Method of and an arrangement for burning a liquid or gaseous fuel in a combustion chamber of an internal combustion engine

A method of and an arrangement for burning a liquid or gaseous fuel in a combustion chamber of an internal combustion engine. A method of and an arrangement for burning a liquid or gaseous fuel in the presence of air or another oxidant and by the use of water in a combustion chamber (12) of an internal combustion engine, especially a reciprocating or rotary piston-type engine. To reduce the fuel consumption and the emission of harmful substances and to increase the efficiency when low-octane fuels, especially regular gasoline or acetylene, are used, water is injected during one or several selected phases, in particular during the entire operation, in an operation-dependent quantity direct into the combustion chamber (12) in such a way that a progressive "primary combustion" of fuel/air just below the critical "knock" temperature (T.sub.c) occurs which initiates a "secondary combustion" of the admixed water at any point of combustion. The "secondary combustion" causes overall smooth progressive combustion within the combustion chamber (12).

The invention relates to a method of and an arrangement for burning a 
liquid or gaseous fuel in the presence of air or another oxidant and by 
the use of water in a combustion chamber of an internal combustion engine, 
especially a reciprocating or rotary piston engine. 
Conventional internal combustion engines, especially spark ignition-type 
piston engines such as used in motor vehicles and stationary plants 
exhibit a maximum thermal efficiency of about 30%; therefore the ratio of 
the energy value of the fuel supplied to the combustion chamber and the 
finally available energy is only about 30%. Turbines, rotary piston 
engines or the like exhibit a similarly low efficiency. 
It is generally known to increase the efficiency of internal combustion 
engines of the specified kind by introducing water or other non-fuels into 
the combustion chamber, and the following three different ways of adding 
water are considered advantageous: 
(1) direct injection of water into the combustion chamber (for example 
DE-A-3,432,787 or U.S. Pat. No. 4,408,573); 
(2) introduction of steam or high-humidity air into the intake passage 
upstream of the combustion chamber (for example U.S. Pat. No. 4,479,907 or 
DE-A-2,602,287); and 
(3) forming of a fuel-in-water emulsion and introducing it into the 
combustion chamber (for example DE-A-3,236,233 or U.S. Pat. No. 
4,412,512). 
All of these known systems operate in response to one or several operating 
parameters, usually in response to the engine speed (for example U.S. Pat. 
No. 4,191,134), the vacuum in the intake passage (for example U.S. Pat. 
No. 4,240,380), a knock sensor (for example U.S. Pat. No. 4,406,255), the 
exhaust gas pressure (for example U.S. Pat. No. 4,191,134) and/or the 
temperature in the intake passage (EP-A-0,009,779). All of these systems 
result in a greater or lesser improvement of the efficiency with a 
simultaneous reduction in the emission of ecologically harmful exhaust 
gases, mainly a reduction of CO and NO.sub.x. The improvement in 
efficiency of the known designs should be somewhere from about 10 to 15%, 
which is quite remarkable. Also, the fuel consumption can be reduced by as 
much as 50% (U.S. Pat. No. 4,479,907). 
For further increasing the efficiency and reducing the fuel consumption it 
has already been proposed, among other things, to inject water direct into 
the combustion chamber in the region of the compressed air-fuel mixture 
ahead of the flame front during combustion, i.e. after ignition of the 
air-fuel mixture but prior to self-ignition of the final gas (see 
DE-A-3,133,939). This is intended to keep the temperature in the 
combustion chamber reliably below the "uncontrolled" or critical 
detonation or "knock" temperature at higher compression ratios of up to 
18.7:1. 
Proceeding from the above-mentioned diverse prior art the inventors have 
set themselves the task of providing a method and an arrangement of the 
above-specified kind which, while the efficiency is still further improved 
and fuel savings of up to approximately 60 to 65% and a significant 
reduction of harmful substances are achieved, would permit extremely 
smooth combustion even at very low engine speeds, especially when using 
low-octane fuel such as regular gasoline or fuel of octane number "0" such 
as acetylene or the like. 
As regards the method, the specified object is solved by the characterizing 
measures according to claim 1 and especially the subsequent method claims, 
and as regards the arrangement, the object is solved by the characterizing 
features according to claim 13 and especially the subsequent apparatus 
claims. 
