Explosion-protected diesel engine

A diesel engine has a fresh-air intake, an exhaust-gas output, and a cooling system in which a liquid coolant is circulated. This system is provided with an antiexplosion system having an intake flame arrester in the intake and a jacketed exhaust-pipe section connected to the output and receiving exhaust gases therethrough from the engine. The cooling system is connected to the jacketed exhaust-pipe section to cool same and to cool the exhaust gases therein by indirect heat exchange with the coolant. An exhaust-gas heat exchanger is connected through the jacketed pipe section to the output. The cooling system is also connected to the heat exchanger to cool the exhaust gases therein by indirect heat exchange with the coolant. An output flame arrester is connected via another exhaust-pipe section to the heat exchanger for conducting cooled exhaust gas from the exchanger to the arrester. Both of the flame arresters have an arrester housing and at least one plate therein defining a multiplicity of parallel passages of very small flow cross section and a similar output flame arrester. In addition the system has a venturi-type exhaust-gas diluter downstream of the output flame arrester for mixing the cooled exhaust gas with ambient air.

FIELD OF THE INVENTION 
The present invention relates to a diesel engine. More particularly this 
invention concerns such an engine which is specifically set up so as to be 
protected from causing an explosion so it can be used in a mine or the 
like. 
BACKGROUND OF THE INVENTION 
When a diesel engine is used in a mine, either on a railed vehicle, 
suspended monorail, or for a standard tractor, loader, or when it is used 
in close proximity to people and to explosive gases and the like, it is 
necessary to provide it with certain safety features. The exhaust gases 
must normally be cooled considerably, to at most about 70.degree. C., 
before being released to the surrounding air. Furthermore in a mine it is 
essential to avoid the ignition of surrounding explosive gases, either by 
suckihg them into the engine intake and having them flash back or by 
igniting them directly with the engine exhaust. Although a properly tuned 
diesel engine will generate minimal pollutants except for easy-to-filter 
particulates, it is extremely difficult to dissipate the large amount of 
heat generated in such a high-compression machine. 
In British Pat. Nos. 549,398 filed July 23, 1942 by A. Flatt and 670,732 
filed June 23, 1950 by F. Staddon plate-type flame arresters are described 
which each have a stack of plates that form a plurality of relatively 
circuitous passages of a width of about 0.8 mm, which is large enough to 
pass particulate matter without clogging. Any spark or flame in the gas 
passing through such a device, whether going into the intake manifold of 
the engine or coming from the exhaust manifold thereof, will be cooled and 
quenched. 
British Pat. No. 903,493 filed May 1, 1961 by D. Brown describes an exhaust 
pipe which is jacketed so that a liquid coolant can flow through it to 
cool the exhaust gases therein. In addition some of water is sprayed 
directly into the flow of exhaust gas to scrub and cool it. The thus 
cooled gases are then passed through a flame arrester and mixed with 
ambient air prior to discharge to the atmosphere. Thus the temperature of 
the exhaust gases is reduced greatly and any harmful constituents of the 
gas are eliminated and/or attenuated. Another such jacketed exhaust pipe 
is described in British Pat. No. 1,303,336 filed Sept. 17, 1971 by N. 
Parfitt. 
The system of British Pat. No. 1,037,339 filed Aug. 27, 1964 by H. 
Hammitzsch et al aims at reducing water consumption in a system such as 
described immediately above by cooling the exhaust gases wholly by 
indirect heat exchange. To this end the exhaust gases pass meander-fashion 
through a succession of individual tube assemblies enclosed in a housing 
filled with a liquid coolant. By the time the gas has traversed all these 
tube assemblies its temperature is reduced to a safe level. In addition 
the tube assemblies are set up with manifolds of large flow cross section 
to strip particles from the gas stream being cooled. 
A complex cooling and control system is described in British Pat. No. 
1,246,888 filed May 12, 1969 by Envirotech Corporation. This arrangement 
employs the latent heat of evaporation of water that is injected into the 
exiting exhaust-gas stream to cool it. The flow of water to the injectors 
is controlled in accordance with various engine operating parameters. 
Similarly U.S. Pat. No. 3,621,652 filed July 2, 1970 by J. Demaree passes 
the exhaust gases through a pair of chambers. In the first the gas gives 
up heat and in the second it is cooled directly by spraying water into it. 
