WO1982001394A1

WO1982001394A1 - Method for use in the conversion of turbocharged diesel engines,and engines converted according to the method

Info

Publication number: WO1982001394A1
Application number: PCT/DK1981/000091
Authority: WO
Inventors: Power Eng As Int
Original assignee: Hvidtfeldt Rasmussen Knud
Priority date: 1980-10-20
Filing date: 1981-10-20
Publication date: 1982-04-29
Also published as: DK444380A; EP0062677A1; DK146745C; JPS57501686A; NO821894L; DK146745B

Abstract

In order to achieve oil saving in the operation of Diesel engines, in particular marine engines, which are provided with impulse driven turbo chargers, such an engine is converted by replacing the connections which connect the turbines of the turbochargers and the exhaust valves of the engine, as regards each turbine, with an exhaust gas collector (15, 16, 17, and 18, respectively) which is separate for the respective turbine. Each of the collectors (15, 16, 17, and 18) is connected between the inlet (25, 26, 27, and 28, respectively) of the respective turbine and the exhaust valves belonging to the respective turbine. The collectors (15, 16, 17, and 18) have a volume which is so adapted that the maximum pressure created in each of the collectors (15, 16, 17 and 18) by the gas outflow from the corresponding cylinders lies closely adjacent to but does not exceed the average pressure in the scavenging and charging air receiver (31) of the engine.

Description

METHOD FOR USE IN THE CONVERSION OF TURBOCHARGED DIESEL ENGINES, AND ENGINES CONVERTED ACCORDING TO THE METHOD.

The invention relates to a method for use in the conversion of 2-stroke impulse turbocharged Diesel engines wherein the cylinders are grouped three by three and four by four, and wherein the ignition intverval corresponds to 120° and 90° crank shaft angle, respectively, and to engines converted according to the method .

Two forms of 2-stroke turbocharged Diesel engines are known, viz. engines the turbochargers of which are driven according to the impulse principle, and engines the turbochargers of which are driven according to the constant pressure principle. In impulse turbocharged engines the grouping of the cylinders for each exhaust gas driven turbocharger is dictated by the ignition interval between the cylinders . For 6-, 9- and 12-cylinder engines, the ignition order normally is so selected that groups of 3 cylinders have a uniform ignition interval of 120° and each such group is connected to a turbocharger. As regards 4- and 8-cylinder engines, each turbine nozzle normally is divided into subsections each having its own sub-iniet. To each sub-inlet two cylin ders are connected which have the greatest ignition interval which normally will be 180° corresponding to a group having an equal ignition interval of 90°. Impulse turbocharged engines have a comparatively small pipe volume in front of the turbines, and high pressure impulses are caused in the pipes when the exhaust gas flows out of the cylinder through the exhaust valve to the turbine. Accordingly, the engines need a comparatively early opening of the exhaust valves of the engine in order to achieve a sufficiently large pre-escape for reducing the cylinder pressure down to the scavenging pressure when the piston of the engine uncovers the scavenging ports . The impulse turbochargϊng principle offers a high amount of energy for operating the turbochargers, however, at the expense of an unnecessarily high consumption of combustion oil .

It is the object of the present invention to provide an easy method for use when the conversion of turbocharged Diesel engines from the impulse turbocharging principle to the constant pressure turbocharging principle is contemplated, in order to achieve a reduction of the specific consumption of combustion oil .

One might consider converting an engine having impulse driven turbochargers into an engine having constant pressure driven turbo chargers by converting the engine in question into an engine with the charging system which is conventional for engines, the turbocharger or turbochargers of which are driven according to the constant pressure principle. A conventional engine of the last mentioned kind comprises an exhaust gas collector which is common to all the cylinders and which feeds the turbocharger or the turbochargers of the engine according to the constant pressure principle. An exhaust gas collector which is common to all the cylinders offers the advantage that a good leveling out of the pressure impulses from all of the corresponding cylinders is achieved, and , accordingly, an approximately constant feeding of the turbochargers connected to the corresponding exhaust gas collector is achieved.

The present invention is based on the recognition that the mounting of a common exhaust gas collector upon an existing engine which, originally, was not constructed with due regard to such use, results in considerable difficulties not only as regards the space available, but also in view of the precautions which must be taken due to the large expansions in the longitudinal direction to which such a common exhaust gas collector will be subjected by being heated to the operating temperature. Moreover, such conversion may necessitate a damping of the pressure oscillations in a long big exhaust gas collector in order to counteract disturbances in the scavenging and charging conditions of the individual engine cylinders.

