Gas delivery system

A gas delivery system for gas fuelled internal combustion engines, comprising a gas fuel delivery means for delivering a controlled amount of gaseous fuel to a region adjacent a source of ignition. The gas fuel delivery means comprises first and second delivery means for delivering gaseous fuel to a pre-combustion zone and a combustion zone respectively. Gas control means control the relative proportions of gaseous fuel delivered by the first and second delivery means respectively so that combustion in the combustion zone can be achieved with minimum gaseous fuel by initiating ignition of gaseous fuel in the pre-combustion zone. Thus, the fuel/air ratio within the combustion zone can be minimized (lean burn regime) without the onset of engine misfire.

FIELD OF THE INVENTION 
This invention relates to a gas delivery system for an internal combustion 
engine and more particularly, but not exclusively, to a spark ignition 
engine which operates on gaseous fuel. In one arrangement this invention 
relates to a spark ignition engine converted from a diesel fuelled or 
compression ignition engine. In another arrangement this invention relates 
to a dual fuel engine operating as a compression ignition engine. In such 
an engine operating in the dual fuel mode, it is common for a gaseous fuel 
to be mixed with the air before induction of the air into the engine 
whilst reducing the amount of diesel injected. In this specification the 
term "compression ignition engine" is intended to refer not only to an 
engine operating on a constant pressure, that is a diesel cycle, but also 
to an engine operating on a compression ignition cycle. 
BACKGROUND TO THE INVENTION 
When operating an engine with a gaseous fuel it is a well known practice to 
introduce the gaseous fuel with the inlet air to the cylinder during the 
air inlet stroke, thus causing a relatively homogenous mixture of gas and 
air during the combustion stroke. It is advantageous to reduce the 
fuel/air ratio to a minimum value in the combustion of gas as a fuel, as 
this reduces the carbon monoxide and hydrocarbon content of the exhaust 
and enhances fuel efficiencies. If the ratio is reduced sufficiently 
beyond the stoichiometric value a substantial reduction in the nitrous 
oxide content of the exhaust gas may also be achieved. This is commonly 
called a lean burn regime. With current gas engines the limiting factor in 
the reduction of the ratio to achieve lean burn is that which occurs when 
the average ratio of fuel to air is lowered to a level where the density 
of the fuel is such as to prevent initiation of fuel ignition, and thus 
the engine misfires. 
SUMMARY OF THE INVENTION 
The present invention was developed with a view to providing a method of 
gas delivery and a gas delivery system for a gas fuelled internal 
combustion engine wherein the fuel/air ratio can be minimised without the 
onset of misfire of the engine. 
According to the present invention there is provided a gas delivery system 
for a gas fuelled internal combustion engine, the system comprising: 
gas fuel delivery means for delivering a controlled amount of gaseous fuel 
to a region adjacent a source of ignition, said region comprising a 
pre-combustion zone located in a separate pre-combustion chamber which is 
located in immediate proximity to said ignition source and which is in 
direct communication through an orifice with a combustion zone located in 
a cylinder of the engine, said gas fuel delivery means comprising first 
and second gas delivery lines for delivering a controlled amount of 
gaseous fuel to said pre-combustion zone and combustion zone respectively 
from a common gas injector, and further comprising gas control means for 
controlling the relative proportions of gaseous fuel delivered by said 
first and second delivery means respectively whereby, in use, combustion 
in said combustion zone can be achieved with minimum gaseous fuel by 
initiating ignition of gaseous fuel in said pre-combustion zone. 
In this specification the pre-combustion zone is that zone within which it 
is desirous to initiate the combustion process, and the combustion zone is 
that region to which the resultant effects of gaseous fuel ignition in the 
pre-combustion zone are directed to achieve combustion of the remaining 
gaseous fuel. 
Advantageously said gas control means comprises a gas flow valve for 
controlling the quantity of gaseous fuel delivered to said pre-combustion 
zone and/or combustion zone. More particularly, said gas flow valve may be 
a one way valve for controlling the quantity of gaseous fuel delivered via 
said first gas delivery line to said pre-combustion chamber. 
