EXHAUST MANIFOLD THERMAL REACTORS A SOLUTION TO THE AUTOMOTIVE EMISSIONS PROBLEM J. J. Mikita and E. N. Cantwell FOR PRESENTATION AT THE 68TH ANNUAL MEETING OF THE APRIL 5-8, 1970 SAN ANTONIO, TEXAS MANIFOLD THERMAL REACTORS FOR EXHAUST EMISSION CONTROL This paper will describe an exhaust emission control system developed by Du Pont which will meet the 1975 gaseous exhaust emission standards proposed by the U.S. government. These proposed standards can be met without any changes in present-day fuel composition and, more specifically, without restrictions on the use of lead antiknocks. The paper also will present data which give promise that the 1980 goal for gaseous emissions also can be met with further development of the system. are: The gaseous emission control system combines two major devices. These 1. An exhaust manifold thermal reactor to control the hydrocarbons and carbon monoxide to very low levels. This device has been shown capable of controlling emissions for the normal lifetime of the car without attention or maintenance. 2. An exhaust gas recirculation system to control nitrogen oxide levels. Although not yet tested as extensively as exhaust manifold reactors, the exhaust gas recirculation system has been operated for 25,000 miles without maintenance. In addition to the system for controlling gaseous emissions, two separate systems have been developed to reduce particulate matter in the exhaust. Data will be presented to show that these systems are very effective for removal of particulate lead salts from the exhaust. One system has been operated on a car for 67,000 miles without maintenance or attention, the other for 26,000 miles. EMISSION STANDARDS Before examining the performance of these emission-control systems, consider first the standards put forth by the U.S. government and the State of California for emission levels from automobiles. Shown in Table 1 are the maximum allowable concentrations in grams per mile of the various components of the exhaust for the different years. The proposed standards for 1975 require that hydrocarbons be reduced to less than 0.5 gram per mile, carbon monoxide to 11 grams per mile, nitrogen oxides to 0.9 gram per mile and particulate matter to 0.1 gram per mile. For the year 1980, goals of approximately one-half of the 1975 standards have been proposed. EFFECTIVENESS OF THERMAL REACTOR SYSTEMS Shown in Table 2 are the exhaust emission levels obtainable with exhaust manifold thermal reactors and an exhaust gas recirculation system installed on two 1970 models of a popular four-door sedan. The vehicles are equipped with V-8 engines and automatic transmissions. Emission levels are 0.2 gram per mile of hydrocarbon, 8 grams per mile of carbon monoxide and 0.7 gram per mile of nitrogen oxides. Comparing these values to the 1975 and 1980 levels, it is clear that the gaseous emissions from these vehicles are well below the 1975 levels in all cases and, in the case of the hydrocarbons, are below the 1980 levels. These low-emission levels are achieved with little sacrifice in economy or vehicle performance. As shown in Table 3, the fuel economy of these equipped vehicles averaged about 14.5 miles per gallon when driving a city-suburban course on the road as compared with 15.3 miles per gallon average for two production 1970 vehicles of the same model. This loss of 0.8 mile per gallon represents only a 5 percent loss in fuel economy to achieve these very low emission levels. Similarly, only slight losses occur in terms of full-throttle acceleration capability. The general driveability of the vehicles is quite good. They start readily when cold, they warm up normally, and the warmedup driveability is equivalent to current production vehicles in all respects. HOW THERMAL REACTORS WORK The exhaust manifold reactors are mounted on the engine in place of the conventional exhaust manifolds and air is injected into the exhaust ports from the air injection system used on many production cars. The reactors provide a high-temperature zone in which the hydrocarbons and carbon monoxide are oxidized thermally to carbon dioxide and water. No catalytic device is employed. The reactor, as shown in Figure 1, consists of an outer shell in which is mounted a tubular core and a shield to insulate the hot core from the cooler outer shell. Exhaust gases mixed with the air supplied by the air injection system first enter the tubular core which is designed to promote mixing and initiate oxidation. The reacting gases then pass sequentially through the spaces between the core and the shield and between the shield and the outer shell. Oxidation is completed during this passage before the gases exit into the conventional exhaust system. Shown in Figure 2 is a photograph of one of the exhaust manifold reactors cut away to reveal the details of the inner core and the radiation shield. Shown in Figure 3 is a set of reactors mounted on the engine in the car in place of the exhaust manifolds. Air is delivered to the reactors from the air pump to a manifold with individual branches leading to each of the exhaust ports. The capability of exhaust manifold reactors in controlling emissions of unburned hydrocarbons and carbon monoxide when used alone without exhaust gas recirculation is shown in Table 4. Hydrocarbons are less than 0.25 gram per mile and carbon monoxide less than 4.5 grams per mile. These levels are well below both the 1975 proposed levels and essentially at the 1980 goal levels. As mentioned before, the reactors have little effect on vehicle economy or performance. Shown in Table 5, the fuel economy of the vehicle equipped with the exhaust manifold reactors is essentially equivalent to that of the standard 1970 vehicle equipped with the conventional emission-control system. Furthermore, the performance as measured in terms of the time in seconds required to accelerate at wide-open-throttle from 0 mph to 60 mph on a level road is essentially equivalent to that of the production model. DURABILITY OF THERMAL REACTORS Long-term tests of reactors show that they are capable of controlling hydrocarbons and carbon monoxide emissions for the normal life of the vehicle or 100,000 43-166 O 70 pt. 2 6 |