Title: Compression ignition by air injection cycle and engine
Abstract: The herein disclosed Compression Ignition By Air Injection (CIBAI) cycle and internal combustion engine has following advantages over Otto and Diesel cycles: higher thermal efficiency and operating like a stratified charge engine on lean mixtures. More reliable by lack off: spark ignition, high-pressure fuel pump and injectors; throttle valve and cold starting problems. Only one valve is required in addition to the usual I.C. engine components. However the CIBAI cycle requires one or more pairs of piston/cylinders to operate together in phase. During the compression stroke a closed cylinder-connecting valve isolates the cylinders. One cylinder compresses an air-fuel mixture to below knock level. The other cylinder compresses only air to high pressure and temperature. Near top dead center, the cylinder-connecting valve opens allowing the high-pressure air to compress, heat and ignite the pre-evaporated air-fuel mixture. This valve remains open during following power stroke and scavenging of exhaust products.
Patent Number: 6,899,061 Issued on 05/31/2005 to Loth
| Inventors:
|
Loth; John L. (P.O. Box 4094, Morgantown, WV 26504)
|
| Appl. No.:
|
755134 |
| Filed:
|
January 9, 2004 |
| Current U.S. Class: |
123/27R; 123/70R |
| Intern'l Class: |
F02B 011/00 |
| Field of Search: |
123/27 R,70.R,317,25.C
|
References Cited [Referenced By]
U.S. Patent Documents
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| 3623463 | Nov., 1971 | De Vries.
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| 3675630 | Jul., 1972 | Stratton.
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| 3774581 | Nov., 1973 | Lundy.
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| 3863613 | Feb., 1975 | Petrie.
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| 3880126 | Apr., 1975 | Thurston et al.
| |
| 4314539 | Feb., 1982 | Schade.
| |
| 5239959 | Aug., 1993 | Loth.
| |
| 5309713 | May., 1994 | Vassallo.
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| 6223729 | May., 2001 | Matsuda et al.
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| 6227171 | May., 2001 | Matsuda.
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| 6338328 | Jan., 2002 | Mower et al.
| |
| 6340004 | Jan., 2002 | Patton.
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| 6343596 | Feb., 2002 | Hajji et al.
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| 6640773 | Nov., 2003 | Ancimer et al.
| |
| 6651432 | Nov., 2003 | Gray, Jr.
| |
| 6662760 | Dec., 2003 | Stanglmaier et al.
| |
| 6666185 | Dec., 2003 | Willi et al.
| |
| 6789514 | Sep., 2004 | Suh et al.
| |
| Foreign Patent Documents |
| 1380941 | Jan., 1975 | GB.
| |
Primary Examiner: Yuen; Henry C.
Assistant Examiner: Castro; Arnold
Claims
1. A novel sequence of thermodynamic processes comprising:
operating a closed internal combustion engine cycle which contains one or more
pairs of cylinders with their heads in close proximity and pistons moving in phase
and having a cylinder-connecting valve mounted in-between said cylinder heads,
which is closed while one piston compresses an air-fuel mixture to a knock free
level while the other piston compresses air to a substantially higher pressure,
so that at the end of their compression stroke, when the cylinder-connecting valve
is opened, the high-pressure air will compress, heat and ignite the air-fuel mixture
resulting in constant volume heat addition at top dead center, to a substantially
higher pressure and thus thermal efficiency than possible with a spark ignition
Otto cycle, and also higher efficiency then with a Diesel cycle, while during the
power/expansion stroke, the cylinder-connecting valve remains open to assure equal
pressure acting on both pistons.
2. The method of claim 1 wherein said two pistons can have different stroke length
and displacement volume as long as they arrive at close to the same time at the
end of their compression and expansion strokes and the opening of the cylinder-connection
valve near the end of the compression strokes does not significantly alter the
compression volume in each cylinders.
3. The method of claim 1 wherein output power can be controlled by means of regulating
the air-fuel mixture ratio in the cylinder compressing air and fuel, without need
for a throttle valve.
4. The method of claim 1 wherein the internal combustion engine does not require
spark ignition or ignition by high-pressure fuel injection.
