DK153240B - Dual fuel diesel motor as well as fuel injector for the same - Google Patents

Abstract

The fuel system of a motor features injectors with separate inlets (8, 21) for main fuel and pilot fuel. Each injector has a single set of side nozzle holes (5) and an axially shiftable glider (10), which in a foremost extreme position closes off the nozzle holes. The main fuel can flow to the nozzle holes (5) through an internal glider hole (11, 13), which open into the wall of the slider and after a certain backwards movement of the glider stand opposite the nozzle holes. The pilot fuel can flow through a non-return valve (22) to a chamber (14) in front of the glider's foremost end face. A narrow hole (15) leads from the chamber to the glider hole. When the injection period ends upon the forward movement of the glider, this pumps the pilot fuel from the chamber (14) in to the glider hole (11, 13). As a consequence the main fuel which is injected in the first phase of each injection period contains a high amount of pilot fuel. Problem free ignition is hereby assured with minimal use of pilot fuel and with an uncomplicated assembly and direction of the fuel system.<IMAGE>

Description

in

DK 153240B

The invention relates to a dual fuel diesel engine with a fuel system containing at least one main fuel injector and a liquid pilot fuel in each engine cylinder, and a common source of supply of pilot fuel to each injector through an associated check valve, and individually activated means. for dispensing the main fuel to the individual injectors, and each injector having a pre-closed closed dust at its front end, which in its side wall has a single set of nozzle holes for injecting both fuels.

In the present context, a dual fuel diesel engine is understood to be an internal combustion engine which simultaneously uses two different fuels, namely pilot fuel and main fuel.

The pilot fuel is liquid and has characteristics that make it usable in a conventional diesel engine, while for the main fuel, its self-ignition capability (usually expressed by the cetane number of the fuel 20) is insufficient to establish a safe ignition of the injected fuel at that optimized for the work process. desirable time of process. Examples of such main fuels are highly aromatic mixtures of 25 hydrocarbons, including "solvent refined coal", and residual products from refining processes with extensive cracking of the heavy fractions. Furthermore, alternative fuels such as methanol and ethanol, which are of particular interest to smaller engines, and various 30 gases, including natural gas, coal gas and biogas, whose cetane numbers are very low and may even be negative. It may also be a solid in suspension, e.g. carbon dust in suspension in a liquid. The interest in using the less flammable fuels is mainly due to the fact that they are cheaper and / or locally available for 2

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available in larger quantities than more traditional fuels.

In order to utilize the less combustible fuels, without having to resort to very high compression ratios, and / or charge pressure and / or charge air temperatures, it is known to add a certain amount of a flammable pilot fuel, e.g. gas oil or diesel fuel, for the less flammable main fuel. Adding the engine to a homogeneous mixture of the two fuels allows the use of existing injection equipment with little or no change, but this technique requires a rather large proportion of the more expensive pilot fuel, typically 10-20% of the total fuel volume. In addition, the technique is only applicable when the main fuel is liquid, and for some fuel combinations it is further necessary to add emulsion-forming additives and to take precautions to avoid phase separation during storage of the mixture.

The present invention is based on a divergent technique which, inter alia, is known from EP-A1 0 064 146, which describes a dual fuel injector for use in a diesel engine of the type mentioned initially. The injector is designed for successive injection of pilot and main fuel and has a central spring loaded valve needle which, depending on the pressure in the main fuel supply, opens and closes fuel injection through nozzle holes at the front end of the injector. The main fuel is directed to the seat of the valve needle via an approach incorporating a so-called relief valve with a spring-loaded valve body which is designed so that after closing for further supply of main fuel, a further piece of countercurrent main fuel is displaced. This offset has one

DK 153240B

3 such size # that the amount of main fuel entrained in the inlet between the valve needle seat and the relief valve is substantially completely de-pressurized. The pilot fuel is passed on the last piece 5 before the valve needle seat through a central bore in the valve needle, which, immediately before the seat, opens into the main fuel supply. In the bore is arranged a spring-acting check valve acting in the direction of the pilot fuel flow, which is adapted to open at a very low pressure (about 2 bar). Thus, the pilot fuel supplied under a pressure of 3-4 bar will flow past, after the injection process, the check valve and into the main fuel inlet, where it will settle immediately around the valve needle seat. As the pressure in the main fuel supply increases at the beginning of the next injection, the non-return valve is closed and thus the amount of pilot fuel entered will be injected first, followed by main fuel. During the remainder of the injection, the 20 closed check valve will prevent main fuel from entering the pilot fuel system.

