Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02262~ 1999-01-29
LIQUID GAS ENGINE
The invention relates to a liquid gas engine.
Liquid gas engines are spark ignition Otto engines
which are supplied with liquid gas.
The main components of liquid gas, which is a mixture
also designated as LPG (Liquefied Petroleum Gas), are
propane and butane. It is obtained during the
extraction of crude oil and in refinery processes and
can be liquefied under pressure. Liquid gas is
distinguished by a high octane number (RON > 100).
Liquid gas engines differ from gasoline engines in the
different mixture preparation which is necessitated by
the great tendency of liquid gas to evaporate. Liquid
gas is supplied, as a liquid under pressure, to the
engine in corresponding delivery lines. In an
evaporator, the liquid gas is converted into the
gaseous state by the supply of heat. The evaporator is
a heat exchanger, to which heated cooling water is
supplied in order to heat and evaporate the liquid gas.
The evaporator is combined with a pressure regulator,
in order to keep the then gaseous liquid gas within a
specific pressure range. The liquid gas is then
supplied to a gas/air mixer which mixes liquid gas with
air. Such a gas/air mixture is known, for example, from
DE 33 32 923 C2. The mixer consists of an annular
element which supplies liquid gas from outside to a
central air stream passing through the annular element
and which swirls them together.
The company DAF presented a liquid gas engine for buses
under the type designation LT 160 LPG. This liquid gas
engine corresponds to a diesel engine which is
converted to a liquid gas engine. In contrast to the
known liquid gas engines, the engine presented by DAF
is equipped with a liquid gas injection system which
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injects liquid gas into an intake port. This injection
system corresponds entirely to those employed at the
present time in Otto engines (passenger vehicles). When
the liquid gas is being injected into the intake port,
the mixture temperature is to be reduced, and higher
efficiency established, as a result of the evaporation
of the liquid gas. This cooling by evaporation may lead
to the icing up of the injection valves in the starting
phase and in the case of high air humidity, and,
because of this, it is not possible to ensure that the
engine will operate at cold outside temperatures. This
could be counteracted by mixture preparation with
simultaneous heating, as is known from the already
conventional liquid gas engines. However, heating an
ignitable mixture entails considerable risks.
Known from FR-A-2 629 516 is an internal combustion
engine which is intended for the use of a fuel with a
higher vapor pressure and significantly lower viscosity
than gas oil. The engine works in accordance with the
diesel process, and comprises a device for direct
injection of the fuel under high pressure into the
combustion chambers via passive mechanical injection
nozzles, the device having a low-pressure feed pump,
which is capable of regulating the pressure of a fuel
to a value which suffices for the fuel not to reach the
boiling point of 80~C, and a high-pressure pump which
is arranged in the vicinity of the injection nozzles.
The high-pressure pump has a cylinder and a piston with
smooth surfaces for relative displacement and sealing,
the surfaces being separated from one another by a
radial play of the order of magnitude of 1 ~m, and the
piston having open surface pores which are impregnated
with a lubricant which is resistant to friction and the
effect of the fuel.
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_ ~ _
This known injection device is of complicated design
and requires a low-pressure feed pump. Moreover, the
injection device does not work effectively enough.
The object on which this invention is based is to
provide a liquid gas engine which has a simple design
and ensures reliable operation along with a high power
output.
The object is achieved by means of a liquid gas engine
having the features of claim 1. Advantageous
embodiments are specified in the subclaims.
The liquid gas engine according to the invention is an
Otto engine with a high pressure injection device which
injects liquid gas directly into the combustion
chamber. The liquid gas is thereby conveyed as far as
the combustion chamber of the engine in the liquid
state of aggregation, in which it can be handled simply
and safely.
By means of the injection device, the liquid gas is
injected directly into the combustion chamber, atomized
and evaporated. The transition from the liquid to the
gaseous state of aggregation thus takes place only in
the combustion chamber. Thls affords ~~ ci~b ~
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CA 02262~ 1999-01-29
necessary for an injection operation is injected and
the simultaneous compression of the liquid gas/air
mixture occurring in the combustion chamber counteracts
cooling due to the evaporation of the liquid gas, so
that, even during the cold starting phase, icing up of
the injection device is prevented and reliable
operation is ensured.
