TECHNICAL FIELD

As a rule, water cooled diesel engines are cooled with fresh water which is circulated in a closed circuit through the cooling jackets arranged around the cylin¬ ders of the engine and is thereafter heat exchanged in a raw water or air ventilated fresh water cooler arran¬ ged outside the engine.

BACKGROUND ART

For certain large compressor charged engines, in addi¬ tion to the cooling of the engine itself, there is al¬ so a need for intermediate cooling of the air of com¬ bustion before this is driven into the cylinders. Gene- rally, the cooling system for such so-called air inter- cooled Engines usually comprises a conventional fresh water cooling circuit for the jacket cooling and a special raw water (salt water) circuit for the air intercooling. However, in order to fulfil all func- tions, such a system must contain many components which require much space, placed outside the engine, which makes its installation and operation complicated and expensive. Special, expensive materials and compo¬ nents are also needed in the raw water circuit. Entire- ly fresh water cooling systems for both jacket cooling of the engine and intercooling of the air of combustion are already in use for e.g. diesel locomotives and some marine and stationary engines , but as far as we know not of any design such as the system described in the followinσ.

DISCLOSURE OF INVENTION

The present invention thus relates to a fresh water cooling system for compressor charged IC engines pri¬ marily of the type medium speed diesel engines, com- prising in addition to the cooling jackets at the cylinders of the engine and a conventional fresh water cooler also an air intercooler for cooling of the air of combustion after this has left the compressor but before it is fed into the respective cylinders. Furth- er/ the cooling system according to the invention is divided up into a high temperature circuit, a low temperature circuit and a heat exchanging circuit, which are connected with each other in pairs via temperature regulators which control the mixing pro- portion between the flows running together from the respective temperature circuits so that the respective output flow obtains a nearly constant temperature. In the high temperature circuit, ±n addition to the coo¬ ling jackets for the engine, a circulation pump is arranged before the engine in the direction of flow of the cooling water and after the pump there are arranged de-airing, expansion, pressure maintaining and flow adjusting systems. The low temperature cir¬ cuit includes an air intercooler and in the heat ex- changing circuit there is a fresh water cooler. The connection between these three temperature circuits is arranged in such a way that the hot cooling water in the high temperature circuit, after this has left the engine, is deflected into three parts, of which the first one via the heat exchanging circuit is con¬ veyed through the fresh water cooler while the second one is mixed with the first one after the cooler in pro¬ portions which are determined by a first temperature regulator arranged in the crossing between these twc

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circuits and it is thereafter via the low temperature circuit conveyed through the air intercooler and there¬ after at a second temperature regulator it is mixed with the cooling water from the third of the deflected parts from the high temperature circuit in proportions which are determined by this second temperature regula¬ tor and it is thereafter anew, at a constant temperatu¬ re, fed to the high temperature circuit and via this to the cooling jackets of the engine.

According to the invention, the two temperature regu¬ lators thus control the mixing proportion between coo¬ ling water of different temperatures. The size of the flow of cooling water is determined by the capacity of the circulation pump and the flow adjustment device arranged in the high temperature circuit.

It is also indluded in the invention that the de-airing, expansion and pressure maintenance systems comprised in the high temperature circuit are built together into a unit or tank which is fitted directly on the engine, and the expansion space of which consists of a chamber arranged in the lower part of the tank.

The advantages of the present cooling system would primarily be its simple design, comprising few and sturdy components, and its great flexibility as regards the temperature regulation in the system within the entire power and speed range of the engine and under varying external. conditions .

Further, the combined de-airing, expansion and pressure maintaining tank comprised in the system offers a very good solution of all of these functions in one single sturdv unit which at the factory can be fitted direct-

ly on the engine and which owing to the fact that the expansion space is arranged under the de-airing chamber does not increase the installation height of the en¬ gine when it is installed with the intake from the eή- gine at the most advantageous height from the point of ^' view of flow.

In accordance with the present invention, the fresh water cooling system has been defined in the following claims, and will now be further described with referen- ce to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

In the drawings, figure 1 shows a simplified diagram of the cooling water system while figure 2 shows a sec¬ tioned side projection of the combined de-airing, ex- pansion and pressure maintaining tank, ^' and figure 3 shows a characteristic of the entire system measured at one particular engine.

In figure 1 , a double dot-dash line shows the parts which it is appropriate to fit directly on or are con- prised in the engine itself. These should thus appro¬ priately be delivered as one unit from the factory. From the cooling jacket 1 with, in the present case, its four cooling flows which are shown, the cooling water follows a main flow 2 to the combined de-airing, expansion and upper de-airing chamber 4 of the pressure maintaining tank 3. Under this chamber, and separated from it by means of a separating wall 5 there is the expansion and pressure maintaining chamber 6 of the tank. The design of the tank will be described in more detail with reference to figure 2. After the de-airing in the chamber 4 the coolinc water leaves this in the