Typically the relative proportions of gaseous fuel delivered by said first 
and second delivery means is fixed for a particular engine. The relative 
proportion of gaseous fuel delivered by said first delivery means may be 
in the range of 1 to 10 percent of the total quantity of gaseous fuel 
delivered to said region by said gas fuel delivery means. 
In one embodiment said gas control means is provided with a first input to 
enable the control means to control the supply of gaseous fuel at a 
predetermined rate to the pre-combustion zone and/or the combustion zone 
in accordance with at least one operating parameter. The gas control means 
may be provided with a second input derived from a feedback signal 
indicative of the amount of gaseous fuel injected into the pre-combustion 
and combustion zones, and the control means being adapted to adjust the 
supply of gaseous fuel whilst still responding to that signal by the first 
input. 
In one embodiment the gas fuel delivery means may include continuous flow 
valves and the gas control means controls the proportion of gaseous fuel 
being delivered to the pre-combustion zone and the combustion zone 
respectively, as well as the total quantity of gas being supplied over 
time to the engine as a whole. In another embodiment the gas fuel delivery 
means may include incremental flow valves. 
In relation to the previously mentioned embodiments, said at least one 
operating parameter of the engine may comprise the engine speed, or the 
position of the speed control (that is, the throttle) of the engine, alone 
or in combination with the engine speed. Further examples of said at least 
one operating parameter of the engine may include singularly or in 
conjunction with any one or more of the following parameters: air supply 
temperature; air supply pressure; gas supply temperature; gas supply 
pressure; engine phase; dynamic engine mode determination; and, battery 
voltage. 
In relation to the previously mentioned embodiments, in one embodiment the 
feedback signal is derived from a measurement directly or indirectly of 
the exhaust gas contents of the engine for the presence of carbon 
monoxides, hydrocarbons, nitrous oxides or other such unwanted emissions. 
One such measurement may be derived from a commonly available lambda 
sensor which monitors the oxygen content of the exhaust gas stream. In a 
still further embodiment instead of a measurement of the exhaust gas 
contents a feedback signal is derived from a measurement of the onset of 
misfire in the engine either indirectly or directly. 
Optimal control of the relative proportions and quantity of the flow of 
gaseous fuel to the pre-combustion zone and the combustion zone can thus 
be determined, in conjunction with test bed testing to give good ignition 
with the minimum amount of gaseous fuel. After initial calibration, it is 
not normally necessary to re-calibrate the engine. It will be appreciated 
that as the engine is used, the amount of gaseous fuel fed to the engine 
by the gas delivery system may be varied. By providing a feed-back signal 
as described, it may be assured that the amount of fuel delivered for the 
given operating conditions of the engine is optimised. 
According to another aspect of the present invention there is provided a 
method of delivering gas for a gas fuelled internal combustion engine, the 
method comprising: 
delivering a controlled amount of gaseous fuel to a region adjacent a 
source of ignition, said region comprising a pre-combustion zone and a 
combustion zone in communication with each other; 
controlling the relative proportions of gaseous fuel delivered to said 
pre-combustion zone and combustion zone respectively whereby, in use, 
combustion in said combustion zone can be achieved with minimum gaseous 
fuel by initiating ignition of gaseous fuel in said pre-combustion zone. 
Preferably, the method further comprises delivering a controlled amount of 
air to the combustion zone to maintain a minimum air to fuel ratio in said 
combustion zone, some of the air/fuel mixture in said combustion zone 
being communicated to said pre-combustion zone during initiation of 
ignition of gaseous fuel in said pre-combustion zone. 
