Exhaust temperature control

An emissions control system for rich-burn internal combustion engines, said control system comprising: PA0 a. a reaction chamber for oxidation of exhaust gas fuel values, PA0 b. passive means to utilize reaction chamber effluent flow energy to mix cooling air into reaction chamber effluent to lower the temperature of said effluent. PA0 c. flame arrestor means to prevent ignition of flammable fuel-air mixtures external to the engine.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to improved systems for control of exhaust emissions 
of gases containing sufficient fuel values to generate high combustion 
temperatures. In one specific aspect the present invention relates to 
catalytic systems for control of exhaust emissions from internal 
combustion engines. More specifically, this invention relates to emissions 
control devices for fuel-rich internal combustion engines with very high 
reaction effluent tempeatures. 
2. Brief Description of the Prior Art 
Exhaust emissions from small internal combustion engines, such as are used 
for lawn mowers and small generator sets, are a significant source of 
atmospheric pollution by hydrocarbons and carbon monoxide. Such engines 
typically operate fuel-rich and therefore are particularly dirty as 
compared to an automotive engine, even without a catalytic converter. 
Although automotive emissions are now controlled by use of catalytic 
converters, such conventional devices are not considered feasible for 
small engine use because of inherently large size, high cost and system 
complexity relating to the need for air addition and to the need to limit 
the temperature of exhaust gases and exposed converter surfaces to safe 
values. The high emission levels of typical small engines means that 
destruction of those emissions results in a greater evolution of heat with 
a consequent higher converter temperature than for typical automotive 
catalytic converters. Further, small engine systems typically are much 
more exposed to gasoline spills and to operator contact, creating a hazard 
even with temperatures comparable to those for automotive catalytic 
converters. Effective means of suitable size and simplicity are thus 
required not only for the conversion reactor itself and for the addition 
and mixing of the air needed for oxidation of the exhaust fuel values to 
carbon dioxide and water but also for limiting temperatures to safe 
levels. 
The present invention meets these needs by providing a passive system for 
dilution cooling of the hot effluent gases from engine emission control 
conversion devices. 
SUMMARY OF THE INVENTION 
Definition of Terms 
As used in the present invention the term "passive" as applied to emissions 
control devices, systems or components thereof refers such devices or 
components which do not require moving parts for function. Thus a 
conventional catalytic converter is a passive device but a converter 
system utilizing a mechanical air pump for air addition is not passive. 
The terms "carbonaceous pollutant" and "hydrocarbon" as used in the present 
invention not only refer to organic compounds, including conventional 
liquid and gaseous fuels, but also to gas streams containing fuel values 
in the form of compounds such as carbon monoxide, organic compounds or 
partial oxidation products of carbon containing compounds. 
The Invention 
It has now been found that the high exhaust temperatures resulting from 
oxidative control of emissions from internal combustion engines can be 
reduced to safe levels by using the kinetic energy of the high velocity 
pulses of the hot converter exhaust flow to induct and mix sufficient air 
into the hot reacted exhaust gases to dilute and cool the exhaust gases to 
a safe level for venting, and that ignition of any fumes in the ambient 
air prevented by use of flame arrestor screens protecting all openings 
connected with possible sources of ignition. This allows use of engines 
with the exhaust gas reactors of the present invention even in hazardous 
locations such as coal mines. Typically the temperature of the converter 
exhaust is reduced to a value no higher than about 600 degrees Kelvin for 
use in such hazardous locations. Converter exhaust temperature is 
advantageously reduced by at least about 200 degrees Kelvin. 
Advantageously, gas phase combustion of a mixture of air and exhaust gases 
is catalytically stabilized by contact with a catalytic surface, as in the 
method of co-pending application Ser. No. 918,250 filed Jul. 23, 1992. 
Although catalytic stabilization offers smooth combustion over a wide 
range of operating conditions, it has been demonstrated that if the 
exhaust gas is hot enough and sufficiently fuel-rich, gas phase combustion 
can be stabilized with the backmixing of a conventional muffler even 
without catalytic stabilization. On the other hand, for engines which 
operate insufficiently fuel-rich even for catalytic stabilization of 
thermal combustion of the exhaust fuel values, the use of a catalytic 
reactor within the muffler allows for a high conversion level solely by 
virtue of heterogeneous reactions on the surface of a platinum metal or 
base metal catalyst, as with a conventional monolithic catalytic converter 
or a microlithic catalytic converter. Thus, the present invention makes 
possible economic achievement of ultra low emission levels of carbon 
monoxide and hydrocarbons even with very small internal combustion engines 
such as small two stroke engines. 
