System and method for feeding fuel to a fine-particle-mixed fuel burning diesel engine

Abstract: An improved system and method for feeding fuel, which obviates the shortcomings of the fuel feeding system in the prior art, in which mixed fuel consisting of fine particles of solid fuel such as pulverized coal or the like and fuel oil, is directly sent under a pressure by means of a high-pressure pump but seizure of a pump plunger is caused, and which enables the fuel feeding system in the prior art to achieve good operations, are disclosed. A predetermined amount of fuel oil containing fine particles of solid fuel is fed into an oil reservoir (12) within an injection valve (9) through a control valve (16), and this fuel oil is injected through a nozzle hole (10) of the injection valve (9) with the aid of oil pressurized by means of a high-pressure pump (3). Thereby, only the above-mentioned fuel oil is injected, but the above-described pressurized oil is not injected, and also it never occurs that the aforementioned fuel oil enters the high-pressure pump (3), resulting in seizure of a plunger of the pump. The oil fed to the oil reservoir (12) is returned to an oil tank (1) via a circulation valve (21), and so, deterioration of the oil can be precluded. In addition, since the control valve (16) is regulated by a signal indicating a position of a control rack which controls a delivery amount of the high-pressure pump (3), fuel oil of the amount corresponding to the delivery amount of the high-pressure pump (3) is sent to the aforementioned oil reservoir (12), and so, only the above-mentioned fuel oil can be reliably injected.

Description: BACKGROUND OF THE INVENTION: Field of the Invention: The present invention relates to a system and a method for feeding fuel to a diesel engine which make use of fuel oil containing fine particles of solid fuel such as pulverized coal or the like. Description of the Prior Art: A prior art fuel injection system for a diesel engine using a high cetane number auxiliary fuel for the burning process is described in EP-A-0 282 819. This known system comprises an injection valve including a needle valve, an oil reservoir provided in the injection valve, a fuel feed pipe for supplying an amount of auxiliary fuel determined by a control valve from an auxiliary fuel tank through a check valve to the oil reservoir. A high pressure pump feeds main fuel from a main fuel tank under pressure to the oil reservoir in the injection valve. In the high pressure pump a recirculation valve is provided which opens and closes periodically with the action of a pump plunger and the control valve in the auxiliary fuel feed pipe which in return is controlled by a control unit in accordance with the pump action. Thus a mixture of main fuel and auxiliary fuel is periodically injected through a nozzle hole of the injection valve. In this known system the problems related to use of fuel containing fine particles of pulverized coal or the like do not occur since the fuel used in this system has sufficient lubricating properties. A method and an apparatus for injecting coal slurry fuel containing fine solid particles into a diesel engine combustion chamber is known from US-A-4 862 837 which represents the closest state of the art. The coal slurry fuel is fed by means of a pump from a fuel tank through a check valve to an oil reservoir within an injection valve comprising a needle valve. The fuel in the reservoir is pressurized by high pressure oil pressurized in a high pressure pump and fed to a diaphragm pump through which the pressure is applied to the coal slurry fuel without mixing the pressure oil and the fuel. Due to the pressure transmission through the diaphragm pump the injection is perfomed by means of a vortex swirl nozzle at a relatively low pressure. Moreover, there is a danger of wear of the portions being in contact with the pressurized coal slurry fuel since there is a comparatively long distance for transportion of the pressurized coal slurry fuel from the diaphragm pump to the injection valve. SUMMARY OF THE INVENTION It is the object of the present invention to provide a system and a method for feeding fuel to a fine-particle-mixed fuel burning diesel engine, which obviate the shortcoming that seizure of a pump plunger would occur, and which can achieve good operations even if mixed fuel consisting of fine particles of solid fuel and fuel oil is employed. According to the present invention there is provided a fuel feed system for a fine-particle-mixed fuel burning diesel engine, for feeding fuel oil containing fine particles of solid fuel into said diesel engine to be burnt, comprising an injection valve including a needle valve for opening and closing a path between an oil reservoir section provided within said injection valve and a nozzle hole; a fuel feed pipe provided between the oil reservoir section and a fuel tank for said fuel containing fine particles; a