs is the same importance, because a failure of electric generator means
an emergency stop of the train.
Pneumatic piston engines (PPE) are used as control and executing units in
s automation, as engine brakes in vehicles, as drives for mining machines and
conveyors in mining industry. PPEs are ecologically clean, but their low
efficiency obstructs their use in the sphere of transport and power
generation.
Various methods of increasing the capacity and efficiency of pneumatic piston
engines are known:
- adding fuel to compressed air and combustion of the mixture in the
over-piston space of the working chamber according to the invention
certificate SU 1553731, 1990;
- usage of liquid air; its evaporating, heating, and recuperation of heat in
the
propulsion system according to the invention certificate SU 1783127, 1992.
However, these well-known methods do not allow essential increase of the
PPE power with simultaneous providing the efficiency, i.e. with simultaneous
reducing fuel consumption.
The nearest to the present invention is the method for operating and
arrangement of a pneumatic piston engine according to certificate SU 663858,
1979, including supply of compressed air to the working chamber of the engine
and subsequent exhaust of oddments of compressed air from the working
chamber when the piston is in the region of bottom dead center (BDC). In the
known method, supply of compressed air to the working chamber begins when
the piston is in the region of top dead center (TDC) and ends when the piston
is
in the region of bottom dead center. To increase the efficiency, before
supplying compressed air to the working chamber of the engine, 3-4% of
hydrogen-oxygen mixture is added to the air and the mixture obtained is passed
through the catalytic oxidizing chamber. Herein the air temperature rises to
170-220 °C and this results in increase of air volume by 1.6-1.8 times.
This
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allows either to reduce proportionally air consumption and pipeline cross
section with the same piston specific power of the engine or to increase it
without air consumption raise. Nevertheless, it does not provide achievement
of
high powers necessary for up-to-date transport and propulsion systems with
simultaneous providing of efficiency.
Proceeding from the above, the purpose of the present invention is to create a
method for operating of PPE providing high output power with high efficiency
of
operating, i.e. to increase piston specific power of the PPE and to decrease
specific fuel consumption simultaneously. The next purpose of the present
invention is to create a new PPE for providing realization of a new operating
method. Creating a new power plant including a pneumatic piston engine
providing the realization of the method stated above is also the purpose of
the
present invention.
Disclosure of Invention
According to the invention, the above purposes are achieved by a method for
operating of a pneumatic piston engine including supply of compressed air to
2o the working chamber of a cylinder and subsequent exhaust of air out of the
working chamber while the piston is in the region of bottom dead center,
wherein
- supply of compressed air starts while the piston (3) is in the region within
the
range from 40° before the top dead center to 25° after top dead
center by angle
of rotation of the crank (4) of the crankshaft (5) depending on engine speed;
- supply of compressed air ends while the piston (3) is in the region within
the
range from 0° to 90° after top dead center by angle of rotation
of the crank of
the crankshaft.
3o Herein a short-term, pulse supply of compressed air is preferable in view
of the
efficiency being achieved.
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To illustrate the achievement of the purpose of the invention, comparative
calculation of the indicated power generated in a PPE (N;E) and of the
indicated
power supplied in an air compressor (N;c) producing compressed air necessary
for operating of the PPE was carried out. In the case under consideration the
air compressor is driven by the ICE. Calculations were made for the PPE
according to the invention and for the known PPE, both having identical
parameters and dimensions of engines, for a special case when the engine
speed was equal to 2.12 s ' and supply of compressed air started when the
piston was in position of 2° before TDC by angle of rotation of the
crank of the
to crankshaft. For the PPE according to the invention calculation was made for
two modes of operating of the engine:
- first: for the case when supply of compressed air ends while the piston is
in
position of 5° after TDC by angle of rotation of the crank of the
crankshaft, and
- second: for the case when supply of compressed air ends while the piston is
in position of 90° after TDC by angle of rotation of the crank of the
crankshaft.
For the known PPE, calculation was made for the mode of operating when
supply of compressed air ends while the piston is in the region of BDC.
Calculations of power for the PPE and the air compressor are given below (see
the chapter "Calculations").