Thus the cooling effect in the second chamber is applied to the upstream 
gases. 
In U.S. Pat. No. 3,831,377 filed July 24, 1972 by A. Morin a separate 
radiator and coolant circuit is used to chill the exhaust gases so much 
that many harmful constituents are condensed out of them. In addition the 
lighter volatile phase is separated out and fed back to the intake 
manifold. 
All of these systems are relatively complex. In addition few of them 
reliably provide the level of explosion protection needed on a diesel 
engine used in a mine or other dangerous location. 
In my above-cited copending patent application I further describe a diesel 
engine having a fresh-air intake, an exhaust-gas output, and a cooling 
system in which a liquid coolant is circulated. This system is provided 
with an antiexplosion system having an intake flame arrester in the intake 
and a jacketed exhaust-pipe section connected to the output and receiving 
exhaust gases therethrough from the engine. The cooling system is 
connected to the jacketed exhaust-pipe section to cool same and to cool 
the exhaust gases therein by indirect heat exchange with the coolant. An 
exhaust-gas heat exchanger is connected through the jacketed pipe section 
to the output. The cooling system is also connected to the heat exchanger 
to cool the exhaust gases therein by indirect heat exchange with the 
coolant. An output flame arrester is connected via another exhaust-pipe 
section to the heat exchanger for conducting cooled exhaust gas from the 
exchanger to the arrester. 
With such an arrangement the exhaust-gas cooling is integrated with the 
engine, and there is no need for a continually replenished external water 
supply. The mess made by engines where water is injected right into the 
exhaust gases is completely eliminated. In addition the pressure-related 
problems of the water-injection systems are completely avoided as well of 
course as the necessity of providing for a mobile water supply either 
connected to or mounted on the vehicle incorporating the engine system. 
This arrangement, which is also generally described in British Pat. No. 
2,093,119, functions well, but is susceptible of refinement. 
OBJECTS OF THE INVENTION 
It is therefore an object of the present invention to provide an improved 
explosion-proof diesel engine system. 
Another object is the provision of such an improved explosion-proof diesel 
engine system which overcomes the above-given disadvantages, that is which 
refine and add to the principles described in my above-cited copending 
application. 
SUMMARY OF THE INVENTION 
The system of this invention corresponds generally to that described above, 
but is provided with an intake flame arrester in the intake and having an 
arrester housing and at least one plate therein defining a multiplicity of 
parallel passages of very small flow cross section and a similar output 
flame arrester. In addition it has a venturi-type exhaust-gas diluter 
downstream of the output flame arrester for mixing the cooled exhaust gas 
with ambient air. 
This combination of features ensures extremely good protection against 
explosion. Not only is flame absolutely prevented from entering and 
leaving the system, but the exiting exhaust gas is cooled so much that 
explosion is completely ruled out. 
In accordance with another feature of this invention each arrester housing 
is of substantially greater flow cross section than the respective intake 
and output and the passages of the arresters measure at most 1.0 mm 
across. The plates of the arresters, which may be provided in several sets 
for extremely effective flame suppression, are of corrugated sheet metal 
with all the corrugations parallel to the throughflow direction. These 
plates are bunched up and held in replaceable cores in the housings. 
The diluter according to this invention includes a large-diameter outer 
tube centered on an upstream-to-downstream axis and having upstream and 
downstream ends open to the atmosphere, and a nozzle-type core in the 
outer tube and forming a plurality of gaps opening radially outward and 
downstream in the outer tube. Such a diluter has an output that is a 
low-velocity stream of gases virtually at ambient temperature.

Specific Description 
As seen in FIG. 1 a drive system 2 for a mine tractor or the like has a 
six-cylinder diesel engine 1 having an intake manifold 7 and an exhaust 
manifold 9 mounted as is standard. At its rear end the engine 1 has a 
flywheel 15 and at its front end is fitted with a two-part radiator 13 
having a fan 14. 
The intake 7 is connected through an angle-type rotary or flap-type valve 8 
to a plate-type flame arrester 5 and therethrough to a filter 4 which 
receives ambient air through a dust screen 3. The arrester 5 prevents any 
flammable gas from being sucked into the engine 1 and then exploding and 
flashing back in the opposite direction. 
