Thermal reactor system for internal combustion engine

A thermal reactor system for internal combustion engines having a reaction chamber provided in the cylinder head. The reaction chamber is provided immediately behind the exhaust valve and has a predetermined capacity for inducing the oxidation of harmful constituents of the exhaust gases.

The present invention relates to a thermal reactor for reducing the harmful 
constituents of the exhaust emission from the engine. 
There has been provided a system for reducing the amount of unburned 
constituents such as carbon monoxide and hydrocarbons in which the 
constituents are oxidized in the exhaust system. In this system it is 
preferable to maintain the exhaust gases at a high temperature for a 
certain period to promote the oxidation of the unburned constituents. On 
the other hand, the maximum combustion temperature in the combustion 
chamber should be lowered in order to reduce nitrogen oxides. To meet 
these requirements, a system in which the spark timing is retarded has 
been provided. In accordance with the retarded spark timing, the maximum 
combustion temperature is low and temperature of the exhaust gases at the 
exhaust port may be elevated. However, because the retarded spark timing 
causes undesirable results such as an increase in fuel consumption, the 
retarded spark timing must be determined in a necessary minimum angle. 
Accordingly, it is an object of the present invention to provide a thermal 
reactor system which has a high reduction rate of harmful constituents 
whereby the retardation of the spark timing may be set in the minimum 
angle enough to decrease nitrogen oxides without further retardation for 
raising the exhaust gas temperature for promotion of the oxidation of 
carbon monoxide and hydrocarbons. 
It is another object of the present invention to provide a thermal reactor 
system which is simple in construction. 
It is still another object of the present invention to provide a thermal 
reactor system which may reduce the harmful constituents to the required 
amount without providing an exhaust gas purification system in the exhaust 
system. 
The present invention is characterized in that a reaction chamber is 
provided in the cylinder head behind the exhaust valve and oxidation of 
exhaust gases occurs in the reaction chamber at a high temperature. 
In the conventional exhaust thermal reactor system, the thermal reactor is 
positioned in the exhaust passage after the outlet of cylinder head. In 
order to maintain the exhaust gases at a high temperature in such a 
system, the exahust passage and thermal reactor are coated with insulation 
material. According to inventor's experiments, it has been found that 
sufficient oxidation cannot be expected in the termal reactor provided in 
the exhaust passage, because of the exhaust gas temperature drop in the 
exhaust passage. In order to elevate the exhaust gas temperature, the 
spark timing is retarded and in order to maintain the temperature at a 
high level sufficient to induce the oxidation, a large scale insulation 
must be provided on a great part of the exhaust system which will increase 
the cost of the system. 
In accordance with the present invention, the exhaust gas temperature drop 
may be prevented, because the reaction chamber is provided closely 
adjacent to the exhaust valve. Further it is possible to greatly reduce 
the harmful constituents of the exhaust gases even if the exhaust gas 
temperature at the exhaust port is lower than that of the conventional 
engine. This means that a large retarded spark timing for obtaining the 
high exhaust gas temperature is not necessary. Accordingly, it is possible 
to provide an internal combustion engine which has high power and low fuel 
consumption because the retardation angle of the spark timing may be set 
in a minimum angle sufficient to reduce the amount of nitrogen oxides to a 
standard level.