Approximate calculations have shown that in the case when the means for
supply of compressed air closes while the piston is in the position of
5° after
TDC by angle of rotation of the crank of the crankshaft, to obtain the power
of
6630 kW in the PPE according to the present invention, a power of
approximately 1108 kW is supplied in the air compressor which provides the
PPE with compressed air, i.e. in this case the specific fuel consumption is
reduced by approximately a factor of 6 comparing with the ICE which serves as
a drive of the compressor, i.e. to any ICE (see the chapter "Calculations").
Herein, when the means for supply of compressed air closes while the piston is
3o in position of 90° after TDC by angle of rotation of the crank of
the crankshaft,
to obtain the power of 17002 kW in PPE according to the present invention, a
power of approximately 8516 kW is supplied in the air compressor which
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provides the PPE with compressed air, i.e. in this case the specific fuel
consumption is reduced by approximately a factor of 2 comparing with the ICE
(see the Chapter "Calculations").
5 It is noteworthy that in the known PPE, in the case of engine speed 2.12 s
and by the known method of operating, when the means for supply of
compressed air closes in the region of BDC, the power generated in the
pneumatic engine equals to 25483 kW, though herein the power of
approximately 25548 kW is supplied in the air compressor as well. So, when
l0 using the known method for operating of the PPE, the effect of reduction of
specific fuel consumption equals to zero comparing with the ICE (see the
Chapter "Calculations").
Thus, for the PPE having engine speed of 2.12 s ' and operating by the
method according to the present invention, the preferable mode of operating is
a short-term (pulse) supply of compressed air while the means for supply of
compressed air closes while the piston is in the position of 5° after
TDC by
angle of rotation of the crank of the crankshaft. Results of calculations
evidence
that it is inexpedient to end filling of the working chamber of the PPE
according
2o to the present invention while the piston is in the region of more than
90° after
TDC by angle of rotation of the crank of the crankshaft.
As a whole, the present invention provides the achievement of positive
technical effect: a higher efficiency of transformation of compressed air
energy
to energy of engine shaft rotation, as compared with the known background art.
On using the PPE according to the present invention, the specific fuel
consumption reduces, and a possibility to increase considerably the pressure
of
compressed air being supplied to the PPE appears as well, that results in
significant raise of specific power of the PPE as compared with the PPE being
3o known by the background art having the same engine parameters.
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Thus, the present invention solves a task of creating a new method for
operating and an arrangement of the pneumatic piston engine providing
increase of efficiency of operating of the engine.
In the present description of the invention, the advantages of short-term
supply
of compressed air are presented clearly for the case of engine speed 2.12 s ~,
yet they are right for the PPE according to the invention in cases of other
engine speed as well. Herein, preferable conditions for supply of compressed
air will be different, within the scope of the Claims of the invention,
depending
to on the engine speed.
It is known that thermo stress is absent in pneumatic engines, contrary to the
ICEs, and this allows to raise the pressure of compressed air being supplied
to
the working chamber of the PPE considerably within the limits of strength of
material of the engine - up to that in the ICE and even higher.
To use the high potential energy of compressed air, a more preferable one is
the method of operating of the pneumatic piston engine according to the
invention, which includes additionally at least one subsequent stage of
operating of the pneumatic piston engine, thus forming a multi-stage method of
operating, wherein:
- pass-by of air from the working chamber of each preceding stage to the
working chamber of the subsequent stage is realized during the power stroke of
the piston of the preceding stage, at a position of the piston while it is not
yet
reaching the region of bottom dead center, and
- exhaust of air out of the working chamber of the last one of the subsequent
stages is realized during the power stroke of the piston, at a position of the
piston while it is not yet reaching the region of bottom dead center, and
- exhaust of air from the working chamber of each subsequent stage is realized
while the piston is in the region of bottom dead center.
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Pass-by allows to use high potential energy of compressed a'ir without
substantial enlargement of the length of the piston stroke that is extremely
essential in the case of limited dimensions of engine.
It is useful to exhaust the air out of the working chamber of any stage of the
engine according to he invention, while the piston is in the region of bottom
dead center, directly to the atmosphere. This provides free back stroke of the
piston.
1o Herein, in the engine, according to the invention, it is more preferable to
exhaust the air out of the working chamber of any stage while the piston is in
the region of bottom dead center, with possibility of reuse. This reduces
energy
losses for PPE operating.
Herein it is more useful to realize the method for operating of PPE according
to
the invention as a mode of two-sided supply of compressed air to the cylinder.