The gist of the present invention resides in the preparation and 
introduction of the air-fuel mixture into a combustion chamber while 
compressing and igniting the same and the introduction of water direct 
into the combustion chamber such that an "initial or primary combustion" 
of the air-fuel mixture occurs at a temperature just below the 
uncontrolled or critical (knock) temperature T.sub.c (knock limit), such 
combustion initiating the correspondingly progressing "secondary 
combustion" of the admixed water. The "primary cycle" and the "secondary 
cycle" take place at any point of combustion, i.e. at any point of the 
flame front, which is in contrast to the solution according to 
DE-A-3,133,939. In contrast to the system known from said publication, the 
invention aims at a "primary combustion" near the uncontrolled or critical 
temperature in the combustion chamber and this is controlled by 
corresponding admixing of water. So far, those skilled in the art have 
endeavoured to effect combustion at a temperature which is as far as 
possible from the critical temperature in the combustion chamber, so that 
in this way knocking of the internal combustion engine could be reliably 
prevented. For this reason high-octane fuels are used in high compression 
engines for motor vehicles, although such fuels are required only in 
critical load ranges while otherwise the engines can also be operated with 
regular gasoline. But the use of high-octane fuel (premium gasoline) 
results in a sufficient antiknock effect at almost any operating 
condition. In accordance with the invention, however, combustion shall 
take place just below the knock limit, wherein the peak temperature in the 
combustion chamber is maintained just below the uncontrolled or critical 
temperature at any operating condition by the controlled admixture of 
water. Therefore a temperature in the combustion chamber is selected which 
is about 1 to 5% below the critical temperature. This depends on the fuel 
used as well as on the critical compression ratio or the critical 
pressure. It has been found that by applying the system according to the 
invention (method and arrangement) it is possible to run the internal 
combustion engine at any operating state just below the knock limit, 
wherein "actual" compression ratios .rho. (fuel/air) of up to 25:1 are 
achieved. 
Surprisingly, it is possible by applying the method and arrangement 
according to the invention to burn highly explosive gases such as 
acetylene without any difficulty in an internal combustion engine having a 
quasi-closed combustion chamber, as will be explained below with reference 
to an embodiment to be explained in detail and using a 1200 cm.sup.3 
Austin automotive engine. 
By applying the method and the arrangement according to the invention it is 
possible to improve the efficiency by up to 70% as compared with 
conventional internal combustion engines of the specified kind. Fuel 
consumption may be reduced by as much as 65%. Also, the emission of CO and 
NO.sub.x is minimized. Above all, the internal combustion engine is suited 
for burning unleaded gasoline. But it should be emphasized again that the 
specified values can be obtained only when the "primary combustion" takes 
place just below the detonation temperature. The "secondary cycle" 
initiated thereby at any point of combustion continues the "primary cycle" 
such that on the whole a progressive "smooth" combustion is achieved. The 
"secondary cycle", as it were, dampens the "initial or primary combustion" 
which takes place just below the knock limit. 
In order to achieve the desired "two-phase" combustion according to the 
invention it is essential that the fuel, air or any other oxidant and 
water are homogenized to a maximum extent in the combustion chamber. Then 
it will be ensured that combustion takes place in the specified way at any 
point of combustion. Preferably, to this end the water is injected into 
the combustion chamber at a correspondingly high pressure in finely 
sprayed and widely distributed form, the injected quantity being 
controlled in response to the "primary combustion" temperature. 
Especially, the supply of water is effected in response to the temperature 
prevailing in the combustion chamber such that combustion starts at a 
temperature which is about 1 to 5% below the critical temperature T.sub.c. 
Desirably, the "primary combustion" takes place under any operating 
conditions just below the critical temperature, if possible approximately 
1 to 2% below the critical temperature. The injection of water is metered 
accordingly. 
Provision is made for an additional (indirect) introduction of water 
controlled by the negative pressure in the intake passage, such 
introduction of water being superposed on the already explained 
introduction of water. Such introduction of water caused by negative 
pressure in the intake passage takes place especially when the "primary 
combustion" temperature rapidly approaches the critical temperature 
T.sub.c or when, irrespective of direct injection of water, the combustion 
temperature reaches a level which is less than 1% below the critical 
temperature. The indirect introduction of water may also be continually 
operative so that also during non-critical operating periods the "primary 
combustion" can be brought close to the critical temperature. 