5. The method of claim 1 wherein the internal combustion engine can operate efficiently
on a wide range of fuels by modifying the compression ratio of the cylinder compressing
the air-fuel mixture.
6. The method of claim 1 wherein the above thermodynamic cycle depends on five
controlling parameters: air-fuel mixture compression ratio, air only compression
ratio, combustion temperature ratio equivalent to the Diesel cycle cut-off ratio,
one polytropic process exponent and the ratio in piston displacement volume between
the cylinder compressing the air-fuel mixture and the cylinder compressing air.
7. The method of claim 1 wherein the thermodynamic cycle is defined by: compression
ignition by air injection, capable of achieving higher thermal efficiency and eliminating
spark ignition, high pressure fuel injection, a throttle valve, diesel engine cold
starting problems and small scale limitations.
8. An internal combustion engine apparatus comprising of at least two cylinders
with their heads in close proximity and separated during the compression stroke
by a closed cylinder-connecting valve while their pistons moving in phase, reaching
the end of their compression stroke simultaneously or nearly so, and one of said
cylinders compressing an air-fuel mixture to a high but knock free level, while
in the other cylinder compressing air to a substantially higher pressure, and opening
said cylinder-connecting valve at or near end of the compression stroke to allow
high pressure air to enter cylinder containing said air-fuel mixture and igniting
same by compression heating for the purpose of achieving explosive near constant
volume combustion followed by an expansion stroke with said cylinder-connecting
valve open to assure equal pressure acting on both pistons and complete combustion
of all fuel present.
9. The apparatus of claim 8 wherein the thermal efficiency exceeds that obtainable
in a conventional engine as compression ignition by air injection can generate
instantaneously a far greater pressure upon ignition of the air-fuel mixture then
is possible without knock in a Otto cycle based engine.
10. The apparatus of claim 8 wherein the thermal efficiency exceeds that obtainable
in a conventional diesel engine because the compression ratio in the air cylinder
is not limited by the need for a finite combustion chamber volume as is in a diesel
engine and igniting air fuel mixture results in constant volume heat addition which
is more efficient than constant pressure heat addition as in a diesel engine with
its finite fuel injection expansion ratio, called cut-off ratio.
11. The apparatus of claim 8 wherein each pair of piston-cylinders must be positioned
with their cylinder heads in close proximity to one-another which can be achieved
by mounting said cylinders either side-by-side, head-to-head inline or head-to-head
in a V-formation.
12. The apparatus of claim 8 wherein at least one cylinder-connecting valve is
used to keep the pair of cylinders isolated during the compression stroke and means
to connect said two cylinders rapidly near or at the end of their compression stroke
without increasing the sum-total of their two compression volumes and to remain
open during at least the power expansion stroke and preferable during scavenging
of the combustion products while actuating said valves by either mechanical, hydraulic,
pneumatic or electric means as timed by the angular position of at least one of
their crankshaft.
13. The apparatus of claim 8 wherein at least one cylinder-connecting valve is
used to keep the pair of cylinders isolated during the compression stroke and means
to connect said two cylinders rapidly near or at the end of their compression stroke
without increase in the sum total of their two compression volumes and to remain
open during at least the power expansion stroke and preferable during scavenging
from combustion products while actuating said valves pneumatically by means of
springs and pressure differences between the two cylinders or pressure in the crankcases
in the case of a two-stroke engine.
14. The apparatus of claim 8 wherein the air-fuel mixture is in general rich,
as it contains approximately only half the air available for combustion therefore,
it can be ignited by high-pressure air injection over a wide range of air-fuel
mixture ratios, like a stratified charge engine, thereby eliminating the need for
a throttle valve and the need for spark plug or a glow plug ignition source and
the diesel engine's problem with cold starting.
15. The apparatus of claim 8 to scale down to very small engines as needed for
portable engine powered equipment.
16. The apparatus of claim 8 wherein the internal combustion engine operates
at high efficiency on liquid and gaseous fuels over a wide range of properties
such as octane number, cetane number, lubricity thereby providing a suitable general
aviation aircraft replacement engine and eliminate the currently used 100 Low Lead avgas.