The invention has for its object to enable constructive and control simplifications of such a fuel system.

To this end, an engine according to the invention is characterized in that the common source of pilot fuel is arranged to deliver the fuel at high exhaust pressure, that the nozzle holes in the nebulizer wall 30 are controlled by an axially displaceable axially slidable locking slider. the nozzle holes when it occupies an anterior position in which its anterior end surface is spaced from the nebulizer end wall and which, after a predetermined migration backwards from its anterior position, opens to the

DK 153240B

4, inflowing the main fuel to the nozzle holes through the inner cavity of the slider and communicating between the end face of the slider and the nebulizer end wall communicates partly with the slider-5 cavity through a relatively narrow bore of the slider and partly with the source of pilot fuel through a duct; which contains the check valve opening towards the chamber.

As will be explained in more detail 10 below, such a slider performed by its reciprocating motion in the nebulizer will not only determine the beginning and end of the injection period, but during its movement forward at the injection termination also act as a plunger 15 which pumps fuel from the chamber in front of the slider's end surface into the front of the slider cavity.

Thus, after the slider has blocked the nozzle holes and thus completed the injection, a quantity of pilot fuel is present in the front 20 of the slider cavity, and as a result, the fuel injected during the very first phase of each injection period contains a high percentage of pilot fuel. This ensures prompt ignition of the fuel jets and thus also guarantees that the fuel injected for the rest of the 25 period will ignite without difficulty, even though it consists almost entirely of main fuel. As will also be apparent from the following description of a couple of exemplary embodiments, during each duty cycle, the chamber is refilled in front of the pilot with the pilot fuel from the common source via the check valve in the channel between the source and the chamber.

An example of the consumption of pilot fuel can be mentioned that in a slow-moving two-stroke marine engine it will be possible to arrange the fuel system,

DK 153240B

5 that the first 4-5% of each fuel injection contains 10-20% pilot fuel, ie. ample to ensure instantaneous ignition, after which for the remainder of the period clean main fuel is injected. The consumption of pilot fuel is thus reduced to 1% or less of the total consumption at full load. In decreasing engine load, where ignition may be more difficult due to the lower pressure and temperature level, the pilot fuel represents a growing proportion of the total injected amount.

It is convenient for the engine to have means for changing the discharge pressure from the pilot fuel source. In this way, the mixing ratio of the two fuels can be easily adjusted according to varying operating conditions, with a higher exhaust pressure leading to a larger proportion of pilot fuel in the fuel which is first injected into the cylinders.

The invention also relates to a fuel injector, characterized in that the nozzle holes are guided by a narrowly slidable axial slider in the nebulizer which is preloaded forward to a closing position in which it locks the nozzle holes and its front end surface is spaced from the nebulizer end wall. the slider has an inner cavity which at its rear-facing open end connects to the main fuel injector approach, and which, after a predetermined slider walk backward from the closing position, connects to the nozzle holes via an opening in the slider wall and that between the slider end surface 30 and the end wall of the atomizer bounded chamber communicates partly with the slider cavity through a relatively narrow bore in the slider and partly with the injector's approach for pilot fuel through a check valve opening towards the chamber.

The invention is explained in more detail below with reference to the partially schematic drawing, in which

DK 153240B

6 FIG. 1 is an axial section through the front end of an embodiment of an injector according to the invention to a motor in which the main fuel is liquid; FIG. 2 shows a similar axial section through a modified embodiment in which the main fuel is gaseous; and FIG. 3 is a graph illustrating the pressure conditions of the nebulizer during an injection period.

