The present invention refers to a system for supplying at least two fuels into an internal combustion engine, as well as to a change over procedure of said fuels .

The increasingly stringent standards for environmental protection have led to regulation of the polluting emissions produced by internal combustion engines. Also in the field of maritime transportation the International Maritime Organization (IMO), has introduced its own standards for preventing atmospheric pollution. These standards require frequent fuel change over procedures in the engines of ships.

The change over procedures in marine engines are carried out in terms of variation of the type of fuel used in the engine, as occurs for example in so called "bi-fuel" automobiles (petrol/GPL or petrol/methane). For example, in order to respect the current standards in given geographical areas, it may be necessary for a ship to change over from a first fuel consisting of heavy oils generally called HFO (acronym of "Heavy Fuel Oil") , typically with high sulphur content, to a second fuel generally called MGO (acronym of "Marine Gas Oil") , typically with low sulphur content, necessary during navigation in certain geographical areas known as ECAs (acronym of "Emission Control Areas") , or during docking in a port .

Each individual change over procedure involves a variation of the chemical-physical parameters between the first fuel currently used for propulsion and the second fuel that must replace the first. These parameters usually consist of the viscosity and the injection temperature of each fuel. In general, the viscosity of a liquid is the resistance to flowing due to the friction forces between adjacent layers of the liquid itself. The viscosity decreases as the temperature increases and it determines the possibility of pumping, of atomisation and of lubrication of the fuel.

In order to preserve engines and the relative accessory components from thermal shocks and from other possible drawbacks, change over procedures must take place in the most gradual and careful manner possible. For example, the viscosity of the fuel in use and the variation in temperature must never exceed certain threshold values in order to avoid damaging the engine supply devices. In some cases auxiliary cooling systems are used to reduce the temperature and best deliver the fuel to the engine.

Every engine manufacturer normally indicates the maximum temperature differential for each single minute that can be considered acceptable for the correct operation of a specific engine during the change over step. The viscosity must also be kept within certain design limits in order for the transition from one fuel to another to take place correctly.

In known change over procedures, such as for example those disclosed in documents DE 198 28 772 B4, EP 2 336 529 A2, US 2011/0000549 Al, WO 2007/109914 Al, WO 2011/088830 Al, WO 2012/117152 Al and WO 2012/136208 Al, particular attention is paid to the temperature variations of the fuel. Conversely, such known change over procedures do not always ensure that the viscosity of the fuel does not exceed its limit values in certain change over conditions.

Also JP 2010 270719 A document discloses a device for supplying fuel for an internal combustion engine in which a change over procedure is performed by mainly controlling the temperature values of the two fuels, and/or of their mixture (defined as a blended fuel), supplied in the internal combustion engine. The control operation of the viscosity of said fuels is in fact considered as a secondary operation.

The aim of the present invention is therefore to provide a system for supplying at least two fuels into an internal combustion engine, as well as a change over procedure of said fuels, which is able to overcome the aforementioned drawbacks of the prior art in an extremely simple, cost-effective and particularly functional manner .

In detail, an object of the present invention is to provide a system for supplying at least two fuels into an internal combustion engine and a change over procedure of said fuels that ensure that the viscosity, during the transition steps from one fuel to another, never exceeds certain limit values.

Another object of the present invention is to provide a system for supplying at least two fuels into an internal combustion engine and a change over procedure of said fuels that preserve the engine and the relative components from potential damage caused by the change over procedure itself.

This aim and these objects according to the present invention are achieved by providing a system for supplying at least two fuels into an internal combustion engine and a change over procedure of said fuels as outlined in the independent claims.

Further characteristics of the invention are highlighted by the dependent claims, which are an integral part of the present description.

The characteristics and advantages of a system for supplying at least two fuels into an internal combustion engine and a change over procedure of said fuels according to the present invention will become clearer from the following description, given as an example and not for limiting purposes, referring to the attached schematic drawings, in which:

figure 1 is a schematic view of a system for supplying at least two fuels into an internal combustion engine according to the present invention;

figure 2 is a graph showing the temperature gradient of the fuel or of the fuel blend during the transition step as a function of time;

figure 3 is a graph showing the viscosity gradient of the fuel or of the fuel blend during the transition step as a function of time; and

figure 4 is a graph showing the percentages of two given fuels that supply a generic engine during the transition step as a function of time.

With reference to the figures, a system for supplying at least two fuels into an internal combustion engine, indicated with reference numeral 10, and a change over procedure of said fuels according to the present invention are shown.