17. The apparatus of claim 8 wherein the internal combustion engine operates
at optimum efficiency on a wide range of fuels by automatically modifying mechanically,
hydraulically, electrically or pneumatically the compression volume at top dead
center on the cylinder(s) which compress the air-fuel mixture, based on sensing
the occurrence of pre-ignition in any one of them.
18. The apparatus of claim 8 wherein with a two stroke engine one can scavenge
exhaust products from both cylinders more thoroughly than is possible in a conventional
engine by placing all exhaust ports at the base of the air-compressing cylinder
and all inlet ports at the base of the air-fuel mixture compressing cylinder thereby
assuring one-way flow of all exhaust products by first scavenging with the cylinder
air charge followed by scavenging with the air-fuel mixture one can assure to prevent
any unburned fuel from escaping through the exhaust ports.
Description
FIELD OF THE INVENTION
This invention relates to a new thermodynamic cycle with associated engine geometry
for increased fuel-efficiency, reliability and simplicity, relative to current
engines based on Otto or Diesel cycle. The herein disclosed new thermodynamic cycle
and engine geometry is referred to as Compression Ignition By Air Injection Cycle
and Engine, abbreviated as "CIBAI" cycle and engine. Its thermodynamic efficiency
has been shown to exceed that of both Otto and Diesel cycles over a wide range
of operating conditions. The need for spark plugs, glow plugs, high-pressure cylinder
fuel injectors and throttle valves has been eliminated thereby enhancing engine
reliability. With the exception of an additional "cylinder-connecting valve" all
components needed are standard for internal combustion engines.
BACKGROUND OF THE INVENTION
All currently operating internal combustion piston engines are based on either:
1) The Otto cycle which requires a near stoichiometric mixture at all power
levels to achieve near constant volume combustion with spark ignition. To maintain
such a mixture ratio at part power, the fresh air intake must be throttled. This
lowers efficiency by power used for cylinder filling. Otto cycle efficiency is
limited by compression ratio, fuel octane number and knock.
2) The Diesel cycle requires compressing air to high pressure and temperature
such that when its fuel injectors spray fine droplets into the hot air, they quickly
evaporate and burn. Good atomization requires a high-pressure fuel pump and fuel
injectors. To complete combustion as fast as it takes to inject the fuel (called
cut-off ratio), a high cetane number fuel is required. The combustion process takes
place during piston expansion, which results in the Diesel cycle having constant
pressure heat addition. This is less efficient than constant volume heat addition
as is possible when igniting a pre-evaporated air-fuel mixture, as in the Otto
cycle. At full power, the cut-off ratio increases, which reduces efficiency and
presents the possibility of incomplete combustion and air pollution by unburned
hydrocarbons leaving the exhaust pipe. Small diesel engines for lawnmowers, chainsaws
etc. do not exist because high-pressure fuel injectors cannot dispense small quantities
of fuel. At cold temperatures the diesel fuel does not atomize nor evaporate well,
and has a tendency to gel which explains its cold starting problems. The diesel
engine is usually more efficient than a spark ignition engine and diesel fuel tax
is less than gasoline tax. The lubricating property of Diesel fuel reduces cylinder
wall wear, unlike gasoline, which dissolves the oil film from the walls. This makes
the Diesel engines last longer than gasoline engines. Therefore the diesel engine
is preferred for long distance hauling. Note: service problems are mostly related
to their fuel-injector systems.
In the automotive, general aviation and small engines industry, reciprocating
piston engines are mostly used because of their efficiency and high power to weight
ratio. Spark ignition engines based on the Otto cycle are currently the lightest
and the least expensive. Their thermal efficiency increases with design volumetric
compression ratio (r
v), which ranges from 7 to 11 and requires a corresponding
increase in fuel-octane number from 80 to 100, to prevent pre-ignition and knock,
and therefore fuel cost. Very high compression ratio fuel-efficient spark ignition
engines are used in general aviation aircraft because their fuel weight is limited,
therefore aircraft range and endurance depend on high fuel efficiency. At most
airports only 100 octane Low Lead avgas and jet fuel are made available. For years
the FAA has been trying to discontinue providing poisonous 100 Low Lead avgas by
replacing such engines with a low cost, low maintenance, light weight, efficient
diesel engine operating on jet fuel. Up till now this has not yet materialized.