The method according to the present invention is characterized in that the connections, which in an engine having otherwise impulse driven turbochargers connect the turbines of said turbochargers with the exhaust valves of the engine, are replaced for each of the turbines, by an exhaust collector which is separate for the respective turbine and is connected between the inlet of the respective turbine and the exhaust valves corresponding to the respective turbine, each of said exhaust gas collectors having a volume which is so dimensioned that the exhaust gas outflow from the cylinders does not increase the pressure In the exhaust gas collector in front of the turbine beyond the average pressure in the scavenging and charging air receiver of the engine.

By means of this method it is achieved that the conversion may be carried out in a simple way because the exhaust gas collector, which is common for the cylinders of conventional engines having a turbocharger or turbochargers working according to the constant pressure principle, is avoided, and instead thereof one exhaust gas collector for each of the existing turbochargers of the engine in question is used, whereby the mounting work is easily and securely carried out and, simultaneous ly, large expansions and contractions are avoided due to the fact that the collectors in question are separate. It has been found that in the case of converting marine engines, the work involved by the conversion may be carried out almost within the time which corresponds to the normal docking period of a ship in order to clean and paint the hull and , accordingly, extra costs for docking time may be avoided in seve ral instances. This is of great importance with due regard to the fact that the costs involved by letting a ship of the size where the method according to the invention may be used most advantageously lie still , may amount up to 200,000 d . Kr. per day. The subdivision into separate collectors for the individual cylinder groups also has other considerably simplifying and cost saving aspects when conversion of existing engines is concerned . The individual exhaust collectors are simple to manufacture and in particular to mount, and due to the fact that they are separate no expansion elements are necessary. Also, a simple trans portation from the work shop and to the ship at the shipyard in question is achieved, and the collectors may be taken on board without being dismounted and, accordingly, are immediately ready for being mounted upon the engine as soon as the ship arrives in harbour. Moreover, due to the division into separate exhaust gas collectors the possibility is achieved that several collectors may be mounted simultaneously, or the collectors may be mounted upon one half of the engine at a time because a marine engine normally Is adapted to be able to propel the ship with only half of the cylinders working .

It will be understood that the smaller the separate exhaust gas collectors are made, the greater will be the advantages achieved by means of the invention, but, of course, the exhaust gas collectors may not be selected arbitrarily small due to the fact that the pressures which are caused in the collectors by means of the exhaust gas will be higher, the smaller the collectors are, and if the average pressure in the collectors rises above the average pressure in the scavenging and charging air receiver of the engine, the engine will , at the best, work very poorly. The advantages of the present invention are achieved at an optimum by reducing the volume of the separate exhaust gas collectors to a size limit, viz. in such a way that the exhaust gas collectors may just accomodate the large pre-escape gas volumes without the pressure in the gas collectors thereby exceeding the average scavenging and charging air pressure. Moreover, the invention ss based upon the recognition that the comparatively high transient pressure fluctuations which may occur in the exhaust gas collectors, and which one normally will do everything In order to avoid , may well be accepted in connection with conversions because collectors of a small length result in a natural frequency which is so high that the amplification becomes insignificant, and In spite of all an air distribution between the cylinders may be achieved which is acceptable under the circumstances . I n this connection It is of importance that the dimensioning referred to is so selected that it secures the advantage of the constant pressure turbocharging principle which consists therein that the opening moment of the exhaust may be delayed to a later moment during the expansion stroke in such a way that the usual oil saving amounting to 6-8% may be achieved, viz. corresponding to the difference in oil consumption between an engine which is Impulse charged, and an engine which is charged according to the constant pressure principle. Accordingly, no incalculable oscillations are to be feared which would necessitate damping , and resonance or interference phenomena, if any, which may occur by using one exhaust gas collector common for all the cylinders may be disregarded . In order to achieve very small dimensions of the separate exhaust gas collectors, such high maximum pressures may, according to a preferred embodiment of the Invention, be accepted in the separate exhaust gas collectors that, at the beginning of the opening of the scavenging ports, reverse flow from the exhaust gas collectors and into the cylinders connected therewith occurs at momentarily low pressures in the scavenging and charging air receiver of the engine, i. e. at pressures in the receiver lying below the average pressure therein because it has been found, according to the present invention , that the drawbacks which may result from such reverse flow, are more than compensated for due to the advantages which the small dimensions of the exhaust gas collectors result In.

According to a preferred embodiment of the invention , exhaust gas collectors are used which together with their connections to the corresponding cylinders and the corresponding turbine respectively, have a volume which is approximately 2.3 times as great as the stroke volume of the cylinders connected to the exhaust gas collector in question.

