GB2194285A - Diesel engine exhaust manifold cooling system - Google Patents

Abstract

Multiple tubular gas passages 12, 13, 14 in the water-cooled stainless steel manifold each contain an insert, of a kind known per se from UK Patent Specification No 2 097 910B, sprung against the passage wall. The inserts provide turbulence which increases the heat transfer, reduce the build-up of carbon deposits and can be removed for cleaning. <IMAGE>

Description

SPECIFICATION Exhaust gas cooling system The invention relates to the cooling of the combustion gases exhausted from internal combustion engines.

It is well known that internal combustion engines of the high-compression oil-ignition type ("Diesel" engines) tend to emit carbon particles in the form of live sparks. And internal combustion engines of the carburettored and spark-ignition type ("Petrol" engines) are known to emit live flame into the exhaust system, as do Diesel engines.

The emission of sparks or flame can occur independently, or can be combined, and although it occurs most frequently in worn engines it nevertheless can occur in any engine if the engine draws gas-laden air-especially air of a high flammable content-into its air intake.

These problems are particularly acute when the engine is a Diesel engine intended to operate in hazardous areas as defined by the Institute of Petroleum Electrical Safety Code and by British Standard 5345 Part 1. One example of a hazardous area falling within this definition is the gas-laden atmosphere of an oildrilling rig. In such an atmosphere even the normally-acceptable tendency of the engine exhaust gas manifold to be hot is unacceptable without modifications.

The Oil Companies Materials Association (OCMA) publishes recommendations for the protection of Diesel engines operating in hazardous areas. One of these recommendations is that the surface temperature of the engine and exhaust system shall not exceed 250"C when tested under full load conditions. The recommendations envisage that in some situations cooling of the exhaust manifold and piping may be necessary. They give the known examples of water jacketing and finned coolers as possible means of achieving this.

It is conventional to cool the hot exhaust gases of Diesel engines intended for operation in these hazardous areas by sending the gases through a water cooled manifold followed by a flame trap and followed again by a spark arrestor. The main cooling occurs in the manifold. Conventionally this manifold comprises two or three successive "passes" of smallbore circular-section tubular passages of which there are quite a number in known manifold designs. These small-bore passages rapidly carbon-up, although they are plain-bore passages, i.e. they contain no substantial impediment to the gas flow.

According to the present invention, a Diesel engine exhaust gas cooler comprises multiple tubular gas passages each with an insert, of the kind defined, sprung against the passage wall, and follows or forms part of the engine manifold.

An insert, of the kind defined, is an insert falling within the scope of any claim of UK Patent No 2 097 910 B.

Inserts, of the kind defined, have been developed by the proprietors of UK Patent No 2 097 910 B primarily for the purpose of cooling liquids-specifically, lubricating oil-flowing through the tubes of an air-cooled heat exchanger. They are currently marketed in the United Kingdom under the Trade Mark HEA TEX. Although the patent defines them as applicable to fluids, not just liquids, their primary application has always been in the field of cooling liquid flows. The main reason for their design, in the face of commercially available twisted-tape inserts, is that they are more efficient than the latter inserts in breaking up the heavy insulative boundary layer which tends to form on the tube wall and leads to "coring".

There is prima facie no advantage to be gained by using them in an exhaust gas flow.

Inserts, of the kind defined, thus come from a field to which the skilled addressee of this present specification, seeking to solve the problem of cooling the combustion gases as they flow through the exhaust manifold, would not refer. As has been stated, conventionally the exhaust manifold comprises a multiplicity of small-bore gas passages. Inserts, of the kind defined, together with their commercial competitors (such as the twisted-tape kind referred to) are designed primarily for use in large-bore pipes.

Inserts, not of the kind defined but forming part of the known art, are shown in UK Patent Specification No 483 642 and UK Patent Specification No 1 570 530. The first of these is for placement in a radiator tube for an internal combustion engine so as to improve the efficiency of cooling of the liquid, usually water, flowing through the radiator tube. The second is for placement in a D-entrainment or reaction apparatus so as to improve interaction between fluids or a fluid and a solid.

Neither of these two inserts just referred to would be considered by the man seeking to solve the problem to which the present invention relates. In the first case, whilst the efficiency of cooling of the water flowing through the radiator may be improved, the drop in temperature and the relative inefficiency of the insert whilst acceptable in a motor vehicle radiator of conventional mobile kind is quite inappropriate for the specialised field to which the present invention relates. In the second case, there is no direct parallel between the two fields at all.

The initial advantage of a manifold embodying the present invention is threefold.

First, it enables the temperature of the exhaust gases passing through the manifold to be lowered dramatically when compared with conventional small-bore water-cooled manifolds. As mentioned above, 250"C is the temperature specified as acceptable for the mani folds of Diesel engines operating in defined hazardous areas. In non-public trials, a Diesel engine fitted with an exhaust gas manifold embodying the present invention and surrounded by a water jacket has achieved surface temperatures of around 150"C.

Second, the service intervals for the manifold-i.e. the intervals of time between which the gas passages need to be cleaned-out of carbon-are extended equally dramatically. Because relatively large-bore tubular passages have to be used, in order to accommodate the inserts, the passages do not carbon-up anywhere near as quickly as the conventional small-bore gas passages. Service intervals of perhaps up to 1,000 hours are possible as compared with 200 hours for a conventional manifold.