However the CIBAI engine might be a viable substitute as it can be operated efficiently
on a wide range of liquid and gaseous fuels!
To extend the life of our hydro-carbon fuel reserves and minimize the atmospheric
carbon-dioxide buildup there is a need for engines to operate on the CIBAI cycle
to: accept a wide range of fuels, be more fuel efficient, reduce air pollution
by unburned hydrocarbons, eliminate maintenance intensive components such as spark
ignition systems and high-pressure fuel injectors, increase the range of general
aviation aircraft and eliminate the need for poisonous 100 Low Lead avgas.
SUMMARY OF THE INVENTION
This invention relates to the design of a new thermodynamic cycle and associated
engine layout for increased fuel-efficiency and reliability relative to current
engines based on either the Otto or Diesel cycle. The herein disclosed Compression
Ignition By Air Injection Cycle and Engine is hereafter referred to as the CIBAI
cycle or engine. The thermodynamic equation for its efficiency has been shown to
exceed that of both the Otto and Diesel cycles over a wide range of operating conditions.
The CIBAI cycle eliminates the need for spark/glow plugs or high-pressure cylinder
fuel injectors, thereby enhancing its reliability. With the exception of an additional
"cylinder-connecting valve" all other components used are standard for I.C. engines.
Described herein are the Compression Ignition By Air Injection (CIBAI) Cycle and
Engine. The engine comprises conventional piston engine components such as: crankshaft
in a casing, cylinders, pistons, carburetor or low pressure inlet manifold injection
and the in case of 4-stroke engines cylinder head valves while for 2 stroke engines
cylinder wall ports with crank-case compression. To enable operation on the CIBAI
cycle the engine must have pairs of cylinders with pistons operating in phase with
their cylinder heads in close proximity. For a single crankshaft configuration,
each cylinder pair is mounted side-by-side inline with the crankshaft. If two crankshafts
are used, then cylinders can be mounted head to head or in a V formation. One of
the cylinders in each pair is used to compress an air-fuel mixture, with a volumetric
compression ratio r
vaf, just short of knock level. The other cylinder
compresses only air to high pressure and temperature with volumetric compression
ratio r
va. One additional item is required: the cylinder connecting
valve which upon opening should not alter the combined volume of the air-fuel mixture
and hot air volume. This cylinder-connecting valve remains closed during most of
the compression stroke, but opens near Top Dead Center. At that instant nearly
all of the hot high-pressure air expands into the cylinder with the air-fuel mixture.
The sudden compression and heating of the pre-evaporated air-fuel mixture causes
spontaneous ignition near Top Dead Center. The combustion pressure rise transfers
some of the combustion products back into the air-compressing cylinder. By the
end of the expansion stroke each cylinder contains nearly the same amount of combustion
products. The sudden rise in air-fuel mixture pressure just prior to ignition gives
the CIBAI cycle a higher effective compression ratio than the Otto cycle. The CIBAI
cycle constant volume heat addition renders it also more efficient than constant
pressure burning Diesel cycles over most commonly used compression ratios. A comparison
of ideal cycle efficiencies for the CIBAI- Otto- and Diesel cycles has been shown
here assuming both pistons used in the CIBAI cylinder pair have the same displacement
volume V
o. The following efficiency controlling parameters have been
kept equal for comparison purposes:
- 1) Polytropic compression and expansion coefficient n (used in: p Vn=constant)
- 2) Air-fuel mixture piston volumetric compression ratio
##EQU1##
- 3) Air-only piston volumetric compression ratio
##EQU2##
- 4) Combustion induced temperature ratio T3/T2=rc,
called cut-off ratio in the diesel cycle.