For realization of the method for operating of a pneumatic piston engine
according to the invention, in a pneumatic piston engine, in which working
fluid
2o is compressed air (gas) and which contains a cylinder, wherein a piston is
kinematically joined via a crank to a crankshaft, and a working chamber, which
is provided with a means for supply of compressed air and a means for exhaust
of air while the piston is in the region of BDC, - the means for supply of
compressed air is arranged with capability to provide the start of supply
while
the piston is in the region within the range from 40° before TDC to
25° after
TDC by angle of rotation of the crank of the crankshaft depending on the
engine speed, and with the capability to provide the ending of supply of
compressed air while the piston is in the region within the range from
0° to 90°
after TDC by angle of rotation of the crank of the crankshaft.
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A more preferable one is the pneumatic piston engine according to the
invention, which contains at least one consequently joined additional cylinder
thus forming a multi-stage engine, herein
- the additional cylinder contains a piston kinematically joined via a crank
to a
crankshaft and a working chamber, which is provided with a means for
exhaust of air while the piston is in the region of BDC;
- each preceding cylinder of the multi-stage PPE is provided with a means for
pass-by of air to the working chamber of the subsequent additional cylinder,
and the last one in a set of additional cylinders is provided with a means for
to exhaust of air; herein the said both means are arranged with capability for
action while the piston of the corresponding cylinder is at a position not yet
reaching the region of the BDC;
- herein the pistons of all cylinders are kinematically joined to the common
crankshaft.
It is preferable that in the pneumatic piston engine according to the
invention, at
least in one of cylinders of the multi-stage engine the means for exhaust of
air
when the piston is in the region of BDC is arranged with possibility to reuse
the
exhausted air.
In the pneumatic piston engine according to the invention, said means for pass-
by of air from the working chamber of the preceding cylinder to the working
chamber of the subsequent additional cylinder can be arranged as a by-pass
channel with a non-return valve in it, herein the inlet port of the by-pass
channel
is connected with a by-pass port of the working chamber of the preceding
cylinder, the by-pass port being located above the region of bottom dead
center
of the piston, and the outlet port of the by-pass channel is connected with an
inlet port of the working chamber of the subsequent additional cylinder.
A power plant intended for realization of the method according to the present
invention preferably contains a pneumatic piston engine according to the
invention and a source of compressed air. This allows to provide high output
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power in a PPE-based system providing simultaneously low specific fuel
consumption.
Herein it is preferable, that in a power plant according to the invention, a
part of
s power generated in a pneumatic piston engine is directed to the drive of
source of
compressed air.
Herein it as also preferable that a power plant intended for realization of
the
method according to the present invention contains a mufti-stage pneumatic
piston
io engine according to the invention, herein the bore of each subsequent
cylinder
and the diameter of its piston are larger than those in case of the preceding
cyiinder.
Brief Description of Drawings
is
The invention will be further described in the following with reference to the
drawings and diagrams:
Fig.1 shows schematically construction of a one-stage one-sided, supply PPE
2o according to the present invention;
Fig. 2 shows an indicator diagram of operating of the'PPE, in accordance with
Fig. 1, for the case the means for supply of compressed air closes while
the piston is in position of S° after top dead center by angle of
rotation of
the crank of the crankshaft;
2s Fig. 3. shows an indicator diagram of operating of the PPE, in accordance
with
Fig. 1', in the case the means.for supply of compressed air closes while
the piston is in position of 90° after top dead center by angle of
rotation of
the crank of the crankshaft;
Fig. 4 shows an indicator diagram of operating of known PPE in the case the
so means for supply of compressed air closes while the piston is in the region
of bottom dead center (for comparison);
Empfanosteit l6.Okt. lb:.OF -~ ~ w E f
. . . .._ ..~.. _.. . . .. ..... ._ ~~~~QE~ ~~~E~'' .. . _.._ -.... . . .. .
._ __.. ._._. _. _.