In FIG. 1, the front end of a combustion chamber of a motor cylinder is partially retracted, the end of an injector generally designed as shown and described in published Danish patent application No. 2532/82. As described in the older application, the injector has an outer housing (not shown in Figure 1) with which the injector is mounted in a cylinder cover for a diesel engine. The housing surrounds a slide guide 1, on whose front end an atomizer 2 is attached, 20 e.g. by electron beam welding or with press fit. Via a conical chest 3 on the nebulizer, it is held in abutment against an opposite chest on the injector housing not shown.

At its front end, which projects into the pre-combustion chamber, the nebulizer 2 is closed by an end wall 4, and some distance behind the end wall the nebulizer has in its side wall a number of inclined nozzle holes 5 for injecting fuel into the engine cylinder.

A spindle 6 is axially displaceable with tight fit 30 in the slide guide 1, and at its front end the spindle 6 is formed with a tapered seat surface which together with an opposite tapered surface of the slide guide 1 forms a shut-off valve 7 for the main fuel supplied through a central channel 8 and inclined bores 9 in the spindle 6.

7

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A slider 10 having a tight fit in the nebulizer 2 is attached to the front end of the spindle 6 on the downstream side of the valve 7. The slider 10 has an internal cavity 11 which connects through inflow 5 openings 12 in the rear of the slider wall. to the downstream side of valve 7. Close behind the forward end face of the slide 10, the cavity 11 terminates with an obliquely outwardly extending portion 13 which opens into an arcuate opening on the cylindrical surface of the slide 10. The aperture is positioned so that it is adjacent to the nozzle holes 5 when the spindle 6 and slider 10 are lifted from the one shown in FIG. 1 to the fully open position.

In the closing position, the end 15 surface of the slider 10 is spaced from the end wall · 4 of the nebulizer and, together with it, defines a chamber 14, from which a narrow channel or bore 15 passes through the sliding wall into the end section 13 of the cavity 11. Through an axis parallel groove 16 in the sliding surface is chamber 14 further communicates with a ring channel 17 in the nebulizer 2 and this channel is through flushing bores 18 and 19 in the nebulizer and slider 1, respectively, in connection with a chamber 20 in the slider wall. An inlet duct 21 for pilot-25 oil opens into chamber 20, where the duct of the duct is normally held closed by a non-return valve consisting of a ball 22 with associated spring 23 and spring holder 24.

When the injector is part of a diesel engine fuel system, the main fuel is delivered in a conventional manner to the injector - through channel 8 - in an amount and at a time of the work process which is adapted to the engine load. Thus, each cylinder injector or injectors are fed from a separate fuel pump or alternatively from a common fuel pump.

DK 153240B

8 high-pressure source via a separately controlled valve, all of the engine's injectors are fed with the more flammable pilot oil from a common high-pressure source connected to all of the injectors' supply channels 21. In this fuel source, an appropriate, preferably adjustable pressure is maintained which is suitably of the same order as the pressure required in the main fuel to initiate the opening of the valve 7 by overcoming the closing force of the spindle 10 6 from the not shown spring, cf. the previously mentioned Danish patent application no. 2532/82.

The operation of the injector is, somewhat schematically, illustrated in FIG. 3, where the lower curve, denoted by I, is the lifting curve of the spindle 6 and 15 the slider 10 with time "t" as abscissa. Above the lift curve, with the same abscesses, is shown a fully drawn curve II which represents the pressure in the chamber 14. Two dotted curve section III represents the pressure in the sliding cavity 11, 13 during the opening and closing movement, where this pressure differs from the pressure in the chamber 14. During the remainder of the work cycle, the two pressures are completely or substantially the same.