The cycle efficiency of the three above-mentioned ideal cycles is shown below
in closed form. For the spark-ignition Otto cycle find:
##EQU3##
For the compression ignition Diesel cycle find:
##EQU4##
For the compression ignition CIBAI cycle find the air to air-fuel mixture mass
ratio to be:
##EQU5##
This mass ratio is needed together with the volume ratio of the combined two
cylinder compression volume, V2, divided by the displacement volume,
Vo, of the air-fuel
piston:
##EQU6##
Inserted below gives the CIBAI cycle efficiency as:
##EQU7##
List of differences between these three cycles
- Hot air injection with CIBAI near Top Dead Center causes instant air-fuel
compression, heating and turbulent mixing, resulting in ignition and combustion
at constant volume, while preventing knock. Spark ignition engine (Otto cycle)
compresses the air-fuel mixture gradually and therefore knock if the compression
ratio is too high prior to spark ignition
- Because the air-fuel mixture is in general rich as it contains only
about half the combustion airhot-high-pressure air can ignite even lean mixtures,
there is no need for a throttle valve to reduce airflow at low power to maintain
a spark ignitable mixture in the CIBAI engine.
- Two-stroke spark ignition (Otto cycle) engine efficiency is limited
by its ability to scavenge all combustion products without loss of unburned fuel
through the exhaust port. The CIBAI cycle scavenges combustion products only in
one direction to the exhaust ports, first using air followed by an air-fuel mixture
from the respective crankcases of the air and air-fuel cylinders. Thus scavenging
can be thorough without loss of fuel through the exhaust port.
- Otto cycle two-stroke spark ignition engine performance is poor at high
altitude due to difficulty in maintaining a near stoichiometric mixture. As the
CIBAI cycle engines are not sensitive to mixture ratio their altitude performance
is good.
- Spark ignition (Otto cycle) engine's maintenance problems associated
with spark plug fouling and high voltage ignition are avoided with CIBAI cycle's
hot air ignition.
- Maintenance problems with direct cylinder fuel injectors in spark ignition
(Otto cycle) stratified-charge engines are avoided CIBAI cycle.
Diesel engine's maintenance problems associated with a high-pressure fuel
pump and individual cylinder fuel injectors are avoided in CIBAI cycle's ignition
by hot air.
- Diesel engine's fuel injection problems under high load resulting in
incomplete combusted hydrocarbons and soot in the exhaust are avoided in CIBAI
cycle's ignition by hot air.
Diesel engine's need for heavy construction for high compression ratio and
efficiency is not needed with the CIBAI cycle because of its reduced sensitivity
to high r
va.
The inability of Diesel engine's fuel injectors to accurately meter small fuel
quantities eliminates their application to the small engine market: lawnmowers,
UAV's, etc. The simplicity and reliability of the CIBAI cycle makes it ideal for
small engine operation.
- Igniting a pre-evaporated air-fuel mixture with an engine operating
on the CIBAI cycle eliminates the Diesel's engine's cold day starting problems,
with its reduced fuel injector atomization with increased fuel viscosity and associated
slower vaporization and ignition.
- The increased efficiency of a CIBAI cycle engine can extend life of
our fossil fuel reserves and reduce automotive exhaust air-pollution and carbon
dioxide emissions.
- The CIBAI cycle engine can tolerate a wide range of cheaper and safer
fuels, eliminating the need for a high octane fuels or high lubricity to minimize
Diesel fuel-injector wear and high cetane number to promote rapid combustion.
- A gradual replacement of Otto and Diesel cycle engines with CIBAI cycle
engines will not stress existing fuel supply network as would replacing with hydrogen
fueled cars.
- Some existing aircraft and automotive piston engines maybe retrofitted
to CIBAI cycle operation for increased efficiency and reliability while using more
economical jet fuel.
- Changing general aviation aircraft piston engines to operation on the
CIBAI cycle increases reliability and efficiency and does not introduce new technology
which would require FAA certification.
- Converting all 100 Low Lead requiring engines to operate on the CIBAI
cycle will solve the poisonous 100 Low-Lead avgas problem.