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Fig. 5 shows schematically construction of a two-stage one-sided
supply PPE according to the present invention, the power stroke
in the first-stage cylinder;
Fig. 6 shows schematically construction of a two-stage one-sided
5 supply PPE according to the present invention, the back stroke in
the first-stage cylinder;
Fig. 7 shows an indicator diagram of operating of the ICE (for comparison)
Indicator diagrams in Fig. 2, Fig. 3, Fig. 4 show the operating of PPE for a
1o particular case of engine speed 2.12 s ~. However in principle, the
mechanism
of operating of the PPE according to the invention, as shown in the diagrams,
is
true for operating of a PPE for other engine speeds too.
Modes for Carrying Out the Invention
Description of a one-stage PPE
A one-stage one-sided supply pneumatic piston engine shown in Fig. 1
contains the following construction elements: 1 - PPE, 2 - cylinder, 3 -
piston,
4 - crank, 5 - crankshaft, 6 - working chamber (over-cylinder space), 7 -
means for supply of compressed air (inlet valve), 8 - means for exhaust of air
(outlet valve), 9 - under-cylinder space.
A PPE shown in Fig. 1 consists of a cylinder 2 containing a piston 3
kinematically joined via a crank 4 to crankshaft 5, and a working chamber 6
(over-cylinder space). The working chamber 6 contains a means 7 for supply of
compressed air to the working chamber arranged as an inlet valve and a means
8 for exhaust of air, while the piston is in the region of bottom dead center,
arranged as an outlet valve. The under-cylinder space 9 is bridged to
atmosphere. The means 7 for supply of compressed air may be joined to an
external source of compressed air.
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The device according to the invention operates as follows.
The operating of a PPE is illustrated by the indicator diagrams given in Fig.
2
and Fig. 3. The diagrams show the change of pressure (p) of compressed air
(gas) in the cylinder 2 of the engine 1 depending on the position of the
piston 3
by angle of rotation (cp°) of the crank 4 of the crankshaft 5.
In a PPE 1 (when engine speed is 2.12 s '), supply of compressed air under
pressure pmaX to the working chamber begins at the moment when the means 7
to for supply of compressed air to the working chamber starts to open when the
piston 3 is in position of 2° before top dead center by angle of
rotation of the
crank of the crankshaft (point a in Fig. 2 and Fig. 3).The means 8 for exhaust
of
air is completely closed by this moment. Pressure in the chamber reaches the
value of pmaX (point b in Fig. 2 and Fig. 3) by the moment when the piston 3
reaches the position corresponding to 5° after top dead center by angle
of
rotation of the crank 4 of the crankshaft 5. The power stroke of the piston
begins.
In the case of the first, preferable mode of operating of PPE according to the
2o invention (Fig. 2), the means 7 for supply of compressed air closes and
supply
of compressed air stops by the moment when pressure in the working chamber
reaches the value of pmaX that corresponds to the piston position of 5°
after top
dead center by angle of rotation of the crank 4 of the crankshaft 5. The
piston 3
goes on moving downwards doing work, the power stroke of the piston
proceeds. While the piston 3 passes the region of bottom dead center, when
pressure in the chamber drops to a value of few atmospheres (1.5-3 atm), the
means 8 for exhaust of air to atmosphere opens (point c), pressure in the
working chamber drops to a value equal to the atmospheric pressure paten
(point
d) and the piston 3 goes upward freely. A free back stroke of the piston
3o proceeds (segment d-a). By the moment when the piston 3 is approaching the
position corresponding to point a in Fig. 2, the means 8 for exhaust of air
closes
again and the means 7 for supply of compressed air starts to open, and the
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working cycle of the engine repeats. During the supply of compressed air, the
piston covers a distance corresponding to rotation of the crank of the
crankshaft
by an angle of approximately 7°. Thus, in case of this mode of
operating, supply
of compressed air to the working chamber of the engine proceeds during
extremely short part of the piston stroke (segment a-b), "in a pulse mode" so
to
say.
In the case of the second variant of the mode of operating of PPE according to
the invention (Fig. 3), the means 7 for supply of compressed air pmaX closes
1o when the piston is in the position of 90° after top dead center by
angle of
rotation of the crank of the crankshaft (point b'). By that time the piston
covers a
distance equal to a half of the piston stroke (segment b-b'). The exhaust of
air
also occurs in the region of bottom dead center (point c), the pressure in the
chamber drops to the atmospheric pressure (point d), and a free back stroke of
the piston occurs (segment d-a).