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form of a main flow which passes a flow adjusting valve 8. At a first branching point 9 arranged after the flow adjusting valve 8 and a second branching point 10 arr¬ anged somewhat farther on in the flow direction the 5 cooling water flow is divided up into three part flows, of which the first one 11 via a first temperature regu¬ lator T ₁ is fed to a heat exchanger 12 functioning as an air intercooler. In the temperature regulator T. the cooling water flow 11 is mixed with a cooling water 0 flow 13 which comes direct from the fresh water cooler 21 preferably arranged outside the engine. This latter cooling water flow comprises one of the two cooling water flows which are separated at the previously men¬ tioned second branching point 10 and which is now re- 5 turned after having passed through the fresh water cooler 21. The temperature regulator ₁ is adapted to constantly feed a cooling water flow 14 with a constant temperature to the air intercooler 12. The temperature regulator thus only determines the mixing proportion 0 between the two cooling water flows 11 and 13. At a second temperature regulator _ arranged immediately after the air intercooler 12 the cooling water flow from the air intercooler is mixed the second cooling water flow 15 of the two part flows separated at the 5 branching point 10. When these two part flows 14 and 15 are combined they again give a main flow 16 with the same flow as the main flow 2 coming from_the cooling jackets of the engine. Also the temperature regulator T_ is adapted to handle the mixing proportion between 0 the part flows 14 and 15, which have different tempe¬ ratures. Thus, the cooling jacket 1 of the engine can constantly be fed with cooling water of a constant temperature. On its way to the cooling jacket of the engine, the cooling .water flow 16 passes the cooling r ^. water pump 17. It is this pump which together with the

previously mentioned flow adjusting valve 8 determines the total cooling water flow system. From the design outlined above, it will be noted that each and every change of the cooling water temperature at any point in the system involves a change of the proportional size of the different part flows 11, 13 and 15, which gives a constant temperature in the flows 14 and 16.

This involves that a practically constant temperature of_the air driven into the engine is obtained, depending upon appropriately chosen pump characteristics, combina¬ tion and choice of the regulating ranges of the thermo¬ stat valves, and choice of cooler area and K-value characteristics for the air intercooler (see charac¬ teristics given in figure 3) .

Figure 1 also shows a pressure maintaining connection 18 and two de-airing connections 19 and 20, respecti¬ vely, for the air intercooler 12 and the fresh water cooler 21. The raw water conductor to the fresh water cooler 21 has been given the designation 22. The raw water circuit of course comprises both a circulation pump and appropriate components for controlling the raw water flow, but these have not been included in the dra¬ wing, as the main purpose of the drawing is to illustrate the fresh water cooling system. Likewise, the lubricating oil cooler and miscellaneous safety and control systems which are usually comprised in an engine installation of this type have been omitted, in order to make the figure as clear as possible.

However, a cooling water preheater 25 connected in an own circulating circuit 23 with a separate cooling water pump 24 has been indicated.

This circuit is usec for maintaininσ the te oerature of

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the engine or, alternatively, during a short time be¬ fore the engine is started during extremely cold condi¬ tions .

As previously mentioned, the combined de-airing, ex- pansion and pressure maintaining tank 3 shown in figure 2 consists of an upper de-airing chamber and a lower expansion and pressure maintaining chamber 6, ^' separated by a separating wall 5. The chamber 6 is accessible from the outside via a cover 26 which is applied press- ure-tight on top of the tank, but with a pressure regu¬ lator, which is fitted over an ascending pipe 27 which leads through the upper chamber 4 to the lower one. The normal fluid area in the lower chamber is shown in the drawing. As will be noted from the figure, the upper de-airing chamber is normally entirely filled with cooling water.

The upper chamber 4 has an inlet 28 and an outlet 29. The inlet and outlet emerge at different parts of the chamber, and between these a guide plate 30 extending across the chamber is arranged.

The cooling water is thereby forced to follow the course indicated in the figure by a dot-dash arrow line. As the impulse of the water flow is reduced by the change of direction effected by the guide plate and the change to a greater cross section in the tank, a change-over to laminar flow takes place, whereby efficient de-airing cf the flow of cooling water is obtained.

The air which has been separated off is collected in the upper part of the chamber, and through a pipe 31 has a passage to the lower chamber of the tank. The z>iOB 31 has an ooeninσ 32 in the UDDer oart of the

Chamber 4 and an opening 33 below the liquid level in the chamber 6. In the figure, also a cleaning plug 34 is shown. In the intake 28 there is a de-airing hole 35 for preventing air from collecting in the pipe bend while the system is being filled. The pressure main¬ taining conductor 18 and the de-airing conductors 19 and 20 from the air intercooler 12 and the fresh water cooler 21 respectively emerge in the lower chamber 6 of the tank, the gas (air) part of which is thus com- pressed and absorbs the expansion when the water in the system is heated (see figure 1).

The safety system not shown in detail in figure 1 in¬ cludes means for keeping the fluid surface in the ex¬ pansion and pressure maintaining chamber 6 within limi- ted variations. For this purpose, a pump start 36 can be engaged in the tank at a low level for feeding in more cooling water to the system from a conventional draining tank (not shown) and a pump stop 37 at the normal level and, finally, an alarm 38 for extremely low level.

