Method and device for preparing a fuel, particularly for diesel engines, by on-line mixture of its components

A C.F.R. engine (26) is alternately supplied with a fuel being manufactured (22), sampled from the discharge line of the mixer and, through a line (24), with a reference product (25) of which the cetane number is known, by two separate supply circuits (22, 24) each having a high pressure fuel pump (33, 34), the C.F.R. engine (26) operating at a constant compression ratio.

FIELD OF THE INVENTION 
This invention relates to a method and apparatus for the preparation of a 
fuel, and particularly a fuel for diesel motors, or a fuel for heating 
systems, by mixing its constituents in line, and possibly incorporating 
additives. 
BACKGROUND OF THE INVENTION 
The fuels for diesel motors are designed to auto-ignite after being 
injected in highly compressed air. They generally consist of a mixture of 
various constituents in proportions such that the fuel has certain 
qualities and meets certain related specifications, for example, cold 
resistance, sulfur content and value of cetane. 
In the refining plants, such a fuel is obtained through a technique called 
in line mixing, by which the various liquid constituents, as well as 
additives, are introduced simultaneously and continuously in one duct 
serving as a mixer. The flow rate of the various constituents is 
controlled and operated by computer and the preparation time of one batch 
of fuel can take up to 30 hours. 
Naturally, the properties of the resulting product are monitored several 
times during the making and analyses are completed on samples taken from 
the outflow of the mixer, or from the: storage tank during the filling. 
From the results of theses analyses, the flow rates of the mixture's, 
constituents and of the additives are adjusted to align the measured 
values with the set values. 
Of course, for each analysis, there is an advantage to limiting as much as 
possible the time periods between the time when the sample of the mixture 
during preparation was taken and the time the measured value was obtained, 
and, in general, the analyzers used for this procedure, called in line 
analyzers, meet this requirement. 
However, one of the most important properties of diesel motors fuels, 
namely their capacity to auto ignite, is not submitted to an on line 
control as it exits the mixer because of the difficulties involved in 
measuring this characteristic. It is defined as the time between the 
injection of fuel and its ignition in a combustion chamber, under 
conditions set by the ASTM D 613 standards, where the unit of measurement 
is conventionally called the cetane number. 
According to the conditions of measurement, the value 15 of this cetane 
number is attributed, to heptamethylnonane, whereas the value 100 
corresponds to the combustion under the same conditions of normal cetane 
(normal hexadecane). An intermediary CN number (Cetane Number, attributed 
to a fuel means that the latter has an auto ignition equal to that of a 
mixture of heptamethylnonane and normal cetane such that: 
EQU CN=x+0.15(100-x) 
where x is the cetane content (% per volume) of the heptamethylnonane and 
normal cetane mixture. 
The measuring, long and complicated, takes place in very precise conditions 
set by the ASTM D 613 standard, with the help of a device defined in the 
same standard. This device contains a diesel motor adjusted by the 
Corporation Fuel Research company and universally known in the field under 
the name of "C.F.R. motor". However, the measurement procedure with this 
device is lengthy (approximately 1 hour), delicate and requires many 
manual interventions. 
Methods and apparatuses have been perfected in order to reduce the 
measuring time while still automatically generating the measurement in 
question. In particular, the application for European patent EP-A-0 610 
118, which relates to the procedure as described in the SAE 890419 
document, proposes a method and apparatus for continuously measuring the 
cetane index. If these methods anti apparatuses enhance the method for 
measuring a fuel's cetane, they nevertheless have some drawbacks, such as 
the use of common circuits and capacities for the standard product and the 
fuel sample during manufacturing, as well as the need to use many 
electrovalves with their pilot systems, 
There are other methods for measuring the auto ignition delay of a fuel, 
such as the calculation of the cetane number from easily measured 
properties, such as density or distillation characteristics. However, the 
results obtained are not very reliable and do not take into account the 
frequent introduction in certain types of fuel of a procetane additive 
designed to increase, if necessary, the cetane number of the mixture. It 
is interesting to note, along these lines, that the CFI motor does in fact 
take the effect of the procetane additive into account in its 
measurements. 