Moreover, in the liquid gas engine according to the
invention, the very fine atomization of the liquid gas
injected at high pressure achieves excellent
distribution in the combustion space and the abrupt
evaporation of the liquid gas achieves perfect
intermixing of the fuel with the air contained in the
combustion chamber, so that the combustion mixture
burns up in an ideal way after ignition. The
advantageous properties of the liquid gas, such as a
high net calorific value (~ 46.1 MJ/kg) and high knock
resistance, are thereby fully utilized, so that, in
contrast to known liquid gas engines, no power losses
have to be taken into account, as compared with
comparable gasoline engines.
The invention is explained in more detail by way of
example with reference to the drawing in which:
Figure 1 shows diagrammatically a single-cylinder
liquid gas engine with an injection device,
Figure 2 shows a longitudinal section through the
30injection device shown in Figure 1,
Figure 3 shows a cross section through an armature of
the injection device shown in Figure 2,
Figure 4 shows a cross section through a valve body of
the injection device shown in Figure 2,~5 Figure 5 shows a part section through a slider crank
engine.
The liquid gas engine according to the invention has an
injection device 1 which injects liquid gas directly
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into a combustion chamber 4 of the liquid gas engine
via an injection nozzle 2. The combustion chamber is
delimited in a way known per se by a cylinder 5, a
~ cylinder head 11 and a piston 12. An injection nozzle 2
and a spark plug 10 are arranged in the cylinder head
11. The injection nozzle 2 is connected to the
injection device 1 via a line 72. The injection device
is connected to a pressure tank 111 (illustrated
diagrammatically in simplified form in Figure 1) via a
liquid gas supply line 113 and a liquid gas return line
92.
In the liquid gas supply line 113, the liquid gas is
kept above the vapor pressure of, for example, 8-12
bar, in order to ensure that it cannot evaporate in the
supply line 113. Via the liquid gas discharge line 92,
liquid gas not discharged by the injection device 1 is
returned into the pressure tank 111. The injection
device 1 conveys the liquid gas in short pressure
pulses at a pressure of 40 bar, preferably of 60 bar,
to the injection device 2, at which the intermittently
injected liquid gas is atomized in very fine droplets
so as to be distributed over the combustion chamber 4.
The droplets evaporate abruptly in the air supplied
into the combustion chamber 4 via the inlet port 8.
This results in an ideally intermixed fuel/air mixture
which can be ignited by means of the spark plug 10. The
ignition timing is controlled by an electronic control
device 6 in conformity with a plurality of parameters,
such as, for example, the outside temperature, the
crankshaft position and the injected liquid gas
quantity. Due to the high calorific value of the liquid
gas, it is expedient for the ignition timing to be
retarded somewhat in relation to comparable gasoline
engines. The burnt-up exhaust gas is then discharged
from combustion chamber 4 via an exhaust gas port 3.
By virtue of the inventive direct injection of liquid
gas, the cooling effect generated as a result of the
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evaporation of the liquid gas occurs in the combustion
chamber 4. In the case of a relatively low load, where
the injected liquid gas quantity is small, the cooling
effect is correspondingly low and is compensated by the
compression generated by means of the compression
stroke of the piston 12. Under high load, a
substantially larger liquid quantity is injected into
the combustion chamber 4. The cooling effect is
increased correspondingly, so that, in the case of high
loads, a marked increase in efficiency is achieved by
virtue of the "internal" cooling.
The injection device 1 is preferably designed as an
electromagnetically driven alternating piston pump 1
which works on the energy accumulation principle, so
that the liquid gas is injected into the combustion
chamber 4 in short pressure pulses. Alternating piston
pumps 1 of this type are known, for example, from
DE-41 06 04 15 A or DE 42 06 817 A.
An exemplary embodiment of the alternating piston pump
is shown in Figures 2 to 4.
The alternating piston pump 1 has an essentially
elongate cylindrical pump casing 5 with an armature
bore 16, with a valve bore 17 and with a pressure
chamber bore 18 which are in each case made one behind
the other in the pump case 15 and form a passage
extending through the entire pump casing 15. The
armature bore 16 is arranged downstream of the valve
bore 17 in the injection direction and the pressure
chamber bore 18 is arranged upstream of the valve bore
17 in the injection direction. The bores 16, 17, 18 are
arranged concentrically to the longitudinal axis 19 of
the pump casing 15, the armature bore 16 and the
pressure chamber bore 18 each having a larger inside
diameter than the valve bore 17, so that the armature
bore 16 and the valve bore 17 are offset relative to
one another by means of a first annular step 21 and the
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valve bore 17 and the pressure chamber bore 18 are
offset relative to one another by means of a second
annular step 22.