Still on this second advantage, a large contributory factor to the dramatically extended service interval is the use of the inserts themselves. They swirl the exhaust gases, and thoroughly mix the gas flow, and hence the carbon deposits are given far less chance to build up on the walls of the passages and on the inserts themselves.

Third, when servicing is necessary, the inserts can be simply pulled through and out of the gas passages-much in the manner of a "flue brush"-and, in so doing, thoroughly dislodge and/or bring with them the inevitable carbon deposits. New inserts or cleaned inserts can then be fitted.

To enhance that last-mentioned advantage, preferably the inserts rely wholly on their springing fit against the passage walls to retain them against the walls. In other words-and again in contrast to the broadest aspect of their use as envisaged in UK Patent No 2 097 910 B they are preferably not bonded to the passage walls when they are first fitted.

Yet another advantage flowing from the use of inserts, of the kind defined, is that the manifold can function as a flame trap and/or a spark arrestor. The design of flame traps in particular has received considerable attention, see for example UK Patent No 1 586 705 which has been commercially very successful.

But it is not a manifold. It is solely a flame trap. The use of inserts, of the kind defined, makes it possible to combine a manifold with a flame trap and/or a spark arrestor.

Preferably, in practical embodiments, an exhaust gas manifold embodying the invention is jacketed within a fluid-cooled jacket; and, again in practical terms, the cooling fluid flowing through the jacket will conventionally be water.

The accompanying drawings show one possible form which a manifold embodying the invention might take.

In the accompanying drawings: Figure 1 shows a Diesel engine exhaust gas cooling apparatus, embodying the invention, when viewed in side elevation and showing one end only of the apparatus; Figure 2 shows the same apparatus viewed in the same way, and to the same scale, but showing the other end only of the apparatus; Figure 3 is a view looking in the direction of arrow A of Figure 1; Figure 4 is a view looking in the direction of arrow B of Figure 1; and Figure 5 is a view looking in the direction of arrow C of Figure 1.

The apparatus shown is a stainless steel manifold. It is waterjacketed. It contains three parallel "passes" of circularcylindrical tubular gas passages, each of which houses removably an insert, of the kind defined. It constitutes the first section of the overall exhaust system which cools, filters and attenuates the noise of the exhaust gases.

Gases enter the manifold as indicated by the flow arrow F in Figures 2 and 5 where a flange, referenced 11, from the manifold bolts to the exhaust gas outlet from the engine cylinder head.

Having entered the manifold, the gases initially expand-and thus slow down-as they follow the curve of the manifold into a first pass 12 of six parallel circular-cylindrical tubular gas passages each containing a respective insert, of the kind defined, sprung against the passage wall.

As the gases enter and traverse this first pass, they accelerate. They slow again as they curve round the manifold endcap (Figure 1) into the second pass 13 of four parallel circular-cylindrical tubular passages. And they accelerate down these passages before slowing again to curve (Figure 2) around the manifold cap at the other end and then accelerating into and through the final pass 14 which again consists of four parallel tubular circularcylindrical gas passages.

The gases leave the manifold as shown in Figure 1 by the arrow '0'.

All three sets of passages 12, 13, 14 have to be traversed in that order by the gases before they leave the manifold at 'O'.

The inserts, details of which may be selected by the intended skilled addressee of this specification from UK Patent Specification No 2 097 910 B are stainless steel and are currently sold under the Trade Mark HEATEX in the United Kingdom by the proprietors of UK Patent No 2 097 910 B. The diameter of each circular-cylindrical gas passage in the embodiment illustrated is approximately 35 mm in contrast to the typically 10 mm diameter plain-tube gas passages of conventional manifolds. The particular manifold illustrated and described was designed to cool the gases of a Ford Marine 6-cylinder Diesel engine of known kind, modified specifically to operate in hazardous areas (zones 1 and 2) as herein before defined; although the invention is not of course to be restricted to any specific manufacturer's Diesel engine nor to Diesel engines solely intended for operation on oil rigs.

Another and extremely important advantage of the invention is the versatility, hitherto quite unattainable, which it gives to gas cooler design. In the conventional manifold reviewed earlier in this specification, there is no way in which the running characteristics of the manifold can be altered. And so, when operating at extremes of temperature and/or load, the manifold could run too hot or alternatively could never reach a proper operating temperature. There is no way in which the plain-bore tubular passages can have their operating characteristics "tuned" to allow for, for example, the load difference between an engine operating a crane and the same engine operating a wire line winch.

With a cooler embodying the invention, by contrast, inserts can be removed and/or aitered in configuration from amongst the range of inserts, of the kind defined, with which the invention operates. And so a given manifold cooler can be "fine-tuned" exactly to suit given surroundings and/or load driving requirements.

Claims (4)

1. A Diesel engine exhaust gas cooler comprising multiple tubular gas passages each with an insert of the kind defined, sprung against the passage wall and following or forming part of the engine manifold.

2. A Diesel engine exhaust gas cooler according to Claim 1, in which the inserts rely wholly on their springing fit against the passage walls to retain them against the walls.

3. An exhaust gas manifold embodying the invention claimed in Claim 1 or Claim 2, in which the manifold is jacketed within a fluidcooled jacket.

4. An exhaust gas manifold substantially as described herein with reference to and as illustrated in the accompanying drawings.