There is therefore a need, in this technique for a fast, reliable and 
automatic measurement system, used in line during the preparation 
procedure of a fuel for diesel motors, that allows to better control the 
auto ignition characteristic represented by the cetane number. 
DISCLOSURE OF THE INVENTION 
This is the problem that this invention intends to solve, by using an in 
line CFR type apparatus, downstream of the mixer and under conditions such 
that the results of the cetane number measurement can be easily known very 
shortly after having taken the test sample. 
The invention also aims to propose an in line mixing method and apparatus 
for the constituents, and possibly for the additives, of a fuel for diesel 
motors, where the measurement of the cetane number of the mixture is fast, 
reliable and completely automated. 
With this end in view, the objective of this invention is a method for 
preparing a fuel, in particular for diesel motors, or a fuel for heating 
systems, through an in line mixing of its constituents with the possible 
introduction of additives, and, since this fuel will be marketed, it 
should. have a specific cetane number; the method consists of continuously 
feeding a mixer with the various constituents at controlled flows, 
measuring, at the output of the mixer and at different time periods, the 
cetane number of the fuel being prepared, calculating the difference 
between the measured values and the set values, this method is 
characterized by the fact that during manufacturing a "CFR" motor is 
alternately fed a fuel, taken from the mixer's exhaust line, then a 
standard product with a known cetane number, through two separate fuel 
systems each comprised of a high pressure injection pump, and where the 
CFR motor is operating at a constant compression ratio. 
The calculation of the cetane number of the sample to be measured as 
compared to the already known cetane number of the standard product, will 
be easy completed by applying the terms of the ASTM D 2885 standard for 
the in line analyzer part, a standard that is already used to determine 
the octane number of gasoline. In practice, the ignition delay of a sample 
of the mixture being manufactured and the ignition delay of a standard 
product with a known cetane number are measured sequentially, under the 
same conditions and with a same CFR motor. These measurements done on the 
fuel during manufacturing and then on the standard product, take less than 
one hour, and even less than ten minutes. 
For each series of measurements, the cetane number of the mixture sample 
being manufactured will be determined based on information provided in the 
form of electrical signals by the CFR motor (auto-ignition delays of the 
sample, the mixture and the standard product), this information is then 
converted, by means of a calculator, in differences of cetane as compared 
to the standard product, the calculator will then complete the calculation 
of the cetane number of the sample to be measured in terms of the known 
cetane number of the standard product. 
This sample cetane number will then be transmitted to a computer programmed 
to pilot the related quantities of the different constituents introduced 
in the mixer. 
In accordance with the ASTM D 2885 standard, the precision of the 
measurement of the cetane number by the apparatus consistent with the 
invention is directly tied to the precision of the cetane number of the 
standard product, this precision is generally equal to or lesser than 1 
cetane point for a standard product having been measured several times and 
whose average value is equal to 50. Advantageously, when compared to the 
precision of the method described in the ASTM D 613 standard, the 
precision of the cetane number measurement by the apparatus in accordance 
with the invention is therefore enhanced by a factor that can vary between 
two and five. 
Note that in the invention's method, the CFR motor is used at a constant 
compression ratio and, therefore, under conditions that are different from 
those of the ASTM D 613 standard this: recommend a variable compression 
ratio and involve a comparison between two perfectly defined sample 
products with cetane numbers respectively higher and lower that of the 
sample. The use or the CFR motor with a constant compression ratio avoids 
having to resort to mechanical drive movements during the measurements and 
is therefore favorable to an automation of the measuring procedure and 
thus to an enhancement of the measurements precision. 
The sample product used will have a cetane number close to that being 
sought for the mixture being manufactured, and where the difference with 
the set value is less than 5 cetane points and preferably less than 2. 