5 The armature bore 16 delimits, in the radial direction,
an armature space 23, in which an approximately
cylindrical armature 24 iS arranged so as to be movable
back and forth in the direction of the longitudinal
axis. The armature space is delimited, in the axial
direction, forwardly by the first annular step 21 and
rearwardly by a front end face 25 of a cylindrical plug
26 which is screwed into that end of the armature bore
16 which is open rearwardly in the injection direction.
15 The armature 24 iS formed from an essentially
cylindrical body with end faces 28, 29 located at the
front and rear in the injection direction and from an
outer surface 30. Material is removed in the region of
the armature circumference from the rear end face 28
20 approximately as far as the longitudinal center of the
armature 24, SO that the armature 24 has a conical
surface 31 running outwardly from the rear forward. The
armature 24 iS inserted with play between its outer
surface 30 and the inner surface of the armature bore
25 16, so that, when the armature 24 moves back and forth
in the armature bore 16, it touches the inner surface
of the armature bore 16 solely if the armature 24
tilts, with the result that friction between the
armature 24 and the armature bore 16 is kept low. The
30 provision of the conical surface 31 on the armature 24
further reduces the contact surface and, consequently,
the frictional surface, with the result that friction
between the armature 24 and the inner surface of the
armature bore 16 and therefore also the generation of
35 heat are further reduced. The armature 24 iS provided,
in the region of its outer surface 30, with at least
one, preferably two or more grooves 32 running in the
direction of the longitudinal axis. The armature 24 has
a cross sectional shape (Figure 3) with two laterally
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arranged semicircular elements 24a and with two wide
shallow grooves 32 in the region between the
semicircular elements 24a. A continuous bore 33 is made
centrally on the armature 24 in the direction of the
longitudinal axis.
A feed piston tube 35 is inserted into the bore 33 of
the armature 24 and forms a central passage space 36.
Seated on the front end face 29 of the armature 24 is a
plastic ring 37, through which the feed piston tube 35
passes. Supported forwardly on the plastic ring 37 is
an armature spring 38 which extends as far as a
corresponding matching bearing ring 39. This bearing
ring 39 is seated on the first annular step 21 in the
armature bore 16.
The feed piston tube 35 is connected nonpositively to
the armature 24. The unit consisting of the feed piston
tube 35 and of the armature 24 is designated below as a
feed piston element 44. The feed piston element 44 may
also be designed in one part or in one piece.
Seated positively in the valve bore 17 is a guide tube
40 which extends rearwardly into the armature space 23
into the region within the helical spring 38. An
outwardly projecting annular web 41, which is supported
rearwardly on the second annular step 22, is provided
at that end of the guide tube 40 which is at the front
in the injection direction. The annular web 41 does not
extend radially quite as far as the inner surface of
the pressure chamber bore 18, so that a narrow
cylindrical gap 42 is formed between the annular web 41
and the pressure chamber bore 18. The guide tube 40 is
secured against rearward axial displacement by means of
the annular web 41.
The feed piston tube 35 connected nonpositively to the
armature 24 extends forwardly into the guide tube 40
and rearwardly into an axial blind bore 43 of the plug
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26, SO that the feed piston tube 35 iS guided both at
its end 45 at the front in the injection direction and
its rear end 46. By virtue of this bilateral guidance
at the ends 45, 46 of the elongate feed piston tube 35,
5 the feed piston element 44 iS guided in tiltfree
manner, so that undesirable friction between the
armature 24 and the inner surface of the armature bore
16 iS reliably avoided.
Mounted axially displaceably the front region of the
guide tube 40 iS a valve body 50 which forms an
essentially cylindrical elongate tenonlike solid body
with a front and a rear end face 51, 52 and with an
outer surface 53. The outside diameter of the valve
15 body 50 corresponds to the clear width of the passage
in the guide tube 40. An annular web 54 iS provided on
the outer surface 53 of the valve body 50 and is
arranged approximately at the end of the front third of
the valve body 50. The annular web 41 of the guide tube
20 40 forms an abutment for the annular web 54 of the
valve body 50 when the latter is in the position of
rest, so that said valve body cannot be displaced
further rearwardly. The valve body 50 iS provided, on
its circumference, with three grooves 55 running in the
25 direction of the longitudinal axis (Figure 4) . The
annular web 54 iS interrupted in the region of the
grooves 55.