Referring to FIGS. 1 and 2, the figures show a part of the cylinder head 
for multi-cylinders. As shown in FIG. 1, the cylinder head 2 is secured to 
a cylinder block 1 with bolts and a cylinder 3 is formed in the cylinder 
block 1. The cylinder head 2 is provided with exhaust and intake ports 4 
and 5 which have exhaust and intake valves 6 and 7 respectively. A 
reaction chamber 8 having a predetermined capacity for inducing the 
oxidation of the harmful constituents is provided in the cylinder head 
immediately behind the exhaust port 4. The reaction chamber 8 is 
communicated to an exhaust passage 9 which is in turn communicated to an 
external exhaust passage (not shown). The inner wall of the reaction 
chamber 8 and exhaust passage 9 is lined with a lining 10 for heat 
insulation. The lining is previously made of heat resisting steel and 
formed into a shape of the reaction chamber. The lining 10 is inserted in 
the cylinder head 2 at the casting thereof. On the outer side of the 
lining projections 11 are provided which are inserted into the cast metal 
to hold the lining. There are also provided projections 12 in the cavity 
of the cylinder head, supporting the lining 10 and forming an insulation 
space 13 between the lining and the cylinder head. 
The reaction chamber 8 has a predetermined capacity sufficient enough to 
obtain a long residence time of the exhaust gases and to effect sufficient 
mixing of the gases, so that carbon monoxide and hydrocarbons are 
sufficiently oxidized. The predetermined capacity of the reaction chamber 
is selected between 1/4 and 2 times the piston stroke volume of the 
corresponding cylinder, preferably at 3/4 thereof. 
According to the experiments, it has been found that the length of the 
residence time of the exhaust gases in the reaction chamber has a great 
influence on the oxidation of the harmful constituents in exhaust gases, 
and that the harmful constituents in the exhaust gases are reduced 
remarkably by increasing the residence time. FIG. 3 shows how the relation 
between the reduction rate of carbon monoxide and hydrocarbons and the 
exhaust gas temperature varies according to residence time in the reaction 
chamber. Curve a is the relation between the reduction rate of harmful 
constituents and the exhaust gas temperature in the conventional thermal 
reactor system in which oxidation takes place in the exhaust passage after 
outlet from the cylinder head for a short residence time and curves b, c, 
and d are relations in the reaction chamber of the present invention 
having long residence times. The graph shows that the reduction rate of 
the present invention is almost twice the reduction rate of the 
conventional system under the same temperature conditions of the exhaust 
gas. In other words, the present invention enables reduction of the amount 
of the exhausted harmful constituents, even if the exhaust gas temperature 
is lower than that of the conventional engine. Therefore, it is not 
necessary to retard the spark timing in order to raise the exhaust gas 
temperature, whereby it is possible to put the power of the engine to the 
utmost and good fuel consumption can be expected. 
FIG. 4 illustrates a comparison of the temperature the exhaust gases out of 
the exhaust valve in the conventional thermal reactor system and in the 
present invention, in which the horizontal axis is equivalent pipe length 
to the volume of the exhaust passage. In the figure, temperature in the 
passage of the conventional thermal reactor system is indicated by d and 
that of the present invention by e. In the conventional system, between 
the exhaust valve and the outlet from the cylinder head, the exhaust gas 
temperature drops rapidly and in the exhaust passage, the drop of 
temperature becomes slow. On the other hand, in the present invention, 
because the exhaust gases are oxidized in the reaction chamber immediately 
after the exhaust valve, the drop rate of the exhaust gas temperature is 
low and the temperature at the outlet point g is much higher than the 
temperature at the point f of the conventional system. Accordingly, it 
should understood that oxidation may be actively take place in the 
reaction chamber of the present invention. It will be understood that a 
sufficient effect can be expected in the present invention if the 
temperature at the point h, where the exhaust gases exit from the exhaust 
valve, is lowered. In the conventional thermal reactor system in order to 
raise the temperature at the point h, which means that active reaction in 
the exhaust system may be expected, the spark timing is retarded. The 
retardation of the spark timing also provides a decrease in the maximum 
combustion temperature which results in the reduction of nitrogen oxides. 
FIG. 5 shows the relations between the spark timing, fuel consumption in 
operation by the ignition of MBT (maximum advance for best torque) and 
amount of nitrogen oxides. As the spark timing is advanced, the fuel 
consumption decreases, but the nitrogen oxides are increased. The amount 
of nitrogen oxides is least at BTDC 5.degree., or thereabout. According to 
the present invention, as mentioned above, it is unnecessary to make the 
exhaust gas temperature higher by retarding the spark timing because 
sufficient oxidation may be expected at a lower exhaust gas temperature at 
the exhaust valve. 
In the conventional thermal reactor system, the spark timing is set about 
the top dead center to obtain the point i. To the contrary the timing in 
the present invention may be advanced about BTDC 15.degree. to obtain the 
same point j as the convention thermal reactor system and to decrease the 
specific fuel consumption. 
In the embodiment shown in FIGS. 6 and 7, the reaction chamber 8 is 
provided over two cylinders 3 and 3 to include both exhaust valves 6 and 6 
which communicate therewith. In this system a boss 14 is provided through 
the reaction chamber at a central portion thereof and a bolt for securing 
the cylinder head 2 to the cylinder block 1 is inserted into the boss 14. 
In accordance with this embodiment, since the reaction chamber 8 is 
provided over two cylinders, exhaust gases from each cylinder flow into 
the chamber at intervals of short time periods thereby the reaction 
chamber is always held at a high temperature and further, subsequent 
exhaust gases would be mixed with previous exhaust gases. Further, the 
boss 14 in the reaction chamber causes the mixing and turbulence of the 
exhaust gases, which enhances the oxidation of the gases. Thus, a greater 
reduction of harmful constituents than with the afore-mentioned embodiment 
may be expected. 
In the embodiment of FIG. 8, the reaction chamber 8 is provided over and 
communicates with three cylinders. In accordance with this embodiment, the 
residence time and mixing effect may be further increased, since the 
capacity of the reaction chamber is enlarged and the exhaust gases may be 
continuously introduced in into the chamber. It should be noted that the 
capacity of the reaction chamber in these embodiments in which the 
reaction chamber is provided to include two or more exhaust pipes is 
selected between 1/4 and 2 times the total piston stroke volume of all of 
the corresponding cylinders. 
In the embodiment of FIG. 9, a couple of reaction chambers are connected to 
a common exhaust passage 9a. In accordance with this embodiment, an 
exhaust manifold 15 to be provided outside of the cylinder head can be 
simplified.