The mixture sample and the sample product that feed the CFR motor are 
introduced through separate circuits in the same injection area of such 
motor; this will avoid having to purge between the two successive 
measurements, and therefore allow for a reduction in the stabilization 
time of such measurements. These two measurements (mixture sample and 
standard product) can be done in any order. 
Each CFR motor feed circuit will be equipped with a separate high pressure 
injection pump, this is an important advantage of the method introduced by 
the invention as it will avoid the use of controlled systems for example 
to trigger the opening and closing of the electrovalves, execute 
intermediary adjustments between the measurements on a single pump, or 
trigger the rinsing of the aforementioned pump when the standard product 
flows through to the fuel in the process of being manufactured. Only one 
preadjustment is necessary for both systems prior to implementing the; 
procedure for a manufacturing cycle. 
The measuring system will therefore be easy to automate since it will only 
be necessary to alternately control one pump of one or the other feed 
circuits of the CFR motor. 
An in line addition, in adjustable quantities, of a procetane additive in 
the mixer, or upstream or downstream of the mixer, can be done, as with 
the previous technique, but, as indicated above, the measurements taken by 
the CFR device take this procetane into account, this is an important 
advantage of the method of this invention. 
The purpose of the invention is also an apparatus for manufacturing a fuel, 
in particular a fuel for a diesel motor, or a fuel for heating systems, by 
mixing its constituents in line with the possible incorporation of 
additives, and, since it will be marketed, this fuel must have a specific 
cetane number; this apparatus will consist of at least two tanks for 
stocking at least two constituents of the mixture, a mixer fed by separate 
lines with adjustable flows of various constituents of the mixture, at 
least one exhaust line for the mixture prepared in the mixer, preferably a 
tank for storing the manufactured product, possibly a source of procetane 
additives with adjustable and automated flow, connected downstream or 
upstream to the mixer and/or the exhaust line, a means of measuring the 
cetane number, at least one means of controlling the debit of various 
feeding lines of the mixer and the procetane feed circuit, with this means 
of control being on the one hand, controlled through comparisons and on 
the other hand, programmed so as to adjust the different flows in order to 
reduce the gaps between the measured values and the set cetane number 
values, this device being characterized by the fact that: 
the means of measurement intended to measure the cetane number of the 
mixture consists of a CFR type motor, preferably shunt connected to the 
exhaust line of the mixer. 
this CFR motor is respectively connected by lines equipped with a 
controlled means of closure, to the aforementioned exhaust line and to a 
source of a standard product with a. known cetane number. 
the CFR motor is pre-adjusted to operate at constant compression ratios and 
with arm advance to the adjusted injection at a predetermined value. 
the CFR motor is equipped to provide, by controlling the flows from 
different feed lines of the mixture's constituents, or possibly of an 
additive, a signal that represents the difference, between the two 
measurements of the cetane number, such measurements being taken 
successively from the mixture and from the standard product or vice versa. 
As indicated above, the feed lines of the CFR motor for the mixture sample 
to be tested and the product with the known cetane number will preferably 
be separate or will only have a small common section, and each will be 
equipped with an injection pump. Non-return valves can obviously be 
provided for on the feed lines of the CFR motor. 
Preferably, the injection pumps will be piloted by an automatic control 
able to activate them at regular intervals set ahead of time, for example 
every five minutes. 
A known fact in itself, the CFR motor's injection pumps for the mixture 
sample and the standard product will consist of two adjustment systems, 
one for the quantity to be injected, the other for the time of injection, 
and both these systems will be able to be adjusted independently. 
The CFR motor will preferably be calibrated by two standard fuels with 
cetane numbers close to that of the sample product.

