GB1488383A - Method and means for reducing pollutants from the exhaust of hydrocarbon fuel combustion means - Google Patents

Abstract

1488383 Treating I.C. engine exhaust gases CORNELL RESEARCH FOUNDATION Inc 18 Sept 1974 [8 March 1974 21 Sept 1973] 40742/74 Heading B1W [Also in Divisions F1 and F4] Oxides of nitrogen are removed from the oxygen-deficient combustion products of a hydrocarbon-fueled combustion device by mixing with the combustion products a quantity of unburned hydrocarbon and maintaining the mixture at a temperature of 2200 degrees Rankine, for a period of time sufficient to effect chemical reduction of the oxides of nitrogen. Fig. 4 shows an apparatus for carrying out the process externally of an I.C. engine, in which exhaust gases are fed by pipe 34 to chamber 21. Chamber 21 is heated by burner 22 which receives air from engine-driven pump 24 at a rate controlled by valve 37 in accordance with engine speed; and fuel from tank 27. The amount of fuel supplied is that needed to heat the chamber to 2200-2600‹R, to maintain a deficiency of oxygen in the mixture and to effect chemical reduction of nitrogen oxides in the mixture. The volume of chamber 21 is determined by the mass flow rate of exhaust gases divided by the mean density of the exhaust gases and multiplied by the selected reaction period which is related to the temperature and the level of reduction of nitrogen oxides which is desired. Treated mixture then passes through thermal reactor 30 which also receives air from pump 24 and in which the temperature is kept below 3300‹R in order to avoid regeneration of oxides of nitrogen. The working cylinders of an engine can be used as the reaction chamber in which nitrogen oxides are reduced, by adding to the combustion products unburned gaseous hydrocarbons at a time when the mixture will be at a sufficiently high temperature i.e. towards the end of the expansion stroke, before the exhaust valve opens. This can be effected by injecting fuel during the expansion stroke, Fig. 5a (not shown); by pockets formed in the piston crown to trap mixture during the compression stroke Fig. 5b (not shown); by trap chambers formed interiorly or exteriorly of the cylinder Figs. 5c, 5d and 5e (not shown); by trap chambers which are also supplied with supplementary fuel Figs. 5f and 5g (not shown); and by using the unburnt hydrocarbons which are scraped off the cylinder wall during the exhaust stroke, Fig. 5h, in which case a metal ring 80 which acts as a hot-spot is situated adjacent the exhaust valve and serves to heat the mixture. The annular space between the central electrode and body of a sparking plug may be used as a trap chamber and communicates with the cylinder by an orifice Fig. 5i. Additional fuel may be supplied to such a chamber. When supplemental fuel is provided it may be mixed with exhaust gas. Figs. 6 to 12 (not shown) illustrate constructions of spark plugs which embody trap chambers into which air/fuel mixture is forced during the compression stroke. During the period of high cylinder pressure following combustion, combustion products are also forced into the trap chamber and the mixture re-issues as the pressure drops during the expansion stroke to provide unburned hydrocarbons which react with oxides of nitrogen present in the combustion products.