At time ten, lifting motion 25 begins, under the influence of the increasing pressure in the main fuel inlet channel 8. Prior to this time, the pressures in the chamber 14 and the sliding cavity 11, 13 are similar and equal to the aforementioned pressures in the pilot oil source connected to the channel 21. During the first 30 of the lifting movement, the pressure in the cavity largely follows the rapidly increasing pressure in the cavity. the access channel 8, as seen in curve III. The pressure in the chamber 14 increases substantially slower due to the small cross-sectional area of the bore 15.

The check valve 22 is closed and through the bore 15 9

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therefore, fuel flows from the slider cavity to chamber 14. At time t2, the slider is lifted so much that it begins to expose the nozzle holes 5. Thus, initially, the pressure drops in both cavity 11, 13 and in chamber 14, check valve 22 opens and pilot oil flows to the chamber 14 and - but only to a very small extent - from this further into the sliding cavity.

By time t3, the spindle 6 with the slider 10 has reached its final position not shown, not shown, where the mouth of the sliding cavity section 13 has exposed the nozzle holes 5 to their full extent. From this point up to time ten +, the main injection takes place below a 15, initially with increasing pressure, see curve II, and during this period the check valve 22 is therefore closed.

When the supply of main fuel to the duct 8 is interrupted, the pressure in the duct and in the sliding cavity decreases steeply, and when the pressure of the main fuel 20 can no longer overcome the force of the closing spring on the spindle 6, ie. at time t 1, the spindle and slider 10 begin to move back to the position of FIG. First

In the first part of the closing movement, the pressure in the slider cavity continues to decrease as steeply as the supply pressure in the duct, as long as the fuel can flow from the slider cavity out through the nozzle holes 5. Conversely, the pressure in the chamber 14 increases with the pressure in the slider cavity because the check valve 22 is still is closed and the slider 10 acts as a pump piston driving pilot oil from the chamber 14 through the bore 15 into the cavity section 13.

When the slider 10 has completely blocked the nozzle holes, the pressure also increases in the slider cavity, see curve 35, but during the entire closing movement which is

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10, closed at time t5, oil is pumped from the chamber 14 into the slider cavity 11, 13 and the pressure in the chamber is, as shown in FIG. 3, larger than in the cavity.

In the following period until the next activation of the spindle 6, these two pressures are first equalized through the bore 15, and then the pressure drops relatively slowly, possibly down to the constant pressure in the channel 21 due to inevitable small leaks between the slider and the nebulizer.

Thus, it will be seen that during the closing movement of the slider, a certain amount of pilot oil flows into the front section 13 of the slider cavity 11, and when the slider next blots the nozzle holes 5, it will be the resulting mixture of main fuel and pilot oil, which is emitted through the nozzle holes during the initial phase of the injection period, i.e. first and foremost in the period t2 ~ t3 of FIG. 3. The relative amount of pilot oil can be changed by changing the discharge pressure from the common pilot oil source, as a higher initial pressure in chamber 14 will cause an increase in the amount of pilot oil flowing from the chamber into the slider cavity during each work cycle.

The FIG. 3 shows a injector in which the diameter of the slider 10 is 8 mm and the diameter of the bore 15 is 1.0 mm. A relatively narrower bore results in a slower pressure equalization in the opening phase and thus a greater amount of pilot oil, but also an increased back pressure on the slider in the closing phase. In this regard, the ratio between the diameter of the slider and the bore should hardly be chosen greater than approx. 16: 1 or less than approx. 4: 1.

In FIG. 2, showing an embodiment of the injector in which the main fuel is gaseous, are the 35 components which fully or substantially respond to

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11 to that of FIG. 1, denoted by the same reference numeral plus 100. The following describes first and foremost the components which differ from the liquid fuel main embodiment.

5 In FIG. 2, the opening and closing of the nozzle holes 105 in the side wall of the nebulizer 102 is controlled by an elongated slider 131 which extends upwardly through both the nebulizer and slider guided 101. The inner cavity of the slider extends correspondingly as a central channel 111 throughout the length of the slider. , and at the rear, not shown end of the injector, the duct 111 is permanently connected to a constant pressure gas supply. This pressure is substantially the same as the pressure prevailing in the source of the pilot oil and thus in the injector access channel 121 for the pilot oil.

