This invention relates to a method and apparatus for improving the fuel efficiency of internal combustion engines and more particularly to such improvements by preheating the liquid fuel and the air prior to entry into the metering device and the manifold.
Much effort has been directed recently toward providing greater efficiencies in motor vehicle internal combustion engine fuel utilization. It is known that greater efficiencies are attained when the fuel is fully vaporized and mixed with the air prior to combustion. Various heat exchange arrangements have been proposed generally utilizing the heat of the exhaust manifold to vaporize the fuel. One such arrangement is proposed in U.S. Pat. No. 4,106,453 in which vaporized fuel, and air heated by exchange with the exhaust manifold, are mixed in a chamber having a turbulence creating mixing cone. As exemplified by this patent various modifications to conventional automobile engine fuel systems are required with proposals of this type. Another such proposal is disclosed in U.S. Pat. No. 3,886,919 which meters fuel through a valve, heats the fuel and air in an exhaust heat gas exchanger, mixes the fuel and air and directs the mixture into the intake manifolds.
One difficulty encountered with systems which pre-heat the fuel to high temepratures is that the fuel vapor pressure is increased and the fuel vaporizes prior to entry into the carburator air flow. If vaporizaton occurs in the feed lines or in the carburator float bowl, the flow of fuel is reduced below that demanded by the engine and the engine will vapor-lock and stall. For this reason high fuel temperatures are avoided, and especially with carburator systems.
It is therefore desireable that the fuel be preheated so that it may be more readily atomized and vaporized, but not heated to too high a temperature prior to entry into the carburator, least vapor-lock will occur. In U.S. Pat. No. 3,672,342 the air in the air cleaner is heated by a heat riser from the exhaust manifold and used to heat the fuel passing through a heat exchanger within the air cleaner. Both the air and the fuel are maintained within a temperature range up to 110.degree. F. Since the fuel is heated within the air cleaner and still has a significant distance to flow to the carburator, vapor-lock conditions would be present if the temperature increased greatly. The desireability of preheating the fuel must therefore be counter-balanced by the problems created by over-heating it and effecting vaporization too early. Moreover, for similar reasons of fuel economy the desireability of preheating the air with which the fuel is mixed is well established. The means for effecting the proper heating conditions must be inexpensive, safe, simple and easy to install especially if such systems are to be retro-fitted to existing engines.