control valve provided within said fuel feed pipe for controlling an amount of fuel flowing through said fuel feed pipe; a check valve provided within said injection valve for allowing only flow of fuel from said control valve towards said oil reservoir section; a high-pressure pump for pressurizing oil fed from an oil tank; a pressure wave propagation pipe connecting a delivery port of said high-pressure pump and said oil reservoir section in the injection valve; a recirculation valve for opening and closing said pressure wave propagation pipe; a recirculation pipe provided between said recirculation valve and said oil tank; and a control device for controlling opening and closing of said recirculation valve and said control valve, such that after ending of the fuel injection said recirculation valve is opened to thereby recirculate oil for use in pressure wave propagation via the recirculation pipe back to said oil tank in such a way that the oil used in pressure wave propagation is not injected. In a preferred embodiment, the fuel feed system of the present invention comprises a control rack detector for detecting a position of a control rack which controls a delivery amount of said high-pressure pump and for delivering a detection signal to said control device. According to the present invention there is also provided a method for feeding fuel to a fine-particle-mixed fuel burning diesel engine, in which fuel oil containing fine particles of solid fuel is to be burnt, comprising the steps of: feeding said fuel oil containing fine particles of solid fuel in a predetermined amount from a fuel tank to an oil reservoir section within an injection valve by means of a pump; pressurizing high-pressure oil fed from an oil tank by means of a high-pressure pump and delivering said pressurized oil through a pressure wave propagation pipe towards said oil reservoir section so as to thereby pressurize the fuel within said oil reservoir section; injecting the thus pressurized fuel contained in the oil reservoir section through a nozzle hole of the injection valve; recirculating said pressurized oil back to said oil tank through a recirculation pipe as soon as the predetermined amount of fuel contained in the oil reservoir section is injected from the nozzle hole so as to not inject said pressurized oil through the nozzle hole. The above method for feeding fuel to a fine-particle-mixed fuel burning diesel engine preferably further comprises the steps of determining a delivery amount of said pressurized oil of the high-pressure pump and controlling said predetermined amount of fuel containing fine particles of solid fuel fed from the fuel tank to the oil reservoir section in accordance therewith. According to the present invention provided with the above-described features, fuel containing fine particles of the amount controlled by the control valve which is in turn controlled by the control device, is sent from the fuel tank through the fuel feed pipe to the oil reservoir in the fuel injection valve. On the other hand, the oil within the oil tank is pressurized by the high-pressure pump, and a pressure wave of the oil is transmitted to the above-mentioned oil reservoir through the pressure wave propagation pipe, and the above-mentioned fuel containing fine particles which is present within the oil reservoir is injected through the nozzle hole of the injection valve. When this injection has finished, the oil sent to the injection valve through the recirculation valve controlled by the control device is returned to the oil tank, and so, deterioration of the oil can be precluded. In this way, fuel containing fine particles is never fed to the high-pressure pump, hence seizure of the plunger of the same pump does not occur, and also, only the fuel containing fine particles is injected through the nozzle hole of the injection valve. In addition, according to the present invention, owing to the additional feature that a detection signal issued from the control rack detector for detecting a position of the control rack which controls a delivery amount of the high-pressure pump is input to the control device, and the amount of fuel containing fine particles to be fed to the oil reservoir is controlled on the basis of the amount of oil delivered from the high-pressure pump by the control device, only the same fuel containing fine particles is surely injected through the nozzle hole of the injection valve, and the oil propagating the pressure wave can be prevented from being injected through the nozzle hole. The above-mentioned and other objects, features and advantages of the present invention will become more apparent by reference to the following description of preferred embodiments of the invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS: In the accompanying drawings: Fig. 1 is a schematic view showing one preferred embodiment of the present invention; DESCRIPTION OF THE PREFERRED