Surprisingly, it has been found that by the method according to the 
invention it is also possible to burn highly explosive acetylene (C.sub.2 
H.sub.2) without any risk and with extremely low consumption. In a test 
run with a 1200 cm.sup.3 Austin engine the following values of consumption 
were recorded: 
running time: 10 minutes 
rotational speed: 3000 r.p.m. 
consumption of H.sub.2 C.sub.2 : 0.30 kg. 
consumption of H.sub.2 O: 3.0 kg. 
The ratio of water to acetylene in this test run was therefore 10:1. The 
emission of harmful substances was also minimum during this test. In the 
combustion chamber a temperature just below the critical temperature was 
maintained for the primary combustion of fuel (acetylene) and air. In this 
test the output of the water injection pump was constant during the 
injection phase. Of course, it is also conceivable to make the output of 
the water injection pump variable in response to the temperature detected 
in the combustion chamber. The closer the temperature in the combustion 
chamber approaches the critical temperature, the higher the output of the 
water injection pump should be; alternatively, the additional indirect 
introduction of water is started. 
Furthermore, the external cooling of the combustion chamber is rather 
important. To this end a further temperature sensor (thermocouple) is 
provided on the water jacket surrounding the combustion chamber and is 
coupled to the control unit for the cooling water pump. For an exact 
detection of the "primary combustion" temperature a temperature sensor is 
preferably also provided in the piston bottom, such sensor being protected 
by a ceramic layer from excessive heat and pressure. It would also be 
conceivable to provide a temperature sensor for the intake and/or exhaust 
valve for coupling to the water pump. 
The method according to the invention permits combustion to be carried out 
with an "actual" compression ratio of up to 25:1, said "actual" 
compression ratio being determined by the volume taken up by fuel and 
oxidant (air) alone. Such high "actual" compression ratios are not 
possible with conventional internal combustion engines. 
The water admixed with the air-fuel mixture can in part be recovered from 
the exhaust gases by means of per se known evaporation and condensation 
methods (see for example DE-C-3,102,088 or U.S. Pat. No. 4,279,223). 
Of course, when the system according to the invention is used the other 
engine parameters must be adapted accordingly; it has been found in 
particular that the ignition timing must be shifted closer to the upper 
dead centre with simultaneous earlier opening and much later closing of 
the intake valve before the upper dead centre and after the lower dead 
centre respectively. Thus the "overlap" is increased in order to achieve 
good filling and flushing of the combustion chamber. 
Apart from the temperature sensors mentioned above it is also possible to 
provide so-called detonation or knock sensors and/or pressure sensors for 
sensing the pressure in the combustion chamber to control the injection of 
pressurized water and/or the external coolant pump. The use of knock 
sensors is known per se; in practical use it has proven insufficiently 
accurate and not specific to combustion. Above all, it is impossible by 
means of knock sensors to control the initial combustion close to the 
knock limit, because usually the knock limit has already been reached or 
exceeded when the knock sensors respond. 
Further details relating to the method and the design are described in the 
subclaims. 
Below, the invention will be described by way of an embodiment of an 
internal combustion engine for the combustion of acetylene and the 
combustion of regular gasoline with reference to the accompanying drawing.

DETAILED DESCRIPTION OF THE DETAILED EMBODIMENT 
Acetylene is used as fuel. 30 indicates a cylinder head including an inlet 
conduit 31, an inlet opening 32 and an inlet valve 33. An intake passage 
11 comprising an intake manifold 26 is connected to the inlet conduit 31, 
the free cross-section of said intake passage being variable by means of a 
throttle valve 21. 28 indicates the cylinder chamber in which a piston 29 
reciprocates up and down in conventional manner and is connected via a 
connecting rod 35 to a crank shaft (not illustrated). The cylinder chamber 
28 is surrounded by a cooling water jacket 36. Water is supplied to the 
cooling water jacket 36 from a cooling water pump 10'. The exhaust valve 
also mounted in the cylinder head is not visible in the FIGURE because it 
is disposed at the rear of the inlet valve 33. A spark plug 37 is also 
mounted in the cylinder head between inlet and exhaust valves. Up to this 
point the conventional design of a four-stroke internal combustion engine 
is concerned. 