Typically the method also includes controlling the total volume of gaseous 
fuel delivered to the engine over time.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The gas delivery system illustrated in FIG. 1 for a gas fuelled-internal 
combustion engine (not shown) comprises gas fuel delivery means 10 for 
delivering a controlled amount of gaseous fuel to a region adjacent a 
source of ignition in the engine. This region in the engine comprises a 
pre-combustion zone 12 and a combustion zone 14 in communication with each 
other. The gas fuel delivery means 10 comprises first and second delivery 
means 16, 18 for delivering gaseous fuel to the pre-combustion zone 12 and 
the combustion zone 14 respectively, and further comprises gas control 
means 20, 22 for controlling the relative proportions of gaseous fuel 
delivered by said first and second delivery means 16, 18 respectively. The 
first and second delivery means 16, 18 deliver gaseous fuel from gas 
supply 24, and may take the form of, for example, gas supply lines. The 
pre-combustion gas control means 20 and combustion gas control means 22 
may take the form of, for example, gaseous fuel injectors. 
In this embodiment, the pre-combustion zone 12 is located in immediate 
proximity to the ignition source 26 which may be, for example, a spark 
plug, to facilitate ignition of gaseous fuel in the pre-combustion zone 
12. The ignition source 26 is under the control of ignition control means 
28. 
Air is delivered to the combustion zone 14 from air supply 30 via air 
delivery means 32 and combustion air control means 34. In this embodiment, 
air is not delivered directly to the pre-combustion zone 12. Combustion 
air control means controls the quantity, temperature and pressure of 
combustion air prior to delivery to the combustion zone 14 via combustion 
air delivery means 36, which is commonly an engine manifold and inlet 
valve system. The products of combustion exit the engine from the 
combustion zone 14 via an exhaust delivery system 38, which commonly takes 
the form of an exhaust valve system and manifold system to an exhaust 
disposal means 40. An exhaust emissions analyser 42 analyses the exhaust 
emissions and generates a signal which is transmitted via signal delivery 
line 44 to an Engine Management System (EMS) 46. 
The EMS 46 provides overall management of the engine operation and both 
monitors and supervises the pre-combustion gas control means 20, ignition 
control means 28, combustion gas control lines 22 and combustion air 
control means 34 via signal delivery lines 48, 50, 52 and 54 respectively. 
The signal delivery means 44, 48, 50, 52 and 54 may take the form of, for 
example, electrical cables, optical fibres or any other suitable signal 
transmission medium. The EMS 46 may also monitor and/or supervise the 
control of other operating parameters of the engine such as engine speed, 
position of the throttle, engine phase, dynamic engine load and battery 
voltage. Each of these operating parameters may have some bearing on the 
ultimate control of the gas delivery system described above, however they 
have been omitted from FIG. 1 for clarity sake. The exhaust emissions 
analyser 42 provides a feedback signal to the EMS 46 and is derived from a 
measurement directly or indirectly of the exhaust gas contents of the 
engine for the presence of carbon monoxides, hydrocarbons, nitrous oxides 
or other undesirable emissions. Such emissions give an indication of the 
extent and degree of combustion of gaseous fuel occurring within the 
engine and may be used by the EMS 46 to adjust the relative proportions of 
gaseous fuel delivered to the pre-combustion zone 12 and/or the combustion 
zone 14, or the total quantity of gas over time being supplied to the 
engine. 
As noted above, combustion air is delivered directly to the combustion zone 
14 only, however, during a compression stroke of the engine some air is 
communicated from the combustion zone 14 to the pre-combustion zone 12 via 
pre-combustion air supply path 56. In practice, pre-combustion zone 12 may 
be located in a separate pre-combustion chamber which is in direct 
communication through an orifice with a cylinder of the engine, the 
combustion zone 14 being located in the cylinder above the piston. 