For comparison, the indicator diagram for PPE operating according to the
method known from background art, where supply of compressed air pmax
proceeds during all power stroke of the piston and ends in the region of
bottom
dead center (point c in Fig. 4), is given. During all period of supply of
compressed air pressure in the working chamber keeps at the level Of pmaX.
The area of the indicator diagram illustrates the work produced by compressed
air in the engine cylinder during one working cycle (the more the area the
more
the power supplied in the cylinder). It is seen from Fig. 2 that the area of
the
indicator diagram of operating of the engine according to the invention, in
the
case of preferable mode is smaller by a factor of 3.84 comparing with the case
of the engine operating according to the method known from the background
art (Fig. 4). In this case power supplied in the engine cylinder is smaller by
a
factor of 3.84 than in the case of known PPE. Comparison of diagrams in Fig. 3
3o and Fig. 4 shows that by the second mode of operating of PPE according to
the
invention, the power supplied in the cylinder is smaller by a factor of 1.5
than in
the case of the known method for operating of PPE.
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Thus, in the case of PPE according to the invention it is possible to supply
compressed air within the specified limits of the operation cycle of engine
according to the Claims, depending on the desirable result. In particular, for
an
engine according to the invention, with the engine speed of 2.12 s ', the
preferable mode of operating is the first mode described above, with a short-
term supply of compressed air when closing of the means for supply of
compressed air is carried out at the angle of rotation of the crankshaft of
5°
after top dead center. Herein the supply of compressed air to the working
chamber of the PPE according to the invention, when the angle of rotation of
to the crank of the crankshaft exceeding 90°, is inexpedient.
The prospective effect of application of the present invention was verified
for
the case of engine speed 2.12 s ' using "Calculation of Powers for the PPE and
for the Compressor" (see the Chapter "Calculations")
When PPE according to the invention operates with a different engine speed
(5 s ', 8.33 s ', etc.), preferable conditions of supply of compressed air
will
differ within the limits of the Claims of the invention.
2o Description of a Multi-Staae PPE
Operating of a multi-stage PPE according to the present invention is
illustrated
by an example of a two-stage one-sided supply PPE, which consists of the
following construction components (Fig. 5 and Fig. 6):
10 - two-stage pneumatic piston engine, 11 - first-stage cylinder (preceding),
12 - second-stage cylinder (additional and/or subsequent), 13 - means for
supply of compressed air to the working chamber of the first-stage cylinder
(inlet valve), 14 - working chamber of the first-stage cylinder, 15 - means
for
exhaust of air out of the working chamber of the first-stage cylinder (outlet
valve), 16 - piston of the first-stage cylinder; 17 - by-pass channel, 18 -
non-
return valve, 19 - by-pass outlet, 20 - inlet port of the working chamber of
the
second-stage cylinder, 21 - working chamber of the second-stage cylinder;
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22 - piston of the second-stage cylinder, 23 - means for exhaust of air out of
the working chamber of the second-stage cylinder (outlet port) while the
piston
is not yet reaching the region of BDC; 24 - under-cylinder space of the first-
stage cylinder; 25 - under-cylinder space of the second-stage cylinder; 26, 27
-
s crank of a crankshaft, 28 - crankshaft, 29 - means for exhaust of air out of
the
working chamber of the second-stage cylinder (outlet valve) while the piston
is
in the region of BDC.
Two-stage PPE consists of a first-stage cylinder 11 and a second-stage
cylinder 12. The first-stage cylinder 11, as well as the cylinder 2 of a one-
stage
engine 1 according to Fig. 1 is supplied with a means 13 for supply of
compressed air pmax to a working chamber 14 of the engine arranged as an
inlet valve and with a means 15 for exhaust of air out of the working chamber
14 to atmosphere, while its piston 16 passes the region of bottom dead center,
IS arranged as an outlet valve. It is possible to join the inlet valve 13 to
an external
source of compressed air. The first-stage cylinder 11 is connected to the
second-stage cylinder 12 via a by-pass channel 17 provided with a non-return
valve 18 in it. The inlet port of the by-pass channel 17 is joined to a by-
pass
outlet 19 of the cylinder 11, the by-pass outlet 19 being located in the
working
2o chamber 14 above the region of bottom dead center of the piston 16. The
outlet
port of the by-pass channel 17 is joined to an inlet port 20 of a working
chamber
21 of the second-stage cylinder 12. The second-stage cylinder 12 is supplied
with a means 23 for exhaust of air, arranged as an outlet port located in the
working chamber above the region of bottom dead center of the piston 22. The
25 outlet port 23 and under-cylinder spaces 24 and 25 of both cylinders are
bridged to the atmosphere. The pistons 16 and 22 of cylinders of both stages
are kinematically joined to cranks 26 and 27 of the common crankshaft 28. In
the working chamber of the cylinder 12, a means 29 for exhaust of air, while
the
piston is in the region of bottom dead center, is placed, arranged as an
outlet
30 (exhaust) valve.