BRIEF DESCRIPTION OF THE DRAWINGS
All but one part needed are standard I.C. engine components. Their unique arrangement
has been shown in FIGS. 1, 2 and 3 schematic format for clarity rather
then perspective or isometric views. Four-stroke engines with an even number of
cylinders in line might be converted to operate on the CIBAI cycle. This would
require a new crankshaft so that each adjacent pair of cylinders reaches Top Dead
Center at the same time. Next the cylinder head must be changed for two reasons.
a) A cylinder-connecting valve between each pair of cylinders must be added which
stays open during the expansion and scavenging strokes but closes during the intake
and compression strokes. b) Half of the inlet and exhaust manifolds openings must
be blocked off. The compression ratio in the air-fuel cylinders must be selected
based on fuel used. Spark ignition, throttle valve and high-pressure fuel pump
plus cylinder injectors will not be needed.
FIG. 1 is a schematic drawing of a pair of piston/cylinders, operating side-by-side
on the CIBAI cycle in a 4-stroke engine. The right cylinder compresses an air-fuel
mixture while the left cylinder compresses air to high pressure and temperature.
Conventional cylinder head valves are used here for both air and air-fuel intakes
as well as exhaust and cylinder-connecting valve. Other optional cylinder-connecting
valve geometries are shown in FIGS. 2 and 3. These valves are actuated by: mechanical,
hydraulic, electric or pneumatic means.
FIG. 2 is a schematic drawing of a pair of piston/cylinders, operating side-by-side
on the CIBAI cycle in a 2-stroke engine. The right cylinder crankcase compresses
an air-fuel mixture while the left cylinder crankcase compresses air to high pressure
and temperature. During scavenging, air and air-fuel mixture enter through the
right cylinder wall ports and push combustion products out of the left cylinder
exhaust port while the cylinder-connecting valve stays open. The cylindrical shaped
cylinder-connecting valve shown here is actuated pneumatically using available
internal pressure differences. This valve can also be actuated by mechanical, hydraulic
or electric means.
FIG. 3 is a schematic drawing of a pair of piston/cylinders, operating head
to head on the CIBAI cycle in a 2-stroke engine mounted end-to-end to maximize
engine balance. Scavenging is done by air and air-fuel discharging through ports
in the lower cylinder pushing out exhaust products through ports in the upper cylinder.
The cylinder-connecting valve is closed during the compression stroke. The bottom
cylinder compresses an air-fuel mixture while the upper cylinder compresses only
air. Near Top Dead Center the cylinder-connecting valve is opened to induce ignition
followed the expansion stroke. The cylinder-connecting valve shown here is in the
form of a rotating shaft, milled down in the middle to form into a rectangular
butterfly like valve and rotating at half the rpm of the two crankshafts. The two
crankshafts use 2:1 reduction gearing or chain to drive the power output shaft
which also contains the cylinder connecting valve.
FIGS. 4
a and 4
b show a comparison of efficiencies between
the ideal Otto, Diesel and CIBAI cycles, for different compression ratios as indicated
using the equation shown in the summary of the invention.
FIG. 5
a shows typical ideal CIBAI cycle temperature changes in each cylinder
for a 2-stroke engine during compression from station 1 to 2
a
and 2
af, mixing of 2a and 2
af to produce 2, combustion
from 2 to 3 and expansion from 3 to 4, exhaust return from 4 back to 1.
FIG. 5
b shows typical ideal CIBAI cycle pressure changes in each cylinder
for a 2-stroke engine during compression from station 1 to 2
a
and 2
af, mixing of 2
a and 2
af to
produce 2, combustion from 2 to 3 and expansion from 3 to 4, exhaust return from
4 back to 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
To operate a piston internal combustion engine on the Compression Ignition By
Air Injection (CIBAI) cycle requires at least one pair of pistons operating in
phase, with their heads near one another. One of the pistons compresses an air-fuel
mixture to a pressure ratio limited by knock as in spark ignition engines. The
other piston compresses air to high-pressure. When both pistons reach near Top-Dead-Center,
a cylinder-connecting valve opens without increasing the combined compression volumes.