The factor referred to above will vary depending on whether an engine wherein the cylinders are grouped three by three or four by four is concerned . The factor referred to should be a little higher for engines having three cylinders in each group than for engines having four cylinders in each group, and the factor is appropriately, accordin g to the invention , selected between 2.2 and 2.6 for 3-cylϊnder groups and between 2.0 and 2.4 for 4-cylinder groups .

According to the invention the activating cams of the exhaust valves are appropriately adjusted in order to achieve optimum delay of the opening of the exhaust valves corresponding to the future engine load and the future operation of the turbines as turbines working according to the constant pressure principle, whereby a maximum sav ing as regards the specific oil consumption is achieved . According to an embodiment of the method , the activating cams of the exhaust valves are adjusted in order to achieve a delay of the opening of the valves beyond the delay which is usual in connection with usual conversion to constant pressure turbocharging, if it is desired to reduce the future maximum load of the engine. An increased delay amounting to approximately 1º crank shaft angle for each 10 per cent reduction in the future normal engine load has proved to be appropriate.

The invention will hereinafter be further explained with reference to the drawings in which

Figs. 1 and 2 show a side view and an end view respectively of a longitudinally scavenged 2-stroke engine which Is suitable for being converted by using the method according to the present invention , and Figs . 3, 4, and 5 show a side view, an end view, and a plane view respectively of a longitudinally scavenged 2-stroke engine after having been converted by using the method according to the present Invention . The engine shown in figs . 1 and 2 is a 6-cylinder Diesel engine which is turbocharged by means of two turbochargers 1 and 2, the turbine inlets 3 and 4, respectively, of which are connected with the exhaust valves of the engine. Acccordlngly, each of the turbine inlets 3 and 4 is connected with three of the cylinders of the engine, viz. by means of three exhaust tubes, and these cylinders have a uniform ignition interval of 120°. I n figs . 1 and 2 only two of the three exhaust tubes which are conneced with each of the two turbochargers 1 and 2 are visible, and these two exhaust tubes are provided with the reference numerals 5, 6 and 7, 8, respectively. Comparatively short exhaust tubes are used and the exhaust tubes to each turbocharger are con nected with cylinders which work with a phase displacement of 120° with respect to each other. Accordingly, the turbines of the two turbochargers 1 and 2 are fed according to the impulse turbocharging principle, and the pre-escape and the exhaust impulses from each cylinder are fed directly to a sub-inlet in the turbine inlet of the corresponding turbine. This charging principle requires a comparatively long pre-escape period in order to achieve a sufficient power of the turbochargers. On the other hand, the turbochargers are able to feed the engine cylinders even at very low loads. Such feeding is made via a scavengIng and charging air receiver 9.

Figs. 3, 4, and 5 show a twelve-cylinder Diesel engine of fundamentally the same structure as the Diesel engine according to figs. 1 and 2, but after having been converted from Impulse operation to constant pressure operation of the turbochargers by means of the method according to the present invention .

As will be seen by comparing the two engines, the direct connections between the exhaust valves of each cylinder group comprising three cylinders and the corresponding turbocharger 11 , 12, 13, and 14, respectively, have been replaced by an exhaust gas collector 15, 16, 17, and 18, respectively, which by means of a single outlet 20, 21 , 22, and 23, respectively, is connected with the turbine Inlet 25, 26, 27, and 28, respectively, of the corresponding turbocharger, and, moreover, each of the exhaust gas collectors is connected with the exhaust valves of the corresponding group of cylinders by means of three short tube elbows 30a, 30b, 30c, and 30d, respectively. As these connections 30a, 30b, 30c, and 30d there may per se perfectly well be used parts of the tube connections which originally connected the turbochargers in question directly with the cylinders in question, viz. that part of the tube connections which is arranged adjacent to the corresponding cylinder, cf. the downwardly extending elbow in figs. 1 and 2 which In fig . 4 has been rotated 190° after having been cut at an appropriate location .

Accordingly, the exhaust gas collectors 15, 16, 17, and 18 which are individual to the individual cylinder groups are each fed from three cylinders which have a mutual phase displacement of 120° . Each of the exhaust gas collectors 15, 16, 17, and 18 has such a volume that the maximum pressure which occurs therein during the operation of the engine due to the feeding of the gas collectors with exhaust gas from the corresponding cylinders, lies adjacent to but does not exceed the average pressure in the scavenging and charging air receiver 31 of the engine.