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A multi-stage engine operates as follows.
Compressed air under pressure of pmaX is fed to the working chamber 14 of the
cylinders 11 through the inlet valve 13 (Fig. 5), as well as in the case of
one-
s stage engine 1 according to Fig. 1, during a minor part of piston stroke.
During
power stroke of the piston 16, when the piston passes by the by-pass outlet 19
of the cylinder 11 but is not yet reaching the region of the bottom dead
center,
the by-pass channel 17 turns out to be opened into the working chamber 14 of
the cylinder 11 for a short time. The compressed air under residual pressure
of
to pres passes into the by-pass channel 17, and opens the non-return valve 18,
and then the air passes to the working chamber 21 of the second-stage cylinder
12. Herein the pressure levels in the working chambers of both cylinders
equalize and thus turn to be equal to a value of pres' which value is less
than
pres, and the non-return valve 18 closes preventing from the air escape out of
15 the working chamber 21.
Having passed the region of bottom dead center, piston 16 of cylinder 11
makes its back stroke (Fig. 6). While piston 16 passes the region of bottom
dead center, the outlet valve 15 for exhaust of air out of cylinder 11 to the
2o atmosphere opens; and the piston 16 makes a free stroke upwards. The piston
22 of the second-stage cylinder makes its working stroke'. Herein the non-
return
valve 18 is closed.
During the upward stroke, the piston 16 passes by the by-pass outlet 19, the
by-pass channel 17 turns to be opened into the under-cylinder space 24 of the
cylinder 11 which is bridged to the atmosphere. Air pressure upon the non-
return valve 18 from the side of the cylinder 11 turns to be equal to
atmospheric
pressure (parm); air pressure upon the valve 18 from the side of cylinder 12,
which is equal to p,~s , exceeds parm and consequently the valve 18 remains
3o being closed during the back stroke of the first-stage piston 16.
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During its power stroke, the piston 22 passes by the by-pass outlet 23 in the
cylinder 12, the working chamber 21 bridges to the atmosphere. By this air
with
pressure p.es" is exhausted to the atmosphere, and pressure in the working
chamber of the cylinder 12 turns to be equal to atmospheric pressure paten.
Herein pressures on the both sides of the non-return valve 18 turn to be the
same and equal to parm, and remain of that value during the current stroke of
the pistons 16 and 22. The non-return valve 18 remains closed until the first-
stage piston 16 passes by the by-pass outlet 19 during the next power stroke.
Thereafter pressure in the working chamber of the second-stage cylinder 12 is
to created again equal to the value of pas .
While moving upwards, the piston 22 passes by the outlet port 23, the working
chamber of the cylinder 12 turns to be isolated from the atmosphere; and the
piston 22, during its further movement upwards, compresses the air (which
initial pressure is equal to atmospheric pressure parm) in this chamber. This
reduces the efficiency of the entire system of two-stage engine. To avoid
these
losses the cylinder 12 is provided with means 29 (which is similar to the
outlet
valve 15) for exhausting the oddments of compressed air to the atmosphere
when the piston 22 is in the region of bottom dead center. This provides free
2o upwards motion of the piston 22. The means 29 closes before the following
pass-by of air from the cylinder 11.
When number of stages exceeds two, all intermediate stages are provided with
outlet ports 29. In a multi-stage PPE, pistons of all cylinders are joined to
a
common crankshaft.
Herein in PPE according to the invention it is possible to reuse the air being
exhausted when the piston is in the region of bottom dead center, for example
to supply it to the intake of a compressor. This will decrease the energy
losses
for operating of PPE.
