CLIAMS:We claim:
1. An inline fuel pump (10) for a dual fuel engine (12) used in a constant engine speed application, said dual fuel engine (12) operated such that diesel fuel is used for pilot injections and a gaseous fuel is used for main injections, said inline pump (10) comprising at least one barrel and plunger assembly (14),
Characterized in that
said plunger (14b) of a said barrel and plunger assembly is a groove-less plunger and the geometry of said barrel (14a) and plunger (14b) in said barrel and plunger assembly (14) allows pre-defined volume of fuel to be supplied in each delivery stroke for pilot injection of diesel fuel to said dual fuel engine.

2. The inline fuel pump (10) for a dual fuel engine (12) as claimed in claim 1, wherein dimensions of said at least one barrel and plunger assembly (14) allows pre-defined volume of fuel to enter said at least one barrel (14a) and pre-defined volume of fuel to be delivered in each delivery stroke to the dual fuel engine (12).

3. The inline fuel pump (10) for a dual fuel engine (12) as claimed in claim 1, wherein geometry of said at least one plunger (14b) allow pre-defined volume of fuel to be pressurized in said inline fuel pump (10).

4. The inline fuel pump (10) for a dual fuel engine (12) as claimed in claim 1, wherein dimensions of said at least one barrel (14a) is such that the lift of said at least one plunger (14b) in said at least one barrel (14a) allows fuel to be delivered in each delivery stroke to the dual fuel engine (12) for pilot injection.

5. The inline pump (10) for a duel fuel engine (12) as claimed in claim 1, wherein dimensions of said at least one barrel and plunger assembly (14) are such that fuel quantity governing is accomplished by said at least one barrel and plunger assembly (14). ,TagSPECI:The following specification particularly describes the invention and the manner in which it is to be performed.

Field of the invention
[001] This disclosure relates to an inline fuel injection pump for a dual fuel engine.

Background of the invention:
[002] The inline fuel injection pump is perhaps the most widely used fuel injection system in a wide variety of applications both automotive and non-automotive. Over the years, this system has been continually refined and adapted to suit its many areas of application. As a result, a large variety of different versions are still in use today. The particular strength of these pumps is their rugged durability and ease of maintenance. The in-line fuel-injection pump is used all over the world in medium-sized and heavy-duty trucks as well as on marine and fixed installation engines. It is controlled either by a mechanical governor, which may be combined with a timing device, or by an electronic actuator mechanism.

[003] As mentioned earlier in-line fuel injection pump are used for fixed installation engines. One such application of fixed installation engines is used in generator sets i.e. Gensets. Engine-driven, electrical generators are used in a wide variety of applications. Generators are directly driven by engines and are coupled to each other through a common shaft. Generators may be classified based on a variety of parameter, one amongst them is the source of fuel used to run the engine which drives the generators. Based on source of fuel the generators may be classified as diesel based generators, dual fuel generators. For the purpose of this disclosure we will concentrate on dual fuel generators. For the purpose of this disclosure a dual fuel generator is defined as a generator, wherein the engine used to drive the generator uses two fuels typically diesel and a gaseous fuel such as natural gas or any other gaseous fuel.

[004] With reference to this disclosure we will concentrate on dual fuel engines wherein diesel fuel is used only for pilot injection whereas the gaseous fuel is the primary fuel which is used to operate dual fuel engine that drive the generator on a continuous basis. In such type of dual fuel engine the diesel fuel is injected into the dual fuel engine only as a pilot quantity. The pilot quantity of diesel fuel is burnt in the dual fuel engine and the flame propagation in the cylinders of the dual fuel engine is used to burn the gaseous fuel which is later injected into the dual fuel engine as the primary fuel.

[005] As mentioned earlier the in-line fuel injection pump may be controlled by a mechanical governor or an electronic governor. For the purposes of this disclosure we focus only on in-line fuel injection pumps with mechanical governors. The mechanical governor is actuated or controlled such that the amount of pilot injection of diesel fuel can be controlled.

[006] US patent numbered US4278064 discloses one such fuel control system for a dual fuel powered unit. In accordance with the disclosure in this patent document, the diesel governor and fuel pump assembly is modified only by the application of a fuel rack stop for maintaining a pilot flow of diesel fuel and the engine control system is such that the response of the diesel injection system to changes in engine load is normal in general. However, automatic controls are provided for monitoring diesel pump fuel rack position and engine load so that after engine loading is increased a throttle valve in the gas supply to the engine is progressively and relatively slowly opened tending to increase engine speed so that the diesel injection rate is conventionally cut back correspondingly until an equilibrium condition is reached in which engine fuel demand in excess of the pilot minimum diesel fuel flow required to maintain combustion is provided by producer gas. The system is used to directly drive an electric generator.