The system comprises two or more storage tanks 12 for corresponding fuels that are different from each other, like for example Heavy Fuel Oil (HFO) , Marine Diesel Oil (MDO) or Marine Gas Oil (MGO) or mixtures thereof. Each storage tank 12 has a respective switch valve 14 associated with it, capable of selectively managing the sending of one or more predetermined fuels to one or more supply pumps 16 with relative filters 18.

The supply pumps 16 operate to send the fuel or the fuels to a mixing/deaeration chamber 20. From the mixing/deaeration chamber 20, through further pumps 22, the fuel or fuel blend is sent to the engine 10.

On the duct for supplying the fuel or the fuel blend to the engine 10, arranged between the mixing/deaeration chamber 20 and the engine 10 itself, there can be:

- one or more heating means 24;

- one or more cooling means 26;

- at least one temperature sensor 28; and

- at least one viscosity sensor 30.

In the change over procedure the target temperature Γ of the fuel or of the fuel blend, in other words the temperature Γ that such a fuel or the fuel blend should have in the step of introduction into the engine 10, can be selected by the operator, or it can be calculated from a predetermined value of the viscosity with the ASTM D341 equation:

log(log(u + 0,7)) = A— B logT ( 1 ) From which:

^-1og(1og(u+0,7))

T = 10 B (2)

where :

u is the target value of the viscosity that the fuel or the fuel blend should have in the step of introduction into the engine 10;

A and B are the ASTM D341 constants calculated for each fuel as a function of the viscosity and at predetermined temperatures :

^ _ log(log(¾ _@ i40°C+0.7))-log(log(¾ _@50 °c+0,7))

log(50°C+273,15)-log(l40°C+273,15)

A = log(log(u + 0,7)) + (5 log(50°C + 273,15)) ( 4 ) where v _@ so°c is the viscosity of that given fuel at 50°C and f@i4o°c is the viscosity of that given fuel at 140°C. It should be considered that the reference temperatures used up to now are examples: indeed, different temperatures could also be used according to requirements.

During the change over procedure the system must maintain a certain thermal gradient (figure 2) to avoid thermal shocks on the engine 10. The variation in temperature of the fuel δΤ is defined as a parameter by the operator. Normally, it is equal to 2°C per minute. The initial temperature To is equal to the current temperature of the engine 10 supplied with the fuel used prior to starting the change over procedure. The target temperature Γ, on the other hand, is that defined in equation (2) given above.

Consequently, the time t (in seconds) required for the temperature transition step is defined as:

t = ^lTo~Tl (5)

During the change over procedure the viscosity of the fuel or of the fuel blend introduced into the engine 10 must also be controlled to avoid clogging, seizure or other problems to the injectors and/or to the supply pumps 22 of the engine 10. The system must therefore keep the viscosity value within the limits set by the engineer. In order to do this the system will set a certain viscosity gradient, defined in figure

where :

δυ is the viscosity variation or gradient;

u is the target value of the viscosity;

υο is the viscosity of the fuel prior to starting the change over procedure;

t is the time defined in the equation (5) given above.

The system will therefore keep the viscosity of the fuel or of the fuel blend around the function thus generated. The viscosity gradient δυ could also not be constant and thus generate a non-linear function during the change over procedure.

The viscosity transition step can be delayed or brought forward by a few minutes with respect to the temperature transition step, so as to make the change over procedure homogeneous .

In order to keep control of the temperature and viscosity transition steps described up to now it is necessary to control the composition of the fuel blend that is generated during the change over procedure (figure 4) . The composition of a certain fuel blend that is able to respect a given temperature and a given viscosity is defined by the Refutas equation:

VBN = 14,534 * ln[ln(u + 0,8)] + 10,975 (7)

VBN _blend = [% _F1 * VBN _F1 ] + [% _F2 * VBN _F2 ] + ^■■■ + [% _Fn * VBN _Fn ] ( 8 ) where :

VBN is defined as "Viscosity Blending Number" and is a parameter that depends solely on the viscosity of the fuel or of the fuel blend;

%FI is the percentage of the first fuel Fl, or fuel formerly used in the engine 10, which makes up the fuel blend;

%F2 is the percentage of the second fuel F2, or fuel to be used currently in the engine 10, which makes up the fuel blend.

During the change over procedure the calculation of the viscosity and of the VBN value for each of the first fuel Fl and the second fuel F2 is carried out with the following equations:

VBN _F1[t = 14,534 * In [in (u _F1(t) + Ο,β)] + 10,975 (10)

„„ _Μ = 10» ⁽ '* ' ^ώ)) - 0.7 ( 1 1 .

