GB2116254A

GB2116254A - A fuel system for marine diesel engines

Info

Publication number: GB2116254A
Application number: GB08302915A
Authority: GB
Inventors: Sven Olson
Original assignee: IMO AB
Current assignee: IMO AB
Priority date: 1982-02-10
Filing date: 1983-02-03
Publication date: 1983-09-21
Also published as: SE445481B; FI830445L; NO830396L; FI830445A0; JPS58148262A; DE3303932C2; FI70299B; DK54283D0; GB2116254B; DK54283A; SE8200783L; GB8302915D0; NL8300403A; DE3303932A1; FR2521220A1

Abstract

Fuel from a tank 1 and heated fuel returning from the engine fuel injection device 18 are maintained under pressure in a vessel 6 so that fuel components which would otherwise vaporise remain liquid. Fuel, e.g. at 130 DEG C, drawn through a mixer is pumped through a heater 16 to raise its temperature to 150 DEG C. The vessel pressure is maintained substantially constant by a pump bypass valve 11 and a valve 9 vents gas from the vessel 6 in response to a predetermined liquid level. <IMAGE>

Description

SPECIFICATION A fuel system for marine diesel engines The present invention relates to a fuel system for marine diesel engines, and includes at least one fuel tank, a mixing vessel for mixing fuel from the fuel tank with heated fuel which has not been consumed in the engine, and at least one delivery pump for supplying mixed fuel to the engine.

For reasons of economy, low-quality fuel oil mixtures containing both heavy and light hydrocarbons have been utilized in recent time for driving marine diesel engines. In order that the mixtures can be used as fuel in a diesel engine, they must be heated up to about 1 500C to obtain a viscosity suitable for injecting into the engine.

Since the amount of fuel circulating through the delivery pump and mixing vessel is 2-3 times as large as the engine consumption, the mixing vessel is supplied with return fuel from the engine at a temperature exceeding the boiling point of the lighter fractions in the fuel. Gases are therefore boiled off from the mixing tank, which is in communication with the atmosphere, and these gases are vented out into the air. To a large extent, these gases contain combustible, high-calorific hydrocarbons.

Apart from large amounts of energy being lost and the environment being deteriorated in this way, sludge is formed by the heavier fractions in the mixing vessel. The high temperature (over 1 00 C) in the mixing vessel also results in that the delivery pump must work under difficult suction conditions, since the static pressure between the mixing vessel and the pump is lower than the vapour pressure of the fuel. If flow meters, strainers and the like are placed before the delivery pump, the pressure drop will increase further and cause cavitation in the pump. In the worst case, free gases in the piping of the system may cause disturbances in the engine injection pumps and appreciably deteriorate combustion in the engine.

An object of the present invention is to remove the drawbacks with previously known fuel systems and to provide a fuel system in which practically all the combustible fractions in the fuel are made use of, in which delivery and injection pumps function without disturbances and without being worn, and in which the mixing vessel may be given small dimensions and placed relatively low in the vessel.

According to the invention there is provided a fuel system for marine diesel engines, including at least one fuel tank, a mixing vessel for mixing fuel from the fuel tank with heated fuel not consumed by the engine, and at least one pump for delivering mixed fuel to the engine, characterised in that the mixing vessel comprises a pressure vessel which is connected to at least one pump for delivering fuel under pressure to the relatively warmer fuel in the pressure vessel, said vessel being also incorporated, together with the engine and the pump, in a pressure system wherein is maintained a pressure exceeding the vaporization pressure in the system for keeping combustible gases in liquid form.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing which illustrates a fuel system in accordance with the invention.

A tank 1 containing fuel oil comprising a mixture of both iight and heavy fractions is installed in a ship, the diesel engine 2 of which is driven by the fuel oil after the latter has been heated. The fuel oil, at about 800 C, is taken under gravity to a pumping apparatus with two pumps 3 and 4, of which one, 4, is a reserve pump for putting into service should the other pump fail.