In figure 2, a level scale 39 is shown beside the tank 3. This level scale corresponds to a level indication tube arranged on the outside of the tank 3 and connec¬ ted with the expansion and pressure maintaining chamber. The de-airing chamber 4 is moreover provided with an air outlet valve 40. The level indication tube 39 has three indications: "low", "high", and "filling". At normal operation, the level of the chamber 6 should be within the normal operating range, between the indi- cations for high and low water level. The level indi¬ cation "filling" is used when an empty system is being filled up, wnen also the air outlet valve 40 should be water has been filled into this

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level and the valve 40 has been closed and the system is started up _r the water is re-distributed in the sy¬ stem, so that the upper chamber 4 is filled up and an air-filled expansion space is formed in the lower cham- 5 ber 6.

As regards the general function of the fresh water cooling system according to the invention it may also be mentioned that the capacity of the water pump 17 is set with the aid of the flow adjusting device 8 so that

10 a desired temperature increase isobtained over the en¬ gine at full effect. The pressure level in the jacket cooling is thereby also increased so that the tempera¬ ture limit for the formation of steam is increased whereby such formation of steam can be avoided on strong-

15 ly heat-emitting surfaces of the engine. The flow ad¬ justing device 8 can consist of a throttling valve which can be locked, or a fixed throttling washer.

The temperature regulator T. mixes high temperature water with cold water from the fresh water cooler to a 20 constant intake temperature for the air intercooler.

- The temperature regulator T_ mixes high and low tem¬ perature water to a constant intake temperature in the hign temperature circuit (the jacket cooling) .

When the engine is started, during a short time the 25 temperature regulator T_ runs the water circulation through the high temperature circuit only, until the operating temperature has been reached.

However, a certain preheating effect in the air inter¬ cooler is obtained through a small connection hole in 30 the element cf the temperature reσulator and also thr-

ought the derairing pipe of the air intercooler. As soon as the engine has reached normal operating temperature the temperature regulators T ₂ and also run water through the low temperature circuit (the air intercooler and the intake air is thereby tempered, i.e. it is coo¬ led down if required owing to the load applied, or pre¬ heated if required.

When the operating temperature has been reached in the lς> temperature circuit the temperature regulator T.. at an increased load begins to let in water from the fresh water cooler into the low temperature circuit and gives an increased cooling effect to the air intercooler As will be noted, the arrangement is such that an in¬ creased cooling effect is obtained in the air inter- cooler when the load on the engine increases, which has the result that the thermal load on the engine is kept down.

Maintaining of pressure in the system is achieved by the static level of the water in the lower chamber to- gether with the pressure increase through the expansion of the water, and acts through the pressure maintaining pipe 18 which connects the lower chamber 6 with the suction side of the pump 17, which guarantees that there will be no disturbances (cavitation) in the pump. Altεr- natively, an external pressure can be cc nected to the ascending pipe 27. This ascending pipe, which goes from the lower chamber 6, is also provided with a pressure- tight cover 26, including a pressure regulator, which opens at a predetermined over-pressure (safety function) and also opens just below the atmosphere line (vacuum function) .

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It should be mentioned that the flow through the de- airing pipe 31 from the upper chamber to the lower one (the expansion part) emerges below the water level, so that there will be no flushing of the expansion part and therewith a minimal oxygenation of the water in the system. The course of the de-airing pipe 31 moreover involves that no air pocket is drawn up to the upper chamber when the engine has been stopped, which also simplifies the judging of the fluid level.

The adv.antages of the system according to the invention could thus be summarized as follows:

One single cooling system for both the jacket and air intercooling in which all functions are built in on the engine, expect the fresh water cooler.

The effectiveness of the air intercooling in¬ creases when the load on the engine increases, - which keeps a low thermal load on the engine.

- Preheating (tempering) of the intake air takes place at the starting up and during operation under artic conditions (condesation is avoided)

Continuous de-airing (degassification) is en¬ sured.

- Corrosion-proof system, as there is no oxy- genation of the water.

More uniform and cheaper material in tubing, fittings and air intercooler can be used (coitraarec with raw water coolinσ) .

- Simplified operation.

- Considerably simplified engine installation.

Finally, in figure 3 an example of the fresh water cooling system according to the invention is given with relevant data for such a cooling system for a compress¬ or charged air intercooled medium speed diesel engine with developed power and speed according to the prop¬ eller law. As will be noted from the diagram, the en¬ gine in question was provided with a direct-drive water pump. The engine speed is indicated on the X axis and, for the rest, the various curves should be self- ex¬ planatory.

BEST MODE OF CARRYING OUT THE INVENTION

The embodiment described above in figures 1 and 2 can be regarded as the most advantageous ambodiment at pre- ^* sent of the fresh water cooling system according to the invention, although this can be varied within the scope of the claims.

INDUSTRIAL APPLICABILITY

As will be noted from the foregoing text, the fresh water cooling system according to the invention is primarily intended to be utilized industrially for com¬ pressor charged I.C. engines primarily of the type medium speed diesel engines.

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