According to the present invention, during operation of the engine, the 
ignition source 26 is employed to initiate ignition of gaseous fuel in the 
pre-combustion zone 12 where a relatively rich fuel to air ratio is 
present. Indeed, the ratio of fuel to air in the pre-combustion zone is 
selected so that ignition of the gaseous fuel is a certainty. The path of 
the resultant gases from the ignition of gaseous fuel in pre-combustion 
zone 12 to the combustion zone 14 is shown as 58, and in practice would be 
through the same orifice between the pre-combustion chamber and the engine 
cylinder. The volume of the pre-combustion zone 12 is designed to provide 
enough chemical reaction via the path 58 of the resultant gases from the 
pre-combustion zone 12 to the combustion zone 14, to cause ignition of the 
gaseous fuel and air present in the combustion zone 14, which has a lean 
fuel to air ratio. Thus, combustion in the combustion zone 14 can be 
achieved with minimum gaseous fuel by initiating ignition of the gaseous 
fuel in the pre-combustion zone 12 in the manner described above. 
In FIG. 2 a second embodiment of the gas delivery system according to the 
invention is illustrated schematically, and comprises gas fuel delivery 
means 60 for delivering a controlled amount of gaseous fuel to a region 
adjacent a source 62 of ignition, for example, a spark plug in the engine. 
In FIG. 2 only one cylinder 64 of the engine is illustrated showing a 
piston 66 near the top of its compression stroke. The region adjacent the 
ignition source 62 comprises a pre-combustion zone 68 located within a 
pre-combustion chamber 70 and a combustion zone 72 located within the 
cylinder 64 above the piston 66. The pre-combustion chamber 70 is in 
direct communication through an orifice 74 with the cylinder 64. The gas 
fuel delivery means 60 comprises first and second gas delivery lines 76, 
78 for delivering gaseous fuel to the pre-combustion zone 68 and 
combustion zone 72 respectively. The gas delivery lines 76, 78 are 
supplied with gaseous fuel from a single solenoid actuated gas injector 
80. 
The gas fuel delivery means 60 further comprises gas control means in the 
form of a gas flow valve 52 for controlling the relative proportions of 
gaseous fuel delivered by the first and second delivery lines 76, 78 
respectively. In this embodiment, the gas flow valve 82 is a non-return or 
one way valve which opens when the pressure within the pre-combustion 
chamber 70 is lower than the pressure within the gas delivery line 76, but 
which closes when the pressure within the pre-combustion chamber 70 
exceeds the pressure within the gas delivery line 76. Hence, during a 
downward stroke of piston 66 one way valve 82 allows the flow of gaseous 
fuel from the delivery line 76 into the pre-combustion chamber 70, however 
during a compression stroke of the piston 66 the one way valve 82 closes 
to cue off the flow of gaseous fuel into the pre-combustion chamber 70. 
One way valve 82 also isolates the gas delivery line 76 from the gases 
produced as a result of combustion in the pre-combustion zone 68 and 
combustion zone 72. 
The relative proportions of gaseous fuel delivered to the pre-combustion 
zone 68 and the combustion zone 72 is largely controlled by the size of an 
aperture provided within the one way valve 82 in its open condition. 
Typically, the size of the aperture in one way valve 82 is selected so 
that between 1 percent to 10 percent of the gaseous fuel supplied from the 
gas injector 80 passes through the gas delivery line 76 to the 
pre-combustion zone 68, and the remainder of the gaseous fuel is delivered 
by gas delivery line 78 to the combustion zone 72 within cylinder 64. 
Typically, the gas delivery line 78 delivers gas to the combustion zone 72 
via the engine manifold and inlet valve system. In this embodiment, the 
one way valve 82 is selected so that 4 percent of the gaseous fuel from 
the common injector 80 is delivered to the pre-combustion zone 68, however 
the exact relative proportions of gaseous fuel delivered to the 
pre-combustion zone 68 and combustion zone 72 respectively will depend on 
the operating characteristics of the particular engine. From the above 
description, it will be apparent that the relative proportions of gaseous 
fuel delivered by the first and second gas delivery lines 76, 78 is fixed 
for this particular engine, as determined by the size of the aperture 
within one way valve 82. However, it is possible to arrange the gas fuel 
delivery means 60 so that the relative proportions of gaseous fuel 
delivered by the first and second gas delivery lines 76, 78 can be varied, 
by for example, supplying gaseous fuel to the delivery lines 76, 78 from 
separate gas injectors. The amount of gaseous fuel delivered by the gas 
injectors to the respective delivery lines 76, 78 could then be varied, 
for example, under the control of an engine management system. 