The apparatus represented in FIG. 1 is designed to create a gas oil that 
has predetermined properties and in particular a preset cetane number, by 
mixing various constituents in line in a mixer 1 and, potentially in the 
exhaust line 2 of this mixture toward a tank 20. In this case, the mixer I 
is fed various constituents of the mixture, emanating from the storage 
tanks (4, 6, 8, 10) through four lines (3, 5, 7, 9) each equipped with a 
valve that automatically adjusts the flow (3a, 5a, 7a, 9a) These various 
constituents, of which one must have a cetane number of a lesser value 
than that of the set value, can for example be, without however being 
limited thereto, a heavy gas resulting from a catalytic cracker, a light 
fraction resulting from a crude oil distillation column, a gas oil with a 
high sulfur content, or a gas oil with a low sulfur content resulting from 
a gas oil desulfurization unit. 
In a loop circuit 11, shunt connected to the exhaust line 2, an additive 
called procetane such as, for example, 2-ethyl-hexyl-nitrate, can be 
injected through a line 12, equipped with an automatic flow adjustment 
valve 12a, from a tank 13. 
As explained above, various in line analyzers (not represented) are 
connected in a known fashion to line 2 downstream of the procetane 
injection, in order to periodically measure the characteristic properties 
of the mixture and compare the measured values with the set values of 
these properties. These analyzers are connected to a computer 14, which is 
connected by lines 15, 16, 17, 18 and 19 to valves 3a, 5a, 7a, 9a and 12a 
and programmed to set the flows controlled by these valves so as to reduce 
the gap between the measured values and the set values. 
In accordance with the invention, the cetane number of the mixture 
discharged by line 2 is also measured in line and the feeding flows of 
mixer 1 and injection flows of procetane into line 2 are adjusted so as to 
bring the measured cetane number of the desired set value closer to the. 
aforementioned number. 
For this purpose, an apparatus 21 for measuring the ignition delay of the 
mixture being manufactured and that of the product with a known cetane 
number that is close to the set value, is fed: 
on the one hand, a mixture to be tested, by a first line 22, connected to a 
loop circuit 23 for sample taking, shunt connected to line 2, downstream 
of the procetane injection; 
on the other hand, a product with a known cetane number close to the set 
value of the desired creation, by a second line 24, from a tank 25. 
Apparatus 21 is itself connected to a computer 14 and transmits a signal 
reflecting the difference between the measured known cetane number and the 
cetane number for the mixture, sample, in such a way that the flows of the 
various constituents can be adjusted accordingly by the computer. 
Apparatus 21 is represented in detail in FIG. 2. It consists of a CFR type 
motor 26 operating at a constant compression ratio with a set advance, for 
example 13.degree. in relation to the upper dead center (advance set by 
the ASTM D 613 standard). Motor 26 is command fed by lines 22 and 24 and 
results in a rotation of shaft 27, equipped with a flywheel 28. Shaft 27 
is itself coupled, by transmission systems 29 and 30, for example with 
gears, to the two high pressure pumps 33 and 34, placed respectively on 
the feed line 22 of the mixture to be measured and on feed line 24 of the 
known cetane number product. These pumps are connected by lines, 
respectively 35 and 36, equipped with non-return valves, respectively 37 
and 38, to an injection line 39, connected to the motor's injector. 
As explained above, motor 26 is equipped with an automatic control system 
so as to feed the motor successively and periodically first with the 
mixture sample to be measured then with the known cetane number standard 
product. 
The difference in motor response for these two products is converted by a 
calculation method into the difference between it and the cetane number, 
then transmitted in form of an electric signal to computer 14. The latter 
calculates the cetane number of the mixture sample by applying the rules 
of ASTM D 2885 standard, compares the obtained value with the set value 
determined for the mixture and adjusts the feed flows of the different 
constituents of the mixture or the injection of the procetane additive 
accordingly. 
Only line 39, not very long, is common to both feeding circuits of motor 
26, so that after one measurement it is not necessary to purge the circuit 
and the pump that were just used before completing the following 
measurement with the second circuit and the second pump. This is a 
considerable advantage in comparison with the ASTM D 613 method which uses 
one single pump and two standard products with known cetane numbers. 
Therefore, for the first time, this invention offers a cetane number 
measurement system that can be used in line in a fuel preparation unit, in 
particular fuel for diesel motors, by mixing the. constituents of this 
fuel in line.