As regards engines having groups each comprising 4 cylinders, each group is provided with an exhaust gas collector as explained above.

By the conversion of the engine shown in figs . 3, 4, and 5 there has, furthermore, been made an adjustment of the cams which activate the exhaust valves of the engine, viz. in order to delay the opening of the valves corresponding to the intended operation of the turbines as driven according to the constant pressure principle and the oil savings obtained thereby. If, after the conversion , a reduction of the maximum load of the engine is intended in order to save further oil, a delay of the opening of the outlet valves amounting to approximately 1 per cent for each 10 per cent the future maximum engine load is intended to be reduced, has proved to offer optimum results.

According to the embodiment shown in the drawings the volume of each exhaust gas collector 15, 16, 17, and 18, respectively, inclusive the connections 25, 26, 27, 28 and 30a, 30b, 30c, 30d, respectively, has been selected, so as to correspond to approximately 2.3 times the stroke volume of the cylinders connected to each exhaust gas collector. By such dimensioning a maximum pressure will occur in each of the exhaust gas collectors, which lies adjacent to but does not exceed the average pressure in the scavenging and charging air receiver 31 of the engine, and thereby the exhaust gas collectors will be sufficiently small in order to allow an easy handling and mounting at the conversion . According to the embodiment shown in the drawings, where an engine having the cylinders grouped three by three is concerned , the factor referred to above may vary between approximately 2.2 and 2.6. If an engine having four cylinders in each group is concerned , the factor in question may be selected a little lower, viz. between approximately 2.0 and 2.4.

In order to achieve extremely small containers maximum pressures may be accepted therein which are higher than the minimum pressure which may occur due to pressure oscillations in the scavenging and charging air receiver 31.

Due to the conversion into impulse operation , such great oil savings are achieved that the costs connected with the conversion according to the invention are more than compensated for, as seen over the life time of the engine. Moreover, as pointed out above, the con version Is carried out in a comparatively simple way because the exhaust gas collectors, due to the short length thereof, are easily positioned on previously installed engines and, moreover, the original turbochargers may form parts of the converted charging system after adaptation to the desired capacity and the desired pressure. Moreover, the original scavenging and charging air receiver 31 may be used.

Claims

CLAIMS:

1 . Method for use in the conversion of 2-stroke Impulse turbochar ged Diesel engines wherein the cylinders are grouped three by three and four by four, and wherein the ignition interval corresponds to 120º and 90º crank shaft angle, respectively, characterized in that the connections (5, 6, 7, and 8) , which in an engine having otherwise impulse driven turbochargers (1 and 2) connect the turbines of said turbochargers with the exhaust valves of the engine, are replaced for each of the turbines , by an exhaust collector (15, 16, 17, and 18) which is separate for the respective turbine and is connected between the inlet of the corresponding turbine (25, 26, 27, and 28 respectively) and the exhaust valves corresponding to the respective turbine, each of said exhaust gas collectors having a volume which is so dimensioned that the exhaust gas outflow from the cylinders does not increase the pressure in the exhaust gas collector in front of the turbine beyond the average pressure in the scavenging and charging air receiver (31 ) of the engine.

2. Method according to claim 1 , characterized by using exhaust gas collectors, the volume of which is so dimensioned that the maximum pressure created in front of the turbine by the gas flow from the corresponding cylinders into each exhaust gas collector is higher than the minimum pressure which may occur in the scavenging and charging air receiver due to pressure oscillations therein . 3. Method according to ciaim 1 , characterized by using exhaust gas collectors (15, 16, 17, and 18) which together with their connections (30a, 30b, 30c, 30d, and 20, 21 , 22, and 23, respectively) to the corresponding cylinders and to the corresponding turbine, respectively, have a volume which is approximately 2.

3 times as great as the stroke volume of the cylinders connected to the corresponding exhaust gas collector.

4. Method according to claim 3, characterized in that said factor, for an engine wherein the cylinders are grouped three by three, lies between approximately 2.2 and 2.6 and , for an engine wherein the cylinders are grouped four by four, lies between approximately 2.0 and 2.4.

5. Method according to ciaim 1 , characterized in that the activating cams for the exhaust valves are adjusted for optimum delay of the opening thereof corresponding to the future engine load and the future operation of the turbines as constant pressure driven turbines.

6. Method according to claim 4, characterized by the delay of theopening of the exhaust valves being increased by approximately 1º crank shaft angle for each 10 per cent the future maximum engine load Is reduced .

7. Engine converted according to the method according to any of the beforegolπg claims.