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Calculations
Calculation of Powers for the PPE and the Air Compressor
In the following a comparative calculation of powers and air consumption for
the
PPE, operating according to the present invention and according to the known
method, is presented. Power (N;E) generated in PPE and power (N;~) supplied
in the air compressor driven by ICE for obtaining the amount of compressed air
necessary for operating of the PPE were calculated.
to
Calculation was made for a special case when engine speed of PPE equals to
2.12 s ~ and starting of supply of compressed air is realized while the piston
is
in position corresponding to 2° before the top dead center by angle of
rotation
of a crank of a crankshaft.
Calculation was made for two variants of the mode of operating of PPE
according to the invention, which were described above:
- for the case when supply of compressed air ends when the piston is in the
position corresponding to 5° after top dead center by angle of rotation
of a
crank of a crankshaft, and
- for the case when supply of compressed air ends when the piston is in
position corresponding to 90° after top dead center by angle of
rotation of a
crank of a crankshaft.
Calculation for the known PPE, in which supply of compressed air ends in the
region of bottom dead center is made for comparison.
Calculation of powers for comparison of the PPE (under various conditions of
ending of supply of compressed air) and of the air compressor was made for
the following identical parameters of PPEs:
Number of cylinders 5
Cylinder bore 0.48 m
Piston stroke 2 m
Engine speed 2.12 s ~
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Pressure of compressed air 3.73 106 Pa.
Equation for calculating the power generated in the PPE:
rr~Dz~n~S~i ( )
NrE = p. 4 1
where N;E is indicated power of
PPE (kW);
p; is mean indicated pressure
(Pa);
D is cylinder bore (m);
N is engine speed (s ');
S is piston stroke (m);
1o i is number of cylinders.
Equation for calculating the power supplied in air compressor to obtain the
amount of compressed air necessary for operating of PPE is as follows:
Nrc = Pr ~ US
where: N;~ is indicated power of air compressor (kW);
p; is mean indicated pressure of air compressor equal to mean
indicated pressure in PPE (Pa);
VS is the amount of air produced by air compressor per second
(m3/s).
Calculation of the air amount VS produced by the compressor and consumed in
the PPE per second is made as follows.
Volume of the working chamber of one cylinder of PPE is
z
V, _ ~ ~ ~ H (m3)
where D is cylinder bore (D = 0.48 m);
H is length of piston stroke at the moment when supply of compressed
air to the working chamber ends (m).
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The amount of air consumed in PPE per one revolution of the crankshaft in all
cylinders of the engine equals to
V, ~ i (m3)
where i is number of cylinders (i = 5).
Volume of air consumption in PPE per second is
VS = ~V, . i~~ n (m3/s)
where n is engine speed 2.12 s '
l0 Thus
~. _~~Da .~,a.~-3.14~(0.484~a~5~2.12,h,-1.91$H (m3/s)
For the known PPE where supply of compressed air into the working chamber
ends when the piston is in the region of the bottom dead center, the length of
the piston stroke H at the moment of ending of supply makes 2 m, so
VS =1.918 ~ 2 = 3.836 (m3/s)
For the PPE according to the invention, in case when supply of compressed air
ends when the piston is in the position corresponding to 90° after top
dead
center, the length of the piston stroke H at the moment of ending of supply
makes 1 m, so
2o VS = 1.918 1=1.918 (m3/s).
For the PPE according to the invention, in case when supply of compressed air
ends when the piston is in the position corresponding to 5° after top
dead
center, the length of the piston stroke H at the moment of ending of supply
makes 0.166 m. To provide calculation cleanliness, a loss factor, which equals
2, accounting for the dead space, was introduced in this case, thus doubling
the
volume of the working chamber and air consumption:
VS =1.918 ~ 0.166 ~ 2 = 0.637 (m3/s).