The rear end face 52 of the valve body 50 is designed
30 conicallv on its edge region and cooperates with the
end face of the front end 45 of the feed piston tube
35. The spatial shape of the front end 45 of the feed
piston tube 35 iS adapted to the rear end face 52 of
the valve body 50, in which the inner edge of the feed
35 piston tube 35 iS chamfered and the wall of the feed
piston tube 55 iS stripped away somewhat on the inside.
The feed piston tube 35 thus forms, with its front end
45, a valve seat 57 for the valve body 50. When the
valve body 50 bears with its rear end face 52 on the
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valve seat 57, passage through the grooves 55 made in
the region of the outer surface of the valve body 50 iS
blocked.
5 That region of the valve body 50 which projects
forwardly from the guide tube 40 to the pressure
chamber bore 18 is surrounded by a pressure chamber
body 60 which consists of a cylinder wall 51 and of a
front end wall 62, a hole or bore 63 being introduced
centrally into the end wall 62. The pressure chamber
body 60 iS positively inserted with its cylindrical
wall 61 in the pressure chamber bore 18, and is
arranged in such a way that its end face 64, located at
the free end of the cylinder wall 61, butts on the
15 outwardly projecting annular web 41 of the guide tube
40, there being provided in the pressure chamber body
60 radial passage bores 65 which make a connection of
the pressure chamber 66 to the fuel supply bore 76.
20 The pressure chamber body 60 delimits, with its
interior, a pressure chamber 66, into which the valve
body 50 can penetrate and put the fuel located in the
pressure chamber 66 under pressure. The pressure
chamber has a greater clear width on its region located
25 at the rear in the injection direction, said region
extending approximately over half the length of the
pressure chamber body 60, than in the front region. The
greater clear width in the rear region is dimensioned
in such a way that the valve body 50 can penetrate with
its annular web 54 into the pressure chamber 66 with
slight play, whereas the clear width of the front
region is dimensioned in such a way that there is
sufficient space only for that region of the valve body
50 which extends forwardly from the annular web 54 and
for a helical spring 67 surrounding this region. As a
result, the pressure chamber 66 iS designed to be only
slightly larger than the space taken up by the thrust
movement of the valve 50 executed during the injection
operation.
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The helical spring 67 is located, at one end, on the
end wall 62 of the pressure chamber body 60 on the
- inside and, with its other end, bears on the valve body
50 and, in particular, on the annular web 54 of the
latter, so that said spring presses the valve body 50
and the pressure chamber body 60 apart from another.
The pressure chamber body 60 iS axially fixed forwardly
in the injection direction by means of a connection
piece 70 which is screwed into the forwardly open end
of the pressure chamber bore 18. The connection piece
70 limits the position of the pressure chamber body 60
forwardly in the axial direction, so that the valve
body 50 is prestressed rearwardly by the helical spring
67. The connection piece is designed, on the outside,
with a mouth 71 for connecting the fuel feedline 72
(Figure 1). The connection piece 70 has a bore 73 which
is continuous in the direction of the longitudinal axis
and in which a static pressure valve 74 iS
accommodated. The static pressure valve is preferably
arranged so as to be adjacent to the pressure chamber
body 60.
The pressure chamber body 60 iS provided, on its outer
surface, with an annular groove 68, in which is seated
a plastic sealing ring 69 which seals off the pressure
chamber body 60 relative to the inner surface of the
pressure chamber bore 18.
For the supply of liquid gas, a liquid gas supply
orifice 76 iS made on the pump casing 15 in the region
of the pressure chamber bore 18, SO that said orifice
can communicate with the bores 65 in the pressure
35 chamber body 60. On the outside of the pump casing 15,
the liquid gas supply orifice 76 is surrounded by a
socket 77 for a liquid gas supply valve 78 which is
screwed into the socket 77. The liquid gas supply valve
78 iS designed as a one-way valve with a valve housing
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79. The valve housing 79 has two axially aligned bores
80, 81, the pump casing side bore 80 having a larger
inside diameter than the bore 81, SO that an annular
step is formed between the two bores, said annular step
forming a valve seat 82 for a ball 83. The ball 83 iS
prestressed against the valve seat 82 by a spring 84,
which is supported in the bore 80 on the pump casing 15
in the region around the liquid gas supply orifice 76,
so that liquid gas supplied under pressure from outside
lifts the ball 83 from the valve seat 82, SO that the
liquid gas is supplied into the pressure chamber bore
18 through the bore 80 and the liquid gas supply
orifice 76.