The relative proportions of gaseous fuel delivered to the pre-combustion 
chamber and the cylinder for a particular engine can be determined as 
follows. The objective is to achieve a gas/air ratio in the pre-combustion 
chamber (PCC) which will ignite easily from a spark plug. In one 
embodiment, natural gas is used as the gaseous fuel. Natural gas is 
composed mainly of methane and has a stoichiometric gas/air ratio of 0.095 
(9.5%). Ignition can still be achieved within the range of approximately 
6.0 to 15.0% with a PCC, however most reliable ignition is achieved at 
near stoichiometric conditions. 
There are many variables which contribute to the overall determination of 
the desired quantity of gas that should be diverted to the PCC. To 
facilitate the determination, certain variables were fixed and the 
resultant relationship of gas/air ratio in the PCC as a function of spark 
advance angle, and total gas quantity injected as a volume percentage of 
the total cylinder volume was calculated. The compression ratio is fixed 
at a value determined by the mechanical and thermodynamic considerations 
that apply to the particular engine, due to its desired output and gas 
quality. A low PCC/MCC is desirable to reduce the local thermal losses of 
the PCC, however the variability of the gas flow control at the PCC will 
dictate a practical limit. The level of gas/cylinder volume is dictated by 
the designed maximum absolute boost pressure, compression ratio and engine 
output requirements. 
The following definitions and formula apply: 
PCVFRN=Pre-chamber volume fraction-fraction of clearance volume occupied by 
PCC. 
PCGFRN=Pre-chamber gas fraction-fraction of gas injected into the PCC. 
CR=Compression ratio. =Clearance vol+swept vol (100) Clearance vol 
CV=Clearance volume =Swept vol (100) Compression ratio--1 
GV=Gas volume injected by one injector 
PCGV=Pre-chamber gas volume injected =GV.times.PCGFRN 
PCV=Pre-chamber volume =CV.times.PCVFRN 
MCGV=Main Chamber (or cylinder) gas volume =GV-PCGV 
MCAV=Main chamber air volume =100-MCGV 
MCGR=Main chamber gas ratio =MCGV/MCAV 
THETA=Spark advance angle (0-1.57 Radians) 
##EQU1## 
A number of iterations can be performed by varying the PCC/MCC gas ratio 
until near stoichiometric conditions are achieved for the complete range 
of envisaged spark advance settings. In one embodiment this process 
indicated that a PCGFRN of 0.04 (4%) achieved near stoichiometric 
conditions over a range of spark advance settings (THETA) of 0.0 to 0.5236 
radians. PCVFRN was set at 0.08, CR at 12.5 and CV of 8.6956512 (cylinder 
of volume size 100 units). 
The operation of the gas delivery system illustrated in FIG. 2 is similar 
to that of the system illustrated in FIG. 1. During the air inlet stroke 
of piston 66 a mixture of gaseous fuel and air are delivered to the 
combustion zone 72, while simultaneously gaseous fuel only is delivered to 
the pre-combustion zone 68 via one way valve 82. During a compression 
stroke of the piston 66 some of the air fuel mixture within combustion 
zone 72 communicates into pre-combustion chamber 70 via orifice 74, and 
ignition of gaseous fuel is initiated within the pre-combustion zone 68 by 
ignition source 62. By this stage, one way valve 82 has closed. Due to the 
relatively rich fuel to air ratio within pre-combustion zone 68 ignition 
can be readily achieved and a chemical reaction occurs via the path of the 
resultant gases through orifice 74 from the pre-combustion zone 68 to the 
combustion zone 126 to produce ignition of the lean gaseous fuel/air 
mixture in the combustion zone 72. Hence, the gas fuelled internal 
combustion engine can be operated within a lean burn regime without fear 
of engine misfire. 
