Zigzag ignition gap arrangement

The invention relates to an arrangement in such ignition gaps or channels as are used in combustion devices, for example, internal combustion engines, to impart to an injected finely-divided particulate fuel a temperature sufficient for ignition, heat being transferred from the heated walls for the ignition gaps or channels. The novelty of the invention resides in that the ignition gap or gaps are zigzag-shaped or otherwise formed of two or more substantially straight sections connected at an angle to each other.

FIELD OF THE INVENTION 
This invention relates to ignition gaps typically used in 
internal-combustion engines to impart to an injected fuel, preferably in 
the form of a powder, a temperature sufficient for ignition. 
BACKGROUND OF THE INVENTION 
Swedish Patent Specification 8202835-8 describes an ignition gap device for 
diesel engines, where wood powder is supplied into the ignition gaps and 
caused to impinge on the heated gap walls for progressive ignition. 
The major problem in the operation of these type of internal-combustion 
engines employing solid powder fuels is the ignition delay. In diesel 
engines, the ignition delay is defined as the time elapsing from the 
moment the fuel is injected into the combustion chamber until it is 
ignited. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide a controlled 
reduction of the ignition delay and to increase the efficiency of fuel 
ignition. These and other objects are accomplished by arranging the 
ignition gaps in a zigzag configuration. Preferably, the ignition gaps are 
provided in different lengths by using a modular technique that can be 
adapted to prevailing requirements.

DETAILED DESCRIPTION 
FIG. 1 schematically illustrates a preferred embodiment of the present 
invention. A zigzag-shaped path created by ignition gaps or channels 2 is 
formed from several plates or modules 1. Each plate 1 is formed with one 
or more channel or gap sections having one of two different directions. 
The plates 1 are alternately stacked such that adjacent plates 1 have 
channel or gap sections with different directions. The inlets and outlets 
of adjacent plates 1 are located at the same position to form the one or 
more zigzag-shaped gaps or channels. In the embodiment of FIG. 1, the 
mutual directional deviation of the ignition gap or channel 2 in the 
plates 1 is about 140.degree.. 
The plates or modules are preferably made of ceramics. The end surfaces 3 
are accurately ground and lapped to provide a leakproof seal between 
adjacent plates 1 without the need of additional sealing devices. 
FIG. 2 shows an arrangement of plates 1 adjacent an injection nozzle 4. The 
injection nozzle 4 is positioned over a piston 5 in the combustion chamber 
6 of a diesel engine. In this embodiment, the end plates 1a and 1b have 
spherically domed surfaces 7 accurately mating with complementary dome 
shaped surfaces 8 of parts 9 and 10, respectively. Parts 9 and 10 are 
fixed to the engine and arranged at the injection mechanism. Part 10 is 
provided with a movable gland seal 11 taking up the temperature movement 
in the plates. The spherical end plates, 1a and 1b, facilitate mounting. 
The plates 1 are heated during the starting phase by a heating coil or 
winding 12. 
For clarifying purposes, a description of the preferred powder fuel will 
now be given. In the manufacture of powder fuel for internal combustion 
engines, the fuel is ground and sifted. The fuel may be grounded using 
beater mills, ball mills, cylpebs mills or pinned disc mills, as well as 
vacuum mills. Sifting takes place in wind sifters designed as a 
centrifugal fan. A gas laden with powder is caused to flow through the fan 
from the periphery towards the center. The result being that only very 
small particles pass the wind sifter. By varying the flow through the fan 
and its speed of rotation, it is possible to obtain a very fine powder. 
FIG. 3 is a general view partly in section showing how the arrangement 
according to the invention is integrated in an injection mechanism. 
In this embodiment, the fitted plates are designated as 1, and those having 
spherical end surfaces 7 are designated as 1a and 1b, respectively. The 
injection nozzle is designated as 4, and the injection mechanism feeding 
and portioning the fuel is designated as 13. The heating coil is 
designated as 12. Other components in this figure are illustrated for 
clarifying purposes only. 
As will be appreciated, it is vital that the plates 1 be joined together in 
the most accurate manner. 
In order for the ignition gaps to function properly, the temperature must 
be at least 900.degree. C. The engine operates with minimal emissions when 
the temperature is 1100.degree. C. Since metallic materials do not 
withstand such high temperatures, ceramics must be used. 
For working ceramics, diamond tools, such as silicon nitride and aluminum 
oxide, are required. The most economical way of producing ceramics is by 
compression-molding and then sintering at high temperatures. In one 
approach, the compression-molded powder is presintered and then turned and 
drilled before the final sintering takes place. In the diesel engine 
described above, the zigzag-shaped ignition gap is formed with ten plates 
1 having straight channel sections with 140.degree. bends between adjacent 
sections. The ignition gap diameter is preferably 6 mm. The zigzag-shaped 
ignition gap is obtained from a number of round plates having angled 
holes. As mentioned above, the plates have been ground and lapped to 
minimize leakage when pressed together. 
FIGS. 4 and 5 show a modified design of the plates 1. The shape of the 
channel or gap sections vary in the different plates. This embodiment, 
like the others, can be compressed to its final shape before sintering, 
with the only remaining operation being grinding and lapping. 
FIGS. 6, 7, 8, and 9 show yet another plate design which can also be 
compressed to its final shape before sintering and subsequent grinding and 
lapping. In this embodiment, a different channel or gap shape is 
obtainable. 
FIG. 10 is an extended schematic view showing how the transport paths for 
the fuel are formed and how they are given a pronounced zigzag 
configuration. As shown in FIG. 10, the fuel particles are forced to 
repeatedly impinge on the gap or channel walls. These walls are maintained 
at a high temperature which results in the ignition of the fuel when 
injected into the combustion chamber. 
Zigzag-shaped ignition gaps according to the invention can be used for 
igniting all pulverulent fuels made from wood, straw, grass, bagasse, 
peat, coal and brown coal for firing furnaces, internal-combustion 
engines, both Otto and diesel engines, as well as gas turbines. The fuel 
which is undoubtedly the best is Eucalyptus Teriticornis because of its 
extremely low ash content. Depending on its habitat, this tree species has 
less than 0.03% ash based on the dry weight of the wood. 
Practical tests have shown that if the fuel particles are smaller than 16 
.mu.m with a normal distribution around 8 .mu.m and the solid fuel 
consists of wood powder that has been hydrolyzed (with the aid of 
superheated formic acid steam at 200.degree. C. for 2 hours at atmospheric 
pressure), the ignition delay becomes only 15.degree. at a speed of 3600 
rpm if zigzag-shaped gaps or channels having a length of about 200 mm and 
a diameter of 6 mm are used. The reason why a zigzag-shaped channel or gap 
is more efficient than a conical one is that the larger particles will 
impinge on the hot walls a considerable number of times when passing 
through the ignition gap compared with an expanding gap as described in 
Swedish Patent No. 8202835-8.