In a preferred embodiment of the present invention, the engine exhaust is 
ducted through a nozzle attached to the engine and jetted into the open 
end of a duct thereby entraining through a flame arrestor sufficient air 
for oxidation of at least a major portion of the fuel values contained 
therein in a downstream reaction zone. The reacted and heated exhaust 
gases are then ducted through a second nozzle into a second duct thereby 
entraining, again through a flame arrestor, sufficient additional air to 
lower the effluent temperature to a level at least as low as that of the 
engine exhaust. Advantageously, the receiving ducts may be venturi shaped. 
Preferably, gas phase reactions are catalytically stabilized in a well 
mixed thermal reaction zone. The efficient, rapid thermal combustion which 
occurs is believed to result from the injection of heat and free radicals 
produced by the catalyst surface reactions at a rate sufficient to counter 
the quenching of free radicals which otherwise minimize thermal reaction 
even at combustion temperatures much higher than those found to be 
feasible in the method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS 
The present invention is further described in connection with the drawings. 
As shown in the FIGURE, in one preferred embodiment the exhaust from a 
single cylinder gasoline engine 1 passes through exhaust line 2, which 
serves as an air inductor nozzle, into line 3 thereby entraining air from 
shroud 11 through opening 4 in line 3. Air enters shroud 11 through flame 
arrestor 13. The exhaust gas and the mixed in added air pass from line 3 
into reactor/muffler 5 into contact with the catalytic surfaces of swirler 
9 resulting in virgorous recirculation and stable gas phase combustion. 
Contact of gases with the catalytic surfaces of baffle plate 10 aid flame 
stabilization. Hot combustion products exiting vessel 5 are directed by 
deflector 6 which serves as an air inductor nozzle, into the venturi duct 
formed by wall 7 thereby inducting air into duct 8 through flame arrestor 
screen 16 and mixing it with the hot exhaust. Gases exiting through the 
venturi duct formed by wall 7 are more than 200 degrees Celsius lower in 
temperature than the hot gases exiting reactor/muffler 5. Contact of 
entering gases with swirler 9 also serves to create a low pressure region 
near the muffler inlet and thus inhibit backflow of gases through the open 
end of line 3. Typically, muffler 5 is encased in insulation 17 to reduce 
the temperature of surfaces 12 to an acceptable level. Gases exit the 
venturi formed by wall 7 through flame arrestor 14 to contain any flame 
from ignition of fuel in air entering through arrestor 16. 
In place of the insulation, a double walled heat shield may be used to 
enclose the muffler assembly to contain the reaction heat and minimize 
risk of burns or fire. 
EXAMPLE I 
Fuel rich exhaust gas from a small Briggs and Stratton single cylinder 
gasoline powered spark ignition engine driving an electrical generator was 
passed through an exhaust pipe of conventional size discharging as an 
injector nozzle into a larger pipe and inducting air through the opening 
between the discharge nozzle and the outer pipe. The exhaust gases with 
entrained air were passed to a conventional Briggs and Stratton muffler 
which had been modified by the addition of a coating of a platinum 
catalyst to the internal baffle plate surfaces to ignite and stabilize 
thermal reactions in the muffler and by addition of fixed swirler vanes 
opposite the muffler inlet. Reacted effluent from the muffler was passed 
through a second nozzle into a venturi duct to entrain additional air to 
dilute and cool the effluent. Thermal reaction of the fuel values in the 
exhaust gases with the oxygen in the inducted air resulted in a muffler 
exhaust temperature at the muffler exit of 923 degrees Kelvin, or about 
200 degrees Kelvin higher than the 718 degrees Kelvin exhaust temperature 
of a noncatalytic muffler at the same operating conditions. The diluted 
exhaust was reduced from 923 degrees Kelvin to 713 degrees Kelvin or 
slightly lower than the exhaust temperature for the standard muffler at 
the same engine operating conditions. Integrating the venturi duct into a 
full surrounding sheet metal muffler heat shield through which engine 
cooling air is ducted resulted in external surface temperatures below 550 
degrees Kelvin and an exhaust gas temperature below 610 degrees Kelvin, 
i.e. much lower than that of the standard non-catalytic muffler. Thus, not 
only were emissions controlled with a simple system but exhaust and 
surface temperatures were below those for an engine without emissions 
control.