The importance of this invention to internal combustion engines is self-evident. There is a continuing need to not only increase the efficiency of internal combustion engines for both motor vehicles and stationary loads but to also reduce emissions of air pollutants, particularly oxides of nitrogen (NOx). To meet this need, catalytic converters and stratified charge systems have been developed which require either sustained high exhaust temperatures (about 700.degree. F.) or a constant load condition.
U.S. Pat. No. 4,104,989 discloses a stratified charge system in which a layer of air-fuel mixture is preformed between layers of fresh air in the part of the engine manifold that will charge the engine cylinder when the intake valve is opens. The result is a pocket of relatively fuel-lean, air-fuel mixture between layers of air. By stratifying the charge in that manner, the total quantity of air can be adjusted independently of the adjustment for the quantity of air-fuel mixture in order to minimize the formation of NOx and CO.
U.S. Pat. No. 4,135,481 discloses the same stratified charge system in which the air-fuel mixture is diluted with EGR before preforming the alternate layers of air and air-fuel mixture to further control NOx pollution.
U.S. Pat. No. 4,413,593 discloses a variation of the prestratified charge system in which the EGR accumulates near the intake valve while it is closed. When it opens for the intake stroke, the first portion of the charge to enter the cylinder is EGR followed by diluted air-fuel mixture. The layer of EGR remains stratified next to the piston during the compression stroke so that during the power stroke the tendency for air-fuel mixture to preignite at the piston before the flame front reaches it from the spark plug, a condition known as engine knock which imposes a limit on increase of the piston compression ratio for engine efficiency. This technique for stratification of EGR next to the piston during the intake stroke allows increase of the compression ratio of an engine for greater efficiency without risk of engine knock under high load conditions.
From the foregoing, it can be fully appreciated that for optimum reduction of emissions of air pollutants with a catalytic converter in the exhaust passageway, sustained high exhaust temperature is required, and with a stratified charge system a constant load condition is required unless expensive auxiliary rate of flow equipment is installed. Thus limited, neither system fully meets the need to reduce emission of pollutants. In fact, there are circumstances under which both catalytic converters and pre-stratified charge systems still do not fully satisfy the need, as in the case of cold starts.
Efforts to more fully satisfy this need to reduce NOx as well as other emissions, namely CO and HC, have met with well documented stoichiometric curve ratios associated with the power efficient air, fuel and airfuel mixtures, even with homogenous mixtures that include dilute EGR. These "classic" stoichiometric curves have been accepted as being bound by laws of physics, i.e., virtually unchangeable. However, tests of the present invention referred to hereinafter as a cylinder charge system (CCS) have proven that an engine equipped with the CCS system may achieve a better performance that is not restricted to the classic stoichiometric curves without relying on moving parts or catalytic conversion of exhaust gases. In other words, it has been found that reduction of oxides of both nitrogen and carbon by this invention falls outside the "classic" stoichiometric curves, and thus lends impetus to the statement that the invention does change the "classic" physics of the internal combustion engine by changing the shape of the flame front from a progressing bell shape to an expanding cylinder shape along the cylinder axis as the variable length of the cylinder increases during the power stroke.