The lift of the slider 131 from the one shown in FIG. 2 to the open position, where the end section 113 of the sliding cavity III lies adjacent to the nozzle holes 105, is produced by supply of propellant under a suitable pressure through a channel 132 in the slider 101 to an annular chamber 133 where the propellant acts on an annular breast of the slide 131.

To supply the propellant at the correct time 25 of the operation process in the engine cylinder and in a quantity adapted to the engine load, a pump of the same type as conventional fuel pumps can be used.

In FIG. 2, another channel 134 is seen in the slide guide 101 through which a suitable blocking fluid, e.g. an oil having lubricating properties, at a constant pressure higher than the pressure in the gas duct 111. The barrier oil is distributed from an annular chamber 135 through a longitudinal groove 136 in the sliding surface to spaced apart circumferentially.

Claims (4)

5 It will be readily seen that the embodiment of FIG. 2 is substantially similar to that of FIG. 1, however, the pressure conditions during the injection period will be slightly different, taking into account the compressibility of the gaseous fuel and the constant gas pressure at the inlet to the duct 111. The 1 and 2, in which the sliding cavity at the front ends with an oblique outward section, is particularly suitable for engines in which an exhaust valve is mounted in the center of the cylinder cover and the injectors are therefore mounted along the periphery of the cylinder covers with their nozzle holes distributed within a fairly small angular range. In engines with a single injector in the center of the cylinder cover, the injector usually has nozzle holes along the entire perimeter of the nebulizer, and in the sliding wall, individual channels may then be drilled or milled in the direction towards the nozzle holes. 25 1. Dual fuel diesel engine with a fuel system containing at least one main fuel injector and liquid pi-30 fuel in each engine cylinder, and a common source of supply of pilot fuel to each injector through an associated check valve (22) individually activated means for metering the main fuel to the individual injectors, 35 and wherein each injector has a nebulizer (2) closed at its front end, which in its side wall has a single set of nozzle holes (5) for injecting both fuels , characterized in that the common source of pilot fuel is adapted to deliver the fuel at high off-thrust pressure, that the nozzle holes (5) in the nebulizer wall are controlled by an axially slidable in the nebulizer, with an inner cavity (11, 13). (10) which locks the nozzle holes as it assumes a forward position in which its forward end surface is spaced from the nebulizer end wall (4), and which after a predetermined backward travel from its forward position allows for the main fuel to flow to the nozzle holes via the inner cavity (11, 13) of the slider, 15 and that the boundary (14) bounded between the end face of the slider (10) and the end wall (4) connecting partly to the slider cavity (11, 13) through a relatively narrow bore (15) in the slider, and partly to the source of pilot fuel through a duct 20 (16-21) which contains the check valve opening towards the chamber (22). Diesel engine according to claim 1, characterized in that it has means for changing the discharge pressure from the pilot fuel source. Diesel engine injector according to claim 1 or 2, and of the type having a nebulizer (2) closed at its front end for injecting both fuels through a single set of nozzle holes (5) into the nebulizer side wall, characterized in that: The nozzle holes are guided by a snug fit in the nebulizer axially slidable slide (10) which is preloaded forward to a closing position in which it locks the nozzle holes and its front end surface spaced from the nebulizer end wall (4), inner cavity (11, 13) which at its rear-facing open end connects to DK 153240B tf the injector's main fuel approach, and which, after a predetermined slide walk backwards from the closing position, connects to the nozzle holes (5) via an opening in the slide wall, 5 and that the chamber (14) bounded between the end surface of the slider and the chamber (14) bounded by the dust wall (4) communicates partly with the sliding cavity (11, 13) through a relatively narrow bore (15) in the slider; ls with the injector approach for pilot fuel through a check valve opening in the 10 direction (22). An injector according to claim 3, characterized in that the ratio of the diameters of the slider (10) to the narrow bore (15) is between 16: 1 and 4: 1.