EP0071053B1 - Method of preheating fuel for an internal-combustion engine working with heavy fuel, and fuel system therefor - Google Patents

Abstract

1. A method of preheating fuel in an internal combustion engine operable with heavy fuel, in which a fuel feed pump (11) draws preheated heavy fuel from a fuel reservoir (18) and feeds through a downstream-arranged filter (1) the thus filtered heavy fuel to fuel injection equipment (14, 15), and in which during a warming-up stage preceding the start of the engine the feed pump (11) pumps the heavy fuel from the reservoir (18) to the filter (1) and hence through a blockable return duct (6) back to the reservoir (18), characterized in that during the warming-up stage the heavy fuel is pumped through the filter's catch chamber (8) until the heavy fuel in the filter's (1) purified-fuel chamber (9) has been heated by the passing preheated heavy fuel to an extent sufficient to render it flowable, and in that the return duct (6) between the catch chamber (8) and the reservoir (18) is substantially blocked once the fuel in the purified-fuel chamber (9) has reached a predetermined viscosity.

Description

The invention relates to a fuel preheating method for internal combustion engines for heavy oil operation according to the preamble of claim 1 and a fuel system for carrying out the aforementioned method according to the preamble of claim 4.

A fuel preheating system is known from the literature reference “Ship and Port”, Volume 31, No. 5, May 1979, pages 401 to 403, which is intended for internal combustion engines with heavy oil operation. Preheated heavy oil is drawn in from a heated heavy oil storage tank via feed pumps and fed to a fuel injection system via a fuel filter. From the pressure connection of the heavy oil feed pump, a return line branches off in front of the filter, which opens into the fuel supply system. In the warming-up phase before starting the internal combustion engine, the heated heavy oil is pumped through the return line to flowability, with no flow through the filter. Paraffin deposits in the filter cannot be thawed, so it is inevitable that at the end of the warming-up phase, inadmissibly high pressures will occur.

From GB-A-841,261 a fuel system is known in which heavy oil is drawn in via a pump and fed to an intermediate tank via a heating device and a filter, from which the heavy oil is fed to the injection system of the internal combustion engine. In order to avoid impermissibly high pressures in the filter in the case of cold heavy oil, a bypass is provided, which can be shut off by a manually operated valve. If the filter is clogged with viscous heavy oil due to low temperatures, the bypass is opened and unfiltered heavy oil passes directly into the lines to the injection system. This can lead to considerable problems in the fine injection channels of the injection system.

Also in DE-A-28 00 486 it is proposed to open a bypass at impermissibly high pressures in the filter, which connects the dirty space of the filter with its clean room. During a cold start, heavy oil contaminated with dirt therefore gets directly into the injection system of the internal combustion engine and leads to considerable problems in the fine channels of the injection system.

From GB-A-20 51 228 a heating device for a filter is known, which is fed by the leakage oil of the injection pump. In order to achieve heating power, the injection pump must be in operation and draw fuel through the filter; The leakage quantity controlled by the injection pump is led through a central heating pipe in the filter in order to increase the flowability of the fuel flowing through the filter rooms. If the filter sieve is clogged with precipitates of the fuel at low temperatures, increased pressures are created in the filter when the pump starts up before the heating device can even be supplied with heated lubricating oil. Under unfavorable circumstances, if the filter is completely clogged, pump delivery is not possible, so that the heating device remains ineffective.

The invention is based on the object of specifying a fuel preheating method for internal combustion engines for heavy oil operation in which, while avoiding inadmissibly high pressures in the fuel filter, heavy oil filtered even at low temperatures is fed to the injection system.

To solve the problem, it is provided to pump the heavy oil through the dirty space of the fuel filter in the warming-up phase until the heavy oil in the clean room of the fuel filter is heated to flowability by the preheated heavy oil flowing past and when the return line has reached a certain viscosity from the dirty space of the fuel filter to essentially interrupt the fuel supply system. In this way, a small amount of cold, viscous heavy oil is pumped back from the fuel feed pump through the dirty space of the fuel filter back into the fuel supply system under the suction of preheated, flowable or pumpable heavy oil, without the sensitive filter element itself being flown through. Due to the immediately flowing, pre-warmed and pumpable heavy oil, which is then circulated by the feed pump in a circuit, a heating medium is available in the fuel filter that heats the heavy oil in the clean room and makes it pumpable. As soon as it has reached a sufficient temperature, at least the majority of the fuel delivered flows via the filter element to the drain from the clean room.

According to the developments of claims 2 and 3, it is provided to interrupt the return line from the dirty space of the fuel filter to the fuel supply system either as a function of pressure or as a function of temperature.

A fuel supply system for performing the preheating process is specified in claim 4. According to the invention, the dirty space of the fuel filter has a further drain to which the return line is connected. When a certain viscosity of the heavy oil in the fuel filter is reached, the return line is essentially interrupted.

In a simple embodiment, in order to reverse the heavy oil entering the dirty space from the outflow from the dirty space to the outflow from the clean room after the warm-up phase has ended and the heavy oil has been heated in the clean room, the outflow of the dirty space is provided with a throttled cross section compared to the outflow of the clean room . With such a gradation of the cross-sections, a small portion flows continuously from the dirty space back to the fuel supply system.

If the delivery rate of the fuel delivery pump is not designed for the additional amount flowing out of the dirty space, it can be advantageous be in the return line to arrange a pressure control valve or a thermostatic valve as a shut-off device. It may be expedient to design such a shut-off device as a simple, manually operated valve, as is known from GB-A-841 261.

From GB-A-2 028 921 it is known to connect a vent line to the fuel chamber to vent the fuel supply system, which vent line opens into the fuel tank. So that no fuel volume is pumped through the ventilation line, the further outflow of the dirt filter is closed by means of a throttle and a check valve, so that essentially only air can escape. The person skilled in the art can only learn from this document the teaching of making the liquid flow via the vent line to zero.

• Fig. 1 einen Schnitt durch einen Brennstoffilter mit angegebenen Durchflussrichtungen des Schweröls in der Anwärmphase:
• Fig. 2 einen Schnitt durch einen Brennstoffilter nach Fig. 1 nach Beendigung der Anwärmphase;
• Fig. 3 eine schematische Darstellung des erfindungsgemässen Brennstoffsystems.

An embodiment of the invention is shown in the drawings and will be described in more detail below. Show it:

• 1 shows a section through a fuel filter with specified directions of flow of heavy oil in the warming-up phase:
• FIG. 2 shows a section through a fuel filter according to FIG. 1 after the heating phase has ended;
• Fig. 3 is a schematic representation of the fuel system according to the invention.

1 and 2, a fuel filter 1 with a housing provided with a lid and a filter insert 5 is shown in section. The housing has an axial inflow 2 to the dirt space 8 and a radial outflow 3 from the dirt space 8 and a coaxial outflow 7 from the clean space 9 in the interior of the filter insert 5. A return line 6 with a shut-off device 4 connects to the outflow 3 from the dirt space 8.

In Fig. 1, the shut-off device 4 is open. Only the dirt space 8 flows through from the inflow 2 to the outflow 3, while the fuel inside the filter insert 5 is still solid or viscous. After this fuel has been heated by the preheated fuel flowing past, the shut-off element 4 is closed and the fuel flows through the surface of the filter insert 5 via the drain 7 in the direction of the fuel injection system.

3 shows a fuel tank 18 with a heating device 19, to which the suction side of a fuel feed pump 11 is connected via a suction line 10. The pressure side of the fuel delivery pump 11 is connected to a fuel injection pump 14 via a delivery line in which the fuel filter 1 is inserted. An additional heating device 13 is arranged in the delivery line 12, which does not necessarily have to be present, but in the case of long delivery lines is favorable for improved flowability of the fuel. The delivery line 12 is connected on the one hand to the inflow 2 to the dirt chamber 8 and on the other hand to the outlet 7 from the clean room of the fuel filter 1. A return line 6 to the fuel tank 18 connects to the drain 3 from the dirt chamber 8 of the fuel filter 1, and a shut-off element 4 is inserted into it. This also does not necessarily have to be present, but it is advantageous if the fuel delivery pump 11 is of a small size to avoid a loss in delivery. Individual injection lines 15 and a return line 16 extend from the fuel injection pump 14. In the return line 16, which opens into the return line 6 from the fuel filter 1, a pressure control valve 17 is used. The latter two lines 6, 16 can also be routed separately to the fuel tank 18. The fuel tank 18 with the heating device 19, the fuel delivery pump 11 and the additional heating device 11 are generally arranged on the system side away from the internal combustion engine, while the other modules shown are arranged directly on the latter.

Claims (7)

1. A method of preheating fuel in an internal combustion engine operable with heavy fuel, in which a fuel feed pump (11) draws preheated heavy fuel from a fuel reservoir (18) and feeds through a downstream-arranged filter (1) the thus filtered heavy fuel to fuel injection equipment (14, 15), and in which during a warming-up stage preceding the start of the engine the feed pump (11) pumps the heavy fuel from the reservoir (18) to the filter (1) and hence through a blockable return duct (6) back to the reservoir (18), characterised in that during the warming-up stage the heavy fuel is pumped through the filter's catch chamber (8) until the heavy fuel in the filter's (1) purified-fuel chamber (9) has been heated by the passing preheated heavy fuel to an extent sufficient to render it flowable, and in that the return duct (6) between the catch chamber (8) and the reservoir (18) is substantially blocked once the fuel in the purified-fuel chamber (9) has reached a predetermined viscosity.

2. A method of preheating fuel according to claim 1, characterised in that the return duct (6) from the filter's (1) catch chamber to the fuel reservoir is blocked in dependence on pressure.

3. A method according to claim 1, characterised in that the return duct (6) from the filter's (1) catch chamber (8) to the fuel reservoir is blocked in dependence on temperature.

4. A fuel system for carrying out a method of preheating fuel for an internal combustion engine operable with heavy fuel according to any of the claims 1 to 3, the system comprising: the fuel feed pump (11) arranged to draw preheated heavy fuel from the fuel reservoir (18) and to feed through the downstream-arranged fuel filter (1) the thus filtered heavy fuel to the fuel injection equipment (14, 15), and the blockable return duct (6) which branches off the filter (1) and leads back to the fuel reservoir, in which the filter (1) is provided with the catch chamber (8) including an inlet (2) thereinto and with the purified-fuel chamber (9) including an outlet (7) therefrom, and in which the inlet (2) is connected to the delivery side of the fuel pump (11) and the outlet (7) of the chamber (9) to the fuel injection equipment, characterised in that the catch chamber (8) has a further outlet (3) connected to the return duct (6) which is arranged to be substantially blocked once the heavy fuel in the filter has reached a predetermined viscosity.

5. A fuel system according to claim 4, characterised in that the outlet (3) of the catch chamber (8) is cross-sectionally constricted in comparison with the outlet (7) of the purified-fuel chamber (9). 6. A system according to claim 4 or claim 5, characterised in that the return duct (6) includes a pressure-controlled valve as the blocking element (4).

7. A system according to claim 4 or claim 5, characterised in that the return duct (6) includes a thermostatically controlled valve as the blocking element (4).

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