The uniqueness of the illustrated embodiment of an internal combustion 
engine resides in the use of acetylene as fuel, on the one hand, and in 
the possible admixture of water to the air-fuel mixture in the intake 
passage 11 prior to introduction into the combustion chamber 12, on the 
other hand, and in the direct injection of water via a water injection 
nozzle 14 and a water conduit 3 associated therewith. The combustion 
chamber 12 is defined conventionally by the cylinder head wall on the one 
hand and the bottom of the piston on the other hand. Upstream of the 
throttle valve 21 a kind of mixing chamber 22 is formed in the intake 
passage 11, said mixing chamber being defined on the engine side by a 
constriction or venturi 23. A fuel jet 15' and a water jet 13 open into 
said mixing chamber 22. At the upper end of the mixing chamber 22 remote 
from the engine an air cleaner 2 is mounted through which combustion air 
37 may flow into the mixing chamber 22 past the jets 13 and 15'. In the 
illustrated embodiment, the water conduit 4 and the fuel conduit 5 leading 
to the jets 13 and 15' pass laterally through the air cleaner 2. By the 
way, the air cleaner is a commercially available air cleaner for internal 
combustion engines. 
Another fuel conduit 6 opens into the intake manifold 27 and defines a 
tangentially extending fuel inlet 26. This permits additional direct fuel 
supply to the inlet conduit 31, whereby the initial ignition or primary 
combustion of acetylene in the combustion chamber 12 is promoted which 
then initiates smooth secondary combustion of the admixed water, as 
explained above. 
The supply of fuel, viz. acetylene, through the two fuel conduits 5 and 6 
takes place by means of a pressure regulator 1 which is supplied from a 
feed pipe 7. The feed pipe 7 is in communication with an acetylene tank, 
in which the acetylene to be burned is contained in liquid state. Also, 
the pressure regulator 1 comprises a heat exchanger which is in 
communication with the coolant circuit. Through a hot water supply pipe 8 
hot cooling water is supplied to the heat exchanger, in which heat is then 
transferred to the acetylene to be burned. The cooling water cooled 
thereby is returned to the cooling system via a discharge pipe 9. Heating 
of the initially liquid acetylene is necessary to compensate for the 
temperature drop occurring upon expansion and evaporation of the acetylene 
in the mixing chamber and to prevent icing in this region. The same 
applies to the region of the fuel inlet 26. 
Each of the water conduits 3 and 4 is in communication with a water 
reservoir (not illustrated), the water conduit 3 including a water pump 
10' by means of which water under pressure can be injected direct into the 
combustion chamber 12. Water supply by way of the water conduit 4 and the 
water jet 13 associated therewith takes place solely in response to the 
negative pressure prevailing in the intake passage 11 or the mixing 
chamber 22, respectively, said negative pressure being controlled by the 
throttle valve 21. Water supply through the jet 13 is dependent on the 
load in the illustrated example. But it may also be controlled by 
temperature and/or in response to the temperature variation. In that case 
the conduit 4 has an on-off valve (not illustrated) associated therewith 
which is controlled (opening, closing, degree of opening) in response to 
the primary combustion temperature. Water supply by way of the conduit 3 
or water jet 14 into the combustion chamber 12 is in any case temperature 
controlled such that, when a predetermined temperature just below the 
critical temperature T.sub.c (knock temperature) in the combustion chamber 
12 has been exceeded, the pump 10 is activated. Preferably, the pump 10 is 
activated at a temperature which is approximately from 1 to 5% below the 
critical (knock) temperature. Two thermocouples 17 and 18 for sensing the 
temperature are provided in the combustion chamber 12 and connected via 
electrical leads 38, 39 to the control unit of the pump 10. Moreover, a 
thermocouple 20 is provided for the cooling water jacket 36, and the 
signals from said thermocouple can likewise be coupled to the control unit 
of the pump 10. However, the thermocouple 20 is chiefly used for 
controlling the external cooling water pump 10'. The cooling water is 
circulated by the cooling water pump 10' more or less intensively in 
response to the thermocouple 20, whereby overheating of the engine is to 
be prevented. This is important in the present case because primary 
combustion just below the knock limit is desired and controlled. The 
output from the pump 10 may be variable in response to the temperature in 
the combustion chamber 12 as detected by the thermocouples 17 and 18. 