Brief description of the accompanying drawings:
[007] An embodiment of the disclosure is described with reference to the following accompanying drawings;
[008] Figure 1 illustrates a basic system diagram of the inline pump for a dual fuel engine used in a constant engine speed application.

Detailed description of the embodiments:
[009] Figure 1 illustrates a basic system diagram with the inline pump of this disclosure for a dual fuel engine used in a constant speed application. The system comprises a dual fuel engine 12 which operates uses two fuel namely a liquid fuel for example diesel and a gaseous fuel for example CNG. The dual fuel engine 12 receives diesel fuel from an inline fuel injection pump 10 and CNG is received from a plurality of tanks 16 where the CNG is stored. For the purposes of this disclosure we will focus on a disclosure wherein the diesel fuel is only used for pilot injection whereas the CNG is used as the primary fuel for main injections. Further, focus of this disclosure in on the inline fuel pump 10 which supplies diesel fuel to dual fuel engine 12 for constant engine speed applications.

[0010] For better understanding of the inline fuel pump 10, it is necessary to understand working of a dual fuel engine for constant speed applications and pilot and main injections. One such constant speed application as mentioned earlier is for generator sets also known as gensets. One important point to note about gensets is that the gensets operate at a constant speed with minimal variation in engine speed of the dual fuel engine 12. Thus for gensets which are operated by dual fuel engine 12 using two fuels namely liquid fuel diesel and gaseous fuel CNG, the burning of both the fuels in critical for the efficiency of the entire system. A person skilled in the art will already be aware that CNG ignition by itself cannot happen without the aid of a spark or at least high temperature in the engine cylinder. Also that diesel is a compression ignition fuel which does not require any external aid for combustion. Thus in dual fuel engines 12, the diesel fuel is ignited first so as to create temperature inside the engine cylinder sufficient enough to self ignite the CNG. For this purpose, diesel fuel is first injected in a pre-defined quantity which can also be defined as pilot injection and CNG is injected later which is defined as a main injection. The pilot injection of the diesel fuel ensures that a pre-defined quantity of fuel is first combusted which creates temperature high enough for the CNG which is injected as the main injection to self ignite.

[0011] Thus in such cases, where the diesel fuel is only injected in the pre-defined quantity, only for pilot injection in a dual fuel engine 12 used for constant engine speed applications, the quantity of diesel fuel to be injected could be fixed based on the constant engine speed application. Thus the quantity of diesel fuel to be injected would remain constant in every working cycle of the dual fuel engine. Thus there is no requirement of varying the quantity of fuel sent from the inline fuel injection pump 10 to the dual fuel engine 12.

[0012] For this purpose there is provided as a part of this disclosure an inline fuel pump 10 for a dual fuel engine 12 used in a constant engine speed application. The dual fuel engine 12 is operated such that diesel fuel is used for pilot injections and a gaseous fuel is used for main injections. The inline fuel pump 10 comprises at least one barrel and plunger assembly 14. The inline fuel pump 10 is characterized such that the plunger 14b of a the barrel and plunger assembly is a groove-less plunger and the geometry of the barrel 14a and plunger 14b in the barrel and plunger assembly 14 allows pre-defined volume of fuel to be supplied in each delivery stroke for pilot injection of diesel fuel to said dual fuel engine.

[0013] The dimensions of the at least one barrel and plunger assembly 14 allows pre-defined volume of fuel to enter at least one barrel 14a in each delivery stroke and allows pre-defined volume of fuel to be delivered in each delivery stroke to the dual fuel engine 12. The geometry of at least one plunger 14b allows pre-defined volume of fuel to be pressurized in each stroke in the inline fuel pump 10. The dimension of at least one barrel 14a is such that the lift of at least one plunger 14b in at least one barrel 14a allows fuel to be delivered in each delivery stroke to the dual fuel engine 12 for pilot injection. The dimensions of said at least one barrel and plunger assembly 14 are such that fuel quantity governing is accomplished by the at least one barrel and plunger assembly 14.

[0014] The advantages of the fuel injection pump 10 in accordance with this disclosure is that since the diesel fuel is used only for pilot injection, the dimensions of the barrel and plunger assembly is reduced considerably. Further since the use of this inline fuel pump 10 is in a constant engine speed application there is no need any governing mechanism. Thus in accordance with this disclosure there is provided an inline fuel pump 10 without any mechanical governing mechanism.

[0015] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.