The exhaust manifold 9 is connected through a jacketed or double-wall elbow 
17 to a heat exchanger 18. Both this elbow 17, which forms part of the 
exhaust pipe of the engine 1, and the exchanger 18 are traversed in a 
closed circuit by a liquid coolant circulated by a pump 12 through them 
and through a separate and independent portion of the radiator 13. Another 
such pump 11 is provided that circulates a liquid coolant through another 
portion of the radiator 13 and through the engine 1. The portion of the 
radiator dedicated to the engine 1 is larger as indicated in FIG. 1 than 
that portion used for cooling the exhaust gases. As indicated in FIG. 1a a 
straight jacketed conduit or compensator 17a can replace the elbow 17. 
The heat exchanger 18 has a cylindrical housing part 19 closed at one end 
and releasably secured at its other end to a flange 20 so it can be 
removed. Internally it has tube bundles 21 and 22 through which the 
exhaust gases pass, and around which the liquid coolant flows. A 
temperature sensor 23 forming part of an engine-control system is 
connected to the downstream end of the heat exchanger 18 to shut down the 
engine and close the valve 8 if the temperature at this region exceeds 
about 150.degree. C. 
The downstream end of the exchanger 18 is connected via a compensator or 
conduit 24 to an input elbow 25 of a flame arrester 27 and thence through 
another conduit 26 to a gas-diluting muffler 28. The conduits 24 and 26 
can be of any convenient shape or length, as by the time the exhaust gases 
reach them they are relatively cool, that is under 150.degree. C., so that 
the arrester 27 and muffler 28 can be mounted at any convenient location 
on the tractor or vehicle having the engine 1. 
As shown in FIGS. 2, 3 and 4 the plate-type flame or spark arrester 27, 
which is identical to the arrester 5, has a pair of identical housing 
portions 32 between which two sets of plates 30 is held in an annular core 
housing part 31. A fitting 33 is provided for mounting a temperature 
and/or pressure sensor that is also connected to the engine control 
system. Such an assembly can be very compact. 
The plates 30 are formed of very thin and corrugated steel sheeting that is 
wound up to form a filter of fairly small mesh size of typically 0.7 mm. 
To the cross-sectional area occupied by these plates 30, the housing is of 
substantially greater flow cross section at them than upstream and 
downstream, so that the flame arrester does not constitute a flow 
restriction that would increase pressure. 
Furthermore as shown in FIGS. 3 and 4 the plates 30 are held in two 
separate layers between rings 34 formed with spokes 35 and hubs 36. A bolt 
37 passes axially through the two hubs 36 and through the two plates 30 so 
as to hold the assembly together, with a nut 38 holding the unit together. 
Thus the two housing halves 32 can be unbolted to allow replacement of 
this core. 
These plates 30 as seen in FIGS. 7 and 8 include generally straight edge 
plates 30' and a zig-zag plate 30" between them. The spacing between 
adjacent undulations is 2 mm and the perpendicular spacing between the 
plates is 0.7 mm. The plates 30' and 30" have a thickness of 0.15 mm and 
they are angled at 75.degree. to their general plane. 
The operation of the flame arrester is simple: The small mesh size combined 
with the considerable heat capacity of the plates 30 kills any flame by 
reducing its temperature very rapidly. Such an arrester prevents any flame 
from shooting out of the system, and similarly prevents any local flame 
from being sucked into it. 
As seen in FIGS. 5 and 6 the conduit 26 is welded to a steel flange 41 
bolted in turn to an integral aluminum flange 42 of an input pipe 43 that 
opens in the ejector 28 through an upstream primary nozzle gap 39 and 
through two downstream gaps 40. Struts 44 support this pipe 43 as well as 
rings 45, 46, and 47 and a tube 48 that define these gaps 39 and 40. The 
surrounding tube 49 has an outwardly flared upstream end 50. Other 
arrangements of diluters for smaller engines are also usual. 
The gap 39 opens radially outward and slightly downstream in the tube 49 
and the two other gaps 40 open mainly downstream and radially outward. 
This structure will therefore suck in considerable ambient air via the 
intake end 50, so that this air will mix with the expelled exhaust gases, 
diluting them and further reducing the explosion hazard. In fact, like a 
jet pump, such a device will entrain a much greater volume of air than the 
volume of exhaust gases employed. The displacement speed as well as the 
temperature will therefore also be greatly dropped at the ejector 28 to 
less than 60.degree. C. when ambient temperature is below 35.degree. C.