Preferably, one thermocouple 17 is mounted near the inlet opening 32 while 
the second thermocouple 18 is disposed intermediate the inlet opening 32 
and the spark plug 37. By comparison of the temperatures sensed by the 
thus positioned thermocouples, the primary combustion temperature can be 
determined with high accuracy and can be brought close to the critical 
(knock) temperature T.sub.c by way of appropriate control of the fuel and 
water injection. 
As explained above, a homogeneous distribution of fuel to be ignited, 
water, and intake air in the combustion chamber 12 is very important for 
the desired dual-cycle combustion. To this end water is injected into the 
combustion chamber 12 through a kind of spray diffuser disposed close to 
the spark plug 27, i.e. at the point of origin of the primary combustion. 
The admixture of water in the intake region of the engine preferably takes 
place in opposition to the fuel supply and the intake air. The fuel outlet 
is disposed in the mixing chamber 22 somewhat below the downwardly 
directed water jet 13. Due to this configuration in the mixing chamber 22 
of the intake passage 11 an intimate mixing of fuel, air and water is 
achieved. To increase such mixing, the injected water is atomized as it 
exits. To this end the water jet 13 respectively includes a nozzle having 
fine bores through which the water may exit. Preferably, the bores are 
downwardly inclined in the direction of flow. Additionally, they may be 
inclined relative to the radial line so that an additional rotary movement 
about the longitudinal axes of the water jet 13 or the nozzle is impressed 
on the exiting water droplets. The rotary movement impressed on the water 
droplets may be of the same or opposite direction. 
Also, measures may be provided by which the fuel exiting from the fuel jet 
15' is spread out to form a fuel cone. This also contributes to the fine 
distribution and intimate mixing of the mentioned components. 
Within the mixing chamber 22 turbulators may also be provided which are 
configured as noses or baffle plates that project into the mixing chamber 
22. In this way the components to be mixed seemingly dwell in the mixing 
chamber 22 before exiting therefrom through the venturi 23 towards the 
inlet conduit 31. 
An engine driven in accordance with the invention runs extremely smoothly 
down to a speed of about 200 r.p.m. with minimum emission of harmful 
substances. The exhaust gas temperature is comparatively low. The ratio of 
water to fuel consumption is about 2:1 and higher. Among other things this 
also depends on the other design parameters of the engine employed. 
Internal combustion engines fed with acetylene are especially suited for 
stationary use (emergency power units and small power plants). Acetylene 
is readily available; it may be released, for instance, from calcium 
carbide. Also, the use of acetylene as fuel has been known per se for 
quite a long time, for instance in the carbide lamp as it is called, where 
the acetylene burns with atmospheric oxygen to form carbon monoxide or 
carbon dioxide. Nowadays, acetylene is mainly used for polymerization, 
whereby polyvinyl chloride (PVC) is formed. Up to now, however, no 
apparatus or methods have been proposed in the prior art by means of which 
the high energy content of acetylene is utilized for operating an internal 
combustion engine, and that mainly for knock-free operation of such an 
engine. The prior art does not contain any concrete data concerning the 
functionally safe running of an internal combustion engine, especially of 
a conventional automotive engine, by the use of acetylene. And yet 
acetylene offers the advantage that the starting materials for its 
production are sufficiently available almost everywhere without any 
exclusive limitation to a particularly defined geographical or political 
area. 
Thus, there is an abundance of the starting materials lime, coal, water and 
salt. Lime, for instance, may be recovered from limestone in limestone 
quarries or limestone mountains as a very substantial component of the 
earth crust, from chalk or from the seas or inland waters. There is 
likewise a sufficiency of coal and coke for the mentioned purpose. Also, 
there are practically unlimited quantities of water and salt. The 
preparation of acetylene no longer requires any special development, 
because acetylene is already being produced at a large scale for other 
purposes, for instance for welding and cutting processes or, as explained, 
as an important base for plastic materials or synthetic rubber, and also 
for the large-scale production of fertilizers and pesticides. It is a 
further advantage that the combustion of acetylene in the presence of air 
takes place without any soot being formed. Thus, the system according to 
the invention presents itself as being extraordinarily harmless to the 
environment. It is surprising that the explosion limit is headed for 
irrespective of the high explosiveness of acetylene. In this respect the 
invention follows an apparently devious path which, however, has been 
proven by tests to exhibit extreme functional safety and thus to be 
without any risk. 