A passage extends from the pressure chamber 66 through
the grooves 55 of the valve body 50, the distance
between the valve seat 57 of the feed piston tube 35
and the rear end face 52 of the valve body 50 and the
passage space 36 of the feed piston tube 35 into the
blind hole 43 of the plug 26. The blind hole or blind
bore 43 iS arranged to run in the direction of the
longitudinal axis and opens into the armature space 23,
the blind hole 43 extending approximately over
two-thirds to three-quarters of the length of the plug
25 26. One, preferably two or more long bores 88 extend
from the rear region of the blind hole 43 to the
peripheral region 89 of the front end face 2 5 of the
plug 26, SO that a communicating connection is made
between the armature space 23 and the blind hole 43.
An outwardly leading bore 90 is introduced as a liquid
gas outflow orifice on the peripheral region of the
first annular step. The bore 90 is lengthened on the
outside by a connecting nipple 91 for connecting the
35 liquid gas return line 92 (Figure 1).
The cylindrical plug 26 has, on its outer surface, a
peripheral annular web 93 projecting outwardly. The
annular web 93 also serves, inter alia, for the axial
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fixing of a locking ring 94 surrounding the pump casing
15 on the outside or of a coil housing cylinder 95
arranged so as to be directly adjacent to the locking
ring 94. The locking ring 94 forms, in cross section,
5 two legs 96, 97 arranged at right angles to one
another, one leg 96 bearing on the outside of the pump
casing 15 and the other leg 97 projecting outwardly and
bearing on the coil housing cylinder. The coil housing
cylinder 95 consists of a cylinder wall 98 and of a
cylinder bottom 99 which is connected laterally to the
cylinder wall 98 SO as to point inwardly and which has
a hole, so that the coil housing cylinder 95 iS pushed
onto the coil housing 15 from the rear, with the
cylinder bottom 99 pointing rearwardly, until the
15 cylinder wall 98 butts on a housing wall 100 projecting
perpendicularly outwardly from the coil housing 15 and
thus delimits an annular chamber 101 of approximately
rectangular cross section for receiving a coil 102.
20 The coil housing cylinder 95 and the locking ring 94
are thus clamped between the housing wall 100 and the
annular web 93 of the plug 26 and fixed in their axial
position. The leg 96 of the locking ring 94 is
chamfered at the inner edge of its end face, a sealing
25 ring 103, such as, for example, an O-ring, being
clamped between the chamfer, formed in said end face,
and the annular web 93.
The coil 102 iS approximately rectangular in cross
30 section and is cast in a carrying body cylinder 104 of
U-shaped cross section by means of epoxide resin, so
that the coil 102 and the carrying body cylinder 104
form a one-part coil module. The carrying body cylinder
104 has a cylinder wall 105 and two side walls 106, 107
35 which project radially from the cylinder wall 105 and
delimit the space for the coil 102, the cylinder wall
105 extending laterally beyond the rear side wall 106,
so that the end face 108 of the latter, the end face
109 of the side walls 106, 107 and the inner surfaces
CA 02262~ 1999-01-29
of the cylinder wall 106 and the front side wall 107
- come to bear positively in the annular chamber 101.
A material 110 having low magnetic conductivity, for
example copper, aluminum, stainless steel, is
introduced in that region of the pump casing 15 which
is arranged between the coil 102 and the armature space
23, in order to avoid a magnetic short circuit between
the coil 102 and the armature 24.
In this initial position, a liquid gas which is under
an admission pressure is supplied from the liquid gas
tank 111 by means of the feed pump 112 and the liquid
gas supply line 113 through the liquid gas supply valve
15 78 into the pressure chamber 66. The liquid gas flows
from the pressure chamber 66 through the grooves 55
made in the outer surface region of the valve body 50,
through the guide tube 40, into the gap between the
valve seat 57 of the feed piston tube 35 and the rear
end face 52 of the valve body and through the passage
space 36 of the feed piston 35 into the blind hole 43
of the plug 26. The liquid gas under pressure flows
from the rear end region of the blind hole 43 through
the bores 88 of the plug 26 and floods the armature
25 space, the regions of the armature space upstream and
downstream of the armature 24 being connected to one
another in a communicating manner by means of the
grooves 32 made in the armature 24, SO that the entire
armature space is filled with liquid gas. The liquid
30 gas is led through a liquid gas return line 92 back
into the liquid gas tank 111 through the bore 90 and
the connecting nipple 91.
Thus, when the feed piston element 44 iS in the initial
35 position, there is, for the liquid gas, a flow path
extending from the liquid gas supply valve 78 via the
pressure space 66, the passage space 36 of the feed
piston 35, the blind hole 43 and the bore 88 in the
plug 26, the armature space 23 and the bore 90 with the
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- 14 -
connecting nipple 91, so that liquid gas is
continuously supplied and scavenged as a result of the
passage, the pressure chamber being supplied and
- flooded directly from the liquid gas tank 111.
The admission pressure of the liquid gas is higher than
the pressure drop occurring in the flow path, so that
continuous scavenging of the alternating piston pump 1
is ensured, and is lower than the passage pressure of
the static pressure valve 74, SO that no liquid gas is
conveyed into the combustion chamber 4 when the feed
piston element 44 iS in the initial position.
When the coil 102 is energized as a result of the
15 application of an electric current, the armature 24 iS
moved forwardly in the thrust or injection direction by
the magnetic field generated thereby. During a
prestroke over the length s (corresponding to the
distance between the valve seat 57 of the feed piston
tube 35 and the rear end face 52 of the valve body 50
in the initial position), the movement of the armature
24 and of the feed piston tube 35 connected
nonpositively to the latter is counteracted only by the
spring force of the spring 38. The spring force of the
25 spring 38 iS designed to be so low that the armature 24
is moved virtually without any resistance, but is
nevertheless sufficient for returning the armature 24
into its initial position. The armature 24 " floats'~ in
a pressure space 23 filled with liquid gas, and the
30 liquid gas can flow back and forth randomly in the
armature space 23 between the regions upstream and
downstream of the armature 24, SO that no pressure
opposing the armature 24 iS built up. The feed piston
element 44, consisting of the armature 24 and the feed
35 piston tube 35, iS therefore accelerated continuously
and stores kinetic energy.
The use of an injection device working on the energy
accumulation principle makes it possible to inject
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- 15 -
liquid gas under high pressure with very short
injection pulses. By means of such an injection device,
it is also possible to inject the liquid gas with a
plurality of injection pulses during one work cycle, in
order, for example under high load, to introduce a
large quantity of liquid gas into the combustion
chamber or in order to bring about charge
stratification, during which liquid gas is enriched in
the region of the spark plug at the ignition timing
point.
Instead of the abovedescribed embodiment of the
alternating piston pump 1 with a return line 92, such a
pump, which can be connected to conventional liquid gas
tanks, may also be used without a return line.
The liquid gas engine according to the invention is
designed as a slider crank engine, preferably in the
manner of an opposed cylinder engine. It consists
essentially of two mutually opposite coaxially arranged
cylinders 5 and 5', in which the working pistons 12
move back and forth rectilinearly. The pistons are
connected in each case to their piston rods 153 which
likewise execute only rectilinear back and forth
movements. The piston rods 153 are articulated at their
inner ends on a centrally located peripheral slider
crank drive 154 which converts the rectilinear
movements of the piston rods into a rotational
movement. The slider crank drive is located in a slider
crank case 155, to which the cylinders 5 and 5' are
fastened via partitions 156. The slider crank drive has
a slider crank frame 152 which encloses a rectilinear
slotted link 158 arranged transversely to the piston
rod 153. A sliding block 159 moves in the slotted link
158, a crank pin 160 of a crankshaft being mounted
rotatably in said sliding block. Slider crank engines
of this type are known, for example, from
DE 29 62 391 A1, DE 32 18 320 A1 and EP 187 930 B1.
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- 16 -
These engines may, in the for~ of a two-stroke engine,
simply be provided with separate lubrication, so that
the lubricant does not enter the combustion chamber.
The combination of direct liquid gas injection with a
slider crank engine operated as a two-stroke engine
gives an engine with a low weight/power ratio and
extremely low pollutant emission.
. .