Most of the hot high-pressure air transfers into the air-fuel mixture, causing
sudden compression and heating followed by explosive combustion at near constant
volume. This combustion pressure rise drives some of the combustion products back
into the air cylinder. During the subsequent expansion stroke the cylinder-connecting
valve is kept open to keep the pressure the same on both pistons. At Bottom Dead
Center both cylinders will contain approximately the same amount of combustion
products. CIBAI cycle operation eliminates the need for spark plugs with their
required high voltage source and eliminates the need for a high-pressure fuel pump
with its fuel injectors. The CIBAI cycle thermal efficiency exceeds that of the
Otto cycle due to increased pressure prior to ignition and exceeds that of the
Diesel cycle because combustion takes place at constant volume instead of at constant
pressure till the cut-off ratio is reached. The additional needed component is
the cylinder-connecting valve, which can be actuated either by mechanical, hydraulic
or electric valve actuators (lifters) or by pneumatic pressure differences.
FIG. 1 is a schematic drawing of a pair of piston/cylinders, operating side-by-side
in phase on the CIBAI cycle in a 4-stroke engine. The right cylinder compresses
an air-fuel mixture while the left cylinder compresses air to high pressure and
temperature. Conventional type cylinder head valves are used here for both air
and air-fuel intakes as well as exhaust and the cylinder-connecting valve. Shown
here is the start of the scavenging stroke. The cylinder-connecting valve
3
is wide open and shown out of the way in the retracted position. The dashed arrows
show the direction of flow of exhaust gas from cylinders
1 and
2
and out of the one or more open exhaust valves
4. At the end of the scavenging
stroke both the exhaust valve
4 and the cylinder-connecting valve
3
are closed. During the intake stroke an air-fuel mixture is generated in carburetor
8 with air from filter
7 and enters through inlet valve
5
into cylinder
1. At full power, the fuel-air mixture ratio in cylinder
1
may have to be up to twice as rich as in an Otto cycle because it is going to be
diluted when hot air is injected from cylinder
2. Engine power is adjusted
by fuel flow control with needle
9. Air enters through filter
14
and inlet valve
6 into cylinder
2. During the compression stroke
the cylinder-connecting valve
3 remains closed. Near Top Dead Center a mechanical,
hydraulic or electric valve lifter is used to open the cylinder-connecting valve
3. This allows the high pressure and temperature air inside cylinder
2
to compress, heat and ignite the pre-evaporated air-fuel mixture in cylinder
1.
During combustion the pressure in cylinder
1 rises to exceed that in cylinder
2, which causes flow reversal and ignition of any unburned fuel present
in cylinder
2. Cylinder-connecting valve
3 remains open till the
end of the expansion stroke to equalize the pressure in both cylinders. Near bottom
dead center exhaust valve
4 opens and the sequence repeats itself. Power
is extracted from crankshaft
10 which can support several pairs of pistons
in a row. Note piston
11 is shorter than piston
12 because the compression
ratio in cylinder
1 is lower.
FIG. 2 is a schematic drawing of a pair of piston/cylinders, operating side-by-side
in phase on the CIBAI cycle in a 2-stroke engine. The right cylinder
21
is used to compress an air-fuel mixture while the left cylinder
22 is used
to compress air to high pressure and temperature. Shown here are the pistons at
Bottom Dead Center with the dashed arrows showing scavenging of combustion products
out of exhaust port
42, first by means of crankcase pressurized air from
port
27 and followed by the air-fuel mixture from port
28. Note during
scavenging the cylinder-connecting valve is in the open position, "see dashed outline"
24. The cylindrical-connecting valve used here is actuated pneumatically
using internal pressure differences. During the compression stroke springs
40
and
41 on either side of the valve are used to hold it closed in position,
"see solid outline"
25. Near Top Dead Center the pressure in cylinder
22
becomes sufficiently higher than in cylinder
21 to push the valve open against
spring
41. With the help of spring
40 the valve moves to position
"see dotted outline"
26. Then hot high-pressure from cylinder
22
enters cylinder
21, compressing, heating and igniting the air-fuel mixture.
