INLET-AIR CONDITIONING FOR INTERNAL COMBUSTION ENGINES
FIELD OF THE INVENTION
The invention relates to internal combustion engines including compression ignition engines and rotary engines
and more particularly, to a method and apparatus for
conditioning the inlet air thereof.
BRIEF DISCUSSION OF THE PRIOR ART
The prior art contains a vast number of proposals
for conditioning the inlet air of internal combustion
engines the the object of improving their efficiency and
operation. '
British Patent Specification No. 773115, for example,
describes admitting hot air and/or water vapour to the
fuel/air mixture downstream of the carburettor to form a
tubular- curtain in the fuel-intake opening of an internal
combustion engine, capable to taking up the fuel condensate particles on their way from the carburettor to the working
cylinder, evaporating the particles and then returning the
evaporated condensate to the fuel air mixture. It is said,
that this ensures practically complete combustion of the
fuel, reduces the fuel compensation and improves the
working conditions for the engine yielding a longer engine .
life.
British Patent Specification No. 766303, on the other
hand proposes mixing with the cold inlet air, a
controlled amount of hot air tapped from a heating system for the interior of the vehicle in response to the temperatur of air upstream of the carburettor. The objection of this proposal is to p ent the formation of ice in the carburettor.
Other specifications such as British Patent Specification No. 1525021 and British Patent Specification Nos. 1400072 and 2081377A propose adding steam to the
inlet air of internal combustion engines to permit the use of fuel of a lower octant rating, to reduce fuel consumption and pollutant emission.
One disadvantage of previous proposals is that, often complex, modifications are required to existing engines and substantial redesign would be necessary in order to build engines incorporating the necessary
features , which is one reason why most previous proposals have not become widely used. SUMMARY OF THE PRESENT INVENTION
I have now found that good results may be achieved without the need to inject or otherwise add water or steam
to the inlet air since it is possible so to condition the
air at inlet that the water vapour present in the ambient
air at inlet to the engine is condensed to form water
droplets.
What I propose, in accordance with one aspect of the present invention is to condition the inlet air fed to
the engine by mixing streams of air at different temperature to form water droplets which are carried by the air into
the engine. A subsidiary stream of air is preferably
drawn through a heat exchanger for the exchange of heat with the exhaust gases or indeed with the engine coolant
or any other convenient source of heat, prior to mixing with the main intake air. Mixing preferably takes
place upstream of the venture of the carburettor (in the case of the petrol engine) and preferably such that a cross-flow of the main and subsidiary air stream is obtained to produce turbulance and hence ensure thorough mixing.
According to another aspect of the invention I propose an internal combustion engine having means for supplying fuel and air to the combustion chamber or
* chambers and an exhaust system for the combustion gases,
and comprising a main air intake and a subsidiary air intake including a heat exchanger for heating the subsidiary air by exchange of heat with, for example, the
exhaust gases and through which a subsidiary stream of
air is drawn, the subsidiary air intake being connected to
the main air intake, whereby, upon mixing of the main and
subsidiary air streams at different temperatures, water droplets form and are carried by the air into the engine.
Preferably, mixing takes place downstream of an air cleaner element of the engine and disposed in the main
air intake thereof. Normally, the air cleaner element is annular and it is preferred to connect the subsidiary
air intake to the main air intake by a pipe disposed within, preferably, centrally within, the air cleaner
element and to provide, in an end portion of the pipe, transverse openings, that is to say openings in the wall
of the pipe, such that subsidiary air is directed against the radially inward flow of main intake air through the
air cleaner element.
For best results the difference in temperature between the main and subsidiary air streams should be greater than 20 C and, preferably, greater than 30 C. This can be achieved in a variety of ways, for example, by adjusting the flow through the subsidiary air intake
(i.e. by varying the size thereof) or by adjusting the extent to which the subsidiary air stream is cooled in
passing from the heat exchanger to the point of mixing.
In this connection, the length of the pipe and the material
used can be varied according to the requirements of a
particular engine and/or vehicle. Alternatively, expansion chambers or condenser units may be incorporated
in the subsidiary air intake. Relatively minor
adjustments can produce marked changes in the cooling
effect, bearing in mind the flow of air through the engine compartment of a vehicle travelling at speed.
Although it might be thought that the difference in
temperature between the main and subsidiary air streams
will depend largely upon the ambient condition this is
not so. One reason being that the ambient air is cooled
as it is drawn into the main air intake. Also, on hot days the engine tends to run hotter so that a corresponding
increase in the temperature of the subsidiary air stream tends to compensate for an increase in the temperature of the main air stream.
BRIEF DESCRIPTION OF THE DRAWINGS
An embodiment of the present invention will now be described by way of example with reference to the
accompanying drawings of which:
Figure 1 is a schematic view of an internal combustion engine fitted with apparatus according
to the present invention; and
Figure 2 is a cross-section through the air filter of the engine shown in Figure 1, illustrating
how the main and subsidiary air streams are mixed.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The engine, shown schematically in Figure 1, has an
air filter 10 mounted, as is usual, above the carburettor 12, the combustion air being drawn from the filter 10 through a venture 14 at a rate controlled by a butterfly valve 16. In addition to the main air intake to the- air filter at
18, a subsidiary air intake isprovided, this including a heat exchanger 20, in the form of a collar 22 clamped to or
otherwise held in intimate contact with the exhaust manifold 24 of the engine, and connected by a pipe 26 to the air filter. The pipe 26 enters the air filter 10 in the
centre of the top thereof and passes downwardly within the annular air cleaning element 28 as shown In Figure 2. The end of the pipe 26 is closed but openings are formed in the wall thereof such that a subsidiary stream of air, which is drawn, partly by engine suction and partly by induction due to the main air intake flow , issues as
indicated by the arrows in Figure 2, radially outwardly in opposition to the flow of main intake air passing
radially inwardly through the annular air cleaning element 28.
This arrangement gives rise to turbulance and hence ensures
thorough mixing of the main and subsidiary streams of air.
The pipe 26 connecting the heat exchanger 20 and
the air filter 10 may be formed of metal, typically
copper, or in part of a material having a lower thermal
conductivity, (for example, rubber) and further, may incorporate condenser or expansion chambers (not shown)
as required to cool the subsidiary stream of air, after heating, and as appropriate to the particular engine, vehicle and/or operating conditions concerned, to a
temperature higher than the temperature of the main
intake air by an amount sufficient to cause condensation
of at least some of the water vapour present in the
ambient air. In practice the difference in temperature 'of the main and subsidiary air streams will be greater than 20 C and this is largely independent of the ambient conditions.
Tests on a wide range of vehicles in which the internal combustion engine has been modified in accordance with the present invention indicate that fuel consumption can
readily be improved by 10% and in some cases by as much
as 30%.
OM