VBN _F2{t) = 14,534 * In [in (u _F2(t) + Ο,β)] + 10,975 ( 12 ) where :

^Fim is the viscosity of the first fuel Fl at a given temperature Γ as a function of time t;

u _F2(t) is the viscosity of the second fuel F2 at a given temperature Γ as a function of time t.

During the change over procedure the VBN value for the fuel blend consisting of the first fuel Fl and the second fuel F2 is also calculated:

VBN _(t) = 14,534 * ln[ln(u _(t) + 0,8)] + 10,975 ( 13 ) where is the viscosity as a function of time t, based on the equation (6) given above, which the fuel blend should have in the step of introduction into the internal combustion engine 10.

The percentage, for each instant, of each of the first fuel Fl and the second fuel F2 is thus calculated as : VBN _m -VBN _F2(t) )

(vBN _{F t)} -VBN _F2(t) )

VBN _m -VBN _F1(t) )

vBN _F2(t) -VBN _{F t)} )

The percentage %Fi _m of the first fuel Fl and the percentage %F2 _(t) °f the second fuel F2, obtained with the equations (14) and (15) given above, constitute the fuel blend necessary at each instant to ensure the desired instantaneous viscosity at the current temperature. The percentage %Fi _m of the first fuel Fl and the percentage %F2 _(t ) of the second fuel F2 entering into the engine 10 are modified through the switch valves 14 of the system.

The amount of fuel coming out from the system is not identical to the amount of fuel entering the system itself. This is due to the fact that the flow rate of the supply pumps 22 is equal to a multiple of the maximum fuel consumption value of the engine 10, whereas the amount of fuel entering the system is equal to the instantaneous consumption C of the engine 10 itself.

The volume V of the entire system, the instantaneous consumption C and the aforementioned difference in amount of fuel influence the percentage %Fi _m °f the first fuel Fl and the percentage %F2 _(t) °f the second fuel F2. In other words, the percentages %Fi _m ⁼

^% fio«t(t) ^{and %} F2 _(t) = %F2 _0ut(t) of the respective fuels Fl and F2 coming out from the system are not equal to the percentages %Fi _;n(t) ^an d %F2 _;n(t) °f the respective fuels Fl and F2 entering the system.

The volume V of the entire system is defined as a parameter. The fuel consumption is calculated through one or more suitable flowmeters installed in the system.

The percentages % ₁ and % _2/Tl(t) of the respective fuels

Fl and F2 entering into the system are calculated, respectively, with the following equations:

^QF1 ln(t)

% Flln(t) (16)

Qln(t)

® ^F2 ln(t)

% F2 Jn(t) (17)

Qlnit)

where

% _F1;n(t) is the percentage of the first fuel Fl entering into the system;

Q _F i _;n(t) is the amount of the first fuel Fl entering into the system;

% _2;n(t) is the percentage of the second fuel F2 entering into the system;

Q ^F2 m(t) amount of the second fuel F2 entering into the system;

Qm _{( )} is the total amount of fuel entering into the system, equal to the instantaneous consumption C of the engine 10.

The amount of each fuel Fl and F2 entering into the system is calculated with the following equations:

-

(18)

(19) where :

QFi ₀ ut(t amount of the first fuel Fl coming out from the system, calculated as QFi _0utm ⁼ Qt)%Fi( _t) Ί

QF2 _0utm is the amount of the second fuel F2 coming out from the system, calculated as QF2 _0utm ⁼ Qt)%F2( _t) Ί

C( _t ) is the instantaneous consumption of the engine 10.

During the change over procedure the viscosity of the fuels is continuously controlled and a PID (Proport ional-Integral-Derivat ive ) controller corrects possible misalignments between the required viscosity and the actual viscosity of introduction of the fuel blend into the internal combustion engine 10, modifying the operation of the switch valves 14.

It has thus been seen that the system for supplying at least two fuels into an internal combustion engine and the change over procedure of said fuels according to the present invention achieve the purposes outlined earlier .

The system for supplying at least two fuels into an internal combustion engine and the change over procedure of said fuels of the present invention thus conceived can in any case undergo numerous modifications and variations, all of which are covered by the same inventive concept; moreover, all of the details can be replaced by technically equivalent elements. In practice, the materials used, as well as the shapes and sizes, can be any according to the technical requirements .

The scope of protection of the invention is therefore defined by the appended claims.