With a capacity several times exceeding the maximum fuel consumption of the engine 2, the pump 3 delivers oil under pressure, and via a flow meter 5, to a hermetically sealed pressure vessel 6, where it is mixed with unconsumed oil from the engine taken via a return line 7 to the pressure vessel.

Since the oil contains components which are vaporized at the temperature, (about 1300 C) prevailing in the pressure vessel 6, gases collect in the upper part of the vessel. However, the pressure in the vessel is kept relatively high and exceeds the vaporization pressure in the pressure circuit containing the pressure vessel, engine 2 and a booster pump apparatus, described below, and thus only a small amount of these fractions or components is vaporized, while the remaining amount remains in liquid form dissolved in the oil consisting of the heavier hydrocarbons in the vessel.When the quantity of gas in the vessel 6 has increased such that the oil in the vessel is below a predetermined level, a level monitor 8 is actuated for opening a valve 9 in a line 10 between the pressure vessel 6 and tank 1 so that the gases inside the vessel can be taken back to the tank 1 without polluting the surroundings.

The excess pressure in the vessel 6 is kept substantially constant with the aid of an automatically functioning pressure regulating valve 11, connected across pumps 3 and 4. The amount of oil supplied to the pressure vessel is exactly that corresponding to the actual consumption in the engine 2, in spite of the pump 3 having a capacity which is substantially greater.

The oil which is not delivered to the pressure tank will therefore be returned to the suction side of the pump 3 via the valve 11 and will be recirculated several iimes through the pump.

To ensure satisfactory mixing of the oil delivered from the vessel 6, and that the gases in the oil will remain in liquid form, a static mixer 12 has been connected to the outlet of the vessel 6.

The suction side of the pumping apparatus comprising two booster pumps 14 and 15, of which one 1 5 is a reserve pump, are connected to the outlet of the mixer 12, the pressure side of the pumping apparatus being connected to the injection device 1 8 of the engine 2 via a heating means 1 6 and a viscosi-meter 1 7. Each booster pump 14, 1 5 has a capacity about three times as great as the oil consumption in the engine 2, resulting in that a relatively large amount of oil, not consumed in the engine, is returned to the pressure vessel 6 via the line 7. The oil is heated to about 1 500C in the means 16, this temperature being the maximum for the oil when it is injected into the engine.

For the case where both pumps 3 and 4 fail, a valve 13 and the valve 9 may be opened manually, the valve 1 3 being in a line between the suction side of the pumps and the outlet of the meter 5, the pump 14 or 1 5 then being able to draw oil from the pressure vessel, which is supplied by gravity direct from the tank 1 situated relatively higher in the ship, and which is subjected to atmospheric pressure via the open valve 9.

The details 3 to 6, 8, 9, 11 to 13 with associated lines can suitably be arranged together with a control and operating panel, not shown, and connected to an exchangeable unit or module 19 between the tank 1, engine 2 and a separate unit or module 20 comprising the details 14 to 16.

Claims

1. A fuel system for marine diesel engines, including at least one fuel tank, a mixing vessel for mixing fuel from the fuel tank with heated fuel not consumed by the engine, and at least one pump for delivering mixed fuel to the engine, characterised in that the mixing vessel comprises a pressure vessel which is connected to at least one pump for delivering fuel under pressure to the relatively warmer fuel in the pressure vessel, said vessel being also incorporated, together with the engine and the pump, in a pressure system wherein is maintained a pressure exceeding the vaporization pressure in the system for keeping combustible gases in liquid form.

2. A fuel system as claimed in Claim 1, characterised in that the capacity of the pump is substantially greater than the engine fuel consumption.

3. A fuel system as claimed in Claim 1 or Claim 2, characterised by a pressure maintenance valve connected across the pump.

4. A fuel system as claimed in any of Claims 1 to 3, characterised by a static mixer connected between the pressure vessel and pump.

5. A fuel system as claimed in any preceding claims, characterised by a monitor sensing the fuel level in the pressure vessel and at a predetermined level actuating a valve for venting away gas enclosed in the pressure vessel above the fuel, preferably back to the fuel tank.

6. A fuel system for marine diesel engines, substantially as herein described with reference to the accompanying drawing.