The tests have shown that the ratio of water consumption to acetylene 
consumption is between about 2:1 and up to 7:1. The efficiency of the 
engine could be increased by up to 70%. The emission of harmful substances 
was minimum. The exhaust gases contained only negligible quantities of CO, 
and the same applies to nitrogen oxides NO.sub.x. 
Furthermore it has been shown that the operating characteristics 
(performance, torque and consumption) corresponded to those of 
conventional internal combustion engines. 
Tests with gasoline supply have shown that on an average the ratio of water 
to gasoline (regular gasoline) to air is as follows: 0.5:1:20. 
The water introduced into the combustion chamber and/or intake passage is 
at room temperature; preferably it is preheated to a temperature of about 
65.degree. C. This may be done by way of heat exchange with the cooling 
water system or by way of admixture of water recovered from the exhaust 
gas. 
In contrast to the principles which have been universally realized up to 
now, the invention claims protection for the concept of carrying out a 
"VAPOUR CYCLE PRODUCED IN THE INTERIOR OF THE COMBUSTION CHAMBER OF AN 
ENDOTHERMIC ENGINE". 
A thermodynamic cycle in which THE QUANTITY OF THE AVAILABLE (generated) 
VAPOUR, which is called secondary fluid, has a mass which is comparable to 
that of the combustion air required for combustion of the active charge, 
which is called primary fluid. 
A thermodynamic cycle in which actually there are TWO ACTIVE FLUIDS present 
at one and the same reaction time: VAPOUR (which is generated by 
evaporation of the additional water) and COMBUSTION GASES (which are 
produced by combustion of the primary fluid), these being available in 
percentages of the same order of magnitude. 
The injection systems and techniques known so far provide for the injection 
of water masses in very small quantities (a few percent of the mass of the 
air) and yield efficiencies which are slightly above the conventional 
ones. These efficiency values are in no way directly linked to the 
percentage quantity of injected water. 
IN SHARP CONTRAST to that which is known so far, the thermodynamic cycle 
presently proposed can only be performed when SPECIAL THERMOPHYSICAL 
CONDITIONS of temperature, pressure and volume of the charge injected and 
compressed (prepared upstream of the intake valve or the throttle valve of 
the carburetor) are created in the combustion chamber of the endothermic 
engine, so that controlled explosion is achieved and produced in which the 
mass doses of the injected water maintain the reaction at equilibrium, the 
inherent enthalpy content rising immensely by utilizing the energy 
(released in the intentional explosion operation) which otherwise would 
NOT BE USEFUL (or would be irrecoverably lost if there were no exchange 
with the water injected into the charge and homigenized). Hence, the doses 
of water ARE THE HIGHER THE GREATER, MORE VIGOROUS AND MORE BLAZING THE 
EXPLOSION of the air-fuel mixture is. In the final analysis, apart from 
products from the operating cycle of the engine (primary fluid of the 
engine) there are available immense amounts of superheated steam or vapour 
having a very high energy content. 
The part played by the injected water is therefore not the part known up to 
now, viz. the prevention of temperature peaks due to abnormal combustion. 
Rather, and this is in contrast to all of the known and so far accepted 
rules pertaining to engine design, IT IS THE TASK OF THE WATER EMULSIFIED 
IN THE CHARGE TO TAKE T IN THE EXPLOSIVE REACTION (WHICH IS IGNITED IN 
A SUITABLE MANNER) by taking up very large quantities of (otherwise 
useless) energy, increasing its enthalpy content and successively 
releasing the same during the expansion period. 
It follows from the above, for instance, that in a turbine installation it 
is possible to produce thermodynamic cycles of extremely high efficiency 
by combustion processes in the interior of the burner so that considerable 
quantities of superheated steam are obtained which are comparable with the 
air used as oxygen carrier. Subsequently, the steam expands in the 
turbine. By proceeding in the described manner one obtains values of 
global efficiency which are decisively higher than in conventional gas 
turbine units. 
Hence, steam or vapour having a very high enthalpy content can be produced 
beyond the combustion of gases, while at the same time there is a drastic 
reduction in the losses occurring in the various conventional apparatus 
which are typical and necessary for energy producing plants (heaters, 
burners, superheaters, heat exchangers, condensers, etc.). 
All of the features disclosed in the present documents are claimed as 
essential to the invention to the extent that they are novel over the 
prior art either individually or in combination.