In FIG. 3 the cylinder head 84 of a compression ignition engine is 
illustrated in section view. The compression ignition engine of FIG. 3 has 
been converted to a gas fuelled, spark ignition engine, and incorporates 
an embodiment of a gas delivery system according to the invention, which 
is similar to that of FIG. 2. A casing 86 is fixed within a bore 88 
provided in the cylinder head 84, so that cooling water 89 circulating 
within the cylinder head also cools the casing 86. Casing 86 defines a 
pre-combustion chamber 90 therein, and is manufactured from a material 
having a high thermal conductivity so that some of the heat generated 
within the pre-combustion chamber 90 is conducted through the walls of the 
casing 86 to the cooling water 89. The pre-combustion chamber 90 defines a 
pre-combustion zone 92 therein, and is in direct communication with a 
cylinder 94 of the engine, within which a combustion zone 96 is located. 
Casing 86 also houses therein an ignition source 98 (spark plug), and a one 
way valve 100. Gaseous fuel is delivered to the one way valve 100 via a 
gas delivery line 102, similar to that of FIG. 2. 
The operation of the gas delivery system of FIG. 3 is similar to that of 
FIG. 2, and will not be described again in detail here. The one way valve 
100 controls the relative proportions of gaseous fuel delivered to the 
pre-combustion zone 92 and combustion zone 96, via respective gas delivery 
lines and a common gas injector (not illustrated). The combustion process 
is initiated by spark plug 98 within the pre-combustion zone 92, and the 
resultant effects of gaseous fuel ignition in the pre-combustion zone 92 
are directed via orifice 93 to the combustion zone 96 to achieve 
combustion of the remaining gaseous-fuel. 
Obviously, the arrangement of the pre-combustion chamber 90 within the 
cylinder head 84 of the engine may vary considerably from that illustrated 
in FIG. 3 depending on the type of engine, particularly where the 
pre-combustion chamber is incorporated within the cylinder head at the 
time of manufacture of the engine, rather than as a result of a conversion 
of a compression ignition engine to a spark ignition gas fuelled or dual 
fuel engine. In a dual fuel engine, the gas delivery system according to 
the invention can also be used to deliver pilot fuel to the engine. 
It will be apparent from the above description that the gas delivery system 
according to the invention has significant advantages over prior art 
systems which rely on a gas carburettor to supply the appropriate air/fuel 
mixture to the engine. The relative proportions of gaseous fuel delivered 
to the pre-combustion zone and the combustion zone can be accurately 
controlled so that combustion in the combustion zone can be achieved with 
minimum gaseous fuel without fear of engine misfire. Combustion in the 
pre-combustion zone produces a flame front and radical molecules which 
will easily and quickly ignite the relatively lean mixture in the 
combustion zone, thus resulting in high engine efficiencies, i.e., more 
combustion close to piston top dead centre (TDC) and lower losses due to 
dissociation and thermal considerations, which both increase rapidly as 
the peak cycle temperature increases. Furthermore, emissions of carbon 
monoxide, hydrocarbons and nitrous oxides can be lowered due to the 
overall lean combustion process. The simplicity and elegance of the gas 
delivery system according to the invention enables it to be readily 
incorporated in a conventional engine and/or a conventional engine can be 
easily converted to a gas fuelled engine. 
Furthermore, now that preferred embodiments of the gas delivery system have 
been described in detail, it will be obvious to persons skilled in the 
mechanical arts, that numerous modifications and variations may be made to 
the illustrated embodiments, in addition to those already described, 
without departing from the basic inventive concepts. For example, the 
relative proportions of gaseous fuel delivered to the pre-combustion zone 
and the combustion zone respectively, may be determined by the relative 
diameters of the respective gas delivery lines. All such variations and 
modifications are to be considered within the scope of the present 
invention, the nature of which is to be determined from the foregoing 
description and the appended claims.