The resulting combustion pressure rise in cylinder
21 moves the valve back
to the normally open position
24, where during the expansion power stroke
it is kept open by the pressure buildup on diaphragm
43, connected to crankcase
opening
45. As piston
23 nears Bottom Dead Center, exhaust port
42
is cleared by piston
23. This allows combustion products to expand and escape
from both cylinders. Next, air-inlet port
27 is cleared by piston
29
and air under pressure from crankcase of cylinder
22 rushes into cylinder
21 while scavenging more exhaust products out of port
42. Scavenging
continues when port
28 opens up, which allows cylinder
21 to fill
up with an air-fuel mixture and push the air charge ahead of it into cylinder
22.
This clears out the remaining products of combustion. Even if a small amount of
fuel carries over into cylinder
22, the resulting mixture will be too lean
to be auto ignitable, so that its combustion will not take place until the cylinder-connecting
valve is pushed open near Top Dead Center and the process repeats itself. Power
is extracted from crankshaft
37 which can support several pairs of pistons
in a row. Piston
29 is shorter than piston
23 because the compression
ratio in cylinder
21 is lower. More precise timing of the cylinder-connecting
valve opening and closing can be obtained by conventional valve lifters or other
mechanical, hydraulic, electric or pneumatic means.
FIG. 3 shows a schematic of a 2-stroke engine with a pair of cylinders mounted
end-to-end for optimum mass balance with pistons moving in phase. The two intake-
and one exhaust valve shown in FIG. 1 are here in the form of cylinder wall ports
opened by the lower piston at near Bottom Dead Center. The cylinder-connecting
valve is shown as an integral part of the rotating drive shaft
54, which
has been milled down to a bar shape
55 to serve as a rectangular butterfly
type valve. The central driveshaft
54 also serves to extract power via a
2:1 reduction gearing or chain drive from the two separate crankshafts
60
and
61. Note the use of a 2:1 reduction gear ratio is essential as the cylinder-connecting
valve opens twice per revolution. The application shown here is for a small airplane
engine where a propeller
57, with spinner
58, is shown mounted directly
on driveshaft
54. Piston
59 in cylinder
51 is shown at Bottom
Dead Center position where cylinder
51 first fills up with compressed air
from the crankcase of cylinder
52 via external pipe
67 while expelling
exhaust products through port
53. Next, it fills with a compressed air-fuel
mixture from the crankcase of cylinder
51. This scavenges all remaining
combustion products from cylinders
52 and out of exhaust port
53.
Note as soon as scavenging is completed the cylinder-connecting valve
55
is closed during the remainder of the compression stroke. At or near Top Dead Center
the cylinder connecting valve
55 is opened and hot high-pressure air flows
from cylinder
52 into
51 and compression ignition occurs. The cylinder-connecting
valve remains open till Bottom Dead Center where the cycle repeats itself. Note
during the compression stroke, crankcase of cylinder
51 fills with an air-fuel
mixture through filter
64 and carburetor
62 with fuel flow control
by valve
65, and crankcase of cylinder
52 fills with an air through
filter
66.
FIGS. 4
a and
4b are graphs showing how the efficiency
of these three ideal cycles compare with each other. All relevant variables have
been kept the same for each cycle. All but one have been kept constant for easy
comparison. They are:
- 1. Polytropic compression and expansion coefficient n=1.4
- 2. Air-fuel mixture piston volumetric compression ratio
##EQU8##
- 3. Piston displacement volume ratio Vo kept same for both pistons.
- 4. Combustion induced temperature ratio T3/T2=rc=2,
called cut-off ratio in diesel cycle. The efficiency of the Diesel and CIBAI cycle
are shown as a function of air-only compression ratio 14<rvn<22.
Of course Otto cycle efficiency depends only on the air-fuel mixture compression
ratio set here at rvaf=11. The CIBAI cycle efficiency is only higher
than all others at high air-fuel mixture compression ratio as shown in FIG. 4a.
At rvaf=8 it is only better than Diesel up to a compression ratio rva=14.
FIGS. 5
a and
5b are graphs showing how the dimensionless
temperature and pressure vary throughout the ideal CIBAI cycle.
*