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The results of comparative approximate calculation of powers of the PPE (N;E)
and of the air compressor (N;~) according to the above Equations (1 ) and (2)
are presented in the following Table:
5 Table
Indexes For the PPE according to ~ For the
the invention known PPE
1 St mode of 2"d mode of
operating operating
Piston position at the Region
moment of
of ending of supply 5 after 90 after the bottom
top top
of compressed air dead centerdead centerdead center
Mean indicated pressure p; 1.74 4.44 6.66
(MPa)
Length of piston stroke
by ending
of supply of compressed H 0.166 1.0 2.0
air
Amount of air produced
by air
compressor and consumed 0.637 1.918 3.836
in PPE
per second (m3/s) VS
Indicated power of PPE N;E6630 17002 25483
(kW)
Indicated power of air
compressor
(kW ) N;~1108 8516 25548
Calculation of Fuel Consum~~tion for Operating_of the ICE and for operating of
the PPE according to the Invention
To compare the power and economy of operation of the pneumatic piston
engine according to the invention with the requirements to up-to-date
transport
engines and to estimate a possibility to apply this PPE as a powerful engine
alongside with present-day internal combustion engines, operating of the PPE
according to the invention is considered for the case when operating
parameters and dimensions of the PPE are identical to those of the present-day
ICE.
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Operating parameters of PPE:
Number of cylinders 5
Cylinder bore 0.48 m
Piston stroke 2 m
Engine speed 2.12 s
Pressure of compressed air 13.73
MPa.
Power (N;E) 6630 kW
Mean indicated pressure (p;)1.74 MPa.
For comparison an ICE (diesel engine) operating for a ship fixed-stage
propeller
of SULZER, RTA 48 T class was taken.
Operating parameters of the ICE:
Number of cylinders 5
Cylinder bore 0.48 m
Piston stroke 2 m
Engine speed 2.12 s 1
Combustion pressure 13.73 ~ 106
Pa
Power (N;,cE) 5100 kW
Mean indicated pressure (p;) 1.34 MPa.
Comparing the indicated diagrams of the preferable mode of operating of the
PPE according to the invention with engine speed 2.12 s ~ (Fig. 2) and of the
ICE (Fig. 7) one can notice they are similar, but compression stroke is absent
in
the PPE, and this increases the diagram area and, consequently, the mean
indicated pressure and power at least by 30%.
Equation for calculation of fuel consumption per hour in the case of ICE:
Mice = qice ' N.
where M,cE is fuel consumption per hour (kg/s);
q~cE is specific fuel consumption (kg/kW~ s) in ICE, q;cE = 5~ 10-5 kg/kW~ s;
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N; is indicated power of engine (kW).
Thus, in the case of ICE to generate the power of 5100 kW, the fuel, which is
necessary to be consumed, is:
~ M,~E = 5~ 10-5 kg/kW~ s~ 5100 kW = 0.255 kg/s.
According to the above "Calculation of Powers for the PPE and the Air
Compressor", in the PPE (with 2.12 s') according to the invention in the case
of preferable mode of operating, to generate power N;E = 6630 kW, it is
necessary to supply in the air compressor the power N;~ that equals
approximately to 1108 kW, which is smaller by a factor of 6.
Thus, the specific fuel consumption (q) at exploitation of PPE operating by
the
method according to the invention will be:
qE = 5~ 10-5 kg/kW ~ s : 6 = 8.333 10-6 kg/kW ~ s,
I5 at that fuel consumption (M) will be:
ME = 8.333 10-6 kg/kW~ s~ 6630 kW = 0.055 kg/s.
Allowing for all losses, errors and assumptions made, and also keeping in mind
that in practice a wide range of dimensions and parameters of PPE and various
air compressors will be used, it is possible to claim that to obtain the same
shaft
power in the PPE as in the ICE the amount of fuel necessary to be consumed is
smaller by a factor of at least 5, i.e. the specific fuel consumption in the
case of
the PPE according to the invention is smaller by a factor of at least 5 than
in the
case of ICE.
Industrial Applicability
The pneumatic piston engine according to the invention may be arranged using
known technologies and applying known up-to-date materials and equipment.
In the pneumatic piston engines according to the invention alongside with air
3o also other gases, which properties allow to compress it to necessary degree
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and provide safety of engine operating and ecological cleanliness of engine
operating, can be used.
Variants of realization of the present invention are not limited with the
described
above, they include various modifications of arrangement within the limits of
the
Claims of the invention.
The pneumatic piston engine according to the invention may be used as a
motor-car engine and a main marine engine, as well as a railway transport
engine. Nowadays ICEs which have reached their power limit and do not meet
the ecology criteria are used in these fields. The present invention allows to
construct powerful, economic and ecologically more clean transport engines of
various classes. On the basis of the present invention, power plants may be
realized too.
