THE N-O-R SYSTEM

Operation and Description

The N-O-R System reduces emissions of nitrogen oxides in the exhaust by preventing their formation. This is accomplished by recirculating a portion of the exhaust gas and mixing it with the incoming air-fuel mixture which reduces the oxygen concentration and lowers peak temperatures during combustion.

The recirculation is accomplished by taking hot exhaust gas from the heat riser located directly beneath the carburetor, regulating the quantity with a throttle actuated flow control valve, and distributing the recirculated exhaust by means of tubes to each leg of the intake manifold. From 15% to 22% of the exhaust is recirculated to achieve the desired reduction of nitrogen oxides. A schematic diagram showing the components of the system and location within the intake manifold appears in Figure 1. A composite photograph showing various stages of assembly appears as Figure 2.

The concept of exhaust gas recirculation is not new. However, the utilization of recirculated exhaust and the development of systems for control of nitrogen oxides has occurred only in the last decade. The uniqueness of the N-O-R System lies in the many necessary design improvements such as the use of recycle only during selected modes of vehicle operation, taking hot exhaust for recycling, and improving the methods of rate control and recycle

distribution.

Performance

The N-O-R System will reduce nitrogen oxides in vehicle exhaust by 75% to 85% irrespective of the uncontrolled concentration level. Table I shows reductions achieved for six different vehicles, of which the last three were equipped with California approved exhaust emission control systems. Similar results were obtained with laboratory engines and other vehicles. Table II lists all of the specific engines and vehicles equipped with recirculation systems and tested during the investigation.

It is worth noting that systems were supplied to the U. S. Bureau of Mines and the State of California for research involving exhaust emissions and irradiation chamber studies. Furthermore, three vehicles were equipped for the Los Angeles County Air Pollution Control District to evaluate overall vehicle performance. Recently, vehicles were equipped for testing and evaluation by the automobile industry.

For any system to be acceptable it must have no adverse effect on the emissions of other pollutants, must be compatible with other emission control systems, and must not adversely affect vehicle performance. Figures 3 and 4 (taken from the technical paper "Control of Nitrogen Oxides in Automotive Exhaust") show the effect of exhaust recirculation on carbon monoxide, hydrocarbons and other exhaust components. Obviously, no adverse effects occurred.

Table III shows California hot cycle test results obtained when the N-O-R System was installed on the three California equipped vehicles. It will be noted that emissions of carbon monoxide, hydrocarbons and nitrogen oxides all met California standards and vehicle operability was judged acceptable.

The recirculation of exhaust gas does affect certain engine operating variables such as intake manifold vacuum and spark advance. Modifications to the carburetor and ignition systems are made as necessary to compensate for the effect of exhaust

recirculation.

Also of concern are possible effects on mileage and on vehicle performance or driveability. With proper modifications of the carburetion and ignition systems these possible undesirable effects can be minimized or eliminated.