EMBODIMENT: Now one preferred embodiment of the present invention will be described with reference to Fig. 1. In this figure, reference numeral 1 designates an oil tank which accommodates oil for propagating a pressure wave to a fuel valve, numeral 2 designates an oil feed pump, numeral 3 designates a high-pressure injection pump, numeral 4 designates a plunger, numeral 5 designates a barrel, numeral 6 designates a delivery valve, numeral 7 designates a pressure-regulating check valve, numeral 8 designates a pressure wave propagation pipe, numeral 9 designates a fuel injection valve, numeral 10 designates a nozzle hole, numeral 11 designates a needle valve, numeral 12 designates an oil reservoir section, numeral 13 designates a check valve, numeral 14 designates a spring, numeral 15 designates a feed pipe, numeral 16 designates a control valve, numeral 17 designates a fuel feed pipe, numeral 18 designates a fuel feed pump, numeral 19 designates a fuel tank for fuel containing fine particles of coal, numeral 20 designates a control device, numeral 21 designates a recirculation valve, numeral 21' designates a drive motor controlled by the control device 20, numeral 22 designates a recirculation pipe, and numeral 23 designates a control rack detector for detecting a position of a control rack 24 which controls a delivery amount of the high-pressure injection pump. Fuel containing fine particles of coal is fed by the fuel feed pump 18 from the fuel tank 19 through the fuel feed pipe 17 and enters the control valve 16, and during a pause period of fuel injection and after circulation of the oil in the pressure propagation pipe 8 has finished, a predetermined amount of fuel containing fine particles of coal is sent into the fuel injection valve 9 through the feed pipe 15. At this time, representing a valve-opening pressure of the pressure-regulating check valve 7 in the high-pressure injection pump 3 by P R , a valve-opening pressure of the check valve 13 by P P and a valve-opening pressure of the needle valve 11 by P N , and if these values are preset so as to fulfil the relations of P N > P P > P R' the fuel fed from the fuel tank 19 would pass through the check valve 13 and would flow into the oil reservoir section 12 in the fuel injection valve 9. Consequently, the oil for use in propagation of a pressure which was present in this oil reservoir section, is pushed back towards the high-pressure injection pump 3 through the pressure wave propagation pipe 8, and flows inversely into the barrel (plunger chamber) 5 by forcibly opening the pressure-regulating check valve 7. In addition, by detecting a position of the control rack 24 for controlling a delivery amount of high-pressure oil by means of the control rack detector 23 and inputting the detection signal to the control device 20 for controlling an opening/closing timing period of the control valve 16, an appropriate amount of fuel containing fine particles of coal is filled in the oil reservoir section 12. Under the above-mentioned condition, when the plunger 4 in the high-pressure fuel pump 3 rises to push up the delivery valve 6 and oil feed starts, the oil for propagating a pressure wave is sent through the pressure, wave propagation pipe 8 to the side of the fuel injection valve 9, the pressure in the oil reservoir section 12 rises higher than the pressure P N , hence the needle valve 11 opens against the resilient biasing force of the spring 14, and injection through the nozzle hole 10 commences. At this time, fuel of the amount corresponding to the position of the control rack of the high-pressure injection pump has been preliminarily fed into the oil reservoir section, the oil for use in pressure wave propagation is not injected. Also, since the check valve 13 is closed, even if a high pressure is applied the fuel does not flow inversely towards the fuel tank. After finishment of the fuel injection, the recirculation valve 21 is opened via the drive motor 21' as controlled by the control device 20, thereby the oil for use in pressure wave propagation is recirculated via the recirculation pipe 22 to the oil tank 1, and so, deterioration of the oil can be prevented. As will be apparent from the description of the preferred embodiment above, according to the present invention, owing to the above-mentioned structural feature, fuel containing fine particles of solid fuel can be injected at a high pressure from an injection valve into a combustion chamber without introducing such fine-particle-mixed fuel into a barrel (plunger chamber) in a high-pressure pump. Accordingly, seizure of a high-pressure pump plunger caused by fine particles of solid fuel having a high hardness can be precluded, and in addition, since provision is made such that the oil for propagating a pressure wave from a high-pressure pump is also circulated, the fault in propagation of a hydraulic pressure due to deterioration of oil can be also eliminated.

Claims: A fuel feed system for a fine-particle-mixed fuel burning diesel engine, for feeding fuel oil containing fine particles of solid fuel into said diesel engine to be burnt, comprising: an injection valve (9) including a needle valve (11) for opening and closing a path between an oil reservoir section (12) provided within said injection valve (9) and a nozzle hole (10) ; a fuel feed pipe (15) provided between the oil reservoir section (12) and a fuel tank (19) for said fuel containing fine particles; a high-pressure pump (3) for pressurizing oil fed from an oil tank (1) characterized by, a control valve (16) provided within said fuel feed pipe (15) for controlling an amount of fuel flowing through said fuel feed pipe (15); a check valve (13) provided within said injection valve (9) for allowing only flow of fuel from said control valve (16) towards said oil reservoir section (12); a pressure wave propagation pipe (8) connecting a delivery port of said high-pressure pump (3) and said oil reservoir section (12) in the injection valve (9) ; a recirculation valve (21) for opening and closing said pressure wave propagation pipe (8); a recirculation pipe (22) provided between said recirculation valve (21) and said oil tank (1); and a control device (20) for controlling opening and closing of said recirculation valve (21) and said control valve (16), such that after ending of the fuel injection said recirculation valve (21) is opened to thereby recirculate oil for use in pressure wave propagation via the recirculation pipe (22) back to said oil tank (1) in such a way that the oil used in pressure wave propagation is not injected. The fuel feed system for a fine-particle-mixed fuel burning diesel engine of claim 1, further comprising a control rack detector (23) for detecting a position of a control rack (24) which controls a delivery amount of said high-pressure pump (3) and for delivering a detection signal to said control device (20). The fuel feed system for a fine-particle-mixed fuel burning diesel engine of claim 1 or 2, wherein a pressure regulating check valve (7) is provided in said high-pressure pump (3) for allowing only a flow back from said pressure wave propagation pipe (8) into the high pressure pump (3); a valve-opening pressure (P R ) of said pressure regulating check valve (7) and a valve-opening pressure (P P ) of said check valve (13) and a valve-opening pressure (P N ) of said needle valve (11) are preset to fulfil the relation: P N > P P > P R ; and a pressure of said fuel fed from said fuel tank (19) is higher than P P and lower than P N and a pressure of said oil fed from said high-pressure pump (3) is higher than P N . A method for feeding fuel to a fine-particle-mixed fuel burning diesel engine, in which fuel oil containing fine particles of solid fuel is to be burnt, comprising the steps of: feeding said fuel oil containing fine particles of solid fuel in a predetermined amount from a fuel tank (19) to an oil reservoir section (12) within an injection valve (9) by means of a pump (18); pressurizing high-pressure oil fed from an oil tank (1) by means of a high-pressure pump (3) characterized by delivering said pressurized oil through a pressure wave propagation pipe (8) towards said oil reservoir section (12) so as to thereby pressurize the fuel within said oil reservoir section (12); injecting the thus pressurized fuel contained in the oil reservoir section (12) through a nozzle hole (10) of the injection valve (9); recirculating said pressurized oil back to said oil tank (1) through a recirculation pipe (22) as soon as the predetermined amount of fuel contained in the oil reservoir section (12) is injected from the nozzle hole (10) so as to not inject said pressurized oil through the nozzle hole (10). The method for feeding fuel to a fine-particle-mixed fuel burning diesel engine of claim 4, further comprising the steps of: determining a delivery amount of said pressurized oil of the high-pressure pump (3) and controlling said predetermined amount of fuel containing fine particles of solid fuel fed from the fuel tank (19) to the oil reservoir section (12) in accordance therewith. The method for feeding fuel to a fine-particle-mixed fuel burning diesel engine of claim 4 or 5, wherein said fuel fed from the fuel tank (19) to an oil reservoir section (12) by means of the pump (18) is fed in a pressure which is higher than a valve-opening pressure (P P ) of a check valve (13) provided in the injection valve (9) in the fuel path upstream the oil reservoir section (12) and which is lower than a valve-opening pressure (P N ) of a needle valve (11) provided in a path between said oil reservoir section (12) and a nozzle hole (10); and said high-pressure oil fed by means of the high-pressure pump (3) towards said oil reservoir section (12) is pressurized to a pressure higher than the valve-opening pressure (P N ) of said needle valve (11).

Inventors: NAKAGAWA HIROSHI, ODA YUUJI, NAKAGAWA, HIROSHI, ODA, YUUJI, Nakagawa, Hiroshi, c/o Nagasaki Res. &amp; Dev. Center, Oda, Yuuji, c/o Nagasaki Res. &amp; Dev. Center
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI JUKOGYO KABUSHIKI KAISHA
Application year: 1992
Main classification: F02M43
IPC codes: